HLA-DR, like other MHC class II molecules, is a transmembrane glycoprotein composed of a 36 kDa alpha chain (DRA) and 27 kDa beta chain (DRB). The alpha chain 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 polymorphisms in the peptide binding part and acts as the sole alpha chain for DRB1, DRB3, DRB4 and DRB5. Within the DR molecule the beta chain contains all the polymorphisms specifying the peptide binding specificities. Hundreds of DRB1 alleles have been described and typing for these polymorphisms is routinely done for bone marrow and kidney transplantation. HLA-DR is expressed primarily on antigen presenting cells such as B lymphocytes, monocytes, macrophages, thymic epithelial cells and activated T lymphocytes. Three loci, DR, DQ and DP, encode the major expressed products of the human class II region. The human MHC class II molecules bind intracellularly processed peptides, present them to T-helper cells, and have a critical role in the initiation of the immune response.
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Protein Aliases: CD74; CD74 antigen; CD74 antigen (invariant polypeptide of major histocompatibility complex, class II antigen-associated); CD74 molecule, major histocompatibility complex, class II invariant chain; Class-II-associated invariant chain peptide; CLIP; gamma chain of class II antigens; HLA class II histocompatibility antigen gamma chain; HLA-DR antigens-associated invariant chain; HLA-DR-gamma; Ia antigen-associated invariant chain; Ia-associated invariant chain; Ii; MHC HLA-DR gamma chain; p33
Gene Aliases: CD74; DHLAG; HLADG; Ia-GAMMA; II
UniProt ID: (Human) P04233
Entrez Gene ID: (Human) 972
Molecular Function: scaffold/adaptor protein