Scientific article
Open access

Severe COVID-19 is associated with hyperactivation of the alternative complement pathway

Published inJournal of allergy and clinical immunology, vol. 149, no. 2, p. 550-556.e2
Publication date2022-02
First online date2021-11-17

Background: Severe coronavirus disease 2019 (COVID-19) is characterized by impaired type I interferon activity and a state of hyperinflammation leading to acute respiratory distress syndrome. The complement system has recently emerged as a key player in triggering and maintaining the inflammatory state, but the role of this molecular cascade in severe COVID-19 is still poorly characterized.

Objective: We aimed at assessing the contribution of complement pathways at both the protein and transcriptomic levels.

Methods: To this end, we systematically assessed the RNA levels of 28 complement genes in the circulating whole blood of patients with COVID-19 and healthy controls, including genes of the alternative pathway, for which data remain scarce.

Results: We found differential expression of genes involved in the complement system, yet with various expression patterns: whereas patients displaying moderate disease had elevated expression of classical pathway genes, severe disease was associated with increased lectin and alternative pathway activation, which correlated with inflammation and coagulopathy markers. Additionally, properdin, a pivotal positive regulator of the alternative pathway, showed high RNA expression but was found at low protein concentrations in patients with a severe and critical disease, suggesting its deposition at the sites of complement activation. Notably, low properdin levels were significantly associated with the use of mechanical ventilation (area under the curve = 0.82; P = .002).

Conclusion: This study sheds light on the role of the alternative pathway in severe COVID-19 and provides additional rationale for the testing of drugs inhibiting the alternative pathway of the complement system.

  • COVID-19
  • Complement system
  • SARS-CoV-2
  • Alternative pathway
  • Hemostasis
  • Immunology
  • COVID-19 / genetics
  • COVID-19 / immunology
  • COVID-19 / therapy
  • COVID-19 / virology
  • Cardiovascular Diseases / genetics
  • Cardiovascular Diseases / immunology
  • Cardiovascular Diseases / therapy
  • Cardiovascular Diseases / virology
  • Case-Control Studies
  • Comorbidity
  • Complement Activation / genetics
  • Complement Pathway, Alternative / genetics
  • Complement System Proteins / genetics
  • Complement System Proteins / immunology
  • Diabetes Mellitus / genetics
  • Diabetes Mellitus / immunology
  • Diabetes Mellitus / therapy
  • Diabetes Mellitus / virology
  • Disseminated Intravascular Coagulation / genetics
  • Disseminated Intravascular Coagulation / immunology
  • Disseminated Intravascular Coagulation / therapy
  • Disseminated Intravascular Coagulation / virology
  • Female
  • Gene Expression Regulation
  • Humans
  • Hypertension / genetics
  • Hypertension / immunology
  • Hypertension / therapy
  • Hypertension / virology
  • Lectins / genetics
  • Lectins / immunology
  • Male
  • Middle Aged
  • Neoplasms / genetics
  • Neoplasms / immunology
  • Neoplasms / therapy
  • Neoplasms / virology
  • Properdin / genetics
  • Properdin / immunology
  • Respiration, Artificial
  • SARS-CoV-2 / genetics
  • SARS-CoV-2 / immunology
  • SARS-CoV-2 / pathogenicity
  • Severity of Illness Index
Affiliation Not a UNIGE publication
Citation (ISO format)
BOUSSIER, Jeremy et al. Severe COVID-19 is associated with hyperactivation of the alternative complement pathway. In: Journal of allergy and clinical immunology, 2022, vol. 149, n° 2, p. 550–556.e2. doi: 10.1016/j.jaci.2021.11.004
Main files (1)
Article (Published version)
ISSN of the journal0091-6749

Technical informations

Creation03/13/2023 7:53:35 AM
First validation05/25/2023 5:00:42 AM
Update time05/25/2023 5:00:42 AM
Status update05/25/2023 5:00:42 AM
Last indexation05/06/2024 3:58:01 PM
All rights reserved by Archive ouverte UNIGE and the University of GenevaunigeBlack