HLA-A1

HLA-A1
(MHC Class I, A cell surface antigen)
Rendering of 1W72​: α (A*0101 gene product), β2-microglobulin, and MAGE-1 peptide.
About
Protein	transmembrane receptor/ligand
Structure	αβ heterodimer
Subunits	HLA-A*01--, β2-microglobulin
Older names	HL-A1
Subtypes
Subtype allele Available structures A1 *0101 1W72​
Rare alleles
Subtype allele Available structures A1.2 *0102 A1.3 *0103
Alleles link-out to IMGT/HLA database at EBI

HLA-A1 (A1) is a human leukocyte antigen serotype within HLA-A "A" serotype group. The serotype is determined by the antibody recognition of α¹ subset of HLA-A α-chains. For A1, the alpha "A" chain are encoded by the HLA-A*01 allele group and the β-chain are encoded by B2M . This group currently is dominated by A*0101. A1 and A*01 are almost synonymous in meaning. A1 is more common in Europe than elsewhere, it is part of a long haplotype that appears to have been frequent in the ancient peoples of Northwestern Europe. A1 is a frequent component of the AH8.1 haplotype. A1 serotype positivity is roughly linked to a large number of inflammatory diseases and conditions believed to have immune system involvement. Because of its linkage within the AH8.1 haplotype many studies showed association with A1 or A1,B8 only later to show the association drift toward the class II region gene alleles, DR3 and DQ2.5. While it is not clear what role A1 has in infectious disease, some linkage with infection rates in HIV remain associated within the A1 region of the haplotype.

In all instances so far, HLA-A1 has been found to be linked to disease by association, but there are few that define HLA-A1 has a predominant genetic risk relative to other gene-alleles in the vicinity of the A1 gene on the larger haplotype.

A1 serotype was associated with a number of diseases as "HL-A"' antigens were first being described. The associations rapidly expanded to include 'HL-A8' HLA-B8, as the HLA A1 and B8 were found to be commonly linked. As DRw3 was characterized, autoimmune risk drifted toward the class II region.

A1-B58 haplotype (A1-B17 where B58 is dominant) may remain associated with anti-neutrophil cytoplasmic antibody (ANCA)

With the exception of type 1 diabetes, most of the evidence for direct association of A1 with autoimmune diseases evaporated as DR3 and DQ2 genes were characterized. While type 1 diabetes shows an extended association on the HLA A1-B8-DR3-DQ2 haplotype, the association appears not to extend beyond the HLA-B locus. A recent study of DR3-DQ2/DR4-DQ8 phenotype found that A1-cw7-B8 was actually lower than expected relative to other A-B types, indicating that risk associated genes are located between B8 and DR3. However a study elsewhere showed that A*0101 appears to alter risk for type 1 diabetes but not Cw7-B8. The type 1 diabetes example shows the inherent difficulty in the use of linkage analysis alone to cipher risk.