HLA-B — Major Histocompatibility Complex Class I B

Overview

HLA-B (Major Histocompatibility Complex Class I B) is a gene located on chromosome 6p21.3 that encodes the 44 kDa heavy chain of the HLA class I molecule. HLA-B is one of the most polymorphic genes in the human genome, with over 6,000 known alleles^{1The HLA system2000 · N Engl J Med · PMID 10974132Open reference}. It plays a critical role in adaptive immune surveillance by presenting endogenously synthesized peptide antigens to CD8+ cytotoxic T lymphocytes, enabling recognition and elimination of infected or abnormal cells^{2The HLA genomic sequence landscape2009 · Immunogenetics · PMID 19301028Open reference}.

HLA molecules also interact with killer cell immunoglobulin-like receptors (KIRs) on natural killer (NK) cells, regulating NK cell activity through a sophisticated system of activating and inhibitory signals. This HLA-KIR interaction pathway has been implicated in neuroinflammatory processes relevant to Alzheimer’s disease and Parkinson’s disease^{3HLA and Alzheimer's disease risk2021 · Lancet Neurol · PMID 33930305Open reference}.

Molecular Function

Peptide Antigen Presentation

HLA-B folds around an 8-11 amino acid peptide derived from intracellular protein processing. The peptide-binding groove (alpha-1 and alpha-2 domains) contains polymorphic residues that determine which peptides can bind, shaping the repertoire of antigens presented to T-cells^{4Five HLA-B57 allotypes differentially associate with peptide and HIV-1 Gag antigen recognition2012 · Immunol Rev · PMID 23046125Open reference}. Each HLA-B molecule presents approximately 10,000-20,000 different peptide species at the cell surface.

Interaction with CD8+ T-cells

The conserved alpha-3 domain of HLA-B interacts with the CD8 co-receptor on cytotoxic T lymphocytes, providing a co-stimulatory signal that enhances T-cell receptor (TCR) engagement. This HLA-B/CD8 interaction is critical for the activation and clonal expansion of virus-specific and tumor-reactive CD8+ T-cells.

Regulation of NK Cells

HLA-B interacts with KIR receptors on NK cells. Specific HLA-B alleles either activate or inhibit NK cell cytotoxicity through this pathway. In the brain, microglial expression of HLA-B and its interaction with NK cell KIRs may regulate neuroinflammatory responses^{5Loci associated with susceptibility to immune-mediated diseases2009 · Nat Genet · PMID 19380886Open reference}.

Disease Associations

Alzheimer’s Disease

HLA class II genes (including HLA-DRB1) have been associated with AD risk, but HLA-B associations are emerging. Microglial HLA-B expression increases in AD brains, reflecting an active immune response. The HLA-B/KIR interaction pathway may modulate microglial activation states, influencing amyloid clearance efficiency and neuroinflammatory burden^{3HLA and Alzheimer's disease risk2021 · Lancet Neurol · PMID 33930305Open reference}.

Parkinson’s Disease

Specific HLA-B variants modify Parkinson’s disease risk through modulation of the adaptive immune response in the brain. HLA-B alleles may influence autoimmune components of PD pathogenesis, particularly in cases with earlier onset. Microglial HLA-B presentation of neuronal antigens could trigger cytotoxic CD8+ T-cell responses targeting dopaminergic neurons. Several GWAS studies have identified the MHC region on chromosome 6p21 as a PD risk locus.

Multiple Sclerosis

HLA-B27:05 and HLA-B44:02 alleles are associated with MS susceptibility and disease course. HLA-B44:02 may be protective against MS onset, while HLA-B27:05 is linked to atypical MS presentations with prominent spinal cord involvement.

Amyotrophic Lateral Sclerosis (ALS)

HLA associations have been reported in ALS cohorts, suggesting immune-mediated mechanisms may contribute to motor neuron degeneration. The MHC region harboring HLA-B shows pleiotropic effects across neurodegenerative diseases.

Stroke and Cerebrovascular Disease

HLA-B alleles influence susceptibility to ischemic stroke, likely through immune-mediated mechanisms affecting vascular inflammation and atherogenesis^{6HLA-B in stroke and cerebrovascular disease2008 · Cerebrovasc Dis · PMID 18971683Open reference}.

Expression

HLA-B is constitutively expressed at high levels on all nucleated cells:

• Brain — primarily on microglia, low expression on neurons and astrocytes

• Immune cells — macrophages, dendritic cells, B-cells

• Endothelial cells — regulates immune surveillance at the blood-brain barrier

HLA-B expression is upregulated by interferon-gamma (IFN-γ), inflammatory cytokines, and viral infections.

Common Variants

Variant	Association	Effect
HLA-B*07:02	Neutral	Common in European populations
HLA-B*27:05	MS, ankylosing spondylitis	Autoimmune risk
HLA-B*44:02	MS (protective)	Modulates disease risk
HLA-B*57:01	HIV control	Enhanced viral peptide presentation
HLA-B*35:01	Stroke risk	Altered immune response

Therapeutic Implications

• HLA typing is critical for transplantation and predicting graft-versus-host disease

• HLA-B*57:01 testing is required before abacavir prescription to prevent hypersensitivity reactions

• Immunotherapy targets — HLA-B/peptide complexes are being explored as therapeutic targets in autoimmune diseases

• KIR-HLA blockade — therapeutic modulation of the KIR-HLA interaction may offer neuroprotective strategies in neurodegenerative disease

See Also

• Major Histocompatibility Complex — HLA system overview](/entities)

• Microglia in Neuroinflammation — immune cells expressing HLA-B in brain](/cell-types/microglia-neuroinflammation)

• Alzheimer’s Disease — primary disease association

• Parkinson’s Disease — primary disease association](/proteins/parkin)

• Multiple Sclerosis — related autoimmune disorder