Examples of MHC in the following topics:
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- MHC gene families are found in all vertebrates, though they vary widely.
- Chickens have among the smallest known MHC regions (19 genes).
- In humans, the MHC region occurs on chromosome 6 .
- Human MHC class I and II are also called human leukocyte antigen (HLA).
- MHC genes are expressed in co-dominant fashion.
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- MHC molecules mediate interactions of leukocytes, with other leukocytes or body cells.
- In humans, MHC is also called human leukocyte antigen (HLA), because MHC can often act as an antigen for human leukocytes.
- MHC is a polymorphic protein that is attached to the surface of cells.
- MHC I- presented on all cells of the body.
- MHC III- a secreted enzyme that is not membrane bound, nor involved in antigen presenation like MHC I and II.
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- Natural killer cells are part of the innate immune response that recognize abnormal MHC I molecules on infected/tumor cells and kill them.
- If the cell is infected, the MHC I molecules display fragments of proteins from the infectious agents to T-cells.
- An infected cell (or a tumor cell) is often incapable of synthesizing and displaying MHC I molecules appropriately.
- The reduced MHC I on host cells varies from virus to virus and results from active inhibitors being produced by the viruses.
- This process can deplete host MHC I molecules on the cell surface, which prevents T-cells from recognizing them, but which NK cells detect as "unhealthy" or "abnormal" while searching for cellular MHC I molecules.
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- T lymphocytes have a dual specificity: they recognize polymorphic residues of self major histocompatibility complex (MHC) molecules, which accounts for their MHC restriction; they also recognize residues of peptide antigens displayed by these MHC molecules, which is responsible for their specificity.
- MHC molecules and peptides form complexes on the surface of antigen presenting cells (APCs).
- The receptor that recognizes these peptide-MHC complexes is called the T Cell Receptor (TCR).
- The antigen receptor of MHC-restricted CD4 helper T cells and CD8 cytolytic T cell is a heterodimer consisting of two transmembrane polypeptide chains, designated alpha and beta, covalently linked to each other by disulfide bonds.
- The recognition of peptide-MHC complexes is mediated by CDRs formed by both the alpha and beta chains of the TCR.
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- Free peptides flowing through the body are not recognized by T cells, rather the peptides associate with molecules coded for by the major histocompatibility complex (MHC) and it is the complex of MHC molecules + peptide that is recognized by T cells.
- MHC molecules must move between the cell membrane and cytoplasm in order for antigen processing to occur properly.
- However, the pathway leading to the association of protein fragments with MHC molecules differs between class I and class II MHC, which are presented to cytotoxic or helper T cells respectively.
- Generally, proteosomes are used to break up the viral proteins and combine them with MHC I.
- First, pathogens are phagocytized, and then endosomes within the cell break down antigens with proteases, which then combine with MHC II.
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- Typically, immune cells detect major histocompatibility complex (MHC) presented on cell surfaces, triggering cytokine release and lysis or apoptosis in cells that do not express MHC I, or express much less of it than normal cells.
- These receptors recognize Major Histocompatability Complex I (MHC I), a molecule expressed on every cell to signal that the cell belongs to the body.
- When the NK cell recognizes MHC I on a cell using an inhibitory receptor, its killing response is inhibited.
- Some tumor cells may still express MHC I in lower amounts, so they may still evade NK cell destruction based on the balance of activating and inhibiting stimuli.
- T-cells are activated by recognizing antigens, while NK cells are activated by not recognizing MHC I.
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- Positive selection "selects for" T cells capable of interacting with MHC.
- These self-antigens are expressed by thymic cortical epithelial cells that express both MHC I and MHC II molecules on the surface of cortical cells.
- Only those thymocytes that interact with MHC I or MHC II will receive a vital "survival signal. " All that can't interact will die by apoptosis.
- Double-positive cells (CD4+/CD8+) that are positively selected on MHC class II molecules will eventually become CD4+ helper T cells, while cells positively selected on MHC class I molecules mature into CD8+ cytotoxic T cells.
- Negative selection removes thymocytes that are capable of strongly binding with "self" antigens presented by MHC.
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- MHC Class I molecules present antigen to CD8+ cytotoxic T cells.
- With the exception of some cell types (such as erythrocytes), Class I MHC is expressed by almost all host cells.
- This MHC:antigen complex is then recognized by T cells passing through the lymph node.
- Exogenous antigens are usually displayed on MHC Class II molecules, which interact with CD4+ helper T cells.
- The antigen is processed and displayed on a MHC II molecule (3), which interacts with a T helper cell (4).
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- T cells become activated towards a certain antigen once they encounter it displayed on an MHC II.
- To do so, a T cell will become activated by interacting with an antigen of the infecting cell or virus presented on the MHC II of an APC.
- To recognize which cells to pursue, TC recognize antigens presented on MHC I complexes, which are present on all nucleated cells.
- MHC I complexes display a current readout of intracellular proteins inside a cell and will present pathogen antigens if the pathogen is present in the cell.
- Lymphocytes of the adaptive immune response must interact with antigen-embedded MHC class II molecules to mature into functional immune cells.
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- Three main sets of genes are suspected in many autoimmune diseases: immunoglobulins, T-cell receptors and the major histocompatibility complexes (MHC).
- Todd have also provided strong evidence to suggest that certain MHC class II allotypes are strongly correlated with autoimmunity.
- Fewer correlations exist with MHC class I molecules.
- Correlations may exist between polymorphisms within class II MHC promoters and autoimmune disease.
- HLA-DR is a MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31.