title: Protection from autoimmune disease as the third function of the major histocompatibility gene complex.
abstract: The collection of genes known as the major histocompatibility gene complex (MHC) appears to subserve three functions. Firstly, its class I genes, coding for antigens on all nucleated cells, assist clones of cytotoxic T cells to kill virus-infected cells quickly, without being muffled by the myriad numbers of free virus particles. Secondly, the absence of autoimmunity to both class I and class II MHC antigens shows that they impose unbreakable tolerances on the immune repertoire. The class II antigens, which are confined to B lymphocytes (if their apparent occurrence on other dividing cells is a cross-reaction), may have the sole function of tolerance induction, supplementing this activity of the class I antigens. Both sets of MHC antigens serve to diversify immunity-repertoire gaps among individuals of a population, thus hampering epidemic spread of infection and providing a diversity of immunoreactivity that favours survival of at least some members of a population in the face of pestilence. Thirdly, the permanence of the MHC tolerance inductions affords a powerful, adaptable mechanism for curtailment of reproductively disadvantageous autoimmune disease liable to arise through somatic mutations in lymphocytes multiplying under drive from a microbial antigenic stimulus.
mesh_terms: D000818:Animals; D001327:Autoimmune Diseases / Q000235:genetics / Q000517:prevention & control*; D006680:HLA Antigens / Q000235:genetics; D006649:Histocompatibility Antigens / Q000235:genetics; D006801:Humans; D007108:Immune Tolerance; D008285:Major Histocompatibility Complex; D051379:Mice
chemical_list: D006680:HLA Antigens; D006649:Histocompatibility Antigens