Stage-dependent shifts in peritoneal cytokine profiles drive monocyte functional reprogramming in endometriosis

INTRODUCTION: Endometriosis is a chronic inflammatory disease in which monocytes/macrophages play a key pathogenetic role. The peritoneal fluid (PF) cytokine profile can modulate recruited monocyte functions, determining their contribution to disease progression. AIM: To investigate stage-specific changes in the PF cytokine profile and their impact on functional reprogramming of monocytes in endometriosis. METHODS: The study included 26 patients with endometriosis (stages I-III) and 6 controls. PF cytokine concentrations were measured by multiplex analysis (Bio-Plex). The effect of PF on MerTK, CCR2, PD-1 and PD-L1 expression by healthy donor monocytes was assessed by flow cytometry. RESULTS: PF composition changed dynamically with disease stage: At stage I, RANTES and IL-6 increased; at stage II, IL-12 decreased and IL-1ra increased; and at stage III, IFN-γ and IL-12 decreased. Stage I PF inhibited MerTK expression on monocytes, whereas stages II-III PF upregulated MerTK, PD-L1, PD-1 and CCR2. Pro-inflammatory cytokines negatively correlated with MerTK and PD-1 changes, while Th2 cytokines positively correlated with MerTK expression. Th2 cytokine levels were directly associated with serum CA-125 concentration. CONCLUSION: Stage-specific shifts in the PF cytokine profile initiate the switching of monocytes from a pro-inflammatory to an immunosuppressive phenotype. CLINICAL SIGNIFICANCE: Endometriosis diagnosis remains challenging due to the limited sensitivity of CA-125, particularly in early-stage disease. This study demonstrates that stage-specific shifts in peritoneal fluid cytokine and chemokine profiles - including changes in RANTES, IL-6, IL-12, IFN-γ and IL-1ra - drive measurable reprogramming of monocyte surface markers (MerTK, PD-1, PD-L1 and CCR2). These exploratory findings suggest that profiling peritoneal fluid cytokines together with monocyte phenotypic markers may, in principle, provide additional information relevant to disease staging and to the future identification of immune biomarkers; however, the present cohort is small and single-centre, and these observations require validation in larger, independent cohorts before any diagnostic or clinical application can be proposed. Delineating the stage-dependent transition from a pro-inflammatory to an immunosuppressive monocyte phenotype may also help to inform future research into immunomodulatory approaches in endometriosis.