What is the complement system primarily involved in?

The complement system is primarily involved in humoral immunity, which encompasses the immune responses mediated by antibodies produced by B cells. It consists of a series of plasma proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism. When activated, the complement system can opsonize pathogens, meaning it marks them for destruction by immune cells, enhances phagocytosis, and can directly lyse certain pathogens through the formation of the membrane attack complex.

While the complement system does have roles in other aspects of the immune response, such as innate immunity, including the direct recognition and destruction of pathogens, its primary association is with humoral immunity due to its activation through antibody-antigen complexes. This interplay is crucial for an effective immune response during infections, especially in the responses against extracellular pathogens where antibodies are critical.