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Complement activation in patients with post-acute sequelae after SARS-CoV-2 infection.
Madlene Holmqvist1,2, Dick J Sjöström3, Katherine Carlson1
1Division of Infection Medicine, Department of Clinical Sciences, Lund University, Lund, Sweden.
Frontiers in Immunology
|May 29, 2026
Summary
Researchers investigated complement system activation in patients with post-acute sequelae of SARS-CoV-2 (PASC). This study found no convincing evidence of complement system dysregulation in PASC patients, regardless of initial COVID-19 severity.
Area of Science:
- Immunology
- Infectious Diseases
- Post-COVID Conditions
Background:
- Post-acute sequelae of SARS-CoV-2 (PASC) present diverse, long-lasting symptoms after infection.
- Dysregulation of the complement system is a proposed mechanism for PASC development.
Purpose of the Study:
- To analyze complement activation markers in patients with PASC.
- To determine if complement system activation correlates with PASC severity or initial COVID-19 infection status.
Main Methods:
- Measured complement activation markers (C3bc, C3bBbP, TCC) in PASC patients and controls.
- Compared marker levels between PASC patients (mild vs. severe initial infection) and recovered controls.
Main Results:
- No significant differences in complement activation markers were found between PASC patients and controls.
- A trend towards more severe PASC was observed in patients with mild initial SARS-CoV-2 infection, but this did not correlate with complement activation.
Conclusions:
- This study did not find convincing evidence for complement system activation in PASC.
- The role of complement dysregulation in the pathophysiology of PASC remains uncertain based on these findings.
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