Detection of hepatitis A antigen by immunofluorescence.

Hepatitis A antigen (HA Ag) was demonstrated by immunofluorescence (IF) in liver biopsies from chimpanzees with experimental hepatitis A virus infection. Blocking experiments with paired sera from patients with hepatitis types A, B, or non-A, non-B, as well as with purified HA Ag, showed that the fluorescence was specific for HA Ag. HA Ag could be demonstrated only in biopsies from chimpanzees inoculated with hepatitis A virus. In two of four chimpanzees biopsied weekly, HA Ag could be detected by IF before stool shedding of HA Ag, elevation in serum alanine aminotransferase (SGPT), or histopathological evidence of liver disease was seen. The HA Ag was detected for 4 to 5 weeks; the last IF-positive biopsy was obtained after SGPT activity had returned to normal. In the two other chimpanzees, HA Ag could be detected only in the biopsy taken at the time of SGPT elevation. In the early IF-positive biopsies, HA Ag was diffusely distributed in the cytoplasm of many cells, but it later accumulated in a focal distribution in the cytoplasm of a few of the hepatocytes and Kupffer cells. This cytoplasmic distribution agrees with previous electron microscopic data.