HLA-A3 (A3) is a human leukocyte antigen serotype within HLA-A serotype group. The serotype is determined by the antibody recognition of α3 subset of HLA-A α-chains. For A3, the alpha, "A", chain are encoded by the HLA-A*03 allele group and the β-chain are encoded by B2M locus. This group currently is dominated by A*0301. A3 and A*03 are almost synonymous in meaning.A3 is more common in Europe, it is part of the longest known multigene haplotype, A3-B7-DR15-DQ6.