Direct activation of the alternative complement pathway by SARS-CoV-2 spike proteins is blocked by factor D inhibition

Blood. 2020 Oct 29;136(18):2080-2089. doi: 10.1182/blood.2020008248.

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly contagious respiratory virus that can lead to venous/arterial thrombosis, stroke, renal failure, myocardial infarction, thrombocytopenia, and other end-organ damage. Animal models demonstrating end-organ protection in C3-deficient mice and evidence of complement activation in humans have led to the hypothesis that SARS-CoV-2 triggers complement-mediated endothelial damage, but the mechanism is unclear. Here, we demonstrate that the SARS-CoV-2 spike protein (subunit 1 and 2), but not the N protein, directly activates the alternative pathway of complement (APC). Complement-dependent killing using the modified Ham test is blocked by either C5 or factor D inhibition. C3 fragments and C5b-9 are deposited on TF1PIGAnull target cells, and complement factor Bb is increased in the supernatant from spike protein-treated cells. C5 inhibition prevents the accumulation of C5b-9 on cells, but not C3c; however, factor D inhibition prevents both C3c and C5b-9 accumulation. Addition of factor H mitigates the complement attack. In conclusion, SARS-CoV-2 spike proteins convert nonactivator surfaces to activator surfaces by preventing the inactivation of the cell-surface APC convertase. APC activation may explain many of the clinical manifestations (microangiopathy, thrombocytopenia, renal injury, and thrombophilia) of COVID-19 that are also observed in other complement-driven diseases such as atypical hemolytic uremic syndrome and catastrophic antiphospholipid antibody syndrome. C5 inhibition prevents accumulation of C5b-9 in vitro but does not prevent upstream complement activation in response to SARS-CoV-2 spike proteins.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Betacoronavirus*
  • Cell Line
  • Complement Activation / drug effects
  • Complement C3 / metabolism
  • Complement C5 / antagonists & inhibitors
  • Complement Factor D / antagonists & inhibitors*
  • Complement Factor H / metabolism
  • Complement Inactivating Agents / pharmacology*
  • Complement Membrane Attack Complex / metabolism
  • Complement Pathway, Alternative / drug effects*
  • Humans
  • SARS-CoV-2
  • Spike Glycoprotein, Coronavirus / pharmacology*
  • Spike Glycoprotein, Coronavirus / physiology

Substances

  • Complement C3
  • Complement C5
  • Complement Inactivating Agents
  • Complement Membrane Attack Complex
  • Spike Glycoprotein, Coronavirus
  • complement factor H, human
  • spike protein, SARS-CoV-2
  • Complement Factor H
  • Complement Factor D