HLA-A2

# Overview
HLA-A2 (A2) is an HLA-A serotype. The serotype identifies the more common HLA-A*0201, *0202, *0203, *0206, and *0207 gene products. A*02 is globally common, but A*0201 is at high frequencies in Northern Asia and North America. A2 is the most diverse serotye, showing diversity in Eastern Africa and Southwest Asia. While the frequency of A*0201 in Northern Asia is high, its diversity is limited to A*0201 the less common asian variants A*0203, A*0206.

# Serotype
The serotyping for the most abundant A*02 alleles is good. For A*0203, A*0206, A*0207 serotyping is borderline useful. There is a separate serotyping for A203 and A210. There are over 125 alleles identified (mostly by sequence homology) as being A2, of those 8 are nulls, and a large majority have unknown serotypes.

# Disease Associations

### By serotype
A2 Associated with spontaneous abortion in A2+/A phenotypic children

### By haplotype
A*02:Cw*16 is associated with increased higher viral load in HIV

# A2-B Haplotypes
A2-B7  (Node in Netherlands)
A2-B5
- A2-B51
- A2-B52
A2-B8
A2-B13
A2-B14
- A2-B64
- A2-B65
A2-B15
- A2-B62
- A2-B63
- A2-B70,71,75,76
- A2-B46 (Node in Southern China, may be most abundant haplotype)
A2-B16
- A2-B44
- A2-B45
A2-B18
A2-B27
A2-B35
A2-B37  
A2-B39 (Node in North American Amerinds)
A2-B40
- A2-B60
- A2-B61

## A2-Cw5-B44
A2-Cw5-B44 is the multi-serotype designation for the haplotype HLA-A*0201:C*0501:B*4402, the class I portion, of an ancetral haplotype (A2-B44-DR4-DQ8). The full haplotype is (for relative distances see Human leukocyte antigens:
A*0201 : C*0501 : B*4402 : DRB1*0401 : DQA1*0301 : DQB1*0302
Another haplotype that is more common in Central Europe is the (A2-B44-DR7-DQ2)
A*0201 : C*0501 : B*4402 : DRB1*0701 : DQA1*0201 : DQB1*0202
Over northwestern Europe A2-B44 shows a single common ancestor which contributed
the Cw5 allele to the haplotype. The haplotype appears to have been introduced early in european prehistoric period, frequencies of the haplotype generally correlate with A1-Cw7-B8 and A2-B7. The haplotype is considerably more equilibrated relative to A1-B8 and a possible reason is gene flow from iberia or the east with related haplotypes after initial migrations.

## A2-Cw11(1)-B46
This haplotype is rather unique in several regards, first and most importantly the B46 serotype is not from Africa, this distinquishes it from every other known B serotype. It is the result of a recombination event between B62(B*1501) and an HLA-C allele within Asia. This event happened recently as there is only one major allele and minor alleles are at trace frequencies. There has been some recombination between this haplotype, A24 and A11 bearing alleles, probably in a local (or tribal population). B46 is found whereever asian wet-rice farming peoples have traveled and is found at low frequencies in non-farming indigeonous groups. The one exception is the Ninhvet of Siberia and the Eastern Tlinglet of Alaska. This B46 contribution appears to have been recent. Because of the numbers of people represented by the sample groups, and its relative high frequency in those group A2-B46 is one of the most frequent, if not the most frequent A-B haplotype in the world, even though it is absent from the indigeonous populations of most peoples in the world.
The most common haplotype, and probably the ancestral haplotype given its distribution from the Ninhivet to Indonesia is:
A*0207 : C*0102 : B*4601 : DRB1*0901 : DQA1*0302 : DQB1*0303
A different haplotype that is more common in Korea and Japan is
A*0207 : C*0102 : B*4601 : DRB1*0803 : DQA1*0103 : DQB1*0601
B46, or a closely linked allele may have been under positive selection in rice farmers of asia.