Mapping of the cellular immune responses to woodchuck hepatitis core antigen epitopes in chronically infected woodchucks

T-cell responses to hepatitis B virus nucleocapsid antigens (HBcAg and HBeAg) play an important role in disease outcome in those infected with hepatitis B virus (HBV). The woodchuck is naturally infected in the wild with woodchuck hepatitis virus (WHV), which shows a high degree of genetic homology to HBV and produces a similar pattern of infection in its natural host. Twenty-three overlapping peptides were constructed to cover the entire WHV core region and used to identify immunodominant cellular epitopes in the nucleocapsid antigen using peripheral blood lymphocytes from 12 chronic WHV carrier and 4 uninfected control animals. A peripheral blood lymphocyte response was seen in all of the chronic WHV carrier animals to at least one peptide, and in 8 of the 12 chronic carrier animals a response was observed to 5 common peptides: peptide analogues of amino acids 16-30, 38-52, 50-69, 76-90 and 91-105. Peptide 91-105 produced maximal proliferation in 5 out of 12 infected animals. In addition, a difference in response was observed between wild and laboratory infected animals; the latter appeared to have a lower response to peptides than animals infected in the wild. This study provides evidence that the woodchuck has a population of peripheral blood cells which are sensitised to epitopes within the nucleocapsid protein and provides a basis on which to develop the use of the woodchuck as an immunological model of HBV infection for testing therapeutic means of enhancing this response.