Complement C3 is the major plasma proteins of the immune system complement pathways. The synthesis of these proteins is increased in response to inflammation and infection but at a slower rate than for traditional acute phase proteins. Complement protein C3 is the fourth component to attach in the complement reaction sequence. It is a beta-globulin with a sedimentation coefficient of 5.5 and a molecular weight of 185,000. C3 is a central molecule in the complement system whose activation is essential for all the important functions performed by this system. C3 can promote phagocytosis during an inflammatory response against pathogens, but unregulated activation of C3 could lead to host cell damage. Low level of serum C3 associates with hypocomplementaemia, primary biliary cirrhosis