HLA-DRA（major histocompatibility complex， class II， DR alpha），癌症关联基因，基因ID：3122，HLA-DRA是HLAⅡ类α链的一种。这种II类分子是一种由α链和β链组成的异二聚体，它们都锚定在膜中。通过呈现细胞外蛋白衍生的肽，在免疫系统中起到中心作用。Ⅱ类分子在抗原呈递细胞（APC:B淋巴细胞、树突状细胞、巨噬细胞）中表达。α链约为33-35kDa，其基因包含5个外显子。外显子1编码先导肽，外显子2和3编码两个胞外结构域，外显子4编码跨膜结构域和胞质尾。DRA在肽结合部分没有多态性，是DRB1、DRB3、DRB4和DRB5的唯一α链。HLA-DRA is one of the HLA class II alpha chain paralogues. This class II molecule is a heterodimer consisting of an alpha and a beta chain， both anchored in the membrane. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. Class II molecules are expressed in antigen presenting cells (APC: B lymphocytes， dendritic cells， macrophages). The alpha chain is approximately 33-35 kDa and its gene contains 5 exons. Exon 1 encodes the leader peptide， exons 2 and 3 encode the two extracellular domains， and exon 4 encodes the transmembrane domain and the cytoplasmic tail. DRA does not have polymorph。