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.

histocompatibility complex

a group of genes whose products determine the compatibility of tissues or organs transplanted from one individual to another of the same species or from one species to another. The histocompatibility complex of proteins is found on the plasma membrane cells and helps identify tissues as "self" or foreign. In humans the major histocompatibility complex contains 50 genes on the short arm of chromosome number 6. See also HLA complex.

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 ?
Evolutionary Relationship among Major Histocompatibility Complex I or Like Molecules
Molecular genetic analyses of the major histocompatibility complex in pig families and recombinants.
Comparative organization and function of the major histocompatibility complex of domesticated cattle.
Genetic relationship on the Guambiano, Paez, and Ingano Amerindians of southwest Colombia using major histocompatibility complex class II haplotypes and blood groups.
They are then combined with major histocompatibility complex molecules for antigen presentation to T cells.
The remaining markers spanned the major histocompatibility complex region on chromosome 6p21.
Substantial evidence exists that mice and rats can distinguish urinary odors associated with differences in the major histocompatibility complex (MHC; Kavaliers et al.
Human leukocyte antigen (HLA)-G is a non-classical major histocompatibility complex class I or Class Ib molecule that is primarily expressed at the fetal-maternal interface.
Major histocompatibility complex (MHC)-linked micro satellite markers in a founder population" Tissue Antigens .
The restoration of this pathway through expression or up-regulation of TAP in TAP-deficient cancer cells can enhance the functioning of the major histocompatibility complex (MHC) Class 1 antigen-presenting pathway and increase the production of tumour-infiltrating cytotoxic T-cells.
The research used a technique known as micropipette adhesion frequency assay to study the mechanical interactions between T cells and the antigen, known as a peptide major histocompatibility complex (pMHC)--a glycoprotein.
HLA stands for human leukocyte antigen, and HLA-DR is produced in a gene-dense region of the body's immune system, the major histocompatibility complex.