Peng DaXin

Effect of recombinant fowlpox virus expressing chicken interferon-γ on active immunity induced by avian influenza vaccines of H5 subtype in chickens

To evaluate the potential adjuvant effect of chicken interferon-γ (IFN-γ) expressed by recombinant fowlpox virus (rFPV–IFN-γ), SPF chickens and commercial chickens with (MAb + ) and without (MAb − ) maternal antibodies were immunized with rFPV–IFN-γ plus either H5 subtype avian influenza vaccine based on recombinant fowlpox virus (rFPV–HA) or conventional inactivated vaccine. In the assay of humoral responses, rFPV–IFN-γ plus vaccines induced a slightly lower titre of haemagglutinin inhibition (HI) antibody response than either rFPV–HA or inactivated vaccine alone, in both MAb − and MAb + chickens. As for protective efficacy, the combinations of rFPV–IFN-γ and both vaccines induced 95–100% protection against lethal challenge with highly pathogenic avian influenza virus in SPF chickens and MAb − chickens, which were equal to those induced by either vaccine alone. However, immunization of MAb + chickens with 10 6 pfu rFPV–HA plus 10 5 pfu rFPV–IFN-γ showed higher protection efficacy (33.5%) than that (11.4–15.8%) induced by treatments with other dosage combinations. These findings show that IFN-γ expressed by recombinant fowlpox virus could not promote HI antibody response induced by H5 avian influenza vaccines in chickens. The results also suggest that rFPV–IFN-γ enhances the protection of chickens in a dose-dependent and immune status-dependent manner.