C4 Complement, Serum

The complement system is a part of the immune system (a part of innate immunity) which enhances the ability of antibodies and phagocytic cells to destroy microbes and to remove damaged cells from an organism. The complement system promotes inflammation. The complement system contains a number of small proteins that are synthesised by the liver and secreted into the blood. In blood they are present in inactive form (pro-proteins). They are activated by when there is a trigger by proteases and release cytokines. This initiates a cascade of further cleavages, resulting in complement activation (complement fixation). This stimulates the phagocytes to clear the triggering agent. There are three pathways in complement activation, the classical complement pathway, the alternative complement pathway, and the lectin pathway. Deficiencies of the complement system are associated with autoimmune disease and infections (Neisseria meningitidis). Complement system might play a role in many diseases associated with immune component like asthma, lupus erythematosus, glomerulonephritis, various forms of arthritis, multiple sclerosis, inflammatory bowel disease, atypical hemolytic uremic syndrome and rejection of transplanted organs. Complement tests (mostly C3 and C4) are done to determine any deficiency or abnormalities in the complement system. Total complement activity may be done to view the integrity of the classical complement pathway.