Complement C4a

Complement C4a is a protein that is expressed, primarily in the liver and in macrophages, in response to acute inflammation or tissue injury.

Relationship to ME/CFS
Increased C4a levels have been found one to six hours after exercise challenge tests in ME/CFS patients but not in healthy controls. Others found a strong relation between the change in complement C4a level and an increase in post-exertional pain and fatigue in ME/CFS patients. Previously, complement C4a, in combination with other proteins, was being considered as a potential marker of post-exertional malaise in ME/CFS.