MeSH definition : The large fragment formed when COMPLEMENT C4 is cleaved by COMPLEMENT C1S. The membrane-bound
C4b binds COMPLEMENT C2A, a SERINE PROTEASE, to form C4b2a (CLASSICAL PATHWAY C3 CONVERTASE)
and subsequent C4b2a3b (CLASSICAL PATHWAY C5 CONVERTASE).;
The large fragment formed when COMPLEMENT C4 is cleaved by COMPLEMENT C1S. The membrane-bound
C4b binds COMPLEMENT C2A, a SERINE PROTEASE, to form C4b2a (CLASSICAL PATHWAY C3 CONVERTASE)
and subsequent C4b2a3b (CLASSICAL PATHWAY C5 CONVERTASE).