HLA-A3

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 Western Eurasia, it is part of the longest known multigene haplotype, A3-B7-DR15-DQ6.

Serotype
A3 is primarily composed of A*0301 and *0302 which serotype well with anti-A3 antibodies. There are 26 non-synonymous variants of A*03, 4 nulls, and 22 protein variants.

Associated diseases
A3 serotype is a secondary risk factor for myasthenia gravis, lower CD8+ levels in hemochromatosis patients The HFE (Hemochromatosis) locus lies between A3 and B7 within the A3::DQ6 superhaplotype.

In HIV
HLA-A3 selects HIV evolution for a mutation Gag KK9 epitope and results in a rapid decline in the CD8 T-cell response. CD8 T-cells are responsible for quickly killing HIV infected CD4+ cells. This type of evolved response may not be specific for HLA-A3 and since HIV is capable of adapting quickly in situ to selective factors.

Associated diseases
A*0301 modulates increased risk for Multiple Sclerosis

A3-B haplotypes
A3-B7 is part of the A3::DQ2 superhaplotype A3-B8 (Romania, svanS) A3-B35 (Bulgaria, Croatia, E. Black Sea) A3-B55 (E. Black Sea)

A3-Cw7-B7
A3-B7 is bimodal in frequency in Europe with one node in Ireland and the other in Switzerland, relatively speaking Switzerland appears to be higher. A3-Cw7-B7 is one of the most common multigene haplotypes in the western world, particularly in Central and Eastern Europe.

A*0301 : C*0702 : B*0702 : DRB1*1501 : DQA1*0102 : DQB1*0602