C6 is a component of complement cascade. It is part of the membrane attack complex which can insert into the cell membrane and cause cell to lyse. The human complement system forms part of the humeral immune system and consists of a series of proteins. The interaction of antigen (such as components of bacterial outer membranes) and antibody leads to activation of the first component C1q, and consequent activation of part or all of the complement cascade. This has a number of biological effects including the formation on the membrane of the membrane attack complex (MAC) from components C5b, C6, C7, C8 and C9. The MAC is able to mediate lysis of some mammalian cells such as red blood cells, as well as lysis of bacteria and certainviruses. This action of complement has been recognised formany years as playing a major role in defence against infection.4In addition, MAC action is often sublytic on nucleated hostcells, and this interaction can sometimes stimulate cellularbiosynthesis and act in a pro-inflammatory manner.
Meningococcal disease remains one of the most seriousbacterial infections in both Western and developing countries. Despite recent advances in treatment the mortality rate remainsat about 12%. There is a group of South Africans who are particularly vulnerable to this disease. They are individuals with genetically determined deficiencies of individual terminal complement proteins, in particular of the sixth component of complement (C6).
1. Orren A, et al. (2008). Complement component C6 deficiency and susceptibility to Neisseria meningitidis infections. South African Medical Journal, 94(5), 345.