DAMP signaling networks: from receptors to diverse pathophysiological functions.

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This manuscript was supported by grants from the National Natural Sciences Foundation of China ( 82070613 and 82370638 to R.C.), the Science and Technology Innovation Program of Hunan Province ( 2022RC1212 to R.C.), the Natural Science Foundation of Hunan Province China ( 2023JJ10095 to R.C.), and Hainan Province Clinical Medical Center.

DAMPs are known to trigger cellular proliferation signals in a variety of cell types, including endothelial cells [ 178 ], meniscus cells [ 179 ] smooth muscle cells [ 180 ], mesoangioblasts, B cells [ 181 ], T cells [ 182 ], cancer cells [ 183 ], and stem cells [ 184 ] ( Fig. 4 ). For instance, self-DNA released from lymphocytes undergoing activation-induced cell death can stimulate the proliferation and differentiation of B cells in both normal BALB/c mice and lupus-prone MRL +/+ and MRL/lpr mice, thereby promoting the onset of autoimmune conditions such as SLE [ 181 ]. Hyaluronic acid, a prototypical extracellular DAMP, interacts with CD44 to enhance cell migration and proliferation in both inner and outer meniscus cells via the phosphoinositide 3-kinase (PI3K) and MAPK pathways [ 179 ]. Fig. 4 DAMPs in physiological activities. This figure presents an illustrative depiction of the multifaceted roles of DAMPs from diverse cell types in various physiological activities, spanning from fundamental cellular processes such as proliferation and differentiation, to more complex phenomena including migration, inflammatory responses, tissue repair and regeneration, fibrosis development, angiogenesis, bacterial clearance mechanisms, cell death pathways, cellular senescence, effeocytosis, neuroimmune crosstalk, and the orchestration of immune responses. DAMPs in physiological activities. This figure presents an illustrative depiction of the multifaceted roles of DAMPs from diverse cell types in various physiological activities, spanning from fundamental cellular processes such as proliferation and differentiation, to more complex phenomena including migration, inflammatory responses, tissue repair and regeneration, fibrosis development, angiogenesis, bacterial clearance mechanisms, cell death pathways, cellular senescence, effeocytosis, neuroimmune crosstalk, and the orchestration of immune responses. However, distinct DAMP-receptor interactions can have contrasting effects on cell proliferation. In a murine model of inflammatory lung injury, mtDNA is detected by the DNA sensor CGAS, leading to the production of the second messenger cGAMP, which inhibits endothelial cell proliferation by suppressing the proliferation mediator yes-associated protein 1 (YAP1) [ 178 ]. Furthermore, post-translational modifications of DAMPs can modulate their activities and functions. In cancer cells, reduced levels of HMGB1 enhance proliferation, whereas oxidized HMGB1 triggers apoptosis, demonstrating that the redox state of HMGB1 regulates tumor cell survival and death [ 6 , 185 ]. In neutrophils, the calcium-binding S100 calcium-binding protein A9 (S100A9) undergoes phosphorylation, a post-translational modification that influences its subcellular localization and interaction with binding partners. While the referenced study primarily examined neutrophil function, the phosphorylation-dependent structural changes in S100A9 suggest a broader regulatory mechanism by which this modification may influence diverse cellular processes, including proliferation [ 186 ]. Cell differentiation is a complex process in which a less specialized cell transforms into a more distinct cell type. Many diseases are intricately linked to aberrations in cellular differentiation. Therefore, investigating the factors influencing cellular differentiation in both development and disease is crucial. Intracellular and extracellular DAMPs influence the differentiation of various cell types, including myeloid cells [ 187 ], macrophage [ 188 ], T cells [ 189 ], cancer cells [ 190 ], oligodendrocyte progenitor cells [ 191 ] and stem cells [ 192 ] ( Fig. 4 ). In response to diverse stressors, DAMPs act not only as markers of injury but also as signals for regeneration and repair by modulating cellular differentiation. For instance, in a murine model of acute lymphocytic choriomeningitis virus, the alarmin IL-33 promotes the expansion and maintenance of the stemness of Tcf-1 + CD8 + T cells in a suppression of tumorigenicity 2 (ST2)-dependent manner, highlighting the potential benefits of IL-33 blockade in T cell-driven immunopathological conditions such as hemophagocytic lymph histiocytosis and graft-versus-host disease [ 189 ]. Administering exogenous HMGB1 into the mouse heart immediately after MI, prior to the release of endogenous HMGB1, significantly enhanced cardiac function and partially mitigated left ventricular remodeling by initiating regeneration [ 193 ]. Studies using myeloid-specific HMGB1 knockout mice have shown that nuclear HMGB1 in macrophages protects against pressure overload-induced cardiac remodeling by modulating macrophage differentiation towards the M1 phenotype and reducing the inflammatory response [ 188 ]. In addition to pathological conditions, DAMP molecules are also important in physiological processes. Using inducible, stably transfected human embryonic stem cells (hESCs) capable of shRNA-mediated knockdown of HMGB1 and HMGB2, it has been demonstrated that the downregulation of HMGB1 and/or HMGB2 in hESCs significantly affects proliferation, apoptosis, telomerase activity, and differentiation efficiency towards the neuroectodermal lineage [ 192 ]. These findings advance our understanding of the distinct roles of DAMPs during early human development. Extracellular adenosine triphosphate (eATP) plays a critical role in regulating the differentiation of periodontal ligament cells, with its effects on osteogenesis varying depending on the specific purinergic P2 receptors and signaling pathways activated. Additionally, eATP modulates cytokine release, cell proliferation, and immune responses, contributing to periodontal tissue homeostasis [ 194 ]. Cell migration is a fundamental biological phenomenon that plays a pivotal role in various physiological and pathological processes, including embryonic development, tissue regeneration, immune responses, and the dissemination of cancer. It involves a delicately orchestrated sequence of events: cellular polarization, extension of the leading edge, adhesion to the ECM or neighboring cells, contraction of the trailing edge, and detachment at the rear [ 195 ]. These processes are governed by a network of signaling pathways and molecular mechanisms, including cytoskeletal reorganization, cell adhesion molecules, and chemotactic gradients [ 196 ]. Numerous studies suggest that DAMPs serve as potential endogenous chemoattractants, promoting the migration of diverse cell types, such as immune cells [ 197 ], smooth muscle cells [ 198 ], myoblast cells [ 199 ], tumor cells [ 200 ], hepatic stellate cells [ 201 ], stem cells [ 202 ], endothelial cells [ 203 ], and keratinocytes [ 204 ] ( Fig. 4 ). The mechanisms underlying DAMP-mediated cell migration involve signaling transduction pathways, such as MAPK1 (also known as extracellular signal–regulated kinases [ERK]) [ 205 ], cell division control protein 42 (Cdc42) [ 206 ], Ras-related C3 botulinum toxin substrate (Rac) [ 206 ], MAPK8 (also known as JUN N-terminal kinase [JNK]) [ 207 ], PI3K/protein kinase B (AKT) [ 207 ] and SRC [ 208 ], activation of transcription factors (e.g., NF-κB), and the production of chemokines. These findings indicate the role of extracellular DAMPs in facilitating migration, potentially aiding in the recruitment of innate immune cells and stem cells to sites of infection and injury, promoting wound healing and tissue regeneration [ 209 ], atherosclerosis and restenosis after vascular damage [ 210 ], microvascular rolling and adhesion [ 211 ], and tumor invasion and metastasis [ 212 ]. DAMPs such as HMGB1 exhibit dual roles in cell migration, acting both as stimulants and inhibitors. Exogenous HMGB1 selectively impedes vascular endothelial growth factor (VEGF) −induced cell migration in human pulmonary artery endothelial cells (HPAECs) while leaving human umbilical vein endothelial cells unaffected [ 213 ]. Furthermore, the HMGB1-mediated migration inhibition in HPAECs requires the IRF3-dependent TLR4 pathway [ 213 ]. eATP functions as a DAMP when released by injured cells, whereas it serves as a signaling molecule when released by healthy cells. In both contexts, ATP activates purinergic P2 receptors, thereby promoting the migration of immune cells [ 214 ]. Inflammation may manifest as either sterile or infectious, a distinction that unequivocally depends on the recruitment of leukocytes. In the context of infection, the inflammatory cascade is initiated by the recognition of exogenous microbial ligands, referred to as PAMPs, by specific PRRs. Upon engagement of PRRs with their cognate ligands, a series of downstream signaling events is initiated, culminating in the establishment of a pro-inflammatory milieu. This orchestrated response is indispensable for the creation of a robust antimicrobial environment and the prompt activation of the immune system. Conversely, in the absence of an infectious agent, DAMPs, which are immunostimulatory molecular patterns, exploit a similar mechanism during sterile inflammation to evoke cellular damage responses. The progression of sterile inflammation and subsequent tissue repair is contingent upon a meticulously choreographed sequence of leukocyte migration to and from the site of injury. In 1999, the discovery of the secretion of HMGB1 by LPS, shed light on its pivotal role in lethal infection [ 215 ]. It was elucidated that HMGB1 serves as a delayed mediator with cytokine properties in sepsis, a systemic inflammatory response syndrome triggered by microbial invasion. Numerous studies have currently unveiled that a plethora of endogenous DAMPs possess the ability to selectively engage PRRs and non-PRRs, thereby instigating innate and adaptive immune responses by activating a diverse array of cells, including T cells, B cells, monocytes, macrophages, neutrophils, mast cells, DCs, NK cells, eosinophils, astrocytes, keratinocytes, endothelial cells, airway epithelial cells, intestinal epithelial cells and fibroblasts [ 216 , 217 ] ( Fig. 4 ). For example, HMGB1 is a ligand that binds to T-cell immunoglobulin and mucin domain containing 3 (TIM3) on CD4 + T cells, and then inhibits the NF-κB signaling pathway in T cell immunoglobulin and mucin domain-3 (TIM-3 + ) CD4 + T cells to regulate sepsis-induced immunosuppression [ 218 ]. In non-immune cell, recombinant human HMGB1 (rhHMGB1) activates RhoA/ROCK1 pathway via AGER, which phosphorylates MLC inducing stress fiber formation at short time, and HMGB1/AGER reduces AJ/TJ expression at long term independently of RhoA/ROCK1 signaling pathway [ 219 ]. These new findings will help to understand the signaling pathways of rhHMGB1-mediated increase in EC barrier permeability and contribute to establish potential therapeutic targets in the treatment of sepsis. This activation leads to the secretion of a wide range of cytokines, such as TNF, IL-1α, IL-1β, IL-17, as well as various chemokine including CCL5, CXCL1 and others. Additionally, adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin, growth factor, antigens such as CD40 and other inflammatory associated proteins such as tissue factor, inducible nitric oxide synthase (iNOS), mucin 8, inhibitor-signal transducer and activator of transcription-1 (SOCS-1) are also produced. In a mouse model of a cutaneous reverse passive Arthus, HMGB1 blockades reduced the infiltration of neutrophils, DCs, and T cells and decreased the mRNA expression of IL-6 and CCL5 in skin lesions [ 220 ]. The molecular mechanisms driving the potential pro-inflammatory effects of DAMPs involve the activation of several signaling pathways including adaptor proteins MYD88 and TRIF, MAPKs and IKK, transcriptional factors NF-κB, TBK1, phosphorylation of spleen tyrosine kinase (SYK), NLRP3 inflammasome signaling, STING1, p38, MAPK8, phosphoinositide 3-kinase/ protein kinase B (PI3K/AKT), Janus kinase (JAK), SRC, Ets-like protein 1 (ELK-1), sirtuin 1 (SIRT1), and signal transducers and activators of transcription (STATs) [ 221 ] ( Fig. 5 ). Suppression of TLR4-MyD88 signaling pathway attenuated chronic mechanical pain caused by neuroinflammatory cascades in a rat model of endometriosis [ 222 ]. Inhibition of STAT1 attenuates HMGB1 activation and ameliorates chronic kidney inflammation, which highlight the STAT1-HMGB1-NF-κB pathway as a new therapeutic target in cisplatin nephrotoxicity [ 223 ]. Fig. 5 DAMPs in inflammatory response. DAMPs, either alone or in conjunction with other DAMPs/PAMPs, are recognized by PRRs and non-PRRs presented on various immune or non-immune cells. This recognition initiates a cascade of downstream signaling pathways, ultimately culminating in the release of a diverse spectrum of cytokines, chemokines, adhesion molecules, and other inflammatory mediators. In unison, these processes orchestrate the initiation, activation, and amplification of sterile inflammation, thereby facilitating a coordinated response to tissue injury or stress. DAMPs in inflammatory response. DAMPs, either alone or in conjunction with other DAMPs/PAMPs, are recognized by PRRs and non-PRRs presented on various immune or non-immune cells. This recognition initiates a cascade of downstream signaling pathways, ultimately culminating in the release of a diverse spectrum of cytokines, chemokines, adhesion molecules, and other inflammatory mediators. In unison, these processes orchestrate the initiation, activation, and amplification of sterile inflammation, thereby facilitating a coordinated response to tissue injury or stress. Additionally, DAMPs (e.g., HMGB1) have the capacity to interact with other DAMPs or PAMPs (e.g., IL-1β [ 224 ], LPS [ 225 ], cytosine-guanine (CpG)-ODN [ 226 ], Pam3Cys-Ser-(Lys)4 (Pam3CSK4) [ 227 ], lipids [ 228 ], DNA [ 229 ] or nucleosome [ 230 ]) to modulate their pro- or inhibitory-inflammatory effects synergistically. For example, HMGB1 works in combination with IL-1β on ionic and macromolecular barrier permeability through AGER/ERK1/2 is a key signaling pathway, in culturing air–liquid interface 16HBE cells [ 224 ]. Sterile inflammation and inflammatory responses typically involve a variety of DAMPs and DAMP-sensing receptors that collaborate to coordinate the onset, activation, augmentation, and resolution of sterile inflammation. eATP, uric acid crystals, and ROS function as distinct DAMPs that synergistically promote potassium efflux through activation of the P2X7 receptor. This ion flux triggers the assembly of the NLRP3 inflammasome and activation of caspase-1, leading to the cleavage and maturation of pro–IL-1β into its active form. The subsequent release of IL-1β stimulates TNF production by immune cells and promotes neutrophil recruitment, thereby enhancing vascular permeability and amplifying the inflammatory response [ 231 ]. Additionally, interferon-induced protein 35 (IFP35) has been identified as a novel DAMP that triggers inflammatory responses by activating both NF-κB and NLRP3 signaling pathways [ 232 ]. Defense against pathogenic microbes and other stressors is crucial; however, the subsequent repair and regeneration of tissues following infectious or sterile damage are equally essential for the evolutionary fitness of multicellular organisms. Tissue repair and regeneration encompass the intricate processes through which damaged or injured tissues are restored and regrown to their original structure and function [ 233 ]. Numerous dynamic events contribute to tissue repair and regeneration, including wound healing, cellular death, cell dedifferentiation, and the proliferation/recruitment of stem cells [ 234 ]. Furthermore, the polarity and positioning of structures in regenerated tissues must harmonize with preexisting bodily structures [ 235 , 236 ]. In this context, DAMPs, serving as sensors and mediators of inflammation, could potentially act as crucial regulators of tissue repair and regeneration by triggering transient and self-limiting inflammatory and immune responses [ 237 ]. HMGB1 plays a role in facilitating tissue regeneration following acute inflammation. In a mouse model of palatal injury, HMGB1, by binding with its receptor AGER, orchestrates the regeneration of epithelium and connective tissue both in vivo and in vitro during palatal wound healing [ 238 ]. Locally released DAMPs recruit various cell types to aid in tissue reconstruction, such as bone marrow-derived mesenchymal stem cells (MSCs), and foster the proliferation and differentiation of tissue-associated resident stem cells, including dental pulp stem cells [ 239 ], mesoangioblasts [ 240 ], cardiac ckit + cells [ 241 ] and MSCs [ 242 ]. A scaffold immobilized with HMGB1 accelerated the attachment and osteogenic differentiation of MSCs in vitro [ 243 ]. Subsequent subcutaneous implantation and rat calvarial defect repair experiments provided evidence that the HMGB1-immobilized scaffold promoted vascularization and augmented the expression of osteocalcin in vivo [ 243 ]. This study indicated the viability of utilizing HMGB1 as a 'trigger' signal in bone tissue engineering to achieve multiple functions, such as enhancing vascularization, triggering osteogenesis, and attracting stem cells. Angiogenesis is necessary for tissue regeneration, and numerous studies have suggested that DAMPs act as pivotal proangiogenic agents. For instance, endothelial cells express TLRs that act as strategic orchestrators of the immune response while also playing a role in regulating angiogenesis, a crucial process for tissue regeneration [ 244 ]. Biglycan, a recently recognized ECM DAMP, can promote endothelial cell migration, proliferation, and blood vessel formation by activating the hypoxia-inducible factor 1α (HIF-1α) signaling pathway, ultimately leading to VEGF expression in a TLR2- or TLR4-dependent manner [ 244 ]. Since the late 1990s, ATP, along with other nucleotides and their purinergic receptors, has been recognized for their involvement in tissue repair, even before being acknowledged as DAMPs ( Fig. 4 ). eATP may contribute to tissue repair by rapidly stimulating P2RX7-dependent VEGF release from primary human monocytes [ 245 ]. The regenerative capabilities of DAMPs have been studied across various models of tissue injury and repair, including the spinal cord [ 246 , 247 ], liver, skin, muscle, bone, and heart. For instance, a novel fully reduced HMGB1 (frHMGB1)-lysine-diisocyanate (LDI)-glycerol polymer, can form hydrogels that effectively glue tissues together, providing mechanical stability, and scaffolds that release frHMGB1 to enhance cell proliferation to enhance large and deep wounded skin healing [ 248 ]. These findings demonstrate the role of DAMPs in mediating the repair and regeneration processes of various tissues, highlighting their potential as therapeutic targets for enhancing tissue repair and regeneration. Chronic inflammation, coupled with aberrant mechanisms of tissue repair and remodeling, contributes to the pathogenesis of tissue fibrosis. This condition is marked by the abnormal and excessive deposition of ECM components, which impair the function of tissues or organs and, in severe instances, can lead to mortality [ 249 ]. DAMPs, serving as key inflammatory mediators, disrupt the intricate balance between inflammatory responses and tissue regeneration, thereby propelling the remodeling processes that typify fibrosis. Recent literature delineates the role of various DAMPs, such as HMGB1 [ 201 ], S100A8/A9/A12 [ [250] , [251] , [252] ], fibronectin-extra domain A (EDN FN) [ 253 ], tenascin-C [ 254 ], ATP [ 255 ], IL-33 [ 256 ], mitochondrial DAMPs (mtDAMPs) [ 257 ], HSP90 [ 258 ], UA [ 259 ] ( Fig. 4 ), in fibrogenesis. These DAMPs interact with specific receptors including TLRs, CLRs, NLRs, and AGER. Such interactions initiate immune responses and elicit profibrotic reactions in non-immune cells such as hepatocytes [ 260 , 261 ], epithelial cells [ 262 ], endothelial cells [ 263 ], hematopoietic stem cells (HSCs) [ 264 ], and fibroblasts [ 265 ]. DAMPs directly activate fibroblasts, which in turn promotes the activation of myofibroblasts, a process central to fibrosis. S100A4 is a critical DAMP that is released upon cell damage or stress and is significantly associated with fibrosis and mediates its effects through TLR4 or AGER [ 266 ]. One study demonstrated that knockdown of S100A4 inhibits cardiac myofibroblast differentiation after hypoxia and alleviates cardiac fibrosis after myocardial infarction via the Wnt/β-catenin pathway [ 267 ]. Another study also demonstrates that S100A4 drives both inflammatory and fibrotic responses systemic sclerosis (SSc). Targeting S100A4 with monoclonal antibodies effectively attenuated skin fibrosis in murine models and modulated fibrosis-related gene expression in ex vivo human SSc skin [ 268 ]. Extracellular nicotinamide phosphoribosyl transferase (eNAMPT) acts as a DAMP that promotes pulmonary fibrosis via TLR4 signaling, and its neutralization significantly alleviates inflammation and fibrotic progression, highlighting its potential as a therapeutic target [ 269 ]. Furthermore, DAMPs stimulate various innate immune cells, including innate lymphoid cells, plasmacytoid DCs, KCs, and macrophages, to secrete cytokines and chemokines that further recruit cells, sustain inflammation, and enhance profibrotic responses ( Fig. 4 ) [ 249 ]. Consequently, therapeutic strategies targeting DAMPs or their receptors in the context of chronic inflammation have shown potential benefits. However, a refined approach that fine-tunes their activity could prove more advantageous than complete inhibition. Therefore, an in-depth understanding of the interactions among cells during inflammation and tissue regeneration, as well as the signaling pathways mediated by DAMPs, is imperative for effectively regulating excessive inflammation, resolving chronic inflammation and fibrosis, and promoting tissue repair and regeneration. Angiogenesis, the complex process of forming new blood vessels from pre-existing capillaries, is crucial in various physiological and pathological conditions including wound healing, inflammation, infections, autoimmune diseases, and tumor progression. This process encompasses diverse mechanisms such as vasculogenesis, sprouting angiogenesis, intussusceptive angiogenesis, coalescent angiogenesis, vessel co-option, vasculogenic mimicry, and lymphangiogenesis, which collectively contribute to the establishment of new vascular networks [ 270 ]. Extensive studies have identified DAMPs and their receptors as pivotal proangiogenic mediators. For instance, HMGB1 plays a role in neovascularization by recruiting endothelial progenitor cells through integrin activation and facilitating the migration and sprouting of endothelial cells in an AGER/TLR4-dependent manner [ [271] , [272] , [273] ]. Additionally, cytoplasmic TLR9 is essential for HMGB1-mediated cardiac repair and angiogenesis post-MI in murine models, influencing apoptosis and tissue regeneration [ 12 ]. The internalization of HMGB1 via dynamin and AGER, followed by fusion with lysosomes, activation of cathepsin B and L, and the release of VEGF and endoglin, enhances endothelial cell migration, proliferation, and tube formation [ 274 ]. Moreover, in vivo studies show that HMGB1 internalization promotes angiogenesis in models of femoral artery ligation [ 274 ]. HSPs such as HSPA12B [ 275 ], HSP27 [ 276 ], HSP90 [ 277 ], and HSP70 [ 278 ] have also been identified as significant contributors to angiogenesis, with their inhibition presenting potential therapeutic strategies in cancer management [ 279 , 280 ] ( Fig. 4 ). Furthermore, DAMPs foster a proangiogenic microenvironment through interactions with immune cells and stromal components, enhancing angiogenic processes. For example, HMGB1 stimulates endothelial cells and macrophages to release proangiogenic cytokines such as VEGF, TNF, and IL-8 [ [281] , [282] , [283] ]. Additionally, HMGB1 released from leukocytes is crucial in skeletal muscle responses to hypoxia and subsequent angiogenesis following injury [ 280 ]. In response to heat shock and hypoxic stress—both hallmarks of DAMP-induced cellular perturbation—HSP70 promotes endothelial cell proliferation, migration, and angiogenesis through dynamic oligomerization. These findings highlight HSP70’s critical role as a molecular intermediary linking DAMP signaling to vascular adaptive responses [ 284 ]. Collectively, these findings indicate the central role of DAMPs in orchestrating the cellular and molecular dynamics of both physiological and pathological angiogenesis. In response to bacterial infection, DAMPs are released both actively and passively to augment bacterial clearance by direct bacterial killing and the induction of innate and adaptive immune responses ( Fig. 6 ). HMGB1, histones, and mtROS have demonstrated direct bactericidal activity. The extraction of HMGB1 from human and rat testes, using reversed-phase high-performance liquid chromatography, exhibits significant antibiotic efficacy against multiple bacterial strains [ 13 ]. Fig. 6 DAMPs in bacterial clearance. Upon bacterial infection, DAMPs are released to enhance bacterial eradication through direct pathogen killing and the orchestration of innate and adaptive immune responses. Notably, histones have demonstrated robust antibacterial activity against a range of pathogens, like Salmonella typhimurium , Escherichia coli , and Staphylococcus aureus . Additionally, NETosis and macrophage efferocytosis play pivotal roles in tackling bacterial threats. Specifically, HMGB1 activates NETosis through a TLR4-NF-κβ signaling pathway, while mtDNA triggers macrophage efferocytosis in a TLR9-dependent manner, both contributing to the amplification of antibacterial defenses though immune reaction. DAMPs in bacterial clearance. Upon bacterial infection, DAMPs are released to enhance bacterial eradication through direct pathogen killing and the orchestration of innate and adaptive immune responses. Notably, histones have demonstrated robust antibacterial activity against a range of pathogens, like Salmonella typhimurium , Escherichia coli , and Staphylococcus aureus . Additionally, NETosis and macrophage efferocytosis play pivotal roles in tackling bacterial threats. Specifically, HMGB1 activates NETosis through a TLR4-NF-κβ signaling pathway, while mtDNA triggers macrophage efferocytosis in a TLR9-dependent manner, both contributing to the amplification of antibacterial defenses though immune reaction. The bactericidal properties of histones and histone-like proteins are well-documented, with initial reports tracing back to 1942 [ 285 ]. A thorough review has detailed the antibacterial effects of various histones—H1, H2A, H2B, H3, and H4—against pathogens such as Salmonella typhimurium , Escherichia coli , and Staphylococcus aureus ( Fig. 6 ). MtROS plays a dual role in antimicrobial defense and inflammation [ 286 , 287 ]. Produced during mitochondrial energy generation, mtROS also links mitochondrial metabolism to innate immune activation, making cellular ROS a traditional antimicrobial strategy [ 288 ]. Certain antimicrobial agents, such as moxifloxacin, elevate mtROS levels, and contemporary antimycobacterial drugs are known to induce ROS production, which contributes to their antibacterial effectiveness [ 289 ]. The antidiabetic drug metformin, utilized as an adjunct therapy against mycobacterium tuberculosis (Mtb), enhances mtROS production through a protein kinase AMP-activated catalytic subunit alpha 2 (PRKAA2, also known as AMP-activated protein kinase [AMPK])-dependent pathway to inhibit drug-resistant Mtb growth in infected mice [ 290 ]. However, it is important to recognize that mtROS, as a DAMP, may inadvertently enhance bacterial pathogenicity by activating cell death pathways such as pyroptosis and necroptosis, which facilitate bacterial spread and create a pro-bacterial inflammatory milieu [ 291 , 292 ]. NETs are crucial for addressing bacterial threats, comprising elements such as HMGB1, histones, DNA, and various antimicrobial proteins. These components work collectively to suppress and eliminate bacterial pathogens [ 293 ]. The regulation of NET formation and bacterial neutralization is intricately controlled by specific DAMPs and their receptors. For example, HMGB1 can induce NETs through TLR4 activation, enhancing extracellular DNA and histone modification in neutrophils [ 294 ]. Neutrophils from wild-type and AGER knockout mice, when exposed to HMGB1, exhibit increased NET formation, while TLR4 knockout mice show diminished NET generation [ 294 ]. In vitro, treatment with recombinant murine CIRP activates NETs via a TLR4-NF-κβ dependent pathway [ 295 ]. Extracellular vimentin (eVim) and its citrullinated form (CitVim) enhance neutrophil migratory capacity, activate NF-κB signaling, and induce NETs formation, primarily through ROS- and TLR4-dependent pathways. Neutrophils exposed to eVim exhibit increased efficiency in phagocytosing pathogens, such as Escherichia coli and Candida albicans [ 296 ]. Conversely, mtDNA induces NETs in a TLR9-dependent manner, with nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-independent NET release observed in polymorphonuclear neutrophils from healthy individuals; inhibition of TLR9 completely halts NETs [ 297 ]. Macrophages phagocytize lumican, an ECM protein synthesized by fibroblasts, enhancing antibacterial responses via TLR4 but not TLR9. In patients with sepsis, lumican levels are elevated, while mice lacking lumican show reduced bacterial clearance [ 298 ]. These in vitro and in vivo studies highlight that DAMP-mediated bacterial clearance functions through a receptor-specific mechanism. Cell death is a fundamental process in the cellular life cycle, playing a crucial role in development, tissue homeostasis, and immune defense. It is commonly categorized into accidental cell death (ACD) and regulated cell death (RCD) [ 185 , 299 ]. ACD is a rapid and irreversible form of cell demise resulting from overwhelming physical, chemical, or mechanical insults. It is typically characterized by the sudden loss of plasma membrane integrity and passive release of intracellular contents, often provoking strong inflammatory responses. Classical examples of ACD include necrosis induced by ischemia–reperfusion injury, thermal burns, or exposure to extreme toxins. RCD, by contrast, is a genetically encoded, signal-dependent process executed through well-defined molecular pathways. Unlike ACD, RCD is initiated by specific intracellular or extracellular stimuli and can be modulated or inhibited by pharmacological agents or genetic manipulation [ 300 ]. Representative forms of RCD—including apoptosis, necroptosis, pyroptosis, ferroptosis, NETosis, alkaliptosis, cuproptosis, and triaptosis —are closely associated with cellular stress responses such as oxidative stress, metal ion dysregulation, pH imbalance, and impaired autophagy [ [301] , [302] , [303] , [304] , [305] , [306] , [307] , [308] ]. RCD is not entirely passive but rather a precisely orchestrated process, and some of the mechanisms associated with cell death do not invariably result in cell demise (e.g., NETs can be either suicidal or vital) [ 309 ]. Owing to its programmable and tunable nature, RCD plays a central role not only in maintaining physiological homeostasis but also in the pathogenesis of a broad spectrum of inflammatory, autoimmune, and degenerative diseases. In contrast, ACD—particularly necrosis—represents a non-programmed yet immunologically relevant form of cell demise, often characterized by the sudden release of intracellular contents. Both RCD and necrotic ACD are increasingly recognized as major sources of immunologically active DAMPs, which can influence the magnitude and quality of immune responses. Far from being passive byproducts of dying cells, DAMPs actively engage in intercellular communication, modulate immune signaling, and shape inflammatory trajectories. In this section, we focus on the emerging roles of key DAMPs in cell death ( Fig. 7 ). Fig. 7 DAMPs in cell death. Cell death, a cornerstone of the cellular lifecycle, broadly encompasses apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis, NETosis, alkaliptosis, and cuproptosis. Here, we provide a concise overview of the distinctive characteristics of these various cell death pathways. Notably, a multitude of DAMPs play pivotal roles in initiating and modulating these diverse forms of cell death. Additionally, DAMPs can be passively released following various forms of cell death triggered by diverse stimuli or injuries and significantly impact the subsequent immune responses and inflammatory cascades. DAMPs in cell death. Cell death, a cornerstone of the cellular lifecycle, broadly encompasses apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis, NETosis, alkaliptosis, and cuproptosis. Here, we provide a concise overview of the distinctive characteristics of these various cell death pathways. Notably, a multitude of DAMPs play pivotal roles in initiating and modulating these diverse forms of cell death. Additionally, DAMPs can be passively released following various forms of cell death triggered by diverse stimuli or injuries and significantly impact the subsequent immune responses and inflammatory cascades. Initially, pathologists coined the term “necrosis” to describe irreversible tissue damage resulting from severe inflammation. Necrosis, characterized by cell swelling and rupture of the plasma membrane, is considered an uncontrolled and accidental form of cellular damage [ 310 ]. Various chemical or physical agents such as toxins, alcohol, drugs, radiation, heat, trauma, and ischemia–reperfusion (I/R) injuries can lead to necrosis. The loss of cellular boundaries due to membrane breach allows for the release of all cellular constituents, potentially eliciting the release of assorted DAMPs. Conversely, different modes of cell death may exhibit specificity in the types of DAMPs released based on their underlying mechanisms. Tissue ischemia and hypoxia, for example, can induce necrosis by depleting intracellular ATP, disrupting the pump-leak equilibrium, and resulting in an influx of Na + and water, leading to cellular swelling. Reperfusion exacerbates cellular injury by triggering the production of various oxidants and free radicals [ 311 ]. Numerous DAMPs, including but not limited to HMGB1, ATP, histones, HSPs, extracellular RNAs (exRNAs), cfDNA, and potentially CIRP, have been identified as being released during necrosis [ 7 , 312 , 313 ] ( Fig. 7 ). However, it remains unclear whether there is a specific DAMP that can predict the sensitivity of necrosis but not non-necroptotic death. It is also necessary to evaluate whether membrane repair mechanisms differ in response to various necrotic stimuli. Apoptosis, a highly orchestrated form of RCD, occurs across a spectrum of physiological and pathological conditions. It is characterized by distinct morphological hallmarks including cytosolic contraction, membrane blebbing, chromatin compaction, and DNA fragmentation [ 310 ]. Apoptosis can be initiated through two primary pathways: the extrinsic (death receptor) pathway and the intrinsic (mitochondrial) pathway, both of which converge at the activation of the caspase cascade signaling pathway and endonuclease activation. Caspases, a group of intracellular cysteine-aspartic proteases, play a central role in apoptosis and pyroptosis [ 314 , 315 ]. Within the apoptosis process, two categories of caspases exist: initiators (e.g., caspase-8, caspase-9, or caspase-10) and executors (e.g., caspase-3, caspase-6, and caspase-7), which facilitate cleavage of mitochondrial complex 1 protein p75, leading to the release of DAMPs (e.g., HMGB1) during apoptosis [ 316 , 317 ] and activating the immune system. During apoptosis, caspases might increase the immunogenicity of apoptotic cells by generating neoantigens, which can trigger autoimmune responses [ 318 , 319 ]. However, caspases also render apoptotic cells tolerogenic by preventing DAMP signaling induced by mtDNA [ 320 , 321 ]. Thus, caspases can determine both the tolerogenicity and immunogenicity of apoptotic cells by regulating DAMPs. The release of DAMPs from apoptotic cells is typically minimal and promptly cleared via efferocytosis. Thus, apoptotic cells have long been considered to be either intrinsically tolerogenic or incapable of eliciting immune responses specific to antigens associated with dead cells [ 322 , 323 ]. Only under pathological conditions [ 324 ] or as a result of effective anti-cancer therapy [ 325 ] can apoptosis become immunogenic. This form of apoptosis is named “ICD” and is characterized by DAMP [ 14 ]. Disruptions or compromises in apoptosis can lead to post-apoptotic necrosis, leading to release of DAMPs, such as IL-1α, UA, EMAP II, low molecular weight nucleotides, and HMGB1-nucleosome complexes [ 326 , 327 ]. Apoptosis can expose nuclear substances at the cell surface and release them extracellularly, functioning as DAMPs [ 328 ]. Nuclear DAMPs including HMGB1, histones, exRNAs, and cell-free DNA (cfDNA) are released during apoptosis [ 329 ] ( Fig. 7 ). The mechanisms of DAMP release during apoptosis can vary; for instance, histone release is closely linked to DNA fragmentation, orchestrated by caspase-activated DNase/DNA fragmentation factor [ 330 ]. ATP discharge from apoptotic cells triggered by ER stress occurs in a eukaryotic translation initiation factor 2 alpha kinase 3 (EIF2AK3, also known as protein kinase RNA-like endoplasmic reticulum kinase [PERK])-dependent manner [ 331 ], while cfDNA and exRNAs are detected in microparticles emanating from apoptotic cells [ 332 ]. However, a more comprehensive understanding of the specific mechanisms governing the release of each DAMP during apoptosis is needed. Furthermore, DAMPs play pivotal roles as messengers and participants in various facets of apoptosis, influencing both the resolution of cell death and the initiation of immune responses. For example, HMGB1 released from apoptotic tumor cells during chemotherapy or radiotherapy stimulates tumor antigen-specific T-cell immunity, activating antitumor immunity via TLR4 expressed by DCs [ 333 ]. The redox status of HMGB1, influenced by oxidative stress, appears to determine the immunogenicity or tolerogenicity of cell death [ 6 ]. In a mouse model of myocardial ischemia, HSP60 stimulates TLR4, leading to activation of caspase-8 and −3 and MYD88 signaling pathways, inducing apoptosis of cardiomyocytes [ 334 ] ( Fig. 7 ). Following apoptosis, histones H3 and H4 are released extracellularly as DAMPs, where they bind to TLR4 and TLR2 on macrophages, activating the NF-κB signaling pathway and subsequently inducing the secretion of pro-inflammatory cytokines such as TNF and IL-6 [ 335 ]. In the era of 'precision medicine,' liquid biopsies utilizing cfDNA have emerged as promising tools in oncology and inflammation [ 336 ]. For example, the fragment length of cfDNA varies depending on the type of cell death; cfDNA derived from apoptotic cells is approximately 180 base pairs due to fragmentation, while cfDNA released from necrotic cells can extend to over 10,000 base pairs [ 337 ]. Such cfDNA within the DAMP pool has the capacity to orchestrate intra- and inter-cellular signaling cascades, upregulating the transcriptional expression of inflammatory mediators and triggering oxidative stress within cells [ 338 ]. In summary, the release of DAMPs, particularly nuclear DAMPs, from apoptotic cells plays a multifaceted role in immune regulation, inflammation, tissue repair, and disease pathogenesis, underscoring its significance in diverse physiological and pathological contexts. Understanding the interplay between phagocytic clearance mechanisms and DAMP release during apoptosis is essential for comprehending the immunogenicity of apoptotic cells across various stages. Besides classical uncontrolled necrosis, a regulated form known as necroptosis can be triggered by cytokines (such as TNF, IFN-I or IFN-II), viral infections, or chemotherapy, particularly under conditions where caspase activity is inhibited [ 339 ]. Unlike the non-inflammatory apoptosis observed during embryonic development or in maintaining tissue homeostasis, necroptosis leads to early permeabilization of the plasma membrane and elicits a robust pro-inflammatory response [ 340 ]. Moreover, inhibition of caspases can shift apoptosis to necroptosis, suggesting a distinct hierarchy of responses where necroptosis, coupled with the subsequent release of DAMPs, serves as a final recourse. The key components of the necroptosis machinery, including receptor-interacting serine/threonine-protein kinase 1 (RIPK1), RIPK3, and the pseudokinase mixed-lineage kinase domain-like (MLKL), play pivotal roles in promoting necrosome formation through phosphorylation modifications [ 341 ]. A mechanism involving ligand binding recruits RIPK1 to TNF receptor superfamily and TLR complexes, leading to both pro-survival and pro-inflammatory outcomes. Acting as a transition between TNF-induced apoptosis and necrosis, the RIPK3 protein serves as a more precise and specific regulator of necroptosis compared to RIPK1. However, in cases where caspase 8 activity is completely blocked, RIPK1 can interact with RIPK3 through their common RIP homotypic interaction motif (RHIM) domains, triggering autophosphorylation of RIPK3, followed by the phosphorylation and oligomerization of MLKL. Subsequently, MLKL translocates to the cell membrane, causing disruption and ultimately leading to necroptotic cell death [ 342 ]. This process is highly pro-inflammatory due to the release of intracellular contents, such as unprocessed nuclei-containing HMGB1, long genomic DNA, histones, damaged mitochondria, full-length IL-33, IL-1α, S100 proteins, and ATP [ 343 ] ( Fig. 7 ). Animals treated with necrostatin-1, an inhibitor of RIPK1, exhibit reduced serum levels of HMGB1 and are shielded from morphological damage in the jejunum [ 344 , 345 ]. Inhibition of necroptosis restricts the generation of inflammatory molecules, such as HMGB1, and prevents CD8 + cytotoxic T-lymphocyte-induced cell death of myotubes. Conversely, administration of anti-HMGB1 antibodies alleviates myositis-induced muscle weakness, as well as muscle cell inflammation and death within the muscular tissues [ 346 ]. Recent studies have shown that MLKL promotes inflammation not only in a cell non-autonomous manner through the release of DAMPs but also in a cell-autonomous manner by inducing mtDNA leakage and activating the cGAS–STING signaling pathway [ 347 ]. In parallel, RIPK3 has been detected in the plasma of patients with acute myocardial infarction, where elevated levels correlate with poor cardiovascular outcomes following percutaneous coronary intervention. Mechanistically, extracellular RIPK3 binds to AGER on target cells and triggers the activation of calcium/calmodulin-dependent protein kinase II (CaMKII), thereby exacerbating myocardial injury [ 348 ]. Together, the release of DAMPs during necroptosis-induced inflammation serves as a critical link between cell death and the immune response, regulating the inflammatory microenvironment and influencing tissue repair and regeneration processes. In tumor therapy, DAMPs serve as mediators of antitumor immune responses by necroptotic cells. Inflammation-associated pyroptosis predominantly occurs in immune cells, such as macrophages and monocytes, characterized by swift membrane rupture and the release of intracellular molecules (including those belonging to the IL-1 family and DAMPs) through the stimulation of gasdermin family components [ 349 ]. It has been elucidated that plasma membrane rupture is not a passive occurrence but rather a meticulously orchestrated event. Remarkably, the assembly of the ninjurin-1 (NINJ1) protein also governs membrane permeability and the release of DAMPs in apoptosis, necrosis, and pyroptosis, albeit not in necroptosis [ 350 ]. Furthermore, the role of NINJ1 in regulating DAMP release in ferroptosis is still under debate [ 351 ]. Pyroptosis is commonly mediated by the activation of murine caspase-1 (canonical pyroptosis) or caspase-11 (non-canonical pyroptosis, also identified as human caspase 4 or caspase 5 [ 352 ]. In canonical pyroptosis, caspase 1 is activated downstream of inflammasomes comprising self-oligomerizing scaffold proteins [ 353 ]. The activation of inflammasomes requires multiple signals, including K + efflux [ 354 ], Ca 2+ influx [ 355 ], and lipid peroxidation [ 356 ]. Cellular swelling and rupture of cell membranes due to escalated osmotic pressure, alongside the ensuing release of DAMPs, such as ATP, HMGB1, and potentially mtDNA from impaired mitochondria [ 350 , 357 ]. In breast cancer cells, eATP release activates P2X7R and downstream release of NADPH oxidases-generated ROS, calcium/calmodulin dependent protein kinase II beta (CAMK2B) activation, which drives a mixed apoptotic and necrotic mode of cell death associated with activation of caspase-1 and pyroptosis [ 358 ]. Despite pyroptosis likely representing one physiological reaction to infection, such as apoptosis and necroptosis, disproportionate hyperactivation of this pathway can culminate in inflammatory diseases. For instance, in cecum ligation and puncture bacterial sepsis model and endotoxemia model induced by LPS, HMGB1 can facilitate LPS uptake to trigger caspase-11-dependent pyroptosis into the lysosomes of macrophages and endothelial cells via AGER [ 359 ]. Histones, ATP, CIRP, and molecules associated with NETs, also augment the inflammatory cascade to exacerbate cellular and tissue damage, leading to heightened severity of infections [ 329 ]. eATP, binding to purinergic ionotropic receptor (P2XR), results in increases in intracellular calcium, which activates the p38 MAPK pathway, activating the inflammasome with the associated caspase-1 activation and release of pro-inflammatory cytokines IL-1β and IL-18 [ 360 , 361 ]. Removal of eATP to decrease activation of the P2X7 receptor by CD39 attenuates sepsis-induced liver injury in some murine models of sepsis [ 362 ]. Moreover, the recognition of DAMPs by PPRs can trigger the assembly of the inflammasome or directly induce non-canonical pyroptotic cell death in the absence of infection, a phenomenon most prominently observed in sterile inflammation and various diseases [ 363 , 364 ]. Hence, the activation of inflammasome-dependent pyroptosis appears to contribute to the amplification of inflammation triggered by DAMPs released from other forms of cell death. Among the PRRs, TLRs and AGER play a key role in mediating DAMP release by pyroptosis, regulating inflammatory responses in conditions such as I/R injury, RA and cancer [ 363 ] ( Fig. 7 ). Despite incomplete understanding of the underlying mechanisms, TLRs and AGER exhibit the ability to recognize different DAMPs owing to their broad ligand specificity and structural diversity. This characteristic enables them to detect various danger signals and initiate appropriate immune responses. Ferroptosis, a form of iron-dependent regulated necrosis, can be induced by pharmacological agents or small-molecule compounds, resulting in iron accumulation and subsequent lethal lipid peroxidation [ [365] , [366] , [367] ]. This process is characterized by the buildup of lipid peroxidation products (e.g., 4-hydroxynonenal [4HNE] and malondialdehyde [MDA]) and can be mitigated by iron chelators and lipophilic antioxidants [ 368 ]. At the molecular level, the process of ferroptosis is highly context-dependent and can be inhibited by multiple antioxidant systems, including glutathione peroxidase 4 (GPX4)-dependent and −independent pathways [ 369 ]. Morphologically, ferroptosis presents with disrupted mitochondrial morphology [ 370 ]. While not fully understood, it is acknowledged that HMGB1 and cfDNA are released during ferroptosis [ 367 , [371] , [372] , [373] ]. The release of HMGB1 is a common occurrence across various forms of cell death, including ferroptosis, and oxidative stress-induced nuclear damage may disrupt HMGB1 binding to chromatin [ 374 ]. In addition to DAMP release, activation of the rat sarcoma/mitogen-activated protein kinase/extracellular signal–regulated kinases (RAS/MAPK/ERK) pathway during ferroptosis leads to a distinct cytokine production profile compared to pyroptosis [ 365 ]. Ferroptosis also directly triggers arachidonic acid metabolism and eicosanoid synthesis, resulting in the release of lipid oxidation byproducts such as leukotriene B4 (LTB4), LTC4, 4HNE, oxidized phospholipids, LTD4, and prostaglandin E2 (PGE2) [ 375 ]. Additionally, decorin (DCN) is a specific and sensitive DAMP released during ferroptosis, which can activate AGER signaling in macrophages [ 376 ]. Factors secreted during ferroptosis can directly impact inflammation, akin to IL-1 release in pyroptosis. Moreover, the activation of innate immune cells through DAMP production indirectly regulates inflammation. Ferroptosis is initiated by signaling pathway activation, including MAPK/ERK or STING1, in response to various DAMPs such as pannexin 1 and mtDNA [ 377 , 378 ] ( Fig. 7 ). Whether ferroptotic cell death is immunogenic remains debated, and a possible reason is that ferroptotic death not only releases immune-stimulating DAMPs but also immune-suppressive DAMPs [ 370 ]. Moreover, the immunogenicity of ferroptosis may depend on the stage of cell death. Efimova et al. demonstrate that only early-stage ferroptotic cancer cells can facilitate adaptive immune responses by releasing ATP and HMGB1 [ 379 ]. In contrast, Wiernicki et al. recently reported that ferroptotic cells lack immunogenicity at all stages, reducing the phagocytic potential and maturation of DCs and impairing antigen cross-presentation [ 380 ]. Thus, future studies will be needed to elucidate the molecular basis of different DAMPs and their receptor collaboration in ferroptosis. NETosis is a form of RCD predominantly occurred in neutrophils, characterized by the extrusion of a web-like structure comprising histones and chromatin, alongside a mixture of granular and cytoplasmic proteins known as NETs [ 381 ]. Analogous extracellular networks have been observed to originate from various other cell types, including mast cells, macrophages, eosinophils, and even T- and B-cells [ 382 ]. The genesis of NETs is believed to play a pivotal role in microbial defense; however, its impact on maintaining host homeostasis is multifaceted, as it may induce pathological changes leading to tissue damage. The precise mechanisms underpinning NETs remain incompletely elucidated; nevertheless, pivotal processes appear to include the generation of ROS, the translocation of neutrophil proteases such as elastase and myeloperoxidase (MPO) from granules to the nucleus, the modification of histones by peptidylarginine deiminase 4 (PAD4), chromatin decondensation, and the expulsion of chromatin fibers laden with ensnared granular proteins [ 383 , 384 ]. While these events could culminate in cellular rupture and NETotic cell death, subsequent discoveries have revealed that NETs can also be released from live cells [ 329 ]. NET extrusion without cellular death may entail the selective release of mtDNA [ 385 ]. Several observations implicate a mechanistic convergence between NETs and other cell death modalities. For instance, both caspase 11 and gasdermin D are indispensable for plasma membrane rupture and the facilitation of NET release in neutrophil exposure to cytosolic LPS or cytosolic gram-negative bacteria (Salmonella ΔsifA and Citrobacter rodentium), or in vivo during murine Salmonella ΔsifA challenge [ 386 ]. Additionally, necroptosis has been linked to the extrusion of NETs. In both murine and human neutrophils, the necroptotic cell death effector MLKL underwent translocation from the cytoplasm to the plasma membrane, triggering downstream ROS production independent of NADPH oxidase. This process led to the depletion of cytoplasmic granules, disruption of the nuclear membrane, chromatin decondensation, hypercitrullination of histones, and the expulsion of bacteriostatic NETs [ 387 ]. NETs are produced in response to a diverse set of stimuli, including PAMPs, DAMPs, and various inflammatory mediators. These stimuli activate an array of receptors, such as TLRs [ 388 ]. The primary function of NETs is to physically contain pathogens at the site of infection, highlighting the critical role of NET formation in microbial defense [ 389 ]. However, the influence of NETs on host homeostasis is complex, as they also have the potential to induce pathological changes that lead to tissue damage. During NETs, neutrophils with ruptured cell membranes can release DAMPs and a variety of inflammatory mediators, including histones, HMGB1, CIRP, MPO, and the cathelicidin antimicrobial peptide LL37. These cells also release more than 30 constituents from primary and secondary granules, some of which, such as neutrophil elastase (NE) and MPO, possess bactericidal properties, thereby amplifying the inflammatory response [ 390 ] ( Fig. 7 ). Accumulating evidence suggests that NET-associated DAMPs can perpetuate sterile inflammation by activating innate immune receptors, such as TLRs and NLRs, even in the absence of infection [ 391 ]. The persistent presence of these DAMPs in the extracellular milieu contributes to chronic immune activation, impaired resolution of inflammation, and collateral tissue damage. These mechanisms are increasingly recognized in the pathogenesis of chronic inflammatory, autoimmune diseases and ischemic diseases [ 392 ]. Extracellular HMGB1—particularly when derived from activated platelets—plays a critical role in promoting neutrophil activation and intravascular NETosis through TLR4-dependent signaling, thereby exacerbating ischemic brain injury [ 393 ]. Thus, investigating the role of DAMPs in NETs within the context of disease progression holds the potential to yield novel therapeutic applications. Significant advancements have been made in understanding the impact of dysregulated pH on cellular survival and death mechanisms. Intracellular acidification is known to induce autophagy [ 394 ], apoptosis [ 395 ], and necroptosis [ 396 ]. In contrast, alkaliptosis is a regulated necrosis triggered by alkaline agents (such as sodium hydroxide, ammonia, or high-pH buffers) or small molecular JTC801 [ 397 ]. Characterized by distinct shifts in intracellular pH, alkaliptosis was initially identified as a method to selectively target malignant cells while sparing normal cells [ 398 ]. Alkaliptosis proceeds via a sequential molecular pathway influenced by various factors and can be induced in mouse or human pancreatic cancer cells using the small molecule JTC801 [ 399 ]. This molecule activates the NF-κB pathway and suppresses carbonic anhydrase 9, a transmembrane metalloenzyme essential for pH regulation [ 397 ]. Further studies revealed that acetyl-CoA short-chain synthase family member 2 (ACSS2) enhances NF-κB activation in human pancreatic ductal adenocarcinoma cells (PDACs), promoting alkaliptosis via acetyl-coenzyme A production and histone acetylation, effects augmented by the histone deacetylase inhibitor trichostatin A [ 400 ]. As an NF-κB-independent alkaliptosis, increased interaction between ATPase H + transporting V0 subunit d1 (ATP6V0D1) and signal transducer and activator of transcription 3 (STAT3) can result in enhanced expression and activity of STAT3, which sustains lysosomal pH homeostasis in PDACs [ 401 ]. Additionally, sterol regulatory element-binding transcription factor 2 (SREBF2)–mediated upregulation of cytochrome P450 family 51 subfamily A member 1 (CYP51A1) prevents cholesterol accumulation within lysosomes, which in turn facilitates TMEM175-dependent lysosomal proton efflux and ultimately inhibits alkaliptosis [ 402 ]. Similarly, macropinocytosis-mediated uptake of extracellular fatty acids has been identified as an alternative metabolic route that suppresses alkaliptosis by supporting cellular adaptation to pH stress [ 403 ]. The profound pH imbalance in cancer cells offers a therapeutic target for alkaliptosis, impacting tumor growth, spread, and metabolic adjustments [ 398 , 404 ]. During alkaliptosis, HMGB1 and lactate dehydrogenase are released, a process that is blocked by the DNA repair pathway involving FA complementation group D2 (FANCD2) but not affected by ataxia-telangiectasia–mutated proteins [ 405 ]. Released HMGB1 binds to the AGER receptor on macrophages, activating the STING1 pathway to produce pro-inflammatory cytokines (e.g., TNF and IL-6) [ 405 ] ( Fig. 7 ), thereby implicating HMGB1 as an immune mediator in the pH-induced cell death pathway. Future studies need to evaluate whether alkaliptotic cell death is immunogenic and thus capable of promoting adaptive immunity for tumor therapy. Cuproptosis is a recently identified form of programmed cell death that is distinct from other known forms such as apoptosis [ 406 ]. Discovered through studies published around 2022, cuproptosis is triggered by the accumulation of intracellular copper, which leads to toxic effects on cells [ 406 ]. The key mechanism underlying cuproptosis involves copper binding directly to lipoylated components of the tricarboxylic acid cycle [ 406 ]. When copper binds to these lipoylated proteins, it disrupts their normal function. This disruption leads to proteotoxic stress and the aggregation of lipoylated proteins, ultimately causing cell death [ 304 ]. This form of cell death is unique in that it does not depend on the common pathways associated with other types of cell death, such as the activation of caspases in apoptosis. In contrast, ferredoxin 1 is identified as a critical mediator of cuproptosis [ 407 ]. Recent research has demonstrated that mitochondrial impairment leads to ATP depletion, prompting the activation of PRKAA2 to facilitate HMGB1 phosphorylation, consequently enhancing its extracellular release [ 408 ]. Conversely, inhibiting PRKAA2, either genetically or pharmacologically, suppresses cuproptosis and the release of HMGB1 [ 408 ]. HMGB1 is identified as a more sensitive marker of early cuproptosis compared to other DAMPs [ 408 ]. Functionally, the extracellular release of HMGB1 from cuproptotic cells initiates AGER-dependent inflammatory responses, highlighting the critical role of AGER as a receptor mediating HMGB1 activity associated with cell death. A recent study demonstrated that hyaluronic acid–modified zinc–copper bimetallic peroxide nanoparticles (ZCPO@HA) can simultaneously induce ferroptosis and cuproptosis in tumor cells [ 409 ]. In addition to triggering these distinct forms of RCD, ZCPO@HA nanoparticles activate the cGAS–STING signaling pathway, thereby enhancing antitumor immunity [ 409 ]. Furthermore, these nanoparticles exhibit synergistic efficacy when combined with immune checkpoint blockade therapy using anti–PD-1 antibodies, resulting in amplified antitumor immune responses. It remains to be determined whether mtDAMPs or other molecules, such as mtDNA, contribute to the pathogenesis of inflammation induced by cuproptosis ( Fig. 7 ) [ 410 ]. ICD represents a unique form of stress-induced RCD that activates cytotoxic T lymphocyte (CTL)-mediated adaptive immunity and establishes long-term immunological memory specific to antigens expressed by dying cells in immunocompetent hosts [ 300 ]. Necroptosis, ferroptosis, and pyroptosis are three potentially mechanisms implicated in ICD [ 411 ]. The capacity of ICD to stimulate adaptive immunity is determined by two key factors: antigenicity and adjuvanticity [ 412 ]. Moreover, adaptive immune responses triggered by ICD can only be effectively sustained within a permissive microenvironment [ 412 ]. For stress-induced RCD to elicit adaptive immune responses, dying cells must present antigens not subjected to central or peripheral tolerance. [ 412 ]. Antigenicity in ICD arises from various sources, including (1) pathogen-encoded antigens [ 413 ], (2) mutational neoantigens [ 414 ], and (3) a large panel of non-mutational neoantigens [ 415 , 416 ]. Infected or malignant cells are key sources of antigenic determinants, as microbial proteins and cancer-derived antigens escape central tolerance, rendering their epitopes highly immunogenic [ 417 ]. However, when stress-driven RCD exhibits sufficient antigenicity but lacks adjuvanticity, it promotes DC-mediated immune tolerance rather than immunity [ 418 ]. Similar to prophylactic vaccines against pathogens, ICD requires robust adjuvants to enhance APC-mediated adaptive immune responses [ 419 , 420 ]. These adjuvants, commonly known as DAMPs, are typically released or exposed on the plasma membrane in response to pre-mortem cellular stress [ 417 ]. To date, three DAMPs are identified as critical to the immunogenic potential of ICD: the ER chaperone calreticulin (CALR) [ 421 , 422 ], ATP [ 331 ], and HMGB1 [ 423 ]. In addition, several other DAMPs have been shown to enhance immunogenicity in specific experimental contexts, including immunostimulatory cytokines like IFNα [ 424 ], various chaperones of the HSP family, notably HSP70 and HSP90 [ 425 , 426 ], sphingomyelin metabolites (e.g., ceramide and sphingosine-1-phosphate) [ 427 ], a plethora of mitochondrial products (e.g., mtDNA, N-formylated peptides, cardiolipin) [ 428 , 429 ], cytosolic components like urate [ 430 ] and F-actin [ 431 ], as well as products of the breakdown of the ECM (e.g., hyaluronan fragments) [ 432 ]. Importantly, not all DAMPs are immunostimulatory, which contributes to the failure of some RCD modalities to provoke adaptive immunity [ 433 ]. For example, PGE2, which is abundantly released upon CASP3 activation, has potent immunosuppressive effects [ 434 ]. In summary, DAMPs play a multifaceted role in the immunogenicity of ICD, particularly in inflammatory diseases and cancer therapy [ 435 ]. Understanding the mechanisms of DAMP release is critical for comprehending the immunogenic potential of ICD and its therapeutic implications. Cellular senescence is characterized by the irreversible arrest of the cell cycle, which can be induced across various primary cell types in response to DNA damage [ 436 , 437 ]. This state of senescence, when cells accumulate excessively, contributes to adverse outcomes, including cell death and a range of diseases such as inflammation, malignancy, and aging processes [ [438] , [439] , [440] ]. DAMPs serve as biomarkers of senescence and aging, with their release and localization reflecting cellular senescence. For example, HMGB1, when redistributed to the ECM in senescent cells [ 441 ], can instigate p53-dependent cellular senescence in both human and murine cells, both in vitro and in vivo, thereby signifying HMGB1 translocation as a key feature of senescence [ 15 , 16 ]. Mitochondria are critical sources of DAMPs. With aging, disruptions in mitochondrial homeostasis, including compromised DNA repair, protein quality control, and mitophagy, lead to increased release of mtDAMPs [ 442 ]. The association of DAMPs with aging is not merely incidental; they actively drive the senescence process. Immuno-senescence involves the dysregulation of both innate and adaptive immune systems, characterized by the accumulation of age-related DAMPs. This accumulation activates the inflammasome, increases TNF levels, and causes mitochondrial dysfunction [ 443 ]. Extracellular histones can trigger inflammation and senescence in vascular smooth muscle cells by activating the NLRP3 inflammasome and the AMPK-fork head box protein O4 (FOXO4) pathway, thus exacerbating histone-induced damage in mice [ 444 ]. Senescent cells contribute to age-related tissue dysfunction, in part, through the establishment of a SASP. Extracellular HMGB1 promotes the release of inflammatory cytokines via the TLR2/4 and NF-κB signaling pathways, facilitating the production of SASP [ 441 , 445 ]. Mitochondria also regulate SASP, with studies showing that apoptotic stress leads to mtDNA release during senescence, activating SASP through the CGAS–STING1 signaling pathway in human fibroblasts and aged mice [ 77 ]. Moreover, DAMPs enhance the senescence of tumor cells, increasing the effectiveness of chemotherapy [ 437 , 446 ]. For instance, treatment with doxorubicin induces senescence in mouse melanoma cells and multiple other cell lines in a HMGB1-dependent manner. HMGB1 interacts with the promoter of the E3 ligase tripartite motif protein 30α, suppressing its expression and enhancing STING1-induced senescence [ 221 ]. Additionally, within cellular models, highly metastatic cancer cells preferentially enter senescence under genotoxic stress, whereas weakly metastatic cells are more likely to undergo apoptosis. This response depends on the presence of HMGB1, highlighting the crucial role of the HMGB1-p21 axis in stress-induced senescence [ 447 ]. eATP induces a senescence-like phenotype in A549 lung cancer cells following short-term treatment, demonstrating its pro-senescent potential in tumor cells [ 448 ]. These findings support the significant role of DAMPs in inducing cellular senescence and their potential as therapeutic targets in cancer treatment. Efferocytosis, the biological process responsible for clearing apoptotic cells, is critical for the elimination of hazardous and dysfunctional cells, thus maintaining homeostasis. Impairments in efferocytosis can lead to an accumulation of late apoptotic and secondary necrotic cells, which in turn can provoke inflammatory responses. DAMPs serve dual roles in this context: as 'find-me' signals or alarmins that enhance the recognition by phagocytic cells, and, paradoxically, as mediators that can initiate immune reactions and autoimmunity when efferocytosis is defective. This process is facilitated by a complex array of molecules [ 449 ]. A study utilizing mouse models susceptible to liver fibrosis demonstrated that during the efferocytosis of dying hepatocytes, damaged mitochondria release mtDAMPs, with mtDNA being a key active component. This release activates hepatic stellate cells, thereby promoting liver fibrosis [ 450 ]. Moreover, specific DAMPs, such as HMGB1 and histones, are known to negatively regulate efferocytosis. For instance, HMGB1 present in bronchoalveolar lavage fluid from patients with acute respiratory distress syndrome (ARDS) significantly reduces the macrophage-mediated engulfment of NETs and apoptotic neutrophils through an AMPK-dependent mechanism [ 451 , 452 ]. Similarly, the presence of histones H3 and H4, but not H1, significantly impairs the efferocytosis of apoptotic neutrophils or thymocytes by macrophages. Histone H3 binds directly to macrophages, an interaction mitigated by preincubation with the opsonin’s growth arrest–specific gene 6 (GAS6) and milk fat globule-epidermal growth factor 8 (MFGE8) [ 453 ]. Various significant DAMPs and their receptors play roles in efferocytosis, including ATP and P2X7R, milk fat globule–epidermal growth factor 8 (MFG-E8), C1q, mannose-binding lectin (MBL), properdin, ficolins, C-reactive protein ( Fig. 4 ), AGER and TLRs. The balance between MFG-E8 and HMGB1 levels determines pathophysiological effects of chronic alcohol exposure on macrophage efferocytosis in vivo [ 454 ]. C1q promotes macrophage survival during ingestion of excess cholesterol, as well as improves foam cell efferocytic function [ 455 ]. MRP8/14 mediates macrophage efferocytosis through AGER and GAS6/MFG-E8, and induces polarization via TLR4-dependent pathway [ 456 ]. Therefore, each component has a distinct impact on the modulation of efferocytosis and its associated pathways. The dynamic interaction between neurons and immune cells, termed 'neuroimmune communication,' plays a pivotal role in both physiological and pathological processes in humans [ 457 ]. DAMPs act as critical signaling mediators that facilitate communication between the nervous and immune systems. Peripheral primary afferent neurons, which express PRRs, are responsive to inflammatory mediators including DAMPs. This arrangement suggests the existence of an innate neural pathway that transmits signals of inflammation or infection from peripheral sites to the central nervous system (CNS). Sensory nerves are capable of detecting PAMPs, such as unmethylated CpG dinucleotides and LPS, in addition to DAMPs (e.g., DNA, histones, HMGB1, ATP, UA) and cytokines [ 458 ] ( Fig. 4 ). Upon infection or injury, the activation of peripheral immune cells and the resultant cytokine cascade can influence sensory neurons, potentially initiating or altering neural signals to the spinal cord and brain [ 459 ]. Moreover, neural pathways, particularly the vagus nerve, modulate the release of DAMPs. In a severe hemorrhage rat model, the vagus nerve was shown to regulate systemic inflammation and the release of HMGB1 via the alpha 7 nicotinic acetylcholine receptor (α7nAChR), suggesting a neurotransmitter role in controlling HMGB1 dynamics [ 460 ]. Our recent data indicates that the vagus nerve also regulates the release of CXCL9 from CD45 + F4/80 + iNOS + CD206 + macrophages and its interaction with the CXCR3 receptor through an α7nAChR-dependent mechanism, a crucial process in the pathogenesis of acute-on-chronic liver failure in both cellular and mouse models ( Fig. 8 ) [ 461 ]. Exposure of rat carotid bodies to various DAMPs, such as HMGB1 in both its thiol and disulfide forms, and S100A8/A9, trigger the release of dopamine and ATP. These neurotransmitters play a significant role in mediating homeostatic responses of the carotid bodies, as demonstrated in a series of ex vivo studies [ 462 ]. Fig. 8 DAMPs in neuroimmune communication. The activation of peripheral immune cells triggers a cascade of cytokines, which can subsequently modulate sensory neurons, potentially initiating or modulating neural signaling pathways to the spinal cord and brain. Our recent, as yet unpublished data further elucidate this complex interplay, revealing that the vagus nerve regulates the release of CXCL9 from a specific subset of macrophages (CD45 + F4/80 + iNOS + CD206 + ) and its interaction with the CXCR3 receptor via an α7nAChR-mediated mechanism. This finding underscores the pivotal role of neuroimmune communication in the pathogenesis of ACLF, as evidenced in both cellular and murine models. DAMPs in neuroimmune communication. The activation of peripheral immune cells triggers a cascade of cytokines, which can subsequently modulate sensory neurons, potentially initiating or modulating neural signaling pathways to the spinal cord and brain. Our recent, as yet unpublished data further elucidate this complex interplay, revealing that the vagus nerve regulates the release of CXCL9 from a specific subset of macrophages (CD45 + F4/80 + iNOS + CD206 + ) and its interaction with the CXCR3 receptor via an α7nAChR-mediated mechanism. This finding underscores the pivotal role of neuroimmune communication in the pathogenesis of ACLF, as evidenced in both cellular and murine models. Additionally, mtDAMPs—including heme, cytochrome c , cardiolipin, ATP, mtDNA, TFAM, N-formyl peptides, and TCA cycle metabolites such as succinate, fumarate, and itaconate—have been shown to play critical roles in modulating neuroimmune processes within the CNS [ 463 ]. In summary, neuroimmune communication and DAMP release are crucial for rapid defense responses and essential in improving treatments for inflammatory and neurodegenerative diseases. DAMPs do not uniformly elicit the same immune responses, displaying both immunostimulatory and immunosuppressive effects depending on the context, which can lead to beneficial or harmful outcomes ( Fig. 9 ). For example, in response to pathogens or tumors, DAMPs (e.g., ATP, DNA, and HMGB1) can activate immune cells by binding to receptors such as TLR4 and AGER, initiating cytokine release and a systemic inflammatory response involving both innate and adaptive immunity. Specifically, HMGB1 may enhance B cell migration and IgA production in the gut, strengthening intestinal defenses [ 464 ]. However, HMGB1 can also induce immunosuppression and immune paralysis during later infection stages. For instance, extracellular HMGB1 binding to AGER on macrophages triggers dynamin-dependent endocytosis, leading to cathepsin B activation and inflammasome-induced pyroptosis, which impairs the macrophages’ bacterial clearance capabilities [ 465 , 466 ] ( Fig. 9 ). Fig. 9 DAMPs in immune response. DAMPs exhibit a dual nature, capable of eliciting both immunostimulatory and immunosuppressive effects in response to pathogens or tumors. In the context of pathogen encounter, HMGB1 may enhance B cell migration and IgA production in the gut, strengthening intestinal defenses. Conversely, extracellular HMGB1 binding to AGER on macrophages triggers dynamin-dependent endocytosis, leading to cathepsin B activation and inflammasome-induced pyroptosis, which impairs the macrophages’ bacterial clearance capabilities. In the context of tumorigenesis, HMGB1 contributes to the establishment of an inflammatory microenvironment conducive to cancer progression. This environment supports the metabolic demands of tumor cells, facilitates invasion and metastasis, and undermines anti-tumor immune responses. Furthermore, HMGB1 engages with AGER or TLRs to activate myeloid-derived suppressor cells (MDSCs), Tregs, M2-type macrophages, and regulatory B cells. This activation triggers the NF-κB signaling pathway or autophagy, leading to the release of immunosuppressive molecules including PD-L1, IL-10, TGF-β, and IL-35. The dual functionality of DAMPs, particularly HMGB1, plays a pivotal role in orchestrating the intricate balance between sterile inflammation, pathogen-induced infections, and tumor surveillance. Their ability to switch between immunostimulatory and immunosuppressive modes underscores their complexity and the need for further investigation to harness their potential in therapeutic intervention. DAMPs in immune response. DAMPs exhibit a dual nature, capable of eliciting both immunostimulatory and immunosuppressive effects in response to pathogens or tumors. In the context of pathogen encounter, HMGB1 may enhance B cell migration and IgA production in the gut, strengthening intestinal defenses. Conversely, extracellular HMGB1 binding to AGER on macrophages triggers dynamin-dependent endocytosis, leading to cathepsin B activation and inflammasome-induced pyroptosis, which impairs the macrophages’ bacterial clearance capabilities. In the context of tumorigenesis, HMGB1 contributes to the establishment of an inflammatory microenvironment conducive to cancer progression. This environment supports the metabolic demands of tumor cells, facilitates invasion and metastasis, and undermines anti-tumor immune responses. Furthermore, HMGB1 engages with AGER or TLRs to activate myeloid-derived suppressor cells (MDSCs), Tregs, M2-type macrophages, and regulatory B cells. This activation triggers the NF-κB signaling pathway or autophagy, leading to the release of immunosuppressive molecules including PD-L1, IL-10, TGF-β, and IL-35. The dual functionality of DAMPs, particularly HMGB1, plays a pivotal role in orchestrating the intricate balance between sterile inflammation, pathogen-induced infections, and tumor surveillance. Their ability to switch between immunostimulatory and immunosuppressive modes underscores their complexity and the need for further investigation to harness their potential in therapeutic intervention. In the context of tumorigenesis, DAMPs contribute to an inflammatory microenvironment that supports cancer progression by meeting metabolic demands, facilitating invasion and metastasis, and impairing anti-tumor immunity. Yet, DAMPs also exhibit tumor-suppressive activities by enhancing genomic stability and promoting autophagy [ 7 ]. Studies show that HMGB1 can activate myeloid-derived suppressor cells (MDSC), regulatory T (Treg) cells, M2-type macrophages, and regulatory B cells via AGER or TLRs. This activation leads to NF-κB pathway engagement or autophagy, promoting the release of immunosuppressive molecules such as PD-L1, IL-10, TGF-β, and IL-35 [ [467] , [468] , [469] ] ( Fig. 9 ). DAMPs can also enhance anti-tumor immunity. For example, HMGB1 from NK cells can induce metabolic cell death in colon cancer cells by inhibiting mitochondrial respiration [ 470 ]. Furthermore, DNA damage and HMGB1 release induced by topoisomerase II inhibitors enhance the efficacy of immune checkpoint blockade (anti-PD1) therapy by activating STING1-dependent type I IFN signaling and DC activation in colorectal cancer models [ 471 ]. Targeting cholesterol metabolism can enhance the release of DAMPs, such as ATP and CALR, thereby improving the efficacy of ICD. The released ATP and CRT promote immune cell activation, ultimately leading to improved therapeutic outcomes in ICD-based cancer treatments [ 472 ]. The dual functionality of DAMPs plays a critical role in sterile inflammation, pathogen-induced infections, and tumor surveillance, yet the complexities and regulatory mechanisms underlying these phenomena require further elucidation.

DAMP receptors and signaling pathways are essential for responding to cellular damage by initiating repairs and defending against pathogens. However, dysregulation can lead to chronic inflammation and various diseases, emphasizing their critical role in health. Below, we summarize the key receptors and pathways involved ( Table 1 and Fig. 1 ). Table 1 Types of DAMP-sensing receptors in human and mammals. Types of receptors Representative receptors PRRs TLRs TLR1-TLR10 (In human) CLRs MINCLE, DNGR1 (or CLEC9A), CLEC8A, CLEC12A, and CLEC7A (or Dectin-1) NLRs NLRA, NLRB, NLRC, NLRP, and NLRX1 RLRs LGP2, MDA5, and RIG-I Cytoplasmic DNA sensors cGAS and AIM2 Non-PRRs GPCRs Complement receptors (C5aR1, C5aR2, and C3aR); FRPs (FPR1, FPR2, and FPR3); CaSR TREMs TREM1 and TREM2 AGER − Ion channels TRP channels and P2XR (P2X1R-P2X7R) iPRRs CD300a/f, Siglec-2, 3, and 5–11, CEACAM1, LILRB1, LILRB3, TIGIT, PVR, LAIR-1, and SIRL-1 Abbreviations: AIM2 , absent in melanoma 2; AGER, advanced glycosylation end product-specific receptor; CLRs, C-type lectin receptors; CLEC9A, C-type lectin domain containing 9A; CytC , cytochrome C ; C5aR1, complement component 5a receptor 1; CEACAM1, carcinoembryonic antigen cell adhesion molecule 1; cGAS, cyclic GMP–AMP synthase; CaSR, calcium-sensing receptors; DNGR1, dendritic cell natural killer lectin group receptor 1; FRPs, formyl peptide receptors; GPCRs, G-protein-coupled receptors; iPRRs, inhibitory PRRs; LGP2, laboratory of genetics and physiology 2; LILRB1, leukocyte immunoglobulin-like receptor subfamily B member 1; LAIR-1, leukocyte-associated immunoglobulin-like receptor 1; MINCLE, macrophage-inducible C-type lectin; MDA5, melanoma differentiation factor 5; NLRs, NOD-like receptors; PRRs, pattern recognition receptors; P2XR, purinergic ionotropic receptor; RLRs, RIG-I-like receptors; RIG-I, retinoic acid-inducible gene I; SIRL-1, signal inhibitory receptor on leukocytes 1; TLRs, toll-like receptors; TREMs, triggering receptors expressed on myeloid cells; TRP, transient receptor potential; TIGIT, T cell immunoreceptor with Ig and ITIM domains. Fig. 1 PRR-mediated DAMP sensing and signaling pathways Describes DAMP sensing and signaling transduction cascades of the five main PRRs: (A) TLRs are universally expressed across diverse immune system cells, with TLRs 1, 2, 4, 5, and 6 positioned prominently on the cell surface, while TLRs 3, 7, 8, and 9 are intimately associated with endosomal membranes. Upon recognition of various DAMPs by these TLRs, they initiate a complex signaling cascade, leveraging adaptor proteins MYD88 and TRIF as crucial intermediates. These adaptors, in turn, activate downstream MAPKs and IKK, which collaborate to facilitate the production of inflammatory cytokines by activating transcription factors like AP-1 and NF-κB, respectively. (B) CLRs including CLEC4E (MINCLE), CLEC7A (Dectin-1), CLEC8A, CLEC9A (DNGR1), and CLEC12A, play pivotal roles in recognizing endogenous DAMPs associated with cellular death, inflammation, and antitumor immunity. They are crucial in maintaining immune tolerance and modulating autoimmune responses through cytokine regulation, balancing immune activation and suppression. (C) NLRs are intricately structured with three primary domains: an N-terminal domain responsible for signaling, a central NACHT domain, and a C-terminal LRR domain. These NLRs are further classified into five subfamilies, NLRA, NLRB, NLRC, NLRP, and NLRX1, based on their distinct functional properties. A crucial function of NLRs lies in the assembly of inflammasomes, multicomponent complexes that mediate the release of IL-1β and IL-18 cytokines and instigate proinflammatory cell death pathways. For instance, the NLRP3 inflammasome undergoes assembly in response to a diverse range of endogenous DAMPs, thereby regulating inflammatory reactions. (D) RLRs, essential sensors of cytoplasmic nucleic acids, detect RNA virions, replication intermediates, and transcriptional products. This receptor family encompasses three members: LGP2, MDA5, and RIG-I. Notably, LGP2 functions to dampen RIG-I activity while augmenting the response to MDA5. Both MDA5 and RIG-I can be triggered by viral nucleic acids, initiating downstream signaling cascades that ultimately culminate in the release of proinflammatory factors. (E) Cytoplasmic DNA sensors, notably CGAS and AIM2, occupy central stages in orchestrating the DNA-triggered immune response. CGAS orchestrates signaling via the endoplasmic reticulum (ER)-anchored adaptor protein STING1, which in turn recruits and stimulates kinases TBK1 or NF-κB, thereby eliciting the production of type I interferon, IL-6, and TNF. Conversely, AIM2 activation triggers the assembly of the inflammasome and activates caspase-1, facilitating the release of IL-1β and IL-18 and inducing pyroptosis. Overall, the activation conditions for DNA sensors such as CGAS and AIM2 can vary significantly, influenced by factors such as cellular context, DNA type, and other molecular signals. Types of DAMP-sensing receptors in human and mammals. Abbreviations: AIM2 , absent in melanoma 2; AGER, advanced glycosylation end product-specific receptor; CLRs, C-type lectin receptors; CLEC9A, C-type lectin domain containing 9A; CytC , cytochrome C ; C5aR1, complement component 5a receptor 1; CEACAM1, carcinoembryonic antigen cell adhesion molecule 1; cGAS, cyclic GMP–AMP synthase; CaSR, calcium-sensing receptors; DNGR1, dendritic cell natural killer lectin group receptor 1; FRPs, formyl peptide receptors; GPCRs, G-protein-coupled receptors; iPRRs, inhibitory PRRs; LGP2, laboratory of genetics and physiology 2; LILRB1, leukocyte immunoglobulin-like receptor subfamily B member 1; LAIR-1, leukocyte-associated immunoglobulin-like receptor 1; MINCLE, macrophage-inducible C-type lectin; MDA5, melanoma differentiation factor 5; NLRs, NOD-like receptors; PRRs, pattern recognition receptors; P2XR, purinergic ionotropic receptor; RLRs, RIG-I-like receptors; RIG-I, retinoic acid-inducible gene I; SIRL-1, signal inhibitory receptor on leukocytes 1; TLRs, toll-like receptors; TREMs, triggering receptors expressed on myeloid cells; TRP, transient receptor potential; TIGIT, T cell immunoreceptor with Ig and ITIM domains. PRR-mediated DAMP sensing and signaling pathways Describes DAMP sensing and signaling transduction cascades of the five main PRRs: (A) TLRs are universally expressed across diverse immune system cells, with TLRs 1, 2, 4, 5, and 6 positioned prominently on the cell surface, while TLRs 3, 7, 8, and 9 are intimately associated with endosomal membranes. Upon recognition of various DAMPs by these TLRs, they initiate a complex signaling cascade, leveraging adaptor proteins MYD88 and TRIF as crucial intermediates. These adaptors, in turn, activate downstream MAPKs and IKK, which collaborate to facilitate the production of inflammatory cytokines by activating transcription factors like AP-1 and NF-κB, respectively. (B) CLRs including CLEC4E (MINCLE), CLEC7A (Dectin-1), CLEC8A, CLEC9A (DNGR1), and CLEC12A, play pivotal roles in recognizing endogenous DAMPs associated with cellular death, inflammation, and antitumor immunity. They are crucial in maintaining immune tolerance and modulating autoimmune responses through cytokine regulation, balancing immune activation and suppression. (C) NLRs are intricately structured with three primary domains: an N-terminal domain responsible for signaling, a central NACHT domain, and a C-terminal LRR domain. These NLRs are further classified into five subfamilies, NLRA, NLRB, NLRC, NLRP, and NLRX1, based on their distinct functional properties. A crucial function of NLRs lies in the assembly of inflammasomes, multicomponent complexes that mediate the release of IL-1β and IL-18 cytokines and instigate proinflammatory cell death pathways. For instance, the NLRP3 inflammasome undergoes assembly in response to a diverse range of endogenous DAMPs, thereby regulating inflammatory reactions. (D) RLRs, essential sensors of cytoplasmic nucleic acids, detect RNA virions, replication intermediates, and transcriptional products. This receptor family encompasses three members: LGP2, MDA5, and RIG-I. Notably, LGP2 functions to dampen RIG-I activity while augmenting the response to MDA5. Both MDA5 and RIG-I can be triggered by viral nucleic acids, initiating downstream signaling cascades that ultimately culminate in the release of proinflammatory factors. (E) Cytoplasmic DNA sensors, notably CGAS and AIM2, occupy central stages in orchestrating the DNA-triggered immune response. CGAS orchestrates signaling via the endoplasmic reticulum (ER)-anchored adaptor protein STING1, which in turn recruits and stimulates kinases TBK1 or NF-κB, thereby eliciting the production of type I interferon, IL-6, and TNF. Conversely, AIM2 activation triggers the assembly of the inflammasome and activates caspase-1, facilitating the release of IL-1β and IL-18 and inducing pyroptosis. Overall, the activation conditions for DNA sensors such as CGAS and AIM2 can vary significantly, influenced by factors such as cellular context, DNA type, and other molecular signals. Current understanding recognizes that both PAMPs and DAMPs can initiate immune responses by engaging an array of classical PRRs, including TLRs, NLRs, retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), CLRs, and diverse intracellular DNA sensors such as ALRs and cGAS [ 9 ] ( Table 1 ). In plants, PRRs primarily localize to the plasma membrane, classified into receptor-like kinases and receptor-like proteins [ 17 ]. Additionally, DAMPs are recognized by a spectrum of non-PRR DAMP receptors, including advanced glycosylation end product-specific receptor (AGER, also known as RAGE) [ 18 ], triggering receptors expressed on myeloid cells (TREMs) [ 19 ], several G protein-coupled receptors (GPCRs) [ 20 ], complement receptors [ 21 ], and ion channels [ 22 ] ( Table 1 ). Although tissue damage and cellular death are often pathologic, programmed cell death is integral to physiological processes and tissue regeneration. Thus, the immune response requires nuanced, context-specific modulation to avoid undue damage. The immune system must precisely interpret molecular cues provided by activating patterns, necessitating a context-dependent threshold for immune activation. Accordingly, a group of inhibitory receptors, namely iPRRs, has been identified [ 23 ] ( Table 1 ). These iPRRs detect endogenous and microbial patterns associated with danger as well as patterns indicative of homeostasis. By recognizing DAMPs, iPRRs contribute contextual insights, promote microbial tolerance to some extent, and support a balanced response to danger signals [ 24 ]. TLRs, a primary subset within the extensive family of PRRs, have been extensively studied. Currently, ten human TLRs (TLR1–TLR10) and twelve mouse TLRs (TLR1–TLR9, TLR11–TLR13, with the exclusion of TLR10) have been identified [ 25 ]. TLRs are ubiquitously expressed across various cells within the immune system, including macrophages, dendritic cells (DCs), B cells, natural killer cells (NK cells), selected T cells, and also on epithelial, endothelial cells, and fibroblasts. Specifically, TLRs 1, 2, 4, 5, and 6 are localized on the cell surface, whereas TLRs 3, 7, 8, and 9 are associated with endosomal membranes [ 25 ] ( Fig. 1 A). These receptors have distinct specificities; for instance, nucleic acids from damaged cells can activate TLR3, TLR7, and TLR9, while proteins released from cells and extracellular matrix (ECM) components post-tissue injury can engage toll-like receptor 2 (TLR2) and TLR4 [ 26 ]. A wide range of endogenous DAMPs, including HMGB1, heat shock proteins (HSPs), fibrinogen, hyaluronic acid, beta-defensins, and others, are thought to modulate TLR4 signaling either directly or indirectly [ 27 ]. Intriguingly, nucleic acid-sensing TLRs (TLR3, TLR7, and TLR9), located within endosomal compartments [ 28 ], are insulated from unintended activation by endogenous nucleic acids, yet self-nucleic acids that become internalized can trigger these TLRs in certain autoimmune diseases such as systemic lupus erythematosus (SLE) and RA [ 29 ]. Upon DAMP recognition, TLRs initiate signaling cascades via the adaptor proteins myeloid differentiation factor 88 (MYD88) and TIR-domain-containing adaptor inducing IFNβ (TRIF) [ 30 , 31 ]. These adaptors activate downstream MAPKs and IκB kinase (IKK), which facilitate the production of inflammatory cytokines through activation of transcription factors such as activator protein 1 (AP-1) and NF-κB, respectively [ 32 , 33 ]. Additionally, TRIF also engages TANK binding kinase 1 (TBK1), promoting type I interferons (IFN-I) production via IFN regulatory factor 3 (IRF3) activation [ 34 ] ( Fig. 1 A). TLR7 and TLR9 activation uniquely initiates a signaling pathway that involves MYD88, leading to IRF7 activation and IFNα production in DCs [ 35 , 36 ]. Given the broad array of endogenous TLR ligands, the DAMP-TLR axis is critically implicated in the pathogenesis of various sterile inflammatory and malignant conditions. A previously unrecognized neuroimmune pathway has been identified, involving the formation of a functional complex between TLR4 and the dopamine receptor D2 (DRD2) [ 37 ]. This study demonstrates that dopamine acts as a negative regulator of LPS-induced aconitate decarboxylase 1 (ACOD1, also known as IRG1) expression in monocytes and macrophages [ 37 ]. Mechanistically, dopamine inhibits the phosphorylation of the transcription factor cAMP response element-binding protein 1 (CREB1) at Ser133 by disrupting the TLR4–MYD88–MAPK3 signaling cascade, thereby preventing CREB1 from binding to the ACOD1 promoter [ 37 , 38 ]. This downregulation of ACOD1 also leads to reduced expression of its downstream target CD274 (encoding PD-L1), in an itaconate-independent manner, attenuating LPS-driven immunosuppressive signaling [ 37 ]. In vivo , delayed administration of the clinically approved DRD2 agonist pramipexole improved survival in mouse models of endotoxemia and polymicrobial sepsis, decreased proinflammatory cytokine release, and restored T cell function by suppressing the ACOD1–CD274 axis [ 37 ]. In contrast, genetic deletion or pharmacological inhibition of DRD2 exacerbated sepsis outcomes [ 37 ]. Supporting the translational relevance of these findings, clinical analyses revealed an inverse correlation between circulating dopamine levels and ACOD1 expression in peripheral blood mononuclear cells from septic patients [ 37 , 39 ]. Of note, targeting TLR signaling, such as TLR4, in clinical settings has proven challenging, despite its potential to modulate immune responses in conditions, such as autoimmunity and infection. A primary issue is the high redundancy within the immune system; multiple pathways can compensate when one is inhibited. For instance, if a specific TLR pathway is blocked, other PRRs may still trigger similar immune responses, thereby reducing the effectiveness of the intervention. CLRs are predominantly expressed by myeloid cells and exist in both transmembrane and soluble forms. These receptors are integral to the innate immune system, serving historically as sentinels that detect PAMPs and DAMPs, thereby initiating innate and influencing adaptive immune responses. CLRs, such as members of the dectin family including C-type lectin domain family 4 member E (CLEC4E, also known as macrophage-inducible C-type lectin [MINCLE]), dendritic cell natural killer lectin group receptor 1 (DNGR1, also known as C-type lectin domain containing 9A [CLEC9A]), and others like CLEC8A, CLEC12A, and CLEC7A (also known as Dectin-1), are implicated in recognizing endogenous DAMPs linked with cell death, inflammatory diseases, and antitumor immunity [ 40 ] ( Fig. 1 B). For example, MINCLE is known to induce pathogenic proinflammatory responses by binding to ligands such as Sin3A associated protein 130 (SASP130) or β-glucosylceramide under pathological conditions such as ischemic stroke and traumatic brain injury, as well as in APCs [ [41] , [42] , [43] ]. DNGR1, or CLEC9A, targets necrotic cells by recognizing F-actin, a component exposed by necrotic cells, enhancing antigen cross-presentation by conventional type 1 DCs, and presenting a potential target for antitumor immunotherapy [ 44 , 45 ]. Additionally, DNGR1 activation by necrotic cell debris has been observed to diminish IL-10 production in DCs, promoting disease progression in conditions such as atherosclerosis [ 46 ]. CLEC8A, expressed by various cell types including macrophages, DCs, and B cells [ 47 ], interacts with multiple DAMPs such as oxidized low density lipoprotein (oxLDL) [ 48 ], oxidized high density lipoprotein (oxHDL) [ 49 ], apoptotic bodies [ 50 ], Hsp60 [ 51 ] and phosphatidylserine [ 52 ], contributing to the pathogenesis of atherosclerosis, hypertension, and other metabolic and cardiovascular diseases. CLEC12A, mainly found on myeloid cells, acts as an inhibitory receptor within the dectin gene cluster and specifically recognizes monosodium urate crystals, which form from the crystallization of soluble UA in the presence of extracellular sodium (Na + ) during cell death [ 53 ]. Conversely, Dectin-1 binds N-glycans on tumor cells, triggering IRF5-dependent gene expression in DCs and macrophages, thereby enhancing NK cell-mediated tumor eradication [ 54 ]. CLRs play key roles in maintaining immune tolerance and managing autoimmune responses by regulating cytokine release, balancing immune activation and suppression. Members of the mannose receptor family, for example, are linked to allergic diseases and asthma, as they bind to allergens and facilitate their uptake, processing, and presentation. Additionally, certain CLRs affect lipid metabolism and insulin signaling, connecting CLR signaling to type 2 diabetes mellitus (T2DM) and obesity-related inflammation. Given their involvement across various disease contexts, CLRs are critical in both normal immune function and disease pathology, making them promising targets for therapeutic interventions to modulate immune responses and treat immune-related conditions. NLRs are a conserved family of innate immune receptors, initially recognized for responding to intracellular pathogens and endogenous byproducts of tissue damage [ 55 ]. To date, 22 NLRs with diverse functional roles have been identified in humans [ 56 ]. Structurally, NLRs are composed of three main domains: an N-terminal signaling domain, a central NACHT domain, and a C-terminal leucine-rich repeat (LRR) domain [ 57 ] ( Fig. 1 C). The LRR domain, akin to the extracellular domain of TLRs, is crucial for the recognition and modulation of DAMPs, while the N-terminal effector domain interacts with various adaptor molecules and effectors to facilitate signal transduction. NLRs are subdivided into five subfamilies based on functional attributes: NLRA, NLRB, NLRC, NLRP, and NLRX1. These receptors exhibit highly conserved signaling pathways; engagement of a DAMP with the LRR domain induces conformational changes that catalyze the exchange and assembly of ADP/GDP and ATP/GTP into a polymer scaffold, initiating downstream signal transduction [ 58 ]. A significant role of NLRs is in the formation of inflammasomes, complexes that catalyze the secretion of IL-1β and IL-18 and initiate pro-inflammatory cell death [ 59 ]. The NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, in particular, is activated by diverse endogenous molecules, such as HMGB1, histones, mitochondrial DNA (mtDNA), mitochondrial reactive oxygen species (mtROS), cardiolipin, cold-inducible RNA-binding protein (CIRP), hyaluronic acid, monosodium urate crystals, cholesterol crystals, amyloid-β peptides (Aβ) and ATP [ 60 ]. These molecules are thought to induce various intracellular damage-associated processes, such as Golgi dispersion, lysosomal rupture, and mitochondrial dysfunction, facilitating the assembly of the NLRP3 inflammasome. This NLRP3 inflammasome has been implicated in a wide range of inflammatory diseases, including gout, T2DM, atherosclerosis, and inflammatory bowel disease. Moreover, non-canonical activation of the NLRP3 inflammasome can be triggered by oxidized 1-palmitoyl-2-arachidonylsn- glycero -3-phosphocholine (oxPAPC) and Alu-RNA, which activate caspase-4, caspase-5, and caspase-11 [ 61 , 62 ] ( Fig. 1 C). In addition to their roles in inflammatory and autoimmune diseases, the involvement of NLRP3 in oncogenesis is complex, exhibiting both tumor-promoting and tumor-suppressing functions contingent upon the biological context. NLRP3’s contribution to inflammation can foster a pro-tumorigenic environment [ 63 ]; conversely, it may bolster anti-tumor immunity under specific conditions [ 64 ]. Other NLRs also impact cancer progression by modulating inflammatory responses and apoptotic cell death processes. Different subclasses of NLRs can also interact with one another. For example, NLR family card domain-containing 5 (NLRC5) associates with NLRP12, NLRP3, and other cell death-related molecules to assemble the NLRC5-PANoptosome complex, which is responsible for triggering inflammatory cell death [ 65 ]. Collectively, while the universal activation mechanisms of NLRs remain to be definitively elucidated, their pivotal role in mediating inflammatory responses via the recognition of intracellular DAMPs is widely acknowledged. The extensive impact of NLRs on both health and disease positions them as critical subjects of contemporary biomedical research. RLRs are critical cytoplasmic nucleic acid sensors, detecting RNA virions, RNA replication intermediates, and transcription products [ 66 ]. This receptor family comprises three members: DExH-box helicase 58 (DHX58, also known as laboratory of genetics and physiology 2 [LGP2]), interferon induced with helicase C domain 1 (IFIH1, also known as melanoma differentiation factor 5 [MDA5]), and RIG-I. LGP2, which lacks a caspase activation and recruitment domain, modulates the activity of RIG-I and MDA5; it inhibits RIG-I while enhancing the response to MDA5 [ 67 ]. Although traditionally localized to the cytoplasm, recent studies suggest that RLRs may also be present within the cell nucleus. RIG-I preferentially binds to RNA features typical of microbial RNA, such as short RNAs with a 5′ diphosphate or triphosphate (5′pp or 5′ppp) and blunt-ended double-stranded RNAs, while the ligands for MDA5 are less well-characterized compared to those for RIG-I ( Fig. 1 D). Misfolded endogenous RNAs can act as DAMPs, triggering RLR signaling and potentially leading to autoimmune disorders. For example, endogenous RNA produced during the unfolded protein response (UPR) can activate RIG-I-dependent interferon signaling in cells deficient in ski2-like RNA helicase (SKIV2L), which is associated with susceptibility to SLE [ 68 ]. Furthermore, the self-RNA–RLR axis has been explored in cancer research. Recent studies demonstrated that engineered chimeric antigen receptor T (CAR-T) cells expressing RNA component of signal recognition particle 7SL1 (RN7SL1), an endogenous RNA that activates RIG-I/MDA5 signaling, can facilitate the expansion and differentiation of CAR-T cells into effector-memory cells, thereby enhancing their anti-tumor efficacy [ 69 ]. Thus, the self-RNA–RLR axis can have varying roles in tumorigenesis, acting either as pro-tumorigenic or anti-tumorigenic depending on the context. CGAS and AIM2 are critical cytoplasmic DNA sensors that play pivotal roles in antimicrobial immunity [ 70 , 71 ]. Recent discoveries have expanded this category to include several additional soluble receptors for cytosolic DNA [ 72 ], all capable of detecting DNA released during the lifecycle of intracellular pathogens such as viruses, bacteria, and parasites. Importantly, endogenous DNA, originating from nuclear damage or immunogenic cell death (ICD), has been demonstrated to activate CGAS and AIM2 [ 73 , 74 ]. Persistent nuclear DNA damage or insufficient degradation of endogenous DNA can activate CGAS, potentially leading to autoimmune diseases including RA, Aicardi Goutières syndrome, and SLE [ 75 ]. CGAS is known to signal through the ER-based adaptor protein STING1, which recruits and activates kinase TBK1, subsequently activating transcription factor IRF3 to induce type I interferon production [ 76 ]. CGAS also responds to mtDNA that leaks into the cytoplasm, which increases during senescence and activates the senescence-associated secretory phenotype (SASP) through the CGAS-STING1 pathway [ 77 ]. Given its central role in immune responses to DNA damage, the CGAS-STING1 pathway is instrumental in both cancer progression and antitumor immunity [ 78 ]. A CGAS-independent STING1 pathway also contributes to the recognition of DNA damage under certain conditions [ 79 ]. In contrast, activation of AIM2 leads to inflammasome assembly and caspase-1 activation, promoting the release of IL-1β and IL-18 and inducing pyroptosis [ 80 ] ( Fig. 1 E). Ionizing radiation and chemotherapeutic agents are known to activate the AIM2 inflammasome by inducing nuclear DNA breaks in intestinal epithelial cells [ 81 ]. AIM2 is highly expressed in B cells of lupus patients and influences B-cell differentiation by regulating the B-cell lymphoma 6–B lymphocyte-induced maturation protein-1 (Bcl-6–Blimp-1) axis, presenting a new therapeutic target for SLE [ 82 ]. Moreover, endogenous DNA from necrotic cells has been shown to drive an AIM2-dependent pro-inflammatory phenotype that contributes to the perpetuation of chronic kidney injury [ 83 ]. Overall, the activation conditions for DNA sensors such as CGAS and AIM2 can vary significantly, influenced by factors such as cellular context, DNA type, and other molecular signals. Understanding how these variables affect DNA sensor activation in various disease states or physiological conditions is complex yet crucial for developing therapeutic applications. In addition to classical PRRs, a diverse array of non-PRR transmembrane proteins, including GPCRs, TREMs, AGER, and ion channels, have also been reported to sense DAMPs ( Fig. 2 ). Activation of these receptors triggers multiple signaling cascades, playing critical roles in the development of various pathological conditions. Fig. 2 Non-PRR-mediated DAMP sensing and signaling pathways This figure delineates the sensing and signaling transduction cascades orchestrated by the four principal classes of non-PRRs: (A) GPCRs, a diverse group, encompass complement receptors (C5aR1, C5aR2, C3aR), N-FPRs that primarily discern both endogenously N-formylated and unmodified peptides (FPR1, FPR2, FPR3), along with extracellular Ca 2+ -sensing receptors (CaSRs and GPRC6A). Upon specific ligand recognition, these receptors initiate a cascade of inflammatory pathway activations, ultimately fostering the inflammatory response. (B) TREMs, notably TREM1 and TREM2, are innate immune receptors residing on the cellular surface and are members of the immunoglobulin variable domain receptor superfamily, contributing to the body’s natural defense mechanisms. (C) AGER, a multifunctional receptor, exhibits the remarkable ability to bind a broad spectrum of endogenous ligands, ranging from AGEs and non-AGE ligands such as HMGB1, lysophosphatidic acid, phosphatidylserine, complement protein C1q, islet amyloid polypeptide, S100s, Aβ40 and Aβ42, and even DNA. (D) Ion channels can be broadly categorized into two types: TRP channels and P2XR, both of which play pivotal roles in cellular function. In inflammatory contexts, diverse DAMPs can activate specific non-PRRs, which in turn triggers a cascade of downstream signaling events leading to the activation of nuclear transcription factors. This intricate crosstalk between non-PRRs and their signaling cascades is fundamental to the development and progression of numerous pathological conditions. Non-PRR-mediated DAMP sensing and signaling pathways This figure delineates the sensing and signaling transduction cascades orchestrated by the four principal classes of non-PRRs: (A) GPCRs, a diverse group, encompass complement receptors (C5aR1, C5aR2, C3aR), N-FPRs that primarily discern both endogenously N-formylated and unmodified peptides (FPR1, FPR2, FPR3), along with extracellular Ca 2+ -sensing receptors (CaSRs and GPRC6A). Upon specific ligand recognition, these receptors initiate a cascade of inflammatory pathway activations, ultimately fostering the inflammatory response. (B) TREMs, notably TREM1 and TREM2, are innate immune receptors residing on the cellular surface and are members of the immunoglobulin variable domain receptor superfamily, contributing to the body’s natural defense mechanisms. (C) AGER, a multifunctional receptor, exhibits the remarkable ability to bind a broad spectrum of endogenous ligands, ranging from AGEs and non-AGE ligands such as HMGB1, lysophosphatidic acid, phosphatidylserine, complement protein C1q, islet amyloid polypeptide, S100s, Aβ40 and Aβ42, and even DNA. (D) Ion channels can be broadly categorized into two types: TRP channels and P2XR, both of which play pivotal roles in cellular function. In inflammatory contexts, diverse DAMPs can activate specific non-PRRs, which in turn triggers a cascade of downstream signaling events leading to the activation of nuclear transcription factors. This intricate crosstalk between non-PRRs and their signaling cascades is fundamental to the development and progression of numerous pathological conditions. GPCRs constitute the largest family of proteins encoded by the human genome [ 84 ]. Located on the cell membrane, GPCRs mediate the conversion of extracellular signals into critical physiological responses. This family includes complement receptors that recognize proteolytically activated fragments such as C3, C3dg deposited on opsonized surfaces, and soluble anaphylatoxins [ 85 ], N-formyl peptide receptors (N-FPRs), which detect both endogenous N-formylated and non-formylated peptides [ 86 ]; and P2Y receptors, responsive to extracellular nucleotide) [ 87 ]. Additionally, extracellular Ca 2+ detection is facilitated by two types of GPCRs: calcium-sensing receptors (CaSRs) [ 88 ] and G-protein-coupled receptor family C group 6 member A (GPRC6A) [ 89 ] ( Fig. 2 A). GPCRs are implicated in a wide array of diseases, including obesity, T2DM, cancer, depression, AD, and many others [ 90 ]. The current list of recognized complement receptors with GPCR structure includes C5aR1, C5aR2, and C3aR. Both C5aR1 and C5aR2 bind the same ligand, C5a, a potent pro-inflammatory mediator increasingly acknowledged for its role as an immune modulator [ 91 ]. Upon binding to C5a, C5aR1 activates protein kinase C and promotes the expression of the inflammasome-related protein cryopyrin in neutrophils and CD4 + T cells [ 92 , 93 ]. Studies have shown that administration of alarmins such as interleukin 1 alpha (IL-1α) or HMGB1 induces the release of C5a from the culture supernatant of THP-1 cells, initiating an autocrine signal through C5aR1 to trigger extracellular trap formation [ 94 ]. The gene encoding human C5aR2 was identified and sequenced many years after human complement component 5a receptor 1 (HsC5aR1), and its precise functions remain an active area of research [ 95 ]. While the pro-inflammatory role of C5aR1 is well established, the functions of C5aR2 are less clear [ 96 ]. Functionally, selective activation of C5aR2 downregulates cytokine production induced by various TLRs (TLR2, TLR3, TLR4, and TLR7), CLRs (Dectin-1, Dectin-2, and MINCLE), and the cytosolic DNA sensor STING1 in primary human macrophages, highlighting C5aR2’s role as a crucial regulator of innate immune function [ 91 ]. The native ligands for C3aR are C3a and C5a. Agonist-induced phosphorylation of C3aR is critical for signal transduction. In mast cells stimulated by C3a, this phosphorylation is essential for C–C motif chemokine ligand 2 (CCL2) production, though it appears to reduce the degranulation response [ 97 ] ( Fig. 2 A). In a rat model of Heymann nephritis, blocking C3aR alleviated proteinuria, electron-dense deposition, foot process widening, and glomerular basement membrane thickening [ 98 ]. Furthermore, aberrantly activated microglia exacerbate white matter injury via the C3-C3aR pathway during chronic hypoperfusion in a rat model [ 99 ]. Targeting complement receptors offers a promising therapeutic strategy for various diseases characterized by excessive or dysregulated immune responses. The development of monoclonal antibodies, small molecule inhibitors, receptor antagonists, gene therapy, decoy receptors, peptide inhibitors, and strategies to block ligand production are all potential approaches to modulate complement receptor activity and ameliorate disease symptoms. The FPRs are a subset of GPCRs capable of detecting both microbial and endogenous ligands [ 100 ]. In humans, there are three distinct isoforms: FPR1, FPR2, and FPR3. These receptors predominantly recognize N-formyl peptides (excluding FPR3) and a variety of endogenous agonists. FPRs are expressed across various cell types, with the highest expression levels found in neutrophils (excluding FPR3) and monocytes/macrophages [ 100 ]. While the functions and ligands of FPR3 remain relatively unexplored, the physiological and pathological roles of FPR1 and FPR2 have been extensively studied [ 101 , 102 ] ( Fig. 2 A). FPR1 primarily recognizes endogenous N-formylated peptides, which are mitochondrial protein fragments released by damaged cells. This recognition directs phagocytic leukocytes to sites of inflammation and injury [ 103 ]. Genetic deletion or pharmacological inhibition of FPR1 impairs leukocyte accumulation and reduces inflammation in various mouse models of inflammatory conditions, including pancreatic cancer [ 104 ], hypertension [ 105 ], Stevens-Johnson syndrome and toxic epidermal necrolysis [ 106 ], and intestinal oncogenesis [ 107 ]. In contrast, human FPR2 exhibits a moderate affinity for formylated peptides and responds to a diverse array of non-formylated peptides [ 102 ]. FPR2 is unique in its ability to mediate either pro-inflammatory or anti-inflammatory responses depending on the specific ligands involved [ 108 ]. Activation of FPR2 can lead to the production of pro-inflammatory cytokines, exacerbating conditions such as diabetic retinopathy and atherosclerosis [ 109 , 110 ]. FPR2/ALX expression correlated with chemo- and cytokines in human atherosclerotic lesions and leucocytes, and a lower inflammatory state was overserved in Fpr2 (-/-) macrophages [ 109 ]. Conversely, FPR2 exerts anti-inflammatory effects that can suppress disease progression in organs such as the brain, lungs, liver, and kidneys [ 111 ]. Using specialized small-animal model of radiation-induced lung injury, FPR2 exerts protective effects by inhibiting immune-cell recruitment and expression of pro-inflammatory cytokines and fibrotic proteins like collagen production in the lung lesion sites, through crosstalk with NF-κB and TGF-β/SMAD signaling [ 111 ]. The biological function of FPR3 remains largely unknown. Unlike FPR1 and FPR2, FPR3 is primarily expressed in monocytes and DCs and resides within intracellular vesicles rather than on the cell surface [ 112 ]. Known ligands of FPR3 include the acetylated N-terminal fragment of the human heme-binding protein and the neuroprotective peptide humanin [ 113 ]. Further research is necessary to elucidate the role and mechanisms of FPR3 activation in the development of chronic inflammatory diseases in vivo. The physiological and disease-related functions as well as the biological ligands of the CaSR have been more extensively studied [ 114 ]. Necrotic cells release substantial quantities of Ca 2+ into the extracellular environment, which acts as a chemoattractant, recruiting monocytes and macrophages to sites of tissue damage via CaSR activation [ 115 ]. In a murine model of cholera using intestinal perfusion, the administration of magnesium (Mg 2+ ), a key CaSR agonist, effectively mitigates secretory diarrhea in intestinal epithelial cells [ 114 ]. Furthermore, extracellular Ca 2+ can function as a DAMP, triggering the release of ER Ca 2+ and activating the NLRP3 inflammasome through the CaSR/GPRC6A-phospholipase Cβ (PLCβ) pathway [ 89 , 116 ] ( Fig. 2 A). Given the frequent deposition of Ca 2+ at sites of tissue injury or in inflammatory conditions, further investigation into the role of Ca 2+ -sensing GPCRs in regulating the immune response in vivo is warranted. The family of cell-surface receptors known as TREMs is predominantly expressed in granulocytes, monocytes, and tissue macrophages. These receptors are implicated in various conditions, including inflammation, neurodegenerative disorders, bone remodeling, metabolic syndrome, atherosclerosis, and cancer. Among the well-studied TREMs are TREM1 and TREM2 ( Fig. 2 B), both of which are innate immune receptors located on the cell surface and belonging to the immunoglobulin variable domain receptor superfamily [ 19 ]. TREM1 is expressed on myeloid cells such as monocytes/macrophages, neutrophils, and DCs, as well as on non-immune cells such as fibroblasts and epithelial cells [ 117 ]. Conversely, TREM2 is absent in neutrophils but is prominently present in other myeloid cell types, including DCs, bone marrow-derived macrophages, and tissue-specific macrophages [ 118 ]. Various studies have identified extracellular CIRP [ 119 ], HMGB1 [ 120 ], HSP70 [ 121 ], peptidoglycan recognition protein 1 (PGLYRP1) [ 122 ] and extracellular actin [ 123 ] as ligands for TREM1. TREM-1 activation potentiates NET release from human and murine neutrophils and it is also a component of the NET structure. TREM-1 pharmacological inhibition thus reduces neutrophil extracellular traps (NETs) formation that promotes hyperinflammation, thereby decreasing vascular dysfunction, organ injury, and mortality in sepsis shock model [ 124 ]. Beyond infections, TREM1 is implicated in numerous non-infectious inflammatory conditions. The androgen receptor promotes prostate cancer (PCa) cell line migration and invasion in culture via increasing TREM-1 signaling in the macrophage-like THP-1 cell line supports [ 125 ].Targeting TREM1 has shown potential in mitigating sterile inflammation observed in conditions such as cardiovascular diseases [ 126 ], neurodegenerative diseases [ 127 ], autoimmune diseases [ 128 ] and cancer [ 129 ]. TREM2, an activating receptor associated with hematopoietic cell signal transducer (HCST, also known as DNAX activation protein of 10 kDa [DAP10]) and DAP12 [ 130 ], binds to phospholipids and sulfatides [ 131 ], facilitating the recognition of apoptotic cells displaying phospholipids, as well as lipoproteins such as HDL and LDL [ 132 ]. TREM2 has been given special attention for its interaction with HDL containing apolipoprotein E (APOE), which is abundant in the brain [ 133 ]. Additionally, TREM2 binds to microbial lipids, including specific bacterial LPS [ 134 ] and non-glycosylated mycolic acids from mycobacteria [ 135 ]. Furthermore, TREM2 interacts with proteins prone to aggregation and accumulation in neurodegenerative diseases [ 133 ]. Other members of the TREM family include TREML4 [ 136 ], TREML1 [ 137 ], TREML2 [ 138 ], and those exclusively expressed in murine species, such as TREM3, TREM4, TREM5, and TREML6 [ 139 ]. While the precise ligands and signaling pathways involved in TREM activation require further investigation, it appears that DAMPs released during tissue damage facilitate their activation, potentially initiating and amplifying the sterile immune response. The AGER is expressed by various cell types, including monocytes, neutrophils, endothelial cells, smooth muscle cells, and cancer cells. AGER can bind a range of endogenous ligands, including advanced glycation end products (AGEs) and non-AGE ligands such as HMGB1, lysophosphatidic acid, phosphatidylserine, complement protein complement component 1q (C1q), islet amyloid polypeptide, S100s, Aβ40 and Aβ42, and even DNA [ 140 ] ( Fig. 2 C). Both AGER and its ligands are upregulated in various inflammatory conditions, such as RA [ 141 ], liver diseases [ 18 ] and obesity [ 142 ], diabetic vascular complications [ 143 ], inflammatory bowel disease [ 144 ] and several neurodegenerative diseases [ 145 ]. This indicates a positive feedback loop in the inflammatory response mediated by AGER. Initially identified as a receptor for AGEs-elevated in hyperglycemia and diabetes—early studies focused on the AGE- AGER axis in diabetes. Given the strong association between diabetes and atherosclerosis, molecules such as S100A8/A9 [ 146 , 147 ], HMGB1 [ 148 ] and angiotensin II type I receptor (AT1R) [ 149 ] have been reported to accelerate atherosclerosis through AGER-dependent activation of monocytes, endothelial cells, common myeloid progenitor cells, and Kupffer cells (KCs). Activation of the type 1 angiotensin II receptor (AT1) by angiotensin II (Ang II) triggered transactivation of the cytosolic tail of AGER by preforming a heteromeric complex with AGER, subsequently activating NF-κB–driven proinflammatory gene expression profiles to induce atherogenesis, either in the absence of AGER ligands or ligand binding to AGER [ 149 ]. Global or conditional knockout of AGER in specific tissues can attenuate sepsis or sterile inflammation, such as in pancreatitis [ 150 ]. Furthermore, research has demonstrated that AGER signaling in both tumor cells and immune cells can drive tumor progression, metastasis, and immune evasion, thereby contributing to the pathogenesis of various cancers [ 151 ]. For example, depletion of AGER in the pancreas limits kirsten rat sarcoma (KRAS)-driven tumorigenesis by reducing inflammation and the expression of immune checkpoints [ 152 ]. The complex mechanisms underlying AGER signaling in the development of these inflammatory and malignant diseases warrant further investigation. In addition, AGER inhibitors (e.g., FPS-ZM1, TPP488, and AGER229) represent a promising therapeutic approach for managing diseases driven by chronic inflammation and metabolic dysregulation [ 153 ]. Two categories of ligand-gated ion channels, namely transient receptor potential (TRP) channels and P2XR, play crucial roles in stimulating various immune cells ( Fig. 2 D). These channels contribute to the development of sterile inflammatory diseases by detecting ROS and ATP derived from mitochondria, respectively [ 154 , 155 ]. TRP channels are a major group of non-selective cation-permeable channels that act as polymodal cellular sensors involved in numerous physiological and pathological processes [ 156 ]. Specifically, TRP channels respond to external stimuli and DAMPs from the environment, such as heat, acidity, and chemicals, as well as endogenous danger signals released during trauma or tissue injury, including ATP, osmotic stress, UA, and hydroxynonenals [ 157 ]. Additionally, TRP channels can sense other forms of cellular stress, including mechanical stress, leading to the initiation of inflammation [ 158 ]. TRP channels influence innate immunity by activating NF-κB and procaspase-1, which generate mature caspase-1 responsible for cleaving pro-IL-1β into its mature form, IL-1β [ 157 ] ( Fig. 2 D). Recent research has uncovered a unique, non-canonical function of TLRs in sensory neurons, highlighting a direct functional connection between TLRs and TRP channels [ 159 ]. Specifically, a subset of TLRs—including TLR3, TLR4, and TLR7—physically interact with members of the TRP channel family, such as transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1). These interactions enable rapid modulation of ion channel activity and neuronal excitability, occurring within seconds to minutes after ligand binding, and without engaging traditional transcription-dependent pathways. For example, immunohistochemical analysis has demonstrated the colocalization of TLR3 and TRPV1 in mouse dorsal root ganglion nociceptors, and extracellular application of the TLR3 agonist poly(I:C) is capable of inducing rapid TLR3-dependent inward currents in these nociceptors within one minute [ 160 ]. This non-classical TLR–TRP coupling represents a novel mechanism of sensory transduction, enabling nociceptors to detect and respond swiftly to danger signals—an emerging area of considerable interest in neuroimmunology. Among the seven ATP-gated P2X receptors (P2XRs, e.g., P2X1R–P2X7R) that have been cloned, P2X7R stands out due to its ubiquitous expression in both innate and adaptive immune cells [ 161 ]. In inflammatory environments, P2X7R can be activated by various ligands, including cGAMP [ 162 ], HMGB1 [ 163 ], cathelicidin LL-37 [ 164 ], Alu-derived RNAs [ 165 ], amyloidogenic 1–42b-amyloid peptide [ 166 ], and serum amyloid [ 167 ] ( Fig. 2 D). For example, accumulation of apoptotic cells within tumors, triggering a type I interferon response via extracellular ATP (eATP) acting on the P2X7R to facilitate cyclic GMP-AMP (cGAMP)-mediated STING1 activation in macrophages, thus to mobilize anti-tumor immunity [ 162 ]. These findings suggest that P2X7R may serve as a receptor for multiple DAMPs, indicating its potential to sense a broader range of danger signals beyond ATP alone. This concept of 'ligand infidelity' may provide insights into the regulation of P2X7R activation at inflammatory sites. To differentiate between harmless and potentially harmful situations, the immune system must accurately interpret activating signals conveyed by molecular patterns. Consequently, the threshold for immune system activation must be adaptable based on the context. A group of iPRRs has been proposed to transmit inhibitory signals to immune cells ( Fig. 3 ). Extensive insights into their functions have been gained through the study of programmed cell death protein 1 (PD-1) [ 168 ], cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) [ 169 ], indoleamine 2,3-dioxygenase 1 (IDO1) [ 170 ] and killer cell Ig-like inhibitory receptors on NK cells [ 171 ]. These receptors predominantly transmit inhibitory signals through one or more immunoreceptor tyrosine-based inhibitory motifs located in their cytoplasmic tails [ 172 ]. Fig. 3 Iprrs and their diverse ligand landscape (a) iprrs and their exogenous and endogenous ligands (only including damps). The current repertoire of iPRRs encompasses a diverse array of molecules, including Siglec-10, CD300a/f, Siglecs 2, 3, and 5–11, CEACAM1, LILRB1, LILRB3, TIGIT, PVR, leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1), and SIRL-1. This figure comprehensively illustrates the exogenous and endogenous ligands (specifically focusing on DAMPs) that interact with these receptors. The upper section depicts exogenous ligands, while the lower section showcases the endogenous ligands bound by iPRRs. Notably, for a majority of these receptors, both endogenous and exogenous ligands have been elucidated; however, uncertainties persist regarding certain ligands, denoted by question marks, indicating the need for further investigation. (B) The integration of activating and inhibitory signals determines the outcome of the immune response. In scenarios where tolerating damage is advantageous for the host, DAMPs can trigger iPRRs to dampen the immune response. Conversely, when damage cannot be tolerated, DAMPs signal via activating PRRs to initiate a robust immune response. The relative abundance of PRRs and iPRRs, along with their corresponding ligands, dictates the intensity of the ensuing immune reaction. Iprrs and their diverse ligand landscape (a) iprrs and their exogenous and endogenous ligands (only including damps). The current repertoire of iPRRs encompasses a diverse array of molecules, including Siglec-10, CD300a/f, Siglecs 2, 3, and 5–11, CEACAM1, LILRB1, LILRB3, TIGIT, PVR, leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1), and SIRL-1. This figure comprehensively illustrates the exogenous and endogenous ligands (specifically focusing on DAMPs) that interact with these receptors. The upper section depicts exogenous ligands, while the lower section showcases the endogenous ligands bound by iPRRs. Notably, for a majority of these receptors, both endogenous and exogenous ligands have been elucidated; however, uncertainties persist regarding certain ligands, denoted by question marks, indicating the need for further investigation. (B) The integration of activating and inhibitory signals determines the outcome of the immune response. In scenarios where tolerating damage is advantageous for the host, DAMPs can trigger iPRRs to dampen the immune response. Conversely, when damage cannot be tolerated, DAMPs signal via activating PRRs to initiate a robust immune response. The relative abundance of PRRs and iPRRs, along with their corresponding ligands, dictates the intensity of the ensuing immune reaction. The known group of iPRRs currently includes CD300a/f, Siglecs 2, 3, and 5–11, carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1), leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1) and LILRB3, T cell immunoreceptor with Ig and ITIM domains (TIGIT), poliovirus receptor (PVR), leukocyte-associated immunoglobulin-like receptor 1 (LAIR1), and signal inhibitory receptor on leukocytes 1 (SIRL-1) [ 23 ]. Potential DAMPs recognized by iPRRs include oxidized HMGB1 [ 173 ], HSP70 [ 174 ], Hsp90, S100s [ 175 ], LL-37 [ 176 ], and cytokeratin-associated protein [ 177 ] ( Fig. 3 A). Multiple inhibitory receptors can modulate DAMP-induced inflammatory responses by dampening activating signals and fine-tuning the activation levels of immune cells ( Fig. 3 B). For example, Siglec-5 recognizes HSP70 and delivers anti-inflammatory signals to monocytes, which results in decreased production of tumor necrosis factor (TNF) and IL-8 in THP1 cells stimulated with LPS [ 174 ]. Consequently, iPRRs can be exploited for the treatment or prevention of various diseases. Furthermore, the release of iPRRs can modulate and limit inflammatory responses, highlighting their potential in managing inflammation-related conditions. Understanding the switch of a DAMP from a pro-inflammatory to an anti-inflammatory state requires the identification of its modifications, binding partners, and recognized receptors.

The DAMP paradigm has significantly advanced our understanding of how the immune system responds to sterile injury, in the absence of pathogens. Since the introduction of Polly Matzinger’s danger theory in 1994, extensive research has revealed the central role of DAMPs in bridging innate and adaptive immunity, mediating inflammation, and contributing to both physiological processes and a wide range of pathological conditions. Through interactions with diverse receptors—including PRRs and non-PRRs—DAMPs activate complex intracellular signaling pathways that regulate tissue homeostasis, repair, immune surveillance, and defense. However, this dual functionality also underlies their involvement in deleterious outcomes such as chronic inflammation, fibrosis, and immune dysregulation. Despite substantial progress, several critical challenges remain. The mechanisms governing the interactions between DAMPs and their broad repertoire of receptors—including cross-talk among PRR families (e.g., TLRs, NLRs, RLRs) and non-PRR receptors (e.g., GPCRs, TREMs, AGER)—are not fully elucidated. Furthermore, the context-dependent nature of DAMP activity, which can promote both pro-inflammatory and tissue-reparative outcomes, remains incompletely understood, particularly in the setting of different disease states. Defining the molecular determinants that dictate this functional duality will be essential for translating basic insights into effective therapies. Future research should aim to clarify the specific roles of DAMPs in regulating intercellular communication and tissue microenvironments under both physiological and pathological conditions. A key focus should be on delineating receptor-specific signaling cascades and feedback mechanisms that shape the intensity and resolution of DAMP-driven immune responses. Therapeutic strategies may include inhibition of DAMP release, receptor blockade, or selective modulation of downstream pathways to achieve immunomodulation with minimal off-target effects. The integration of multi-omics approaches—including genomics, proteomics, and metabolomics—with advanced computational modeling holds great promise for constructing comprehensive maps of DAMP networks and their interactions with immune and non-immune cells. In parallel, emerging technologies such as gene editing, nanomedicine, and artificial intelligence will further accelerate discoveries in DAMP biology and its clinical translation. In conclusion, the study of DAMPs provides critical insights into the immune response to cellular injury and offers substantial potential for therapeutic innovation. Continued investigation into the mechanisms of DAMP signaling and regulation will not only deepen our understanding of disease pathogenesis but also pave the way for novel interventions across a wide range of clinical contexts. Advancing this field will contribute meaningfully to future breakthroughs in precision medicine and patient care.

Cancer immunotherapy has emerged as a cornerstone of modern anti-tumor strategies, offering the unique ability to selectively eliminate residual tumor cells and suppress disease progression by restoring host immune surveillance. The major modalities of immunotherapy include immune checkpoint inhibitors (ICI), cancer vaccines, oncolytic virus-based therapies, and CAR T-cell approaches [ 473 ]. Among these, ICIs have revolutionized cancer treatment by reactivating the host immune system to recognize and eliminate malignant cells. Within this therapeutic landscape, DAMPs have emerged as critical modulators of antitumor immunity. By enhancing the immunogenicity of dying tumor cells, facilitating antigen presentation, and remodeling the tumor microenvironment, DAMPs influence both the initiation and efficacy of ICI-based therapies [ 474 ]. Increasing evidence supports the central role of DAMPs in initiating and shaping antitumor immune responses. Given their potent immunomodulatory effects, the integration of DAMPs into immunotherapy holds considerable promise for enhancing clinical efficacy and improving durable outcomes. Preclinical and translational studies have demonstrated that ICD–inducing treatments promote the release of DAMPs such as CALR, eATP, HMGB1, histone, and extracellular nucleic acids. These molecules facilitate dendritic cell (DC) recruitment and maturation, enhance neoantigen cross-presentation, and potentiate cytotoxic T cell responses when used in combination with ICIs [ 475 ]. For example, antibody-mediated blockade of extracellular HMGB1 or histone remodels the tumor immune microenvironment and impairs the therapeutic efficacy of ICIs or KRAS-G12D–targeted therapies (MRTX1133) in preclinical cancer models [ 104 , 467 , 476 , 477 ]. Similarly, VEGF 121 /rGel-mediated photochemical internalization induces robust DAMP release (e.g., HMGB1, ATP, HSP90, mtDNA), activates DCs, and synergizes with CTLA-4 blockade in murine tumors [ 478 , 479 ]. A recent study further showed that oxidized mtDNA released from irradiated tumor cells synergizes with TLR7 agonist liposomes to activate inflammasome signaling in DCs, thereby enhancing antitumor immunity [ 480 ]. In another example, eATP released through ultrasound-targeted microbubble cavitation enhances vascular inflammation and immune cell infiltration, synergizing with anti–PD-L1 therapy to boost ICI efficacy [ 481 ]. In summary, strategic modulation of DAMP signaling represents a promising avenue to augment ICI-based therapies. By harnessing their immunostimulatory and pro-inflammatory properties, DAMPs promote DC activation, enhance antigen presentation, and reshape the TME toward a more immunogenic state. These findings support the use of DAMPs not merely as passive biomarkers, but as active immunological adjuvants capable of amplifying antitumor immunity. Incorporating DAMP-targeted approaches into ICI regimens may improve therapeutic outcomes across diverse malignancies. Autoimmune diseases are characterized by dysregulated immune responses in which the immune system aberrantly targets self-tissues. DAMPs—such as HMGB1, S100 proteins, and mtDNA—play critical roles in orchestrating both innate and adaptive immune responses. Aberrant DAMP signaling has been closely linked to the pathogenesis of a broad range of autoimmune diseases affecting multiple organs and tissues, such as rheumatoid arthritis (RA) [ 482 ], adult-onset Still’s disease [ 483 ], SLE [ 484 ], and antiphospholipid syndrome [ 485 ]. In SLE, HMGB1–nucleosome complexes amplify innate immune activation by engaging TLR2 on antigen-presenting cells, leading to the production of hallmark autoantibodies such as anti-dsDNA and anti-histone IgG [ 486 ]. Recent studies also highlight extracellular DNA, particularly non-canonical conformations like Z-DNA, as immunologically active DAMPs in lupus [ 484 ]. Both B-DNA and Z-DNA act as potent autoantigens that drive the generation of cross-reactive anti-DNA antibodies, contributing to immune complex formation and type I interferon production [ 484 , 487 ]. These insights highlight Z-DNA as an unconventional but immunologically significant DAMP in lupus and suggest novel therapeutic avenues aimed at preventing DNA structural transitions or promoting effective clearance of Z-DNA-containing complexes. In RA, S100 family proteins—particularly S100A8/A9 and S100A12—function as classical DAMPs that are highly expressed in inflamed synovial tissue, where they activate TLR4 and AGER pathways [ 482 , 488 ]. Their expression correlates with synovial macrophage infiltration and joint damage. Therapeutic strategies targeting S100 proteins, including neutralizing antibodies, small-molecule inhibitors, and epigenetic modulators, have shown efficacy in experimental arthritis models, supporting the translational potential of DAMP-targeted therapies in RA [ 489 , 490 ]. Collectively, these findings underscore the central role of DAMPs as initiators and amplifiers of autoimmune inflammation, as well as their promise as therapeutic targets. Characterization of DAMPs may also yield valuable biomarkers for disease activity and prognosis in autoimmune disorders [ 491 ]. Neurodegenerative diseases (NDs) comprise a heterogeneous group of chronic disorders characterized by the progressive deterioration of neuronal structure and function within the central or peripheral nervous system, ultimately leading to irreversible neurological deficits [ 492 ]. Common NDs include Alzheimer’s disease (AD), Parkinson’s disease (PD), Amyotrophic lateral sclerosis, motor neuron disease, Huntington’s disease, and spinal muscular atrophy [ 492 ]. In AD and PD, DAMPs act as key mediators of innate and adaptive immune responses by engaging PRRs and non-PRR receptors on neural cells both at the site of pathology and in remote brain regions [ 493 ]. Notable DAMPs implicated in neurodegeneration include HMGB1 [ 494 , 495 ], S100 proteins [ 496 , 497 ], uric acid [ 498 , 499 ], histones [ 500 ], cfDNA [ 501 ], and mtDNA [ 502 , 503 ], which have been proposed as potential biomarkers for diagnosis and therapeutic intervention. For instance, injection of oxidatively damaged mtDNA into the striatum of mice recapitulates PD-like motor deficits, cognitive impairment, and dopaminergic neuronal loss [ 504 ]. These pathological changes spread to regions distant from the injection site, suggesting that extracellular mtDNA may function as a propagating “infectious” DAMP within the neural network. Beyond serving as biomarkers, DAMPs are increasingly recognized as therapeutic targets. Modulating DAMP expression or the signaling pathways they activate has shown promise in attenuating neurodegenerative processes. For example, oxidatively damaged mtDNA—recognized as a biomarker in PD—drives neuroinflammation via TLR4 and TLR9 activation, exacerbating oxidative stress [ 504 ]. In parallel, neuron-derived DAMPs activate the AGER on astrocytes, triggering RIPK3-dependent inflammatory signaling that contributes to neurotoxicity. Pharmacological inhibition of the AGER–RIPK3 axis reduces astrocyte-mediated inflammation and protects dopaminergic neurons in preclinical PD models [ 505 ]. Continued investigation into DAMP-associated signaling pathways holds promise for the development of innovative strategies to slow or halt neurodegeneration.

The conceptual foundation of innate immunity was reshaped in 1989 by Charles Janeway, who proposed that pattern recognition receptors (PRRs) detect pathogen-associated molecular patterns (PAMPs) to initiate immune responses [ 1 ]. This framework was further expanded by Polly Matzinger’s “danger theory” in 1994, positing that the immune system primarily responds to endogenous danger signals rather than solely to non-self-entities [ 2 ]. In 2002, Matzinger refined this concept by identifying damage signals released from stressed or injured cells [ 3 ], and in 2003, Walter Land introduced the term “damage-associated molecular patterns” (DAMPs) to describe these endogenous immunostimulatory molecules [ 4 ]. Collectively, these advances have revolutionized our understanding of immune surveillance and host defense in the context of tissue injury and infection. In contrast to PAMPs, DAMPs are intrinsic components of healthy cells, performing critical physiological roles under homeostatic conditions. These molecules are typically non-immunogenic when confined intracellularly; however, upon cellular stress or death induced by physical, chemical, metabolic, or infectious insults, DAMPs are released or exposed. This relocation alters their concentration or physicochemical properties, rendering them recognizable by the immune system and capable of triggering inflammatory responses. Over the past three decades, numerous DAMPs have been identified and is commonly categorized into five categories: nucleic acids, proteins, ions, glycans, and metabolites [ 5 ]. Among them, high mobility group box 1 (HMGB1) serves as a prototypical DAMP—functioning intracellularly as a DNA chaperone involved in nuclear processes [ 6 ], and extracellularly as a potent pro-inflammatory mediator released by immune or parenchymal cells [ 7 , 8 ]. The biological activity of DAMPs is primarily mediated through interactions with a diverse repertoire of receptors [ 9 ]. These include cytosolic sensors such as NOD-like receptors (NLRs) and absent in melanoma 2 (AIM2)-like receptors (ALRs), membrane-bound PRRs like Toll-like receptors (TLRs) and C-type lectin receptors (CLRs), and soluble pattern recognition molecules such as pentraxins, collectins, and ficolins [ 9 ]. Some DAMP receptors possess inhibitory properties, classified as inhibitory PRRs (iPRRs) [ 10 ], which contribute to immune tolerance and help maintain immune homeostasis. Furthermore, receptor crosstalk—comprising synergistic, enhancing, or suppressive interactions—enables fine-tuned immune regulation and mitigates the risk of hyperinflammatory damage [ 9 ]. Upon receptor engagement, DAMPs activate downstream signaling cascades—such as nuclear factor-κB (NF-κB), mitogen-activated protein kinases (MAPKs), and cyclic GMP–AMP synthase (cGAS)–stimulator of interferon genes (STING)—that regulate critical biological processes, including cell proliferation, differentiation, migration, and inflammation [ 11 ]. These responses are integral to tissue repair, regeneration, angiogenesis, bacterial clearance, cellular senescence, and the execution of RCD [ [12] , [13] , [14] , [15] , [16] ]. In particular, DAMPs and their receptors play pivotal roles in orchestrating sterile inflammation and recruiting immune cells (e.g., neutrophils, phagocytes, macrophages) to sites of damage. However, when DAMP signaling becomes excessive or dysregulated, it can contribute to pathological conditions such as fibrosis, chronic inflammation, and autoimmunity [ 11 ]. This review provides a comprehensive overview of DAMP biology, with a focus on their sensing receptors, downstream signaling pathways, and multifaceted functional roles. By delineating these mechanisms, we aim to facilitate the development of targeted therapeutic strategies that modulate DAMP signaling to reestablish immune homeostasis and improve disease outcomes.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.