HLA-DOB encodes the beta chain of the HLA-DO heterodimer, a non-classical MHC class II molecule that serves as a critical regulator of antigen presentation. The protein functions as a modulator of HLA-DM-mediated peptide loading on MHC class II molecules in B-cells, specifically controlling peptide exchange activity 1. HLA-DOB displays remarkably limited genetic polymorphism, with only one amino acid substitution identified across allelic variants, suggesting strong selective pressure to maintain its specialized function as a co-chaperone interacting with HLA-DM 2. Recent comprehensive sequencing studies have revealed greater diversity than previously recognized, with 47 distinct novel sequences identified, though one dominant protein variant (HLA-DOB*01:01) occurs in >77% of populations 3. The gene has demonstrated clinical relevance in multiple contexts: it serves as a hub gene and potential biomarker in rheumatoid arthritis 45, shows enrichment of the HLA-DOB*01:01 allele in neuroblastoma patients with opsoclonus myoclonus ataxia syndrome 6, and appears as a key immune gene in sepsis 7. The protein's role in regulating antigen presentation makes it significant for immune surveillance and autoimmune disease susceptibility.