[Immunology of liver diseases]

Acute hepatitis A is diagnosed by IgM-anti-HAV antibodies. Cytotoxic immune reactions seem to play a key role in the pathogenesis of hepatitis A, which is an acute self-limited disease. - Acute hepatitis B is diagnosed by IgM-anti-HBc antibodies and can thus be differentiated from other HBV-associated liver diseases. The detection of HBV-DNA in serum serves to differentiate between HBsAg/anti-HBe positive patients, with active viral replication and progressive chronic liver disease, and HBV-DNA negative asymptomatic HBsAg-carriers usually with normal liver histology. In the pathogenesis of HBV-associated liver diseases cytotoxic immune reactions against virus-infected hepatocytes are thought to mediate liver cell destruction. Membrane expressed virus as well as host antigens are candidate target antigens for these immune reactions. Hepatitis delta is always associated with acute and chronic HBV infection. Acute hepatitis delta is diagnosed by delta-RNA in serum and later by antibodies against the delta virus. Little is known about the pathogenesis of delta virus infection. Autoimmune type chronic active hepatitis (CAH) is classified into classical autoimmune type "lupoid CAH" with antinuclear antibodies and liver membrane antibodies as markers, liver-kidney-microsomal (LKM) antibody positive CAH, CAH associated with autoantibodies against a soluble liver antigen (SLA), and CAH associated with high titers of anti-smooth muscle antibodies (SMA). In the pathogenesis of autoimmune type CAH an antibody-mediated cellular cytotoxicity (ADCC) may play a significant role. Primary biliary cirrhosis is to be differentiated as a clinical syndrome associated with cholestasis and anti-mitochondrial antibodies (AMA). By immunoblotting and radioimmunoassay at least two PBC-specific subtypes of AMA can be defined. Immune reactions against self-antigens are thought to be involved in the pathogenesis of PBC, although the precise reactions are unknown.