CIDRAP (Center for Infectious Disease Research and Policy) provided a summary of an analysis published in Science that examined blood samples from patients with long COVID and found significant serum protein changes, opening the door to developing biomarker-based tests to identify the condition.
The protein changes suggest a significant alteration of the complement system, which results in the immune system remaining activated and inflamed after acute infection, the authors explained.
The complement system also controls blood clotting and the repair of damaged tissue, and dysregulation of complement proteins could be behind the wide and varied symptoms experienced by long-COVID patients.
The researchers analyzed blood serum samples collected from 113 patients who either fully recovered from COVID-19 (73) or developed long COVID (40), as well as healthy controls (39).
Samples were collected at baseline and 6 months after acute illness, and researchers screened for serum levels of 6,596 human proteins.
The blood antimicrobial defense systems of complement and pentraxin 3 were elevated in blood samples collected at 6 months in the patients who had developed persistent symptoms associated with long COVID, including fatigue and brain fog.
Long-COVID patients also had significantly more terminal complement complex (TCC) at 6 months, which can result in cell activation, breakdown, and tissue damage.
"Markers of hemolysis, tissue injury, platelet activation, and monocyte–platelet aggregates were increased in Long Covid," the author wrote. "These patients also showed signs of antibody-mediated activation of the classical complement pathway, which was associated with increased anti-CMV (cytomegalovirus, also known as human herpesvirus 5) and anti-EBV (Epstein-Barr virus) immunoglobulin G (IgG) antibody levels."
