Complement component C3b, C4b, and C5b-9 complex (null)

The "Complement component C3b/C4b/C5b-9 complex" as given refers to **distinct molecules or complexes in the complement system**, not a single unified target. **C3b** and **C4b** are opsonins and components of the C3 and C5 convertases, facilitating phagocytosis and immune complex clearance[2][3][4][6]. **C5b-9**, also known as the *membrane attack complex (MAC)*, forms the lytic pore responsible for direct cell lysis following terminal pathway activation[1][2][6]. These molecules play integrated but separate roles in the innate immune response: C3b and C4b are primarily involved in opsonization and convertase assembly, while C5b-9 mediates cell membrane attack[2][6]. In disease, excess activation or inadequate control leads to pathology in autoimmune, inflammatory, and hemolytic diseases. The clinical use of anti-complement drugs (like eculizumab) targets C5, preventing C5b-9 formation for therapeutic effect[5][6]. Note: The submitted target is incorrect or at least ambiguous, as there is **no single molecular entity named 'C3b/C4b/C5b-9 complex'**; it combines discrete molecules/complexes from the complement cascade that do not form one functional or structural unit. The entry likely reflects an attempt to capture the range of complement activation products but should be split into the distinct canonical targets: C3b, C4b, and C5b-9 (membrane attack complex)[1][2][5][6].

Other names

C3bC4bMembrane attack complex (MAC)Terminal complement complexC5b-9

Inhibition of complement cleavage (C5 inhibitor: prevents formation of C5b-9 MAC, blocks terminal complement activation)