major histocompatibility complex

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major histocompatibility complex (MHC) A large multigene family that codes for histocompatibility antigens. Present on the surface of nucleated cells, histocompatibility antigens bind to and present foreign antigens to T cells which in turn may destroy infected cells or invading bodies, and use the histocompatibility antigens to recognize cells as self or foreign. The MHC tends to be highly polymorphic even within a single population, allowing a high level of discrimination between foreign and self, consequently organs transplanted from one member of a population to another are likely to be rejected by the new host unless the two members are very closely related. In different species different symbols are assigned to the MHC, e.g. in humans HLA is used, standing for human leucocyte antigen complex.

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