Immunological responsiveness of Pekin ducks to core antigen of duck hepatitis B virus

Cellular immune responses to the HBc or HBe antigen of hepatitis B viruses contribute to the pathogenesis of hepatitis B and to the elimination of the virus. Insufficient cytotoxic immune reactions against the core antigen may be one major reason for viral persistence in the absence of severe clinical symptoms. We attempted to stop viral persistence in the animal model of congenitally infected ducks by injection of recombinant DHBc particles, together with the strong immunostimulator Freund's adjuvant. However, the duck HBc antigen (DHBcAg)-treated ducks did not develop detectable liver disease, nor was the virus persistence affected. The congenitally infected ducks did not contain antibodies against DHBcAg before injection despite continuous production of duck hepatitis B virus, and developed only a weak transient antibody response after injection of recombinant DHBcAg together with Freund's adjuvant. Noninfected ducks developed, in contrast, a strong antibody response to the injected DHBcAg. We conclude that congenitally infected ducks are immunotolerant to DHBcAg and cannot be cured by immunotherapy with exogenous recombinant DHBcAg.