Plasmid containing CpG oligodeoxynucleotides can augment the immune responses of pigs immunized with porcine reproductive and respiratory syndrome killed virus vaccine

Porcine reproductive and respiratory syndrome virus (PRRSV), the causative agent of porcine reproductive and respiratory syndrome (PRRS), causes serious health problems in swine, resulting in great economic losses to the swine industry worldwide. The porcine reproductive and respiratory syndrome (PRRS) killed virus (KV) vaccine has been widely used in China but has been linked with side effects in pigs and only partial protection. A few studies have demonstrated the immunostimulatory adjuvant effects of the synthetic CpG oligodeoxynucleotide (ODN) motifs in humans and animals. In this study, the adjuvant efficacy and the protective effects of recombinant plasmid containing CpG ODN, in combination with PRRS KV vaccine against PRRSV were evaluated. The concentration of PRRSV-specific antibodies and cytokines and the clinical parameters (body temperature, weight gain and behavior) on the challenge and post-challenge virological profiles (virus distribution in tissues and virus titers in serum at autopsy) were investigated to define the immune responses of pigs. Our findings indicated that the immune responses of the pigs immunized with plasmid containing CpG ODN and PRRS KV vaccine were stronger than those induced by PRRS KV vaccine or PBS alone. Furthermore, the protection ratios, PRRSV titers in serum samples and virus tissue distribution, all demonstrated that the plasmid containing CpG ODN could augment the immune responses and improve the protective effect of PRRSV vaccination.