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MHC loci are some of the most genetically variable coding loci in mammals, and the human HLA loci are no exceptions. Despite the fact that the human population went through a constriction several times during its history that was capable of fixing many loci, the HLA loci appear to have survived such a constriction with a great deal of variation ...
HLA-A is a group of human leukocyte antigens (HLA) that are encoded by the HLA-A locus, which is located at human chromosome 6p21.3. [1] HLA is a major histocompatibility complex (MHC) antigen specific to humans. HLA-A is one of three major types of human MHC class I transmembrane proteins. The others are HLA-B and HLA-C. [2]
All alleles start with "HLA", signifying they are part of the human MHC genes. The next portion (HLA-A or HLA-B) identifies which gene the allele is a modification of. The first two numbers (HLA-A*02) signifies what antigen type that particular allele is, which typically signifies the serological antigen present. [3]
The most diverse loci, namely HLA-A, HLA-B, and HLA-C, have roughly 6000, 7200, and 5800 known alleles, respectively. [39] Many HLA alleles are ancient, sometimes of closer homology to a chimpanzee MHC alleles than to some other human alleles of the same gene. MHC allelic diversity has challenged evolutionary biologists for explanation.
HLA-C is a locus on chromosome 6, which encodes for many HLA-C alleles that are Class-I MHC receptors. HLA-C, localized proximal to the HLA-B locus, is located on the distal end of the HLA region. Most HLA-C:B haplotypes are in strong linkage disequilibrium and many are as ancient as the human species itself.
HLA-DP is a protein/peptide-antigen receptor and graft-versus-host disease antigen that is composed of 2 subunits, DPα and DPβ. DPα and DPβ are encoded by two loci, HLA-DPA1 and HLA-DPB1, that are found in the MHC Class II (or HLA-D) region in the Human Leukocyte Antigen complex on human chromosome 6 (see protein boxes on right for links).
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 ( H uman L eukocyte A ntigen – DR isotype) and peptide, generally between 9 and 30 amino acids in length, constitutes a ligand for the T-cell receptor (TCR).
HLA-DQ (DQ) is a cell surface receptor protein found on antigen-presenting cells. It is an αβ heterodimer of type MHC class II. The α and β chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. Both α-chain and β-chain vary greatly.