The classic pathway of complement activation begins when the complement protein binds to
A)the cell wall of bacteria.
B)the plasma membrane of bacteria.
C)an antibody attached to an antigen.
D)a cell surface antigen.
E)a plasma protein.

Question

Quizplus · Accepted Answer

The classic pathway of complement activation begins when complement protein C1 binds to an antibody that has attached to an antigen on the surface of a pathogen. This initiates a cascade of complement protein activation leading to the formation of a membrane attack complex that can lyse the pathogen.

Answer: D 
 The classic pathway of complement activation can also be initiated by binding of complement protein C1 directly to a cell surface antigen on a pathogen, such as a virus or bacteria. This also activates a cascade of complement protein activation leading to the formation of a membrane attack complex that can lyse the pathogen.

The Classic Pathway of Complement Activation Begins When the Complement