From COVID-19 to clot: the involvement of the complement system
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Updated: Dec 5, 2025

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Published on: August 4, 2023
Mohamed A Hendaus1,2, Fatima A Jomha3
1Department of Pediatrics, Sidra Medicine and Research Center, Doha, Qatar.
Insights
The complement system plays a key role in COVID-19 (coronavirus disease) pathogenesis, inflammation, and thrombosis. Blocking the terminal complement pathway may offer effective treatments for COVID-19 patients with blood clots.
Area of Science:
- Immunology
- Pathophysiology
- Hematology
Background:
- The emergence of coronavirus disease (COVID-19) in late 2019 has been linked to coagulation profile abnormalities.
- Understanding the immune response and pathogenesis of COVID-19 is crucial for developing effective treatments.
Purpose of the Study:
- To discuss the role of the complement system in COVID-19-associated thrombo-genesis, inflammation, and tissue damage.
- To explore potential therapeutic targets within the complement pathway for COVID-19 treatment.
Main Methods:
- Review of current literature on COVID-19, coagulation, and the complement system.
- Discussion of existing thrombosis treatments and novel therapeutic strategies targeting the complement cascade.
Main Results:
- The complement system is implicated in the immune response to COVID-19, contributing to inflammation and thrombosis.
- Blocking the terminal complement pathway presents a promising therapeutic avenue for managing COVID-19-related clotting.
Conclusions:
- The complement system's role in COVID-19 pathogenesis warrants further investigation.
- Targeting the terminal complement pathway could be a vital strategy for treating thrombosis in COVID-19 patients, potentially improving outcomes and facilitating early discharge.
Abstract:
In December 2019, the world observed an unexpected outbreak of an emerging disease named coronavirus (COVID-19) that was first reported in Wuhan city of Hubei province of China. Recent literature has shown the association between COVID-19 infection and derangement in the coagulation profile. In this paper, we are discussing thrombo-genesis, especially the role of the complement system in the immune response against COVID-19 and the pathogenesis associated with tissue inflammation and thrombosis. This role can stipulate a groundwork for further investigation of the pathophysiologic importance of complement in COVID-19, and could propose targets for specific intervention. In addition, we delineated current treatments for thrombosis and the potential therapies by using agents to block the terminal complement pathway. Low molecular weight heparin for all (unless contraindicated) hospitalized COVID-19 patients can be lifesaving. Agents that inhibit the terminal events of the complement cascade might be crucial for ensuring an efficient treatment, decrease clots and permit early discharge in relation to COVID-19.Communicated by Ramaswamy H. Sarma.
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