All modes of complement activation converge on the proteolysis of C3 and C5, generating the potent pro-inflammatory peptides C3a and C5a, while C5b initiates the membrane attack complex (MAC) formation (C5b-9), which is responsible for direct cell lysis (12), The complement system has been linked to the etiopathogenesis of RA. Here, C5 is linked to rheumatoid arthritis.