Carboxypeptidase B Inhibits Over-activation of Anaphylatoxin-neutrophil Extracellular Trap Axis in COVID-19 Patients

Abstract Background: Thrombosis and coagulopathy are highly prevalent in severe patients with COVID-19 and increase the risk of death. Immunothrombosis has recently been demonstrated to contribute to the thrombotic events in COVID-19 patients with coagulopathy. Neutrophil extracellular traps (NETs) are primary components of immunothrombosis, whereas the mechanism of NET formation remains unclear. We aim to explore the clinical roles of NETs and the regulation of complement on the NET formation in COVID-19.Methods: We recruited 135 COVID-19 patients and measured plasma levels of C5, C3, cell-free DNA and myeloperoxidase-DNA. We detected complement-induced NET formation by immunofluorescent staining and evaluated the cytotoxicity to vascular endothelial HUVEC cells by CCK-8 assay.Results: We found that the plasma levels of complements (C3 and C5) and NETs were closely related to coagulopathy and multiple organ dysfunction in patients with COVID-19. By using anti-C3a and anti-C5a antibodies, we revealed that the complement component anaphylatoxins in the plasma of COVID-19 patients strongly induced NET formation. The pathological effect of the anaphylatoxin-NET axis on the damage of vascular endothelial cells could be relieved by recombinant carboxypeptidase B (CPB), a stable homolog of enzyme CPB2 which can degrade anaphylatoxins to inactive products.Conclusions: Over-activation in anaphylatoxin-NET axis plays a pathological role in COVID-19. Early intervention in anaphylatoxins might help prevent thrombosis and disease progression in COVID-19 patients.