Complement C4b

**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).

**Tree numbers:** - D12.776.124.486.274.350.260

**Synonyms:** - C4b Complement - Complement 4b - Complement Component 4b