Induction of potent immune responses by recombinant fowlpox virus with deleted ORF73 or ORF214

Abstract:

Abstract：[Objective] To determine if the fowlpox virus (FPV) ORF73 or ORF214 gene encoding protein has the function of IL-18 binding protein, and assess the role of that ORF73 or ORF214 gene played in the regulation of immune response. [Methods] Recombinant fowlpox virus (rFPV) vector-based rFPVLP-△73LRH5A or rFPVLP-△214LRH5A, expressing avian influenza haemagglutinin gene (H5A) with ORF73 or ORF214 gene deletion, was constructed respectively. The parental recombinant virus expressing avian influenza haemagglutinin （rFPVLP- 12LSH5A）was used as the control virus. In this study, the production of IFN in vitro by splenocytes and peripheral blood mononuclear leukocytes (PBML) of SPF chickens stimulated with rFPVs was detected, and the immune efficacy，antibody responses，ratio of CD4+/CD8+ T lymphocyte and multiplication capacity of PBML induced by the rFPVs vector-based rFPVLP-△73LRH5A, rFPVLP-△214LRH5A and rFPVLP- 12LSH5A vaccine were evaluated in SPF chickens. [Results] The level of IFN production from splenocytes stimulated with rFPVLP-△73LRH5A and rFPVLP-△214LRH5A was significantly higher than that with rFPVLP-12LSH5A in vitro, whereas the ratio of CD4+/CD8+ T lymphocyte in rFPVLP-△73LRH5A and rFPVLP-△214LRH5A groups was significantly lower than in rFPVLP- 12LSH5A groups after 10 days post immunization (dpi). These rFPVs stimulated the proliferation of PBML without significant difference. All chickens immunized with rFPVLP-△73LRH5A, rFPVLP-△214LRH5A or rFPVLP- 12LSH5A produced HI antibodies against H5 AIV HA antigen, and rFPVLP-△214LRH5A induced significantly lower HI titer than rFPVLP- 12LSH5A after 14 dpi. All immunized chickens were fully protected against lethal challenge of H5N1 AIV. [Conclusion] The results show that ORF73 and ORF214 encoding proteins blocks 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.