Complement and tissue factor–enriched neutrophil extracellular traps are key drivers in COVID-19 immunothrombosis

TLDR

Complement and neutrophils drive hyperinflammation and thrombotic microangiopathy, increasing COVID‑19 mortality. We examined how complement interacts with the platelet/NET/thrombin axis in COVID‑19 using patient samples, inhibition studies, and NET/HAEC cocultures. The study employed patient specimens, inhibition assays, and NET/HAEC cocultures to dissect complement‑NET‑thrombin interactions. COVID‑19 patients exhibit elevated NETs, tissue factor activity, and complement activation; neutrophils release TF‑bearing NETs that activate endothelial thrombogenicity, and inhibition of thrombin, NETosis, or C5aR1, as well as C3 blockade, attenuates this effect, supporting complement or NETosis inhibition as therapeutic strategies.

Abstract

Emerging data indicate that complement and neutrophils contribute to the maladaptive immune response that fuels hyperinflammation and thrombotic microangiopathy, thereby increasing coronavirus 2019 (COVID-19) mortality. Here, we investigated how complement interacts with the platelet/neutrophil extracellular traps (NETs)/thrombin axis, using COVID-19 specimens, cell-based inhibition studies, and NET/human aortic endothelial cell (HAEC) cocultures. Increased plasma levels of NETs, tissue factor (TF) activity, and sC5b-9 were detected in patients. Neutrophils of patients yielded high TF expression and released NETs carrying active TF. Treatment of control neutrophils with COVID-19 platelet-rich plasma generated TF-bearing NETs that induced thrombotic activity of HAECs. Thrombin or NETosis inhibition or C5aR1 blockade attenuated platelet-mediated NET-driven thrombogenicity. COVID-19 serum induced complement activation in vitro, consistent with high complement activity in clinical samples. Complement C3 inhibition with compstatin Cp40 disrupted TF expression in neutrophils. In conclusion, we provide a mechanistic basis for a pivotal role of complement and NETs in COVID-19 immunothrombosis. This study supports strategies against severe acute respiratory syndrome coronavirus 2 that exploit complement or NETosis inhibition.