C3 convertase is an enzyme complex that plays a crucial role in the complement system, which is part of the immune response. It is responsible for cleaving the protein C3 into two fragments, C3a and C3b. This activation helps to enhance inflammation and opsonization, marking pathogens for destruction by immune cells. There are two main forms of C3 convertase: C4b2a in the classical and lectin pathways, and C3bBb in the alternative pathway. Both forms contribute to the amplification of the immune response, leading to the formation of the membrane attack complex that can directly destroy pathogens.