The immunopathology of hepatitis B and delta virus infections of the liver are reviewed. It is clear there are several antigen/antibody systems of importance in acute and chronic HBV infection. Antibodies to HBs, HB core/HBe and antibodies to Dane specific determinants are involved in virus neutralisation. Elimination of virus infected hepatocytes is dependent on recognition of viral determinants in association with HLA proteins on the infected hepatocytes by cytotoxic T cells. The HLA protein display is modulated by exposure to interferon and may regulate the cytotoxic T cell and NK lytic processes. During chronic HBV infection there is evidence of failure of interferon activation of the infected liver cells so that viral protein synthesis is not decreased and there is no enhancement of HLA protein display. These complex interactions between the virus and the immune system determine the heterogeneity of the clinical syndromes seen in patients infected with this agent. The delta virus replicates only in patients with co-existent HBV infection. The agent is cytopathic and therefore always produces liver disease. When there is delta virus superinfection in a carrier of chronic HBV, there is an acceleration of the rate of progression of the liver disease. The presence of delta infection results in IgM and IgG anti-delta responses.
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