Complement component C6 deficiency and susceptibility to Neisseria Meningitidis infection
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2004
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South African Medical Journal
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University of Cape Town
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Abstract
Meningococcal disease remains one of the most serious bacterial infections in both Western and developing countries. Despite recent advances in treatment the mortality rate remains at about 12%.1 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).2 The human complement system forms part of the humeral immune system and consists of a series of proteins.3 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 certain viruses. This action of complement has been recognised for many years as playing a major role in defence against infection.4 In addition, MAC action is often sublytic on nucleated host cells, and this interaction can sometimes stimulate cellular biosynthesis and act in a pro-inflammatory manner.5 Many other complement proteins, and products of complement activation, also interact with the cellular immune system and the inflammatory system. If activation is caused by pathological processes such as ischaemia, complement can be an important contributor to host tissue necrosis.6 The effects of complement activation are very complex and can be detrimental as well as beneficial.
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Reference:
Orren, A., & Potter, P. C. (2004). Complement component C6 deficiency and susceptibility to Neisseria meningitidis infections: clinical practice: SAMJ forum. South African Medical Journal, 94(5), p-345.