Monoclonal antibodies raised to purified woodchuck hepatitis virus core antigen particles demonstrate X antigen reactivity.

Woodchuck hepatitis core antigen (WHcAg) particles purified from the liver of chronically infected animals were used for monoclonal antibody production. Most of the putative clones demonstrated anti-WHc specificity. However, the supernatants from several putative clones bound X antigen sequences from woodchuck hepatitis virus (WHV) and hepatitis B virus (HBV). One monoclonal antibody, designated WC9-85 (an IgM), specifically bound hepatitis B X antigen (HBxAg) residues spanning positions 115-131 (peptide 100). WC9-85 also specifically detected liver-derived WHcAg and duck hepatitis B core antigen (DHBcAg) particles in the same CsCl density gradient fractions as did specific anticore and cross-reactive polyclonal anti-x. WC9-85 did not bind to HBcAg particles made by recombinant DNA techniques, in which only the C-gene sequences are expressed, but did bind to liver-derived HBcAg in identical assays. A second monoclonal anti-x, WC8-62, had similar characteristics. Identification of the immunoreactive species in liver-derived core particles by Western blotting showed that WC9-85 bound the major DHBcAg polypeptide having an apparent molecular weight of 35,000 Da. WC9-85 also bound WHcAg-associated bands at approximately 37,000 and 27,000 Da, but little or no binding at the apparent molecular weight of the major WHcAg polypeptide (about 21,000 Da) was observed. These results are consistent with the conclusions that X determinants are associated with core particles purified from naturally infected livers, that such determinants are associated with the major DHBcAg polypeptide and at least two minor WHcAg-associated polypeptides, and that X reactivity is distinct from core and/or e reactivity in hepadnavirus core particles.