histocompatibility

n., pl., -ties.
A state or condition in which the absence of immunological interference permits the grafting of tissue or the transfusion of blood without rejection.

histocompatible his'to·com·pat'i·ble adj.

A term used to describe the genes that influence acceptance or rejection of grafts. When grafts of tissue are exchanged between genetically dissimilar individuals, profound immunological rejection generally takes place. In contrast, grafts between genetically similar individuals, such as identical twins, are normally tolerated; they are histocompatible. Most known examples of histocompatibility (or H) genes encode polymorphic (that is, tending to differ between individuals) cell-surface proteins.

The major histocompatibility complex (MHC) contains a set of histocompatibility genes, termed major because mismatching at these genes invokes rapid rejection. The main function of MHC genes involves distinguishing self from nonself in the immune system, as part of preventing the spread of infectious disease. The body employs special mechanisms to avoid rejection of the fetus, which is effectively an allograft, that is, a graft from a donor to a genetically dissimilar recipient of the same species; in this case, the mechanisms include a diminution of MHC gene expression.

The MHC contains a spectrum of genes, many of which influence processing and presentation of antigens to the immune system. In mice, the MHC is designated the H-2 complex; in humans, it is referred to as the HLA complex (for human leukocyte A system). Mice and other mammals seem to have a similar arrangement of genes in their MHCs. See also Antigen; Cellular immunology; Mendelism; Transplantation biology.

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n

The compatibility of the antigens of donor and recipient of transplanted tissue.

The quality of a cellular or tissue graft enabling it to be accepted and functional when transplanted to another animal.

• h. antigen — 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.
• h. genes — genes that code for the histocompatibility antigens.
• major h. 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.

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Common misspelling(s) of histocompatibility

• histocompatability