The End Result of the Classical and Alternative Pathways of Complement

Question

The end result of the classical and alternative pathways of complement activation is
A) an increase in pyrogen release.
B) release of histamine.
C) activated C3B attached to the cell wall.
D) C1 bound to two antibodies.
E) activation of properdin.

Accepted Answer

The classical and alternative pathways of complement activation both result in the formation of the membrane attack complex (MAC) on the target cell. This involves the cleavage of C5 into C5a and C5b, and the subsequent binding of C5b to C6, C7, C8, and C9, forming the MAC. The classical pathway is initiated by the binding of C1 to an antigen-antibody complex, while the alternative pathway is activated by the presence of foreign substances on the surface of a microbe. The end result in both cases is the attachment of activated C3b to the target cell wall.