Major histocompatibility complex
The major histocompatibility complex is the set of cell surface proteins essential for the acquired immune system to recognize foreign molecules in vertebrates. The human MHC is also called the HLA (human leukocyte antigen) complex.
Human lymphocyte antigens are important in organ transplantation, and presumably because of their physical association with other genes with which they have co-evolved some of them also act as markers for increased or decreased susceptibility to assorted diseases, eg diabetes mellitus.
The MHC is also involved in recognition of antigens. MHC proteins on antigen presenting cells (APCs) combine with antibodies, and it is this complex of MHC and antigens that is presented to the immune system.
MHC proteins are genetically determined, and, while there is a wide range of them, the range is limited, which goes some way to explaining why some individuals are unable to generate an immune response to certain antigens. This may be significant in vaccination.
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