Relationship of hepatitis A antigen to viral hepatitis

Progress in research on hepatitis type A has begun to accelerate because of the recent discovery of an antigen associated specifically with hepatitis type A infection and the development of tests for antibody to the antigen. Hepatitis A antigen is associated with 27 nm virus-like particles found in the liver and stool of animals experimentally infected with hepatitis type A and in the stool of humans experimentally or naturally infected with the virus. The density of the particulate antigen when isolated from the liver is 1.34, but antigen particles with densities ranging from 1.32 to 1.40 have been detected in stool. However, antigens from the liver and from the stool appear to be antigenically related. Using immune electron microscopy as a serologic tool for detecting antibody to hepatitis A antigen, we detected antibody in convalescent sera from 100 per cent of patients experimentally or naturally infected with hepatitis type A. In contrast, patients with hepatitis type B or non-B hepatitis not epidemiologically compatible with a diagnosis of hepatitis type A did not have a serologic response to hepatitis A antigen. Antibody was found in approximately 50 per cent of normal individuals tested; the frequency was directly related to age. By the use of immune electron microscopy for the detection of hepatitis A antigen and antibody, the temporal relationship of antigen, antibody and liver damage was determined in experimentally infected humans and chimpanzees. On the basis of serologic comparisons, hepatitis type A does not appear to be related to experimental hepatitis caused by the GB agent of Deinhardt, nor is the hepatitis A antigen serologically related to the fecal antigen of Cross.