Clinical meaning
Autoimmune hepatitis (AIH) is a chronic, progressive inflammatory liver disease characterized by immune-mediated destruction of hepatocytes, leading to interface hepatitis, fibrosis, and ultimately cirrhosis if untreated. AIH affects approximately 10 to 17 per 100,000 persons, with a strong female predominance (3.6:1 female to male ratio) and a bimodal age distribution peaking in adolescence/young adulthood and again between ages 40 to 60.
The pathogenesis of AIH involves a breakdown of self-tolerance to hepatocyte autoantigens, resulting in T-cell-mediated liver injury. The process begins when hepatocyte surface antigens are presented to CD4+ T-helper cells by antigen-presenting cells (APCs) in the context of major histocompatibility complex (MHC) class II molecules. Certain HLA haplotypes, particularly HLA-DR3 (DRB1*0301) and HLA-DR4 (DRB1*0401), confer genetic susceptibility by presenting hepatocyte autoantigens more effectively. The activated CD4+ T-helper cells secrete proinflammatory cytokines (interferon-gamma, interleukin-2, TNF-alpha) that recruit and activate CD8+ cytotoxic T lymphocytes, natural killer (NK) cells, and macrophages. These effector cells directly attack hepatocytes through perforin-granzyme-mediated cytotoxicity, Fas/FasL-mediated apoptosis, and antibody-dependent cellular cytotoxicity (ADCC).
AIH is classified into two types based on the pattern of circulating autoantibodies. Type 1 AIH (most common, accounting for 80% of cases) is characterized by antinuclear antibodies (ANA) and/or anti-smooth muscle antibodies (ASMA). The target antigen for ASMA is F-actin, a component of the hepatocyte cytoskeleton. Type 1 affects all ages, has a more gradual onset, and is more commonly associated with other autoimmune diseases (thyroiditis, ulcerative colitis, rheumatoid arthritis, Sjogren syndrome). Type 2 AIH (less common, primarily affects children and young adults) is characterized by anti-liver kidney microsomal type 1 antibodies (anti-LKM1) targeting cytochrome P450 2D6 (CYP2D6) and/or anti-liver cytosol type 1 (anti-LC1) antibodies. Type 2 has a more aggressive clinical course with more frequent acute presentations and higher rates of progression to cirrhosis.