Final answer:
The classical pathway for complement activation is initiated by antigen-antibody reactions.
Step-by-step explanation:
The classical pathway for complement activation is initiated by antigen-antibody reactions. In the classical pathway, complement activation is triggered when antibodies bind to antigens on the surface of pathogens. This binding activates the complement system, leading to a cascade of reactions that ultimately results in the formation of a membrane-attack complex (MAC) to destroy the pathogen.