Complement Activation in the Disease Course of Coronavirus Disease 2019 and Its Effects on Clinical Outcomes
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Background: Excessive activation of immune responses in coronavirus disease 2019 (COVID-19) is
considered to be related to disease severity, complications, and mortality rate. The complement
system is an important component of innate immunity and can stimulate inflammation, but its role
in COVID-19 is unknown.
Methods: A prospective, longitudinal, single center study was performed in hospitalized patients
with COVID-19. Plasma concentrations of complement factors C3a, C3c, and terminal complement
complex (TCC) were assessed at baseline and during hospital admission. In parallel, routine
laboratory and clinical parameters were collected from medical files and analyzed.
Results: Complement factors C3a, C3c, and TCC were significantly increased in plasma of patients
with COVID-19 compared with healthy controls ( P < .05). These complement factors were
especially
elevated in intensive care unit patients during the entire disease course (P < .005
for C3a
and TCC). More intense complement activation was observed in patients who died and in those
with thromboembolic events.
Conclusions: Patients with COVID-19 demonstrate activation of the complement system, which is
related to disease severity. This pathway may be involved in the dysregulated proinflammatory
response associated with increased mortality rate and thromboembolic complications. Components
of the complement system might have potential as prognostic markers for disease severity and as
therapeutic targets in COVID-19.
Keywords: ARDS; COVID-19; Coagulation; Complement; Inflammation; SARS-CoV-2.
Reference
de Nooijer, A. H., Grondman, I., Janssen, N. A., Netea, M. G., Willems, L., van de Veerdonk, F. L., ... & Joosten, L. A. (2021). Complement activation in the disease course of coronavirus disease 2019 and its effects on clinical outcomes. The Journal of infectious diseases, 223(2), 214-224.
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