histocompatibility locus antigen


Also found in: Dictionary, Thesaurus, Encyclopedia.

histocompatibility locus antigen

Abbreviation: HLA
Any of the multiple antigens present on all nucleated cells in the body that identify the cells as self. Immune cells compare these antigens to foreign antigens, which do not match the self and therefore trigger an immune response. These markers determine the compatibility of tissue for transplantation.

They are derived from genes at seven sites (loci) on chromosome 6, in an area called the major histocompatibility complex (MHC); each histocompatibility antigen is divided into one of two MHC classes.

In humans, the proteins created in the MHC are called human leukocyte antigens (HLA) because these markers were originally found on lymphocytes. Each gene in the MHC has several forms or alleles. Therefore, the number of different histocompatibility antigens is very large, necessitating the identification and matching of HLAs in donors and recipients involved in tissue and organ transplantation. (The identification of HLAs is called tissue typing.)

The identification of HLA sites on chromosome 6 has enabled researchers to correlate the presence of specific histocompatibility and certain autoimmune diseases (e.g., insulin-dependent diabetes mellitus, multiple sclerosis, some forms of myasthenia gravis, rheumatoid arthritis, and ankylosing spondylitis).

Synonym: human leukocyte antigen See: major histocompatibility complex
See also: antigen