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The major histocompatibility complex (MHC) is a set of genes that encodes cell surface molecules which controls a major part of the immune system in all vertebrates by determining histocompatibility. The main function of MHC molecules is to bind to peptide fragments derived from pathogens and display them on the cell surface for recognition by the appropriate T-cells.〔Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001 (The Major Histocompatibility Complex and Its Functions ) 〕 MHC molecules mediate interactions of leukocytes, also called white blood cells (WBCs), which are immune cells, with other leukocytes or with body cells. The MHC determines compatibility of donors for organ transplant, as well as one's susceptibility to an autoimmune disease via crossreacting immunization. In humans, the MHC is also called the human leukocyte antigen (HLA). In a cell, protein molecules of the host's own phenotype or of other biologic entities are continually synthesized and degraded. Each MHC molecule on the cell surface displays a molecular fraction of a protein, called epitope.〔(Kimball's Biology ) Histocompatibility Molecules〕 The presented antigen can be either 'self' or 'nonself', thus preventing an organism`s immune system targeting its own cells. In its entirety, the MHC population is like a meter indicating the balance of proteins within the cell. The MHC gene family is divided into three subgroups: class I, class II, and class III. Class I MHC molecules have β2 subunits so can only be recognised by CD8 co-receptors. Class II MHC molecules have no β2 subunits so can be recognised by CD4 co-receptors. In this way MHC molecules chaperones which type of lymphocytes may bind to the given antigen with high affinity, since different lymphocytes express different TCR co-receptors. Diversity of antigen presentation, mediated by MHC classes I and II, is attained in at least three ways: (1) an organism's MHC repertoire is polygenic (via multiple, interacting genes); (2) MHC expression is codominant (from both sets of inherited alleles); (3) MHC gene variants are highly polymorphic (diversely varying from organism to organism within a species).〔Janeway CA Jr, Travers P, Walport M, ''et al'', ''Immunobiology: The Immune System in Health and Disease'', 5th edn (New York: Garland Science, 2001), ("The major histocompatibility complex and its functions" ).〕 Major histocompatibility complex and sexual selection has been observed in male mice making mate choices of females with different MHCs and thus demonstrating sexual selection. Also, at least for MHC I presentation, there has been evidence of antigenic peptide splicing which can combine peptides from different proteins, vastly increasing antigen diversity. ==Discovery== The first descriptions of the MHC were made by British immunologist Peter Gorer in 1936.〔Klein J 1986, "Seeds of time: Fifty years ago Peter A. Gorer discovered the H-2 complex",''Immunogenetics'' 24:331-338〕 MHC genes were first identified in inbred mice strains. Clarence Little transplanted tumors across differing strains and found rejection of transplanted tumors according to strains of host versus donor.〔Little CC 1941, "The genetics of tumor transplantation", pp 279–309, in ''Biology of the Laboratory Mouse'', ed by Snell GD, New York: Dover.〕 George Snell selectively bred two mouse strains, attained a new strain nearly identical to one of the progenitor strains, but differing crucially in histocompatibility—that is, tissue compatibility upon transplantation—and thereupon identified an MHC locus.〔Snell GD & Higgins GF 1951, "Alleles at the histocompatibility-2 locus in the mouse as determined by tumor transplantation", ''Genetics'' 36:306–310〕 For this work, Snell was awarded the 1980 Nobel Prize in Physiology or Medicine, together with Baruj Benacerraf and Jean Dausset. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Major histocompatibility complex」の詳細全文を読む スポンサード リンク
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