HLADRB

HLADRB refers to a group of genes encoding the beta chain of the HLA-DR class II molecule, part of the human leukocyte antigen system. These genes are located in the major histocompatibility complex on chromosome 6p21.3 and are central to the presentation of extracellular antigens to CD4+ T cells.

The HLADRB family includes HLA-DRB1, as well as HLA-DRB3, DRB4, and DRB5. HLA-DRB1 is the most polymorphic and widely expressed across individuals, while DRB3, DRB4, and DRB5 occur on specific haplotypes and contribute as alternative beta chains in certain antigen-presenting cells. The HLA-DR molecule is a functional heterodimer composed of an invariant alpha chain (DRA) and a variable beta chain (encoded by HLADRB family genes). It presents peptide antigens to CD4+ T cells, with the peptide-binding groove formed by the N-terminal regions of both chains.

Genetic diversity in HLADRB genes is extensive, producing numerous alleles that influence peptide binding and T cell recognition. This polymorphism underpins individual differences in immune responses and susceptibility to autoimmune diseases. Certain HLADRB alleles have been associated with increased risk or protection for conditions such as rheumatoid arthritis, type 1 diabetes, and multiple sclerosis, among others. The HLADRB region is also a key factor in organ and tissue transplantation, where HLA-DR matching reduces the likelihood of graft rejection and influences transplant outcomes.

Expression of HLA-DR molecules is highest on professional antigen-presenting cells (B cells, dendritic cells, macrophages) and can be upregulated by inflammatory signals such as interferon-gamma.