The membrane attack complex formed by the complement cascade is

Activation of the complement cascade by the classical or alternative pathway leads to the cleavage of complement fragments and the formation of active enzymatic complexes. The C5b fragment aggregates with complement proteins C6, C7, CS, and C9, resulting in the polymerization of the final product, known as the “membrane-attack complex” (MAC). MAC lyses cells by inserting into the plasma membrane and destroying the permeability barrier.