Association of Vascular Netosis with COVID-19 Severity in Asymptomatic and Symptomatic Patients Infected by Delta and Omicron Variants

In light of the multi-organ damage and systemic symptoms of COVID-19, the mechanistic explanation of its pathophysiology has yet to be fully elucidated. Recently, neutrophil extracellular traps (NETs) were postulated as playing a key role in pathophysiology, with several studies reporting an elevated level of NETs in COVID-19 patients. To delineate whether the uncontrolled NETs formation observed is a cause or a consequence of this disease, we examined from a large exploratory study cohort (N=549) a validated panel of NETs markers in different categories of disease severity (asymptomatic, mild, moderate, severe, and critical). NE, MPO, and circulating nuclear DNA (cir-nDNA) levels in plasma were seen to gradually increase with the disease severity: mild (3.7, 48.9, and 15.8 ng/mL, respectively); moderate (9.8, 77.5, and 27.7 ng/mL, respectively), severe (11.7, 99.5, and 29.0 ng/mL, respectively); and critical (13.8, 110.2 and 46.0 ng/mL, respectively). These differences are statistically significant as compared with the other categories (P< 0.0001), as well as with healthy individuals (N=140; P< 0.0001). The diagnostic power of NETs markers to detect infected individuals is high and slightly increased with disease severity, as determined using Area Under Receiver Operating Curves (AUROC), from 0.95 to 1.0 AUC. In addition, we unexpectedly observed significantly higher levels of NETs in asymptomatic individuals as compared to healthy subjects (P <0.0001, for cir-nDNA, MPO, and NE), thus confirming an early and significant innate immune response to Delta and Omicron SARS-CoV2 infection in which netosis participates. Although the Omicron patient cohort is low (42 mild/moderate and asymptomatic patients), our data for that cohort are in line with all observations made in relation to both the Delta variant infected individuals and (except for their higher cir-nDNA level) the asymptomatic Delta infected patients. Moreover, this study showed that the balance of cir-nDNA and circulating mitochondrial DNA amounts was affected in COVID-19 infected patients. This may attest to a lower mitochondria production arising from impaired mitochondrial protein synthesis or some other mitochondrial dysfunction. Altogether, our study suggests that uncontrolled NETs formation is associated with disease severity. This could explain the deleterious micro-thrombotic events we previously proposed as a key player in the COVID-19 pathogenesis. Lastly, this work further validates the use of our NETs markers panel to improve patient follow-up, as well as its predictive potential as to the evolution of the disease severity.