[Immunopathology of chronic liver diseases]

Chronic inflammatory liver diseases can be induced by virus infections, toxic-metabolic factors and/or autoimmune mechanisms. This overview deals with the immunopathogenesis of chronic hepatitis B and C and autoimmune hepatitis (AIH). 1. Chronic hepatitis B: The immune response to HBV-antigens is responsible both for viral clearance and disease pathogenesis during HBV-infection. The humoral immune response to HBsAg contributes to the clearance of circulating virus particles, the cell mediated immune response to HBsAg, HBcAg and polymerase antigen eliminates infected cells. The class I- and class II restricted T-cell-responses to HBV is strong, polyclonal and multispecific in acute HB with successful clearance of the virus, but weak or incomplete in chronic HB with viral persistence. In addition to ineffective immune response host and viral factors as well as abnormalities in virus-host interactions may be the main reasons for the maintenance of HBV-carrier status. 2. Chronic hepatitis C develop in more than 60% of infected patients. There is increasing evidence that the immune response to HCV-epitopes plays an important role in the course and the pathogenesis of the disease. It has been shown that CD4+ and CD8+ T-cells recognize viral peptides in the presence of class I and II molecules. The fine specificity and functional significance of liver infiltrating and peripheral blood T-cells demonstrate HCV specific immunodominant epitopes targeted by class Ii restricted CD4+ cells in patients with chronic HCV infection. The T-cell response correlates with disease activity. The cytokine release of T-cells resemble a TH1-like profile. Studies of the humoral immune response to HCV show a correlation between IgM-anti-HCV and disease activity. In vitro and in vivo anti-HCV secretion by PBMC is due to persistent antigenic stimulation of B-cells by ongoing production of viral antigens and reflects HCV replication in PBMC. Of special interest are several immune mediated disease and immune abnormalities in chronic hepatitis C. 3. Autoimmune hepatitis (AIH) is a distinct group of acute and chronic necro-inflammatory disorders of unknown etiology characterized by immunological and autoimmunological features including the presence of autoantibodies but without an antecedent of viral infections. Marker autoantibodies define 3 subtypes: Type I (ANA/SMA), Type II (LKM1-AB), Type II (SLA-AB). AIH is associated with a distinct genetic background (HLA A1, B8, DR3 or DR4). Several studies clearly demonstrate that liver cell damage in AIH is mediated by autoimmune reactions against normal constituents of hepatocytes. Although the precise mechanisms are not yet fully understood, there is now considerable evidence that autoantigens of the hepatocellular membrane in particular the ASGPR are important targets of liver damaging autoreactions in AIH. Cellular and humoral immune reactions against the human ASGPR correlate with disease activity and usually disappear under immunosuppressive therapy.