histocompatibility complex


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histocompatibility complex

a family of 50 or more genes on the sixth human chromosome that encodes cell surface proteins and play a role in the immune response.

Histocompatibility genes control the production of proteins on the outer membranes of tissue and blood cells, especially lymphocytes, and are essential elements in cell-cell recognition and interaction. Surface proteins also determine the level and type of immune response, are involved in the presentation of antigens to the immune system, and may serve other biochemical and immunologic functions. In human beings, proteins encoded by multiallelic genes of the major histocompability complex (MHC) on chromosome 6 are known as human leukocyte antigens (HLA). MHC molecules are divided into two classes on the basis of distinctive polypeptide subunits and biologic function. Class I MHC molecules, which are found on all nucleated cells, consist of an α chain (45 kD) and a small peptide called β2-microglobulin (12 kD). They are involved in presentation of antigens to cytotoxic (CD8) lymphocytes. Class II MHC molecules consist of an α chain (30-34 kD) and a β chain (26-29 kD). They are expressed by all B lymphocytes, interdigitating dendritic cells, and thymic epithelial cells. Other cells, including T lymphocytes, macrophages, and endothelial cells, can be induced by cytokines to express them. They function in presenting antigen to CD4 helper lymphocytes. Class I MHC molecules are encoded by HLA-A, HLA-B, and HLA-C genes; class II MHC molecules by HLA-D (DP, DQ, DR) genes. In the case of allografts, the greater the histocompatibility (that is, the closer the match between donor and recipient cell surface antigens), the less is the likelihood of rejection. HLA typing of a potential marrow donor and a potential transplant recipient is used to predict graft rejection and graft-versus-host disease. The possession of certain allelic HLA genes predisposes to specific diseases. For example, the HLA-B27 allele is found in 90% of patients with ankylosing spondylitis; HLA-DR4 is associated with rheumatoid arthritis, HLA-DR2 with both Goodpasture syndrome and multiple sclerosis. The association of HLA alleles with specific diseases has prompted speculation that some infectious agents may use HLA molecules to gain access to host cells, may mimic HLA molecules so as to be recognized as self by T cells, or may combine with certain HLA molecules to form a complex not recognized at all by T cells.

his·to·com·pat·i·bil·i·ty com·plex

(his'tō-kŏm-pat'i-bil'i-tē kom'pleks)
A family of 50 or more genes on the sixth human chromosome that code for cell surface proteins and play a role in the immune response. Histocompatibility genes control the production of proteins on the outer membranes of tissue and blood cells, especially lymphocytes, and are vital elements in cell-cell recognition. The proteins also determine the level and type of immune response, and may serve other biochemical or immunologic functions. In the case of allografts, it is necessary to determine whether donor and recipient possess compatible sets of proteins (histocompatibility antigens), to minimize the likelihood of rejection. Histocompatibility testing (human leukocyte antigen tissue typing) provides this information.
References in periodicals archive ?
Soluble molecules of the major histocompatibility complex are intercellular protein communicators and occupy one of the important positions in the realization of the immune response [16, 17, 35-38].
The antigens of the HLA system are determined by genes present in the major histocompatibility complex which is located on the short arm at the 6th chromosome (6p21.3) in humans and extends over some 4 centimorgans of DNA, about 4 x[10.sup.6] base pair.
Flavell, "Class II transactivator (CIITA) is sufficient for the inducible expression of major histocompatibility complex class II genes," Journal of Experimental Medicine, vol.
Comparative organization and function of the major histocompatibility complex of domesticated cattle.
Okada also has experiences for analyzing genetic polymorphisms in the major histocompatibility complex (MHC) region and HLA genes, which have substantial impacts on genetics of human diseases.
Major histocompatibility complex II (MHCII) overexpression has been previously shown to play a role in the activation of both the innate and adaptive immune responses to [alpha]-synclein aggregation in PD.
Genetic polymorphism of the swine major histocompatibility complex (SLA) class genes, sla-1, -2 and -3.
The final chapter considers how new insights into the mechanisms of self tolerance, the biological role of the major histocompatibility complex, and the nature of antigen recognition by T cells have led to a deeper understanding of autoimmunity.
The major histocompatibility complex (MHC) gene of sheep is located on Chromosome 20 and is called Ovar [1].
By far the most important are those encoding the major histocompatibility complex I and major histocompatibility complex II (MhC I and MHC II).
Miles et al., "High resolution structures of highly bulged viral epitopes bound to major histocompatibility complex class I: implications for T-cell receptor engagement and T-cell immunodominance," The Journal of Biological Chemistry, vol.