Generation And Immunological Characterization Of Recombinant Fowlpox Viruses Expressing Immunogens Of Other Avian Viruses

Fowl poxvirus (FPV) plays an amazing role in the development of virology, immunology, and vaccinology. Several antigen genes from avian pathogens have been successfully expressed in FPV vector and recombinant FPV displayed a prospective protection in the control of avian diseases.In the present study, four recombinant FPVs were generated, which express the chicken infectious bronchitis virus (IBV) S1 gene (rFPV-IBVS1), or the chicken interferon gamma gene (rFPV-ChIFNγ) alone, or co-express the IBV S1 gene and the chicken interferon gamma gene (rFPV-ChIFNγS1); the infectious laryngotracheitis virus (ILTV) gB gene and the Newcastle disease virus (NDV) F gene (rFPV-gBF), respectively. These recombinant viruses were then assessed for their immunological efficacies in specific-pathogen-free (SPF) chickens.One hundred and twelve 4-week-old SPF chickens were randomly divided into 7 groups, and inoculated with the parental fowl poxvirus (S-FPV-017), rFPV-IBVS1, rFPV-ChIFNyS1, rFPV-ChIFNγ, live IB vaccine, rFPV-ChIFNγ plus live IB vaccine (H120), and PBS (control), respectively. Four weeks post-vaccination, all chickens were challenged with virulent IBV LX4 strain. The results showed that 15 out of 16 chickens immunized with rFPV-ChIFNγS1 were well protected, and 14 out of 16 chickens were protected in the group immunized with rFPV-ChIFNγ plus H120. The protection rates in groups immunized with rFPV-IBVSl or live IB vaccine alone were 12/16 and 13/16, respectively. After challenge, chickens of rFPV-ChIFNγSl and rFPV-ChIFNγ plus H120 vaccinated groups had a shorter time period of virus shedding from respiratory tract and the viral antigen persisting in kidney, in comparison with rFPV-IBVS1 or H120 group. Slight pathological findings could be seen in liver, spleen, kidneys, lungs and tracheal of chickens in H120 and all recombinant FPV groups, and rFPV-ChIFNγS1 and rFPV-ChIFNγ plus H120 groups performed even better than others, abnormal changes could only be seen at 7 and 10 days post-challenge, which was three days shorter than that of other groups. All chickens immunized with vaccines containing IBV or S1 gene of IBV developed antibodies against IBV at 3 weeks post-immunization, and the rFPV-ChIFNγSl group had the lower antibody titer than other groups. Except CD4~+ T cell population decreased and TCRγδ~+ and CD8~+ T cell population increased for rFPV-ChIFNγSl vaccinated group before challenge, others remained no significant change. Above results demonstrated that ChIFN-γ can promote CD8~+T cell maturation and improve cellular immunity.