HLA-A3 is a human leukocyte antigen

Human leukocyte antigen

The human leukocyte antigen system is the name of the major histocompatibility complex in humans. The super locus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encodes cell-surface antigen-presenting proteins and...

 serotype

Serotype

Serotype or serovar refers to distinct variations within a subspecies of bacteria or viruses. These microorganisms, viruses, or cells are classified together based on their cell surface antigens...

within HLA-A

HLA-A

HLA-A are a group of human leukocyte antigens that are encoded by the HLA-A locus on human chromosome 6p. The HLA genes constitute a large subset of the Major histocompatibility complex of humans. HLA-A is a component of certain MHC class I cell surface receptor isoforms that resides on the...

 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

B2M

B2M may refer to:*Boyz II Men, a singing group*Mitsubishi B2M, an aircraft*Back to Mine, a series of albums*Beta-2 microglobulin, a gene or protein*Business to machine, the practice of E-commerce where companies link directly to machines...

 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

Eurasia

Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

, it is part of the longest known multigene haplotype

Haplotype

A haplotype in genetics is a combination of alleles at adjacent locations on the chromosome that are transmitted together...

, 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

Myasthenia gravis

Myasthenia gravis is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatiguability...

, 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.

Alleles

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