Construction And Immunogenicity Of DNA Vaccine Co-expressing Swine IL-18 And GP5 Protein Of Porcine Reproductive And Respiratory Syndrome Virus (PRRSV)

Porcine reproductive and respiratory syndrome (PRRS), which is characterized by severe reproductive failure in sows, and respiratory distress in piglets and growing pigs. In 1987, the disease was first detected in the United States. In China, the virus was isolated in abortive fetal pigs, and first was confirmed in 1996. PRRS occurs in most major pig-producing areas throughout the world. It has severely threatened the swine industry, causing tremendous economic losses throughout the pork industry in the world. The causative agent, PRRS virus (PRRSV), is a positive-strand, enveloped RNA virus belonging to the family Arteriviridae, Nidovirales. Currently PRRSV include two major antigenic types, the European and the American type.In the present study, two different DNA vaccine constructs, expressing GPS alone and co-expressing GP5 and swine IL-18 genes (pEGFP-GP5 and pEGFP-IL18-GP5), were constructed and evaluated for their abilities to induce humoral and cellular responses in piglets, and the effects of swine IL-18 in the modulation of a DNA vaccine-induced immune responses in swine. Meanwhile, we investigated the efficacy of two different types of commercial vaccines against PRRSV was evaluated based on humoral and cell mediated immunity in piglets.In the present study, all piglets were given booster vaccinations at 28 days after the initial inoculation at 0 days. All piglets inoculated with pEGFP-IL18-GP5 developed PRRSV-specific neutralizing antibodies at 35 and 42 days after primary immunization. However, only some piglets developed low levels of neutralizing antibodies in groups immunized with pEGFP-GP5. The pigs immunized with pEGFP-IL18-GP5 groups developed the higher level of IFN-γresponse, as well as significantly increased CD4+ and CD8+ T-lymphocytes responses and a specific T-lymphocyte proliferation response, compared with pEGFP-GP5 inoculated piglets (P<0.05). Interestingly, significantly enhanced GP5-specific ELISA antibody could also be detected in piglets immunized with pEGFP-IL18-GP5, compared with piglets immunized with pEGFP-GP5 (P>0.05). These results demonstrated that IL-18 has a positive inductive effect on the activation of vaccine-induced virus-specific cellular immune responses in swines, and co-expression of GP5 and IL-18 protein can significantly improve the potency of DNA vaccination, which could be used as a strategy to develop a new generation of vaccines against highly pathogenic PRRSV.