SARS-CoV-2 triggers complement activation through interactions with heparan sulfate

Abstract

The complement system has been heavily implicated in severe COVID-19 with clinical studies revealing widespread gene induction, deposition, and activation. However, the mechanism by which complement is activated in this disease remains incompletely understood. Herein we examined the relationship between SARS-CoV-2 and complement by inoculating the virus in lepirudin-anticoagulated human blood. This caused progressive C5a production after 30 minutes and 24 hours, which was blocked entirely by inhibitors for factor B, C3, C5, and heparan sulfate. However, this phenomenon could not be replicated in cell-free plasma, highlighting the requirement for cell surface deposition of complement and interactions with heparan sulfate. Additional functional analysis revealed that complement-dependent granulocyte and monocyte activation was delayed. Indeed, C5aR1 internalisation and CD11b upregulation on these cells only occurred after 24 hours. Thus, SARS-CoV-2 is a non-canonical complement activator that triggers the alternative pathway through interactions with heparan sulfate.

Competing Interest Statement

Trent M. Woodruff is an inventor on patents pertaining to complement inhibitors for inflammatory diseases. He has consulted to Alsonex Pty Ltd (who are commercially developing PMX205) and has received honorarium from Alexion Pharmaceuticals (who developed eculizumab) for participation in industry conferences and meetings. Vito Ferro is an inventor on patents for Pixatimod/PG545. All other authors declare no conflicts of interest.