Objective: To determine if the fowlpox virus (FPV) ORF73 or ORF214 gene encoding protein has the function of IL-18 binding protein, and to assess the role that ORF73 or ORF214 gene in regulating the immune response.
Methods: We constructed recombinant fowlpox virus (rFPV) vector-based rFPV(LP)-delta73LRH5A or rFPV(LP)-delta 214LRH5A, expressing avian influenza haemagglutinin gene (H5A) with ORF73 or ORF214 gene deletion, respectively. The parental recombinant virus expressing avian influenza haemagglutinin (rFPV(LP)-12LSH5A) was used as the control virus. The production of interferon (IFN) in vitro by splenocytes and peripheral blood mononuclear leukocytes (PBML) of SPF chickens stimulated with rFPVs was detected. The immune efficacy, antibody responses, ratio of CD4+/ CD8+ T lymphocyte and multiplication capacity of PBML induced by the rFPVs vector-based rFPV(LP)-delta73LRH5A, rFPV(LP)-delta214LRH5A and rFPV(LP)-12LSH5A vaccine were evaluated in SPF chickens.
Results: The level of IFN production from splenocytes stimulated with rFPV(LP)-delta73LRH5A and rFPV(LP)-delta214LRH5A was significantly higher than that with rFPV(LP)-12LSH5A in vitro, whereas the ratio of CD4+/CD8+ T lymphocyte in rFPV(LP)-delta73LRH5A and rFPV(LP)-delta214LRH5A groups was significantly lower than that in rFPV(LP)-12LSH5A groups after 10 days post immunization (dpi). These rFPVs stimulated the proliferation of PBML without significant difference. All chickens immunized with rFPV(LP)-delta73LRH5A, rFPV(LP)-delta214LRH5A or rFPV(LP)-12LSH5A produced HI antibodies against H5 AIV HA antigen, and rFPV(LP)-delta214LRH5A induced significantly lower HI titer than rFPV(LP)-12LSH5A after 14 dpi. All immunized chickens were fully protected against lethal challenge of H5N1 AIV.
Conclusion: ORF73 and ORF214 encoding proteins blocked induction of IFN, suggesting that they are provided with IL-18BP functionality. Despite of decreasing humoral response and cell-mediated immune response, rFPV with deleted FPV73 or FPV214 gene could induce the effective efficacy in SPF chickens.