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Updated: Oct 10, 2025
Depletion of Specific Cell Populations by Complement Depletion
Published on: February 5, 2010
The state of complement in COVID-19
Behdad Afzali1, Marina Noris2,3, Bart N Lambrecht4,5,6
1Immunoregulation Section, Kidney Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA. ben.afzali@nih.gov.
Insights
Severe COVID-19 involves overactive complement and coagulation systems. Complement inhibition shows promise as a potential therapy for severe cases, with early clinical evidence supporting its use.
Area of Science:
- Immunology
- Hematology
- Virology
Background:
- COVID-19 is linked to overactive complement and coagulation systems.
- SARS-CoV-2 infection triggers both systemic and local complement activation.
- These activations contribute to hyperinflammation and thrombosis in COVID-19 patients.
Purpose of the Study:
- To review the roles of systemic and local complement activation in COVID-19.
- To explore the relationship between complement activation, hyperinflammation, and thrombosis.
- To update on clinical findings and trial evidence for complement inhibition therapies.
Main Methods:
- Literature review of complement and coagulation system activation in COVID-19.
- Analysis of the relationship between viral infection and host immune/coagulation responses.
- Review of early clinical data and ongoing trials on complement inhibitors.
Main Results:
- Systemic and local complement activation are key features of severe COVID-19.
- Complement activation contributes significantly to the hyperinflammatory and pro-thrombotic state.
- Emerging evidence suggests complement inhibition may be a viable therapeutic strategy.
Conclusions:
- Targeting the complement system offers a promising therapeutic avenue for severe COVID-19.
- Further clinical trials are needed to confirm the efficacy of complement inhibition.
- Understanding complement's role is crucial for managing COVID-19 complications.
Abstract:
Hyperactivation of the complement and coagulation systems is recognized as part of the clinical syndrome of COVID-19. Here we review systemic complement activation and local complement activation in response to the causative virus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and their currently known relationships to hyperinflammation and thrombosis. We also provide an update on early clinical findings and emerging clinical trial evidence that suggest potential therapeutic benefit of complement inhibition in severe COVID-19.
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