STUDENT CONSULT Serum conc Protein ( g/mL) Function Initiates the classical pathway, C1q (C1qr2S2) binds to Fc portion of antibody; Clr and c1s are proteases that lead to C4 and C2 activation C4 300-600 C4b covalently binds to surface of microbe or cell where antibody is bound and complement is activated C4b binds to C2 for cleavage by C1s C4a stimulates inflammation C2 as an active enzyme of C3 andng C2b is a serine protease function C5 convertases @ElsevierAbbas&Lichtman:BasicImmunologyUpdated2e-www.studentconsult.com ownloaded from Student Consut (on 1 June 2006 04: 16 PM) 82005 ElsevitDownloaded from: StudentConsult (on 1 June 2006 04:16 PM) © 2005 Elsevier