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an antigen on the surface of nucleated cells, particularly leucocytes and thrombocytes.
See also: H-2 antigens.
See also: H-2 antigens.
Synonym(s): transplantation antigen
Any of the genetically determined antigens on the surface of cell membranes that identify a cell as self or nonself and that determine whether a tissue graft will be accepted by an organ transplant recipient.
Etymology: Gk, histos + L, compatibilis, agreeable
the quality of a cellular or tissue graft enabling it to be accepted and functional when transplanted to another animal.
genetically determined antigens present on the cell membranes of nucleated cells of most tissues, which incite rejection when tissues are grafted to a different individual and thus determine the compatibility of tissues in transplantation. Major histocompatibility antigens exert the strongest effect on transplanted tissues, while the many minor histocompatibility antigens, such as blood group substances and the secretory alloantigen system, have a weaker, though often highly significant role in graft rejection.
genes that code for the histocompatibility antigens.
major histocompatibility complex (MHC)
a cluster of loci on one autosomal chromosome containing the genes that code for the major histocompatibility antigens. The best studied MHC is the H2 complex of the mouse followed by the HLA (human leukocyte antigen) of humans. In other species it is further specified: the dog leukocyte antigen (DLA), the bovine leukocyte antigen (BOLA), the swine leukocyte antigen (SLA), etc.
MHC class I is a polymorphic set of transmembrane heterodimeric proteins consisting of an α chain, encoded within the MHC gene complex, associated noncovalently with β2-microglobulin expressed on nearly all nucleated cells and which form a trimeric complex with typically 9-mer peptides that are then transported and presented on the surface of the cells and serve as targets for cytotoxic T lymphocytes (CTL or Tc), CD8 cells. A major defense mechanism against viral infections.
MHC class II is a polymorphic set of transmembrane heterodimeric proteins that consist of noncovalently associated α and β proteins, both encoded within the MHC gene complex. They form a trimeric complex with antigenic peptides, which may be up to 35-mers, in antigen presenting cells which are then transported to the surface of the cell for presentation to T helper lymphocytes. The basis for all T lymphocyte responses.