Upon activation, the complement system has multiple functions in the body. Its main function is its ability to defend the body against harmful pathogens like bacteria and viruses. It does this by identifying and then targeting these pathogens to eliminate them from the body. Phagocytosis is initiated by opsonizing antigens. The complement system also initiates inflammation to reduce the risk of infections. The complement system also forms membrane attack complexes (MACs) which create pores in the membranes of pathogens, leading to their destruction.