Major histocompatibility complex
Say it: MAY-jur his-toh-kum-pat-uh-BIL-ih-tee KOM-pleks
The major histocompatibility complex is a set of genes whose proteins display protein fragments on cell surfaces so that T cells can inspect them.
Also: MHC, human leukocyte antigen, HLA, MHC molecules
Definition
What is the major histocompatibility complex?
The major histocompatibility complex, or MHC, is a cluster of genes found in humans and many other animals, and the name is also used for the cell-surface proteins these genes encode. In humans the cluster lies on chromosome 6 and is known as the HLA (human leukocyte antigen) complex. MHC genes are highly variable, with hundreds of versions of some genes in the population, so nearly every person carries a distinct combination.
MHC proteins hold short peptides in a groove and show them to T cells. Class I molecules, present on almost all nucleated cells, display pieces of proteins made inside the cell; if these include viral or tumor proteins, cytotoxic T cells destroy the cell. Class II molecules occur mainly on antigen-presenting cells, namely macrophages, dendritic cells and B cells, and display pieces of material the cell has taken in, which activates helper T cells. Because T cells recognize antigen only when MHC holds it, these molecules sit at the center of adaptive immunity.
The name comes from transplant research: the closer the HLA match between donor and recipient, the lower the risk of graft rejection. Particular HLA variants are also linked to autoimmune diseases and to severe drug reactions.
Word parts
Where does the term “major histocompatibility complex” come from?
- histo-
- tissueGreek histos, web or tissue
- compatibility
- ability to exist togetherLatin compati, to suffer with
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Terms that go with it
- AntigenAn antigen is any molecule the immune system can recognize as a target, especially one that prompts antibodies or T cells to respond against it.
- T cellA T cell is a white blood cell that matures in the thymus and drives cell-based immunity, directing other immune cells or killing infected cells.
- Cytotoxic T cellA cytotoxic T cell is a white blood cell of adaptive immunity that finds and kills body cells infected by viruses or turned cancerous.
- Helper T cellA helper T cell is a CD4 T lymphocyte that coordinates immune responses, releasing cytokines that activate B cells, killer T cells and macrophages.
- MacrophageA macrophage is a large white blood cell that engulfs and digests microbes, dead cells and debris, and signals other immune cells to act.
- Adaptive immunityAdaptive immunity is the branch of the immune system that learns to recognize specific antigens and remembers them, so it responds faster next time.
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Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Microbiology, 18.2 Major Histocompatibility Complexes and Antigen-Presenting Cells
- MedlinePlus Genetics: HLA-B gene
- OpenStax Biology 2e, 42.2 Adaptive Immune Response
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