Immunology of chronic hepatitis.

Of the two major types of chronic active hepatitis, that associated with autoimmunity, CAH-Type A, has been the more extensively studied and is better recognised. On the other hand, the type associated with the HBV carrier state, CAH-Type B, is the more prevalent, particularly so in South East Asia, and the time is ripe for the immunology of this type to be clarified. Whilst most encounters between host and HBV will result in an acute hepatitis with lasting immunity, a non-sterilizing outcome with a persisting carrier state may ensue. The reasons for persistent infection with HBV are still not elucidated, but may include: (i) incorporation of viral DNA into the host genome, (ii) a carrier state in which there is full T cell tolerance to the virus and its surface antigen, or (iii) an unstable tolerance marked by a persisting damaging immune response to viral antigens expressed on the liver cell membrane, with associated CAH. Whether an autoimmune-type CAH can be included as one possible outcome of HBV infection is uncertain; whilst the association of an HB viral antigen with a liver cell membrane component is one theoretical way by which an autoimmune response could be generated, most cases of autoimmune hepatitis, at least in Caucasian areas, show no evidence of current or past infection with HBV or indeed with any other virus. Thus, pending further knowledge, CAH-Type A must be regarded as a primary autoimmune disease of the liver, and CAH-type B as resulting from an ineffective host response to a chronic virus infection of the liver.