Effects of porcine reproductive and respiratory syndrome virus and porcine circovirus type 2 co-infection on apoptogenic cytokine mRNA expression in peripheral blood mononuclear cells of piglets.

Six-week-old healthy piglets were experimentally inoculated with porcine reproductive and respiratory syndrome virus(PRRSV) or porcine circovirus type 2(PCV2) alone or in combination(PRRSV and PCV2).The viral loads and the levels of mRNA expression for apoptogenic cytokines,i.e.Fas,FasL,TNFR1 and TNF-α,in peripheral blood mononuclear cells(PBMC) were measured by real-time PCR.The percentages of apoptosis of PBMC were detected by flow cytometry.The results showed that the piglets co-infected with PRRSV and PCV2 exhibited significantly higher amounts of both PRRSV and PCV2 in PBMC,and significantly higher percentages of apoptosis of PBMC,in comparison to the piglets infected with either virus alone.All virus-infected groups showed significant upregulation of gene expression of Fas,FasL,TNFR1 and TNF-α in PBMC compared to the control group.Furthermore,the PRRSV and PCV2 co-infected group showed significantly increased levels of mRNA expression of Fas,FasL,TNFR1 and TNF-α,in comparison to the PRRSV-or PCV2 group.These results suggest that the markedly increased expression of Fas,FasL,TNFR1 and TNF-α may play an important role in the synergistic induction of apoptosis by PRRSV and PCV2 co-infection.