Plasmids expressing porcine interferon gamma up-regulate pro-inflammatory cytokine and co-stimulatory molecule expression which are suppressed by porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the pro-inflammatory immune response following infection of myeloid antigen-presenting cells. A reduced pro-inflammatory immune response modulates PRRSV replication, clinical disease, and persistent infection of the virus. Numerous efforts have been made to enhance the pro-inflammatory immune response to PRRSV, but only a few attempts have so far elicited satisfactory results. The present study aims to evaluate in vitro the potential of plasmids expressing porcine interferon gamma (pcDNA-IFNγ) to enhance the expression of pro-inflammatory immune parameters in PRRSV-inoculated monocytes. Naïve blood monocytes from eight PRRSV-seronegative pigs were inoculated with PRRSV and subsequently transfected with pcDNA-IFNγ or pcDNA (empty plasmid vector) and stimulated with lipopolysaccharide (LPS). The mRNA expression levels of IFNγ, interleukin-1 beta (IL-1β), IL-10, IL-12p40, tumor necrosis factor alpha (TNFα), transforming growth factor beta (TGFβ), CD80, and CD86 were evaluated by real-time PCR. The IFNγ, IL-10, and TNFα protein production was determined by ELISA. Compared with PRRSV-inoculated monocyte control, transfection with pcDNA-IFNγ, but not pcDNA, significantly enhanced IFNγ, TNFα, CD80, and CD86 mRNA expression, and IFNγ and TNFα protein production. A slight increase in IL-1β and IL-12p40 mRNA expression was also observed. Neither pcDNA-IFNγ nor pcDNA transfection affected IL-10 and TGFβ expression. Our results thus suggest that pcDNA-IFNγ may be an effective immunostimulator for potentiating the pro-inflammatory immune response to PRRSV.