C4b is primarily associated with which immune function?

C4b is primarily associated with facilitating the lysis of pathogens. It plays a crucial role in the complement system, which is a part of the innate immune response. When the complement pathway is activated, C4 is cleaved into C4a and C4b. The C4b fragment can bind to the surfaces of pathogens, which serves several functions, including marking the pathogen for destruction.

One of the key roles of C4b is its involvement in the formation of the C3 convertase enzyme complex, which subsequently leads to the cleavage of C3 into C3a and C3b. C3b also binds to pathogens, enhancing opsonization (the process by which pathogens are marked for phagocytosis) and leading to the formation of the membrane attack complex (MAC) that directly causes lysis of the pathogen’s cell membrane. This action can effectively result in the destruction of the pathogen.

While enhancing phagocytosis is indeed an important function of the complement system, through the action of C3b, the specific association of C4b is more directly linked to the pathway leading to the lysis of pathogens. Thus, the correct answer reflects C4b's pivotal role in the complement cascade that culminates