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| HLA-B | |
|---|---|
| Name | HLA class I histocompatibility antigen, B-XX alpha chain |
| Uniprot | P01889 |
| Organism | Homo sapiens |
| Gene location | Chromosome 6p21.3 |
HLA-B is a human leukocyte antigen class I molecule encoded within the major histocompatibility complex on chromosome 6. It presents peptide fragments to cytotoxic lymphocytes and interacts with natural killer cell receptors, influencing immune responses to pathogens, neoplasms, and alloantigens. Variation at the locus contributes to differential susceptibility to infectious diseases, autoimmune disorders, adverse drug reactions, and outcomes in transplantation and population genetics.
The locus resides in the MHC (human) region on chromosome 6 (human), adjacent to HLA-A and HLA-C in the major histocompatibility complex. The HLA-B protein is a 44–45 kDa transmembrane glycoprotein composed of a heavy alpha chain encoded by the gene and a noncovalently associated beta-2 microglobulin encoded by B2M (gene). The extracellular region contains alpha1, alpha2, and alpha3 domains; the peptide-binding groove formed by alpha1 and alpha2 accommodates peptides of 8–11 residues. Classical class I motifs, including the peptide anchor pockets, are encoded by exons 2 and 3, which show extreme allelic polymorphism. Gene expression is regulated by promoter elements responsive to interferon-gamma and other cytokines, and HLA-B alleles demonstrate differential transcriptional control across cell types such as hepatocyte, dendritic cell, and epithelial cell lineages.
As an antigen-presenting molecule, HLA-B presents endogenous peptides derived from proteasomal degradation and the transporter associated with antigen processing pathway to CD8+ cytotoxic T lymphocytes, including clones expanded in responses against pathogens like HIV-1, influenza A virus, and Epstein–Barr virus. Interaction of HLA-B:peptide complexes with T cell receptors contributes to immune surveillance and tolerance, while engagement with inhibitory and activating receptors of natural killer cells—such as members of the KIR family expressed by natural killer cell subsets—modulates NK cell cytotoxicity. HLA-B alleles also influence peptide repertoire shaping, cross-presentation, and immunodominance hierarchies observed in responses to vaccines developed by organizations like Pfizer and Moderna in pandemic settings. Differential presentation of tumor neoantigens affects recognition by tumor-infiltrating lymphocytes in cancers treated at centers such as Memorial Sloan Kettering Cancer Center and MD Anderson Cancer Center.
HLA-B is one of the most polymorphic human loci with thousands of alleles catalogued by the IPD-IMGT/HLA Database and curated in registries associated with organizations like the National Marrow Donor Program. Common serotypes—historically defined by serology—include B7, B27, B35, B40, and B51, while molecular typing resolves alleles such as B*27:05, B*57:01, and B*58:01. Allelic variation concentrates in peptide-binding pockets, producing differences in anchor residue preferences and peptide repertoires that underlie functional and clinical heterogeneity. High-resolution typing is performed using methods developed by groups including Illumina and Oxford Nanopore Technologies for applications in histocompatibility laboratories at institutions like Stanford University and the Johns Hopkins Hospital.
Specific HLA-B alleles associate strongly with autoimmune and inflammatory disorders: B*27 subtypes with ankylosing spondylitis and related spondyloarthropathies commonly managed in clinics like Hospital for Special Surgery; B*51 with Behçet's disease referenced in cohorts from Turkey and Japan; B*57:01 with slower progression of HIV/AIDS described in cohort studies at University of California, San Francisco. HLA-B alleles also predict severe adverse drug reactions: B*57:01 is linked to abacavir hypersensitivity identified in pharmacogenetic research at The Scripps Research Institute, and B*58:01 predicts allopurinol-induced severe cutaneous adverse reactions reported in multinational pharmacovigilance data coordinated by agencies including the FDA and EMA. Allelic associations influence outcomes in infectious diseases tracked by organizations such as the WHO and CDC, and contribute to differential vaccine efficacy and correlates of protection studied at institutes like the NIH.
HLA-B mismatches between donors and recipients strongly affect graft survival and graft-versus-host disease risk in hematopoietic stem cell transplantation coordinated by registries like the Be The Match program. Solid organ allocation policies at agencies including UNOS incorporate HLA-B matching among other loci to optimize outcomes for kidneys, hearts, and livers transplanted at centers such as Cleveland Clinic and Mayo Clinic. Donor selection algorithms weigh HLA-B allele-level matching, donor-specific antibodies detected by histocompatibility laboratories, and crossmatch results performed in transplant immunology units affiliated with institutions like Fred Hutchinson Cancer Research Center.
HLA-B allele frequencies vary markedly across global populations documented by consortia including the 1000 Genomes Project and the Human Genome Diversity Project. Certain alleles display geographic and ethnic enrichment—B*27 prevalence in northern European cohorts studied in Sweden and Finland, B*51 among populations in Turkey and Japan, and B*15 and B*40 lineages across diverse East Asian and Southeast Asian groups. Balancing selection, pathogen-driven selection exemplified by historic epidemics such as the Black Death, and reproductive fitness effects have been invoked to explain HLA-B diversity, with population genetics analyses employing data from HapMap and paleogenomic findings from archaeological sites and museum collections. Molecular phylogenies and linkage disequilibrium patterns reflect recombination and gene conversion events shaping the locus over human evolutionary history.
Category:Human proteins