HLA-A

HLA-A is a group of human leukocyte antigens (HLA) that are coded for by the HLA-A locus, which is located at human chromosome 6p21.3. HLA is simply the major histocompatibility complex (MHC) specific to humans. HLA-A is one of three major types of human MHC class I cell surface receptors. The others are HLA-B and HLA-C. The receptor is a heterodimer, and is composed of a heavy α chain and smaller β chain. The α chain is encoded by a variant HLA-A gene, and the β chain (β₂-microglobulin) is an invariant β₂ microglobulin molecule. The β₂ microglobulin protein is coded for by a separate region of the human genome.

MHC Class I molecules such as HLA-A are part of a process that presents short polypeptides to the immune system. These polypeptides are typically 7-11 amino acids in length and originate from proteins being expressed by the cell. There are two classes of polypeptide that can be presented by an HLA protein: those that are supposed to be expressed by the cell (self) and those of foreign derivation (non-self). Under normal conditions cytotoxic T cells, which normally patrol the body in the blood, "read" the peptide presented by the complex. T cells, if functioning properly, only bind to non-self peptides. If binding occurs, a series of events is initiated culminating in cell death via apoptosis. In this manner, the human body eliminates any cells infected by a virus or expressing proteins they shouldn't be (e.g. cancerous cells).

HLA-A36

HLA-A36 (A36) is a human leukocyte antigen serotype within HLA-A serotype group. The serotype is determined by the antibody recognition of α³⁶ subset of HLA-A α-chains. For A36, the alpha "A" chain are encoded by the HLA-A*36 allele group and the β-chain are encoded by B2M locus. This group currently is dominated by A*3601. A36 and A*36 are almost synonymous in meaning.

A36 is more common in Africa (North and East) and Central Asia. A36 is rare HLA-A allele group.

Serotype

A36 has a high false serotyping rate to A1.

Distribution

A36 is largely limited to Africa. Outside Africa more than half of the populations have no A36 and the majority that do, have only trace levels. The exception is in Central/East Central Asia. This appears not to be coincidental. HLA DR3-DQ2 linkage and frequency indicates a strong possibility of a recent migration from either North or West Africa in which the DR3-DQ2 (notably DRB1*0302) and A*33-B*58 haplotypes were carried into and redistributed from Central Asia into the surrounding populations.

HLA-A33

HLA-A33 (A33) is a human leukocyte antigen serotype within HLA-A serotype group. The serotype is determined by the antibody recognition of α³³ subset of HLA-A α-chains. For A33, the alpha "A" chain are encoded by the HLA-A*33 allele group and the β-chain are encoded by B2M locus. A33 and A*33 are almost synonymous in meaning. A33 is a split antigen of the broad antigen serotype A19. A33 is a sister serotype of A29, A30, A31, A32, and A74.

A33 is more common in Subsaharan Africa.

Serotype

A33 has a poor serotyping rate.

A33 frequencies

A33 shows two different distributions that can be discriminated by subtyping capability of SSP-PCR.

A*3301 distribution

The first distribution appears to have a Western distribution that introgresses into Europe as a result of the Post-neolithic periods. It is commonly found in linkage disequilibration within the A*3301-Cw*0802-B*1402 haplotype which can be extended to DRB1 and DQB1 in certain instances(See Below). The source of its general expansion appears to be the middle east or the levant, as it is found in the Palestinian population. B14 splits into B64 (B*1401) and B65 (B*1402) but the only Arabian people which show both antigens are the United Arab Emirates.