HLAAllele

HLA allele refers to a variant form of a gene within the human leukocyte antigen (HLA) system, a cluster of genes on chromosome 6 that encode cell-surface proteins involved in immune recognition. Each gene has multiple alleles, and HLA alleles are co-dominantly expressed, so an individual presents two different HLA molecule sets (one from each parent) on each cell. HLA molecules bind and present peptide fragments to T lymphocytes, helping distinguish self from non-self and shaping immune responses.

The HLA region includes class I genes (HLA-A, -B, -C) that present peptides to CD8+ T cells, and class II genes (HLA-DR, -DQ, -DP) that present to CD4+ T cells. Allele-specific differences determine which peptides are bound and presented, contributing to immune surveillance and risk profiles for certain diseases. The extensive polymorphism of HLA alleles underpins diverse immune repertoires across individuals and populations.

HLA alleles are among the most polymorphic in the human genome; thousands of variants exist across loci. Polymorphism is maintained by balancing selection and pathogen-driven diversity. Inheritance is codominant, and haplotypes containing particular allele sets influence transplant compatibility and disease associations.

Clinically, HLA typing is used to match donors and recipients for organ and bone marrow transplantation; higher-resolution DNA-based typing reduces graft rejection. HLA alleles are also studied in autoimmune diseases and adverse drug reactions. Examples include HLA-B*57:01 with abacavir hypersensitivity, HLA-B*27:05 with certain spondyloarthropathies, and HLA-DQ2/DQ8 with celiac disease. Nomenclature follows standardized formats (for example, HLA-B*57:01), with databases documenting observed alleles.