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人类白细胞抗原(HLA)是细胞表面蛋白质,可分为Ⅰ类和Ⅱ类,它们在结构、功能和组织分布方面不同,由一系列紧密联锁的多态基因控制,总称为组织相容性复合体(MHC)。 HLA的结构和多态性 MHC基因位于第六对染色体的短臂上,末端以Ⅰ类位点臂内延伸为Ⅱ类位点。近来,用X线结晶学确定了Ⅰ类分子的结构,发现存在于细胞表面的蛋白质复合物是由二对结构相似的区域构成。α_3区域及其连接的β_2-微球蛋白表明免疫球蛋白恒定区的相似性,这些区域可能影响HLA复合物的特异性,强度和稳定性。α_3区是T细胞上辅助蛋白CD8的结合位点,是Ⅰ类抗原有效限制T细胞活化所必需的。α_1、α_2区在C-末端被2个α螺旋联在一起,形成一单个的β折叠结构。在两个螺旋之间,是假设的抗原结合位点。对α_3区和α_1区位点间作比较,无明显差别。然而α_1区在α螺旋中是多变的,在β折叠中有稳定的成份,提示这可能为肽的结合提供支架,在β折叠中α_2区是多变的,并且可能与T细胞受体(TCR)的相互作用有关,以及在肽的选择中起作用。Ⅱ类或HLA-D区蛋白质由DR、DQ和DP位点编码。它由一个33kd的A链和一个29kd的B链
Human leukocyte antigen (HLA) is a cell surface protein, which can be divided into class I and class II. They are different in structure, function and tissue distribution and are controlled by a series of closely linked polymorphic genes, collectively known as histocompatibility complex Body (MHC). Structure and Polymorphism of HLA The MHC gene is located on the short arm of the sixth chromosome and ends in the arm of the class I site as a class II site. Recently, the structure of class I molecules has been determined by X-ray crystallography and found that the protein complexes present on the cell surface consist of two pairs of structurally similar regions. The α_3 region and its associated β_2-microglobulin indicate similar immunoglobulin constant regions that may affect the specificity, strength and stability of the HLA complexes. The α3 region is the binding site for the accessory protein CD8 on T cells and is required for class I antigens to effectively limit T cell activation. α_1, α_2 region in the C-terminal by two α-linked together to form a single β-sheet structure. Between the two helices is the putative antigen binding site. There was no significant difference between the sites of α_3 and α_1. However, the α_1 region is variable in the α-helix and has a stable composition in the β-sheet, suggesting that this may provide a scaffold for the binding of the peptide in which the α_2 region is variable and may interact with the T cell receptor ( TCR) interactions, as well as in the selection of peptides. Class II or HLA-D region proteins are encoded by the DR, DQ and DP sites. It consists of a 33kd A chain and a 29kd B chain