Immune responses of pigs inoculated with a recombinant fowlpox virus coexpressing ORF2/ORF1 of PCV2 and P1 2A of FMDV

Abstract

A recombinant fowlpox virus (rFPV-ORF2ORF1-P12A) containing the open reading frame ORF2)/ORF1 DNAs of the porcine circovirus 2 (PCV2) (strain, Inner Mongolia) and foot-and-mouth disease virus (FMDV) capsid polypeptide of O/NY00 was evaluated for its abilities to induce humoral and cellular responses in piglets. In addition, we examined its abilities to protect cell cultures against a homologous virus challenge. To approach the feasibility of different united ways of immunization, the recombinant fowlpox virus rFPV-ORF2ORF1-P12A and the recombinant DNA plasmid pVAX1-IL18-ORF2ORF1 were used to immunize the pigs in “prime-boost”programme. We observed that priming the pigs with DNA plasmid pVAX1-IL18-ORF2-ORF1, followed by boosting with the recombinant virus rFPV-ORF2ORF1- P12A produced partially cellular immunity and humoral immunity. Control groups were inoculated with wild-type fowlpox virus (wtFPV) and phosphate buffer saline (PBS). All animals vaccinated with rFPVORF2ORF1- P12A developed specific anti-PCV2/anti-FMDV enzyme-linked immunosorbent assay (ELISA) and neutralizing antibodies and also showed T lymphocyte proliferation response. The antibody level produced by PCV2 was lower than that of O type FMDV to 1:20 and 1:200 respectively. We examined specific cytotoxic T lymphocyte (CTL) production in pigs serum and T lymphocytes (CD4, CD8, and CD4/CD8 double positive T cells) in the peripheral blood. First inoculating pVAX1-IL18- ORF2ORF1 and then rFPV-ORF2ORF1-P12A, had considerably higher CD4+, CD8+ and CD4+CD8+ T lymphocytes subgroups compared with the control groups. Whether the ratio between effective cells and target cells was 50:1 or 25:1, the specific CTL of experimental groups had much more significant differences with the control (FPV), even still the group of priming nucleic acid vaccine boosting recombinant virus had the bravest cytotoxicity of specific CTL. Moreover, the E/T ratio of 50:1 was more excellent. Following infection respectively with a mixture of a pathogenic strain of PCV2 (strain, Inner Mongolia)/FMDV (O/NY00) and neutralizing antibody, PK15 cells (BHK21) inoculated with recombinant fowlpox virus (rFPV) showed less (P < 0.05) yellow-green fluorescence and cytopathogenesis, suggesting the establishment of partial protection against PCV2/FMDV infection. The results show that the immunization programme here, in which pVAX1-IL18-ORF2ORF1 DNA vaccine was inoculated firstly and rFPV-ORF2ORF1-P12A was followed, is viable and indicates the potential use of a fowlpox virusbased recombinant vaccine for the control and prevention of PCV2/FMDV infections.

Key words: PCV2, rFPV, FMDV, immune response, prime-boost.