Major histocompatibility complex, class II, DQ alpha 1

Function

HLA-DQA1 belongs to the HLA class II alpha chain paralogues. This class II molecule is a heterodimer consisting of an alpha (DQA) and a beta chain (DQB), both anchored in the membrane. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. Class II molecules are expressed in antigen-presenting cells (APC: B lymphocytes, dendritic cells, macrophages).

Gene structure and polymorphisms

The alpha chain contains 5 exons. Exon one encodes the leader peptide, exons 2 and 3 encode the two extracellular protein domains, exon 4 encodes the transmembrane domain and the cytoplasmic tail. Within the DQ molecule both the alpha chain and the beta chain contain the polymorphisms specifying the peptide binding specificities, resulting in up to 4 different molecules. Typing for these polymorphisms is routinely done for bone marrow transplantation.

Alleles

DQ1

There are four commonly encountered DQA1 alleles: DQA1*0101, *0102, 0103, 0104. These alleles are always found in haplotypes with HLA-DQB105 (DQ5) and HLA-DQB106 (DQ6). DQ1 is a serotype, rare among serotypes for human class II antigens, in that the antibodies to DQ1 react to the alpha chain of HLA DQ, these DQA1 allele gene products.

Other

The other DQA1 alleles have no defined serotype. There are 5 groups, DQA102, 03, 04, 05, 06. DQA1 within these groups are either invariant or produce the same α-chain subunit. DQA102 and DQA106 contain only one allele. DQA103 has three alleles which each produce nearly identical α3. For DQA105, the DQA10501 and DQA10505 produce identical α5. Other DQA105 exist that produce variant α5var, but these are rare.

References

References

1. "Entrez Gene: HLA-DQA1 major histocompatibility complex, class II, DQ alpha 1".
2. (1994). "International Cell Exchange, 1994". Clin Transpl.