In a groundbreaking study published on January 19, 2024, in Science , researchers led by Carlo Cervia-Hasler and colleagues have made significant strides in understanding Long COVID, a condition characterized by persistent symptoms following an initial severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The study, titled “Persistent complement dysregulation with signs of thromboinflammation in active Long Covid,” reveals critical insights into the biological underpinnings of this condition.
The research team conducted a comprehensive analysis of blood samples from COVID-19 patients, comparing those with confirmed SARS-CoV-2 infection to uninfected controls. They discovered that patients experiencing Long COVID exhibited notable changes in blood serum proteins. These changes indicate activation of the immune system’s complement cascade, altered coagulation, and tissue injury. Specifically, the study found that Long COVID patients showed signs of increased complement activation during acute disease, which persisted even at a 6-month follow-up.
The complement system, a crucial part of the innate immune system, plays a significant role in immunity and homeostasis by targeting pathogens and damaged cells. In Long COVID patients, there was an imbalance in the formation of the terminal complement complex (TCC), composed of complement components C5b-9.
This imbalance suggested increased membrane insertion of TCCs in Long COVID patients, contributing to tissue damage. Furthermore, these patients exhibited elevated tissue injury markers in blood and a thromboinflammatory signature, characterized by markers of endothelial activation and red blood cell lysis.
Additionally, the study highlighted that Long COVID patients had elevated platelet activation markers and monocyte–platelet aggregates, particularly in cases where Long COVID persisted for 12 months or more. These findings suggest that active Long COVID is accompanied by a blood protein signature marked by increased complement activation and thromboinflammation.
The research also points to the possibility of complement activation being driven by antigen–antibody complexes, involving autoantibodies and antibodies against herpesviruses, as well as cross-talk with a dysregulated coagulation system.
This study provides a valuable resource of potential biomarkers for the diagnosis of Long COVID and may inform directions for future treatments. It underscores the complexity of Long COVID and the need for further research to develop effective diagnostic tools and therapeutic solutions for those affected by this condition.
Journal Reference – Cervia-Hasler, C., Brüningk, S. C., Hoch, T., Fan, B., Muzio, G., Thompson, R. C., … Boyman, O. (2024). Science, 383(6680). doi:10.1126/science.adg7942
