IntroductionPost-COVID syndrome represents a major global health challenge which is characterized by immune dysregulation, although many aspects of the immune response remain incompletely understood, particularly the antibody response and the role of the complement system. We previously studied a post-COVID syndrome cohort in comparison to a COVID-recovered control cohort from Comunidad de Madrid (Spain) and found that post-COVID syndrome patients exhibited readily detectable serum anti-Nucleocapsid antibodies while showing deficient antibody production against the full-length Spike, despite maintaining a well-preserved anti-receptor binding domain (RBD) response.MethodsIn the present study, we quantified anti-Nucleocapsid secretory immunoglobulin A (sIgA) in saliva and analyzed selected key components of the complement system, including C3, C4, factor B (FB), factor H (FH), and total hemolytic activity (CH50).
Additionally, we quantified circulating immune complexes. We conducted general, stratified, correlation, and regression analyses.ResultsAnti-Nucleocapsid sIgA was increased in post-COVID syndrome samples compared with COVID-recovered controls.
Although CH50 levels were similar, we detected a reduced concentration of C3. The levels of C4 were decreased but not significantly.
Frontiers in Immunology published a clinical update in Infectious Disease on 14 May 2026.
The item focuses on Increased anti-nucleocapsid secretory IgA and consumption of complement component 3 in post-COVID syndrome patients.
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