The C5b-9 complex, also known as the membrane attack complex (MAC), is a crucial part of the complement system, which helps the immune system fight infections. It is formed when proteins C5b, C6, C7, C8, and multiple C9 molecules come together. This complex creates pores in the membranes of target cells, leading to cell lysis or death. The formation of the C5b-9 complex is an important mechanism for eliminating pathogens, such as bacteria and viruses. By disrupting the integrity of the target cell's membrane, the MAC enhances the body's ability to clear infections and maintain overall health.