Use of a monoclonal antibody in the detection of HBsAg in the liver by immunofluorescence.

IF and IP techniques using conventional antibodies have been successfully applied in the detection of tissue HBsAg. However, they present problems related to specificity and sensitivity as well as in the recognition of the membranous expression of HBsAg. In this study two monoclonal antibodies to HBsAg have been used in the indirect IF and IP techniques for HBsAg demonstration in cryostat and paraffin sections of liver and other tissues (kidney, skin). The results were compared for specificity, sensitivity and histochemical patterns to those obtained by the same techniques with conventional anti-HBs antibodies of human and animal origin (rabbit, guinea-pig, baboon). IF staining with 1:40 dilution of an IgG2a monoclonal anti-HBs (5 C3) using a second layer of absorbed FITC-conjugated anti-mouse antibody, was superior as compared to IP and IF with conventional antibodies. It worked successfully both on frozen and paraffin sections. The main advantages compared to conventional antibodies were: absolute specificity with completely negative background staining, clear-cut demonstration of weak HBsAg reactions usually unrecognizable by conventional antibodies to HBsAg and unequivocal recognition of the membranous HBsAg expression on the surface of hepatocytes. The latter was frequently observed not only in patients with chronic liver disease but also in healthy HBsAg carriers, thus suggesting that surface expression of HBsAg is unrelated to the pathogenesis of HBV-induced chronic liver damage.