Genetic Susceptibility: HLA-DR3 and HLA-DR4 Associations in Autoimmune Hepatitis

Background: Autoimmune hepatitis (AIH) is a chronic, progressive inflammatory liver disease characterised by immune-mediated hepatocellular destruction. Genetic susceptibility to AIH is strongly influenced by the human leukocyte antigen (HLA) system, particularly alleles encoding HLA-DR3 (DRB1*03:01) and HLA-DR4 (DRB1*04:01). These alleles modulate antigen presentation via MHC class II molecules, thereby shaping autoreactive T-cell responses directed against hepatic antigens. Objective: This review comprehensively examines the molecular basis of HLA-DR3 and HLA-DR4 associations in AIH, with particular emphasis on structural features of the peptide-binding groove, differential clinical phenotypes, population-specific genetic epidemiology, and emerging therapeutic targets derived from immunogenetic insights. Methods: A systematic review of literature published between 1980 and 2024 was conducted using PubMed, MEDLINE, EMBASE, and Cochrane databases. Search terms included 'HLA-DR3', 'HLA-DR4', 'DRB1*03:01', 'DRB1*04:01', 'autoimmune hepatitis', 'immunogenetics', 'MHC class II', and related combinations. Studies reporting genetic associations, clinical outcomes, mechanistic data, and population genetics were included. Key Findings: HLA-DR3 (DRB1*03:01) is the predominant susceptibility allele in Northern European and North American populations (OR: 3.0–9.0), associated with earlier disease onset, higher biochemical activity, and increased relapse rates post-treatment withdrawal. HLA-DR4 (DRB1*04:01) confers susceptibility primarily in Japanese, Latin American, and elderly Caucasian populations, associated with a milder but relapsing course responsive to corticosteroids. The shared epitope hypothesis, structural analysis of the DRβ1 chain, and molecular mimicry mechanisms collectively explain the pathogenic basis of these associations. Dual heterozygosity (DR3/DR4) further amplifies disease risk and severity. Conclusion: HLA-DR3 and HLA-DR4 are pivotal determinants of AIH susceptibility, clinical phenotype, and prognosis. Integration of HLA genotyping into clinical practice holds promise for risk stratification, personalised treatment algorithms, and identification of novel immunotherapeutic targets.