Which component polymerizes to form the transmembrane pore of the membrane attack complex?

Which component polymerizes to form the transmembrane pore of the membrane attack complex?

• A. C9
• B. C3
• C. C4
• D. C5

Answer: (A)

The crucial point is that C9 polymerizes to form the transmembrane pore of the membrane attack complex. After C5b binds C6–C8 and docks on the target membrane, C9 monomers are recruited and assemble into a polymer that creates a ring-like channel through the lipid bilayer, leading to membrane disruption and cell lysis. The other components play earlier roles in the cascade: C3 and C4 are involved in forming the C3 convertases and opsonization, while C5b initiates MAC assembly but does not itself form the pore.

The crucial point is that C9 polymerizes to form the transmembrane pore of the membrane attack complex. After C5b binds C6–C8 and docks on the target membrane, C9 monomers are recruited and assemble into a polymer that creates a ring-like channel through the lipid bilayer, leading to membrane disruption and cell lysis. The other components play earlier roles in the cascade: C3 and C4 are involved in forming the C3 convertases and opsonization, while C5b initiates MAC assembly but does not itself form the pore.