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Histocompatibility, or tissue compatibility, is the property of having the same, or sufficiently similar, alleles of a set of genes called human leukocyte antigens (HLA), or major histocompatibility complex (MHC). Each individual expresses many unique HLA proteins on the surface of their cells, which signal to the immune system whether a cell is part of the self or an invading organism. T cells recognize foreign HLA molecules and trigger an immune response to destroy the foreign cells. Histocompatibility testing is most relevant for topics related to whole organ, tissue, or stem cell transplants, where the similarity or difference between the donor's HLA alleles and the recipient's triggers the immune system to reject the transplant. The wide variety of potential HLA alleles lead to unique combinations in individuals and make matching difficult.
The major histocompatibility complex (MHC) is a large locus on vertebrate DNA containing a set of closely linked polymorphic genes that code for cell surface proteins essential for the adaptive immune system. These cell surface proteins are called MHC molecules.
The human leukocyte antigen (HLA) system or complex is a complex of genes on chromosome 6 in humans which encode cell-surface proteins responsible for regulation of the immune system. The HLA system is also known as the human version of the major histocompatibility complex (MHC) found in many animals.
Chromosome 6 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 6 spans more than 172 million base pairs and represents between 5.5 and 6% of the total DNA in cells. It contains the major histocompatibility complex, which contains over 100 genes related to the immune response, and plays a vital role in organ transplantation.
HLA-DR is an MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31. The complex of HLA-DR and peptide, generally between 9 and 30 amino acids in length, constitutes a ligand for the T-cell receptor (TCR). HLA were originally defined as cell surface antigens that mediate graft-versus-host disease. Identification of these antigens has led to greater success and longevity in organ transplant.
HLA class II histocompatibility antigen, DRB1 beta chain is a protein that in humans is encoded by the HLA-DRB1 gene. DRB1 encodes the most prevalent beta subunit of HLA-DR. DRB1 alleles, especially those encoding amino acid sequence changes at positions 11 and 13, are associated risk of rheumatoid arthritis.
MHC Class II molecules are a class of major histocompatibility complex (MHC) molecules normally found only on professional antigen-presenting cells such as dendritic cells, mononuclear phagocytes, some endothelial cells, thymic epithelial cells, and B cells. These cells are important in initiating immune responses.
Leukocyte surface antigen CD53 is a protein that in humans is encoded by the CD53 gene.
Leukocyte immunoglobulin-like receptor subfamily B member 1 is a protein that in humans is encoded by the LILRB1 gene.
HLA class II histocompatibility antigen, DP(W2) beta chain is a protein that in humans is encoded by the HLA-DPB1 gene.
HLA class I histocompatibility antigen, alpha chain F is a protein that in humans is encoded by the HLA-F gene. It is an empty intracellular molecule that encodes a non-classical heavy chain anchored to the membrane and forming a heterodimer with a β-2 microglobulin light chain. It belongs to the HLA class I heavy chain paralogues that separate from most of the HLA heavy chains. HLA-F is localized in the endoplasmic reticulum and Golgi apparatus, and is also unique in the sense that it exhibits few polymorphisms in the human population relative to the other HLA genes; however, there have been found different isoforms from numerous transcript variants found for the HLA-F gene. Its pathways include IFN-gamma signaling and CDK-mediated phosphorylation and removal of the Saccharomycescerevisiae Cdc6 protein, which is crucial for functional DNA replication.
Pre-B-cell leukemia transcription factor 2 is a protein that in humans is encoded by the PBX2 gene.
Large proline-rich protein BAT2 is a protein that in humans is encoded by the BAT2 gene.
Leukocyte-specific transcript 1 protein is a protein that in humans is encoded by the LST1 gene.
NF-kappa-B inhibitor-like protein 1 is a protein that in humans is encoded by the NFKBIL1 gene.
Serine/threonine-protein kinase 19 is an enzyme that in humans is encoded by the STK19 gene.
Protein G6b is a protein that in humans is encoded by the G6B gene, or C6orf25.
CD8a, is a human gene.
Ly6 also known as lymphocyte antigen 6 or urokinase-type plasminogen activator receptor (uPAR) is family of proteins that share a common structure but differ in their tissue expression patterns and function. Ly6 are cysteine-rich proteins that form disulfide bridges and contain a LU domain. These proteins are GPI-anchored to the cell membrane or are secreted. A total of 35 human and 61 mouse Ly6 family members have been identified. Depending on which tissues they are expressed in, LY6 family members have different roles. They are expressed in various types of tissues and their expression dependent on the stage of cell differentiation. For example, they are involved in cell proliferation, cell migration, cell–cell interactions, immune cell maturation, macrophage activation, and cytokine production. Their overexpression or dysregulation, for example due to point mutations, is associated with tumorogenesis and autoimmune diseases. This family was discovered in the 1970s, and these proteins are still used as markers of distinct stage of leukocyte differentiation.
MHC class III is a group of proteins belonging the class of major histocompatibility complex (MHC). Unlike other MHC types such as MHC class I and MHC class II, of which their structure and functions in immune response are well defined, MHC class III are poorly defined structurally and functionally. They are not involved in antigen binding. Only few of them are actually involved in immunity while many are signalling molecules in other cell communications. They are mainly known from their genes because their gene cluster is present between those of class I and class II. The gene cluster was discovered when genes were found in between class I and class II genes on the short (p) arm of human chromosome 6. It was later found that it contains many genes for different signalling molecules such as tumour necrosis factors (TNFs) and heat shock proteins. More than 60 MHC class III genes are described, which is about 28% of the total MHC genes (224). The region previously considered within MHC class III gene cluster that contains genes for TNFs is now known as MHC class IV or inflammatory region.
References
- ↑ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ↑ "Entrez Gene: Lymphocyte antigen 6 complex, locus G6E pseudogene)".
- ↑ Mallya M, Campbell RD, Aguado B (July 2002). "Transcriptional analysis of a novel cluster of LY-6 family members in the human and mouse major histocompatibility complex: five genes with many splice forms". Genomics. 80 (1): 113–23. doi:10.1006/geno.2002.6794. PMID 12079290.
