The Complement System
The complement system is part of the innate immune system, consisting of a network of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens. It can be activated through three pathways: classical, lectin, and alternative.
Activation Pathways
- Classical: Classical: Triggered by antibody-antigen complexes
- Lectin: Lectin: Activated by pathogen surface patterns
- Alternative: Alternative: Spontaneous activation on pathogen surfaces
Overactivation in PAIS
Research has documented signs of complement overactivation in both ME/CFS and Long COVID:
- Elevated C4a and C3a split products
- Increased terminal complement complex (TCC)
- Correlation with symptom severity
- Evidence of tissue damage from complement deposition
Therapeutic Potential: Complement inhibitors are being investigated as potential treatments for PAIS, with early studies showing promise.