HLA-DRB1 encodes a major histocompatibility complex class II molecule that functions as a cell-surface receptor for antigen presentation and immune recognition. The protein consists of alpha and beta chains that assemble in the endoplasmic reticulum and are transported to the cell surface, where they present exogenous peptide antigens to CD4+ T cells. HLA-DRB1 also acts as a receptor for Epstein-Barr virus on lymphocytes. The beta chain contains two extracellular domains with highly polymorphic regions, particularly in the first domain, which determine serological specificity and peptide-binding properties. Specific HLA-DRB1 alleles associate with multiple autoimmune and infectious diseases. In occult hepatitis B infection carriers in the Shaanxi Han population, DRB1*07:01 shows strong susceptibility association, with particular amino acid variants at positions 4β, 57β, 60β, and 78β influencing risk 1. HLA-DRB1*0102 and *0306 alleles show increased frequency in psoriatic patients 2, and DRB1*11 associates with lichen planopilaris 3. Pharmacogenetically, the DRB1*07:01 allele associates with ximelagatran-induced hepatotoxicity, where the drug directly competes with peptide ligands for the HLA-DRB1 binding groove 4. These allele-specific associations underscore HLA-DRB1's role in determining immune response outcomes across infection, autoimmunity, and drug toxicity.