Detection by immunofluorescence of a new "core-like" Ag/Ab system in liver and serum of patients with NANB hepatitis.

Using direct immunofluorescence, a nuclear antigen was found in liver of chronic hepatitis patients with circulating NANBe Ag or anti-NANBe, and selected sera from either group were used as source of conjugates. The new Ag/Ab system was designated NANBc Ag and anti-NANBc since it behaved like the core Ag of HBV . NANBc Ag was detected in coded frozen liver biopsies from patients with chronic persistent 15/25 (60%) or active 27/50 (54%) hepatitis and cryptogenic cirrhosis 16/30 (53.3%) devoid of HBV markers. Only 2/30 alcoholic cirrhosis cases (7%) used as controls were positive (p less than or equal to 0.001). The homologous anti-NANBc antibody was always detectable by indirect immunofluorescence in the patients' serum when NANBc Ag was found in the liver. It was also found in 11/135 (8%) additional cases without any other NANB marker. A correlation was observed between coded detection of the NANBc Ag/Ab system by immunofluorescence and demonstration of NANBe Ag or anti-NANBe by immunodiffusion. In acute post-transfusion NANB hepatitis, anti-NANBc was first detectable 14 days after transfusion and persisted as long as ALT remained elevated, or longer. IgM anti-NANBc present at onset became associated with an increasing proportion of IgG after the 28th day. The prevalence of anti-NANBc in sporadic NANB hepatitis (11/50 = 22%) was significantly lower (p less than or equal to 0.001) than in cases with parenteral exposure such as post-transfusion, occupational or drug addict hepatitis (47/72 = 65%). Immunofluorescent tests for NANBc Ag and Ab are promising assays for the serological diagnosis of NANB hepatitis.