Monoclonal IgM radioimmunoassay for hepatitis B surface antigen: high binding activity in serum that is unreactive with conventional antibodies.

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Abstract
Using a monoclonal IgM antibody (anti-HBs) to hepatitis B surface antigen (HBsAg) in a radioimmunoassay for hepatitis B, high binding activity in human serum that was unreactive in assays employing conventional anti-HBs reagents was detected. The binding material was isolated from serum by affinity chromatography on monoclonal IgM anti-HBs, and comparison of the material with HBsAg (by sodium dodecyl sulfate/polyacrylamide gel electrophoresis) demonstrated that the 2 shared several similar polypeptides. Comparison of the binding properties of HBsAg and concentrated monoclonal immunoreactive material with conventional and monoclonal anti-HBs reagents demonstrated some antigenic crossreactivity. The MW of the monoclonal immunoreactive material was .apprx. 2 .times. 106. Immunoprecipitation of the material with monoclonal IgM antibodies and examination by EM revealed clumped and spiculated particles that resembled 22-nm hepatitis B particles coated with the same antibody. Thus, the high-binding-activity material, detected in serum only by the monoclonal radioimmunoassay, seemingly is not identical with HBsAg, but it shares some common properties.