Complement component 4B (C4B)

Complement component 4B (C4B) is a central protein of the classical and lectin complement pathways, encoded by the C4B gene. Upon activation, the C4 protein is cleaved to produce the fragment C4b, which covalently attaches to pathogen and altered self-cells. C4b acts as an opsonin, enabling marked cells to be cleared by immune cells, and provides a scaffold for the formation of the C3 and C5 convertases that mediate further complement activation. Deficiency in C4B is associated with a predisposition to autoimmune diseases (notably systemic lupus erythematosus), while abnormal activity or regulation can contribute to inflammatory conditions. C4b is not an enzyme or receptor but is a functional protein fragment critical for opsonization and immune complex clearance.

Other names

C4bChido blood groupComplement component 4BC4B

Acts as an opsonin, marking pathogens and altered self-cells for phagocytosis. Platform for assembly of C3 and C5 convertases, enabling downstream complement activation.