What is a Membrane Attack Complex (MAC) and what is its function?

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Multiple Choice

What is a Membrane Attack Complex (MAC) and what is its function?

Explanation:
Pore formation in target cell membranes is the function of the membrane attack complex, the terminal product of the complement cascade. It assembles as C5b binds C6, C7, C8, and multiple C9 molecules to form a ring-shaped pore in the lipid bilayer. This hole disrupts membrane integrity, allowing ions and water to flow uncontrollably, causing swelling and lysis of the target cell. The MAC’s role is to directly lyse pathogens rather than neutralize them by antibody binding, and it isn’t the main mechanism for enhancing phagocytosis (that's the job of opsonins like C3b) or for triggering B cell activation (other fragments such as C3d aid that process).

Pore formation in target cell membranes is the function of the membrane attack complex, the terminal product of the complement cascade. It assembles as C5b binds C6, C7, C8, and multiple C9 molecules to form a ring-shaped pore in the lipid bilayer. This hole disrupts membrane integrity, allowing ions and water to flow uncontrollably, causing swelling and lysis of the target cell. The MAC’s role is to directly lyse pathogens rather than neutralize them by antibody binding, and it isn’t the main mechanism for enhancing phagocytosis (that's the job of opsonins like C3b) or for triggering B cell activation (other fragments such as C3d aid that process).

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