Abstract: 【Objective】The aim is to analyze the immune responses and the effects of the cytokines induced by GP5 recombinant plasmids of PRRSV. 【Method】SPF piglets were immunized with DNA recombinant plasmids pCI-GP5 which expresses PRRSV GP5 by co-administration of pcDNA-IFN- , pcDNA-IL-2 and pcDNA-IL-4 for three inoculations. The vaccinated pigs were challenged intranasally with PRRSV BJ-4. 【Result】DNA immunization with pCI-GP5 resulted in the production of both neutralizing antibodies (1:19.2) and cellular immune responses two weeks after the third immunization. The pCI-GP5 showed significantly better protection from the PRRSV challenge compared with the control plasmid. The protection was characterized with a decrease of 39% PRRSV-positive tissues. In addition, the co-administration of pcDNA-IL-4 increased the immune response induced by pCI-GP5. This immune response was characterized by a significant enhancement of a lymphoproliferative response and a higher percentage of CD4-CD8+T cell, showing a higher viral neutralization titer of 1:35.5, a lower percentage of PRRSV-positive tissues and a significantly decreased frequency of viraemia (a drop of 64% and a drop of 17%, respectively, compared with the control group). Delivery of pcDNA-IL-2 paired with pCI-GP5 resulted in enhanced cellular immune responses, remarkably reduced percentage of PRRSV-positive tissues and frequency of viraemia (a drop of 59% and a drop of 50%, respectively, compared with the control group). In contrast, the co-administration of pcDNA-IFN- had no adjuvant effects. 【Conclusion】The results indicated that IL-4 and IL-2 could be used as adjuvant of PRRSV DNA vaccine.

Key words: PRRSV, DNA recombinant plasmid, cytokine, immune response