What is the activation pathway initiated by antibodies called?

The activation pathway initiated by antibodies is known as the classical pathway. This pathway is a crucial component of the immune response and is one of the three main pathways that activate the complement system, which plays a key role in enhancing the body’s ability to fight infections.

In the classical pathway, the process begins when antibodies bind to antigens on the surface of pathogens. This antibody-antigen complex then interacts with the first component of the complement system, C1, leading to a cascade of further complement protein activations. The overall result is the opsonization of pathogens, increased inflammation, and the formation of the membrane attack complex that can lyse (kill) certain pathogens.

The other options refer to different complement activation pathways. The alternative pathway is activated by microbial surface structures in the absence of antibodies, while the lectin pathway is initiated by the binding of mannose-binding lectin to specific carbohydrates on the pathogen's surface. The term "secondary pathway" is not recognized in the context of complement activation, and thus does not correctly describe any established pathway. Hence, the classical pathway is the accurate term for the antibody-initiated activation pathway.