Immunization with recombinant woodchuck hepatitis virus nucleocapsid antigen or hepatitis B virus nucleocapsid antigen protects woodchucks from woodchuck hepatitis virus infection

Woodchucks were immunized with recombinant woodchuck hepatitis virus (WHV) nucleocapsid antigen (WHcAg) or hepatitis B virus (HBV) nucleocapsid antigen (HBcAg) and challenged with 10⁶ WHV ID₅₀. Six out of six woodchucks immunized with WHcAg and four out of six immunized with HBcAg were protected from WHV infection. Woodchucks immunized with WHcAg or HBcAg developed high serum antibody titres against WHcAg or HBcAg. Antibodies against WHc and HBc displayed little cross-reactivity (<1%). This confirms and extends previous reports of protection against homologous challenge after immunization with HBcAg/WHcAg which are both internal viral antigens. As the dominant B-cell epitope(s) on particulate WHcAg and HBcAg appear not to be conserved it also demonstrates that antibodies against HBcAg/WHcAg are not important for this protection. Woodchucks immunized with WHcAg/HBcAg reacted with a fast serum antibody response against viral envelope proteins upon challenge with WHV, indicative of functional intrastructural/intermolecular T-cell help as one potential mechanism of protection after immunization with an internal viral antigen.