HLAB

HLAB, more commonly written HLA-B, is a gene in the human leukocyte antigen (HLA) system that encodes the HLA-B protein, a class I major histocompatibility complex (MHC) molecule. It is expressed on the surface of nearly all nucleated cells and plays a central role in immune surveillance. HLA-B alleles are located on chromosome 6p21 within the MHC region and are among the most polymorphic genes in the human genome, with hundreds of variants.

The HLA-B protein forms a trimer with beta-2 microglobulin and a peptide-binding groove, presenting endogenously derived peptide antigens to CD8+ cytotoxic T cells. The specific peptide repertoire determined by each HLA-B allele influences how the immune system recognizes infected or malignant cells and can affect susceptibility to certain diseases, autoimmunity, and outcomes in transplantation.

Genetic diversity and nomenclature: Alleles are designated HLA-B*XX:YY, reflecting thousands of possible variants. Individuals inherit two HLA-B alleles, one from each parent, resulting in a wide range of possible HLA-B haplotypes. In populations, the distribution of alleles varies by ethnicity and geography, which has implications for disease associations and donor matching.

Clinical significance: Transplantation relies on HLA-B matching between donor and recipient to improve graft survival and reduce graft-versus-host disease. In pharmacogenomics, certain HLA-B alleles are linked to drug hypersensitivity reactions; for example, HLA-B*57:01 is strongly associated with abacavir hypersensitivity and is screened before therapy, while HLA-B*15:02 is associated with carbamazepine-induced Stevens-Johnson syndrome in some populations. HLA-B alleles also show disease associations, such as HLA-B27 with seronegative spondyloarthropathies, though these links are influenced by population background and other genetic factors.