HLADR4

HLA-DR4, commonly written as HLA-DR4, is a serological specificity within the human leukocyte antigen (HLA) system, part of the MHC class II region. It represents a group of DRB1 gene products whose surface proteins are involved in presenting peptide antigens to CD4+ T cells. The DR4 serotype encompasses several DRB1 alleles, including DRB1*0401, DRB1*0404, DRB1*0405, and DRB1*0408, among others. These DRβ1 proteins share epitopes that define the DR4 serotype and influence peptide binding and immune responses.

Genetically, HLA-DR4 is located on chromosome 6p21 within the MHC. The DR4 serotype is defined by specific peptide-binding motifs and is often studied in the context of haplotypes, such as DR4-DQ8, which can modulate disease risk. The distribution of DR4 alleles varies by ethnicity and population.

Clinically, HLA-DR4 is best known for associations with autoimmune diseases, most notably rheumatoid arthritis (RA). Certain DR4-associated alleles carry the shared epitope motif in the DRβ1 chain, with sequences such as QKRAA, QRRAA, or RRRAA near positions 70–74, and these motifs have been linked to increased susceptibility to RA and, in some cases, more severe disease. DR4 also features in research on other autoimmune conditions and in studies of transplant compatibility, where HLA typing informs donor–recipient matching.

In summary, HLA-DR4 refers to a DRB1-based serotype within the HLA class II system, characterized by specific alleles and epitopes that influence antigen presentation and are associated with certain autoimmune disease risks, particularly rheumatoid arthritis, in a haplotype-dependent manner.