Positive inductive effect of IL-18 on virus-specific immune responses induced by PRRSV-GP5 DNA vaccine in swine.

Two DNA vaccines encoding the envelope protein GP5 of porcine reproductive and respiratory syndrome virus (PRRSV) alone (pEGFP-GP5) and co-encoding GP5 and swine interleukin-18 (IL-18) proteins (pEGFP-IL18-GP5), were constructed and comparatively evaluated for their abilities to induce humoral and cellular responses in piglets. Experimental results showed that among all vaccinated groups, the live PRRSV vaccine elicited the highest titre of serum neutralizing antibody and the strongest cell-mediated immune responses, which means that the live PRRSV vaccine is still the first option for the vaccination against PRRSV. Moreover, the piglets inoculated with pEGFP-IL18-GP5 developed significantly higher IFN-γ production response, significantly increased percentages of CD4(+) and CD8(+) T-lymphocytes and significantly higher specific T-lymphocyte proliferation response than the pEGFP-GP5 inoculated pigs (P<0.05). These results demonstrated the positive inductive effect of IL-18 on the activation of cellular immune responses in swines. Therefore, in order to develop a new type vaccine for PRRS prevention and control, co-encoding of GP5 and IL-18 proteins may be a good choice.