Humoral immune response to the E7 protein of bovine papillomavirus type 4 and identification of B-cell epitopes.

We have previously vaccinated cattle with E7, the major transforming protein of bovine papillomavirus-4, prior to homologous virus challenge. This retarded the development of papillomas and promoted their early regression compared to control animals. To understand the mechanism for this regression, we have studied the B and T cell response in vaccinated animals and compared it to that of non-vaccinated, virus-infected animals. The B cell response is reported here. The development of E7 IgG antibodies was detected after vaccination and before viral challenge, indicating that vaccine E7 is effectively presented to the immune system. In vaccinated animals titres of E7 antibodies remained high 10 weeks after viral challenge, whereas E7 antibodies in control animals were not detectable until 13 weeks post-viral challenge. Further analysis with synthetic overlapping peptides spanning the entire E7 protein mapped major immunodominant epitopes in the N and C termini of the protein and a minor epitope in the middle of the protein.