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. Increased C4a levels have been found after exercise in ME/CFS patients and 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. For these reasons, it has been suggested C4a could be used as a marker of post-exertional malaise in ME/CFS.