Comparison of the complement activation pathway of jawed and jawless vertebrates. In jawed vertebrates, the classical activation pathway of the complement system is triggered by antigen-antibody complex. The binding of complement C1 to the Fc region of the antibody initiates the complement activation pathway, and C4, C2 and C3 are then successively cleaved and activated. Finally, a subunit composition of C5b-C6-C7-C8-polyC9 forms the MAC that initiates the lysis of the target cells. In jawless vertebrates, the VLR-mediated complement pathway is triggered by antigen-VLR complex and C1q molecules. During this complement activation process, C3 is cleaved and activated. Finally, LPFP is recruited to form a pore complex on the membrane of target cells, resulting in the target cell lysis. Together, the two parallel complement pathways achieve similar cytotoxicity. (Source: Wu

International Union of Immunological SocietiesUniversity of South AfricaInstitute of Infectious Disease and Molecular MedicineElizabeth Glazer Pediatric Aids FoundationStellenbosch University