Complement component 8 subunit alpha and Complement component 9 (C8A and C9)

Complement component 8 subunit alpha (C8A) and Complement component 9 (C9) are essential terminal proteins of the complement system that assemble to form the membrane attack complex (MAC). C8A is a subunit of the C8 heterotrimer that initiates the penetration of the target cell membrane, while C9 is the final component that polymerizes into a ring-like structure of 12 to 18 monomers to create a stable transmembrane pore. This pore disrupts the osmotic balance of the target cell, leading to its lysis and death, a process critical for defending against pathogens like Gram-negative bacteria. In various autoimmune and inflammatory diseases, such as paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), uncontrolled MAC formation leads to pathological tissue damage. Therapeutic targeting of C8A and C9 aims to inhibit this terminal lytic step, potentially offering a more specific intervention that preserves upstream complement functions like opsonization and anaphylatoxin production compared to broader C5 inhibition.

Other names

Complement component 8 alpha chainC8 alphaC8AComplement component 9C9Terminal complement complex componentsMAC components C8A and C9

Inhibition of terminal complement complex (TCC) assembly, prevention of C9 polymerization, and blocking C8 insertion into the membrane to prevent osmotic lysis.