Human Leukocyte Antigen (Hla) System

The human leukocyte antigen system (HLA), the major histocompatibility complex (MHC) in humans, is controlled by genes on the chromosome. 6 It encodes cell surface molecules that are specialized in the T-cell receptors (TCR) to present on T cell antigen peptides. MHC molecules presenting antigen (Ag) are divided into two main classes: Class I MHC molecules class II MHC molecules class I MHC molecules exist as transmembrane glycoproteins on the surface of all nucleated cells. Intact class I Molkeüle consisting of one heavy chain which is bonded to a ?2-Mikroglobulinmolekül. The heavy chain consists of two peptide binding function areas, an Ig-like region and a transmembrane region with the cytoplasmic end. The heavy chain of the class I molecules encoded by genes of the HLA-A, HLA-B or HLA-C loci. Lymphocytes that express CD8 molecules react with MHC class I molecules. These lymphocytes have often requires a cytotoxic function, they are able to recognize infected cells. Since every nucleated cell MHC class I molecules expressed, all infected cells may act as antigen presenting cells for CD8 T cells (CD8 binds to the non-polymorphic part of the class I heavy chains). Some of the class I MHC genes do not encode classical MHC molecules, such as HLA-G (a role in protecting the fetus from the mother’s immune response to play) and HLA-E (which peptides to specific receptors on natural killer cells [NK] passes). Class II MHC molecules usually appear only on Ag-presenting cells (B cells, macrophages, dendritic cells, Langerhans cells), on thymic epithelium and on activated (but not resting) T cells; most nucleated cells can be stimulated by IFN-? in the expression of class II molecules. Class II MHC molecules are composed of two polypeptide chains (? and ?), each having a peptide binding function area, have an Ig-like and a transmembrane region with cytoplasmic end. Both polypeptide chains are encoded by genes in the HLA-DP, -DQ-, or -DR region of the chromosome. 6 Lymphocytes that respond to class II molecules that express CD4 and are often helper T cells. The MHC class III region of the genome encodes several molecules that are important in inflammation; they comprise the complement components C2, C4, and factor B, tumor necrosis factor (TNF) -?; Lymphotoxin-?; Lymphotoxin-?, and three heat-shock proteins. ndividual serologically defined antigens, which are encoded by class I and class II gene loci in the HLA system, have a certain default name (for. example, HLA-A1, -B5, -C1, -DR1). Alleles, which are defined by DNA sequencing, are named after the to be identified gene, followed by an asterisk (*), of digits, indicative of the allele group (corresponds often to the serological equivalent of the Ags), a colon and digits describe the specific allele (e.g., A *. 02: 01, DRB1 * 01: 03, DQA * 01: 02). Sometimes example, additional numbers are added after the colon for identification of allelic variants that encode identical proteins and after a further colon are more figures for the description of polymorphisms in introns or in 5 ‘or 3’ untranslated regions (eg. A * 02: 101: 01: 02, DRB1 * 03: 01: 01: 02). The MHC class I and II molecules are the most common immunogenic antigens that are seen during allograft rejection. The most powerful determinant is HLA-DR, followed by HLA-B and HLA-A through. These three loci are therefore most important for the consistency of donor and recipient. Some autoimmune disorders are associated with specific HLA-alleles, for example: Psoriasis with HLA-C * 06: 02 ankylosing spondylitis, reactive arthritis with HLA-B27 narcolepsy with HLA-DR2 and HLA-DQB1 * 06: 02 Type 1 diabetes mellitus with HLA-DQ2 and HLA-DQ8 multiple sclerosis with HLA-DR2, RA with HLA-DR4

Health Life Media Team

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