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. A person often produces two α-chain and two β-chain and thus 4 of DQ. The DQ loci are in close genetic linkage to HLA-DR, and less closely linked to HLA-DP, HLA-A, HLA-B and HLA-C.