High-affinity IgM and IgG monoclonal antibodies (anti-HBs) against hepatitis B surface antigen (HBsAg) determinants were used to study a confined Australian Aboriginal population, 51% of which showed evidence of exposure to hepatitis B virus (HBV). A conventional radioimmunoassay which uses polyvalent anti-HBs antisera indicated that 4.4% ofthe subjects were positive for HBsAg; a monoclonal IgM anti-HBs radioimmunoassay detected all these HBsAg-positive samples and showed enhanced binding activity in a further 5·4% of subjects. Detailed analysis of this binding activity in serum by different IgG and IgM monoclonal anti-HBs antibodies demonstrated additional HBsAg-associated determinants as well as remarkable homogeneity of the determinants in this population. It was concluded that there are HBV or HBV-like agents in this community not previously detected by conventional assays.
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