Porcine parvovirus infection activates inflammatory cytokine production through Toll-like receptor 9 and NF-κB signaling pathways in porcine kidney cells

Porcine parvovirus virus (PPV) is an animal virus that has caused high economic losses for the swine industry worldwide. Previous studies demonstrated that PPV infection induced significant production of interleukin 6 (IL-6) in vitro and in vivo. However, the inflammatory cytokines and specific signaling pathways induced during PPV infection remain largely unknown. In the present study, we analyzed the expression levels of IL-6 in PPV-infected porcine kidney 15 (PK-15) and the results showed that PPV infection induced the increase of IL-6 mRNA expression in a dose-dependent manner. We also detected the expression of toll-like receptor 9 (TLR9) signaling proteins in the mRNA expressing level, when compared with the control group, the TLR9 expression in mRNA level increased at 24 h in PK-15 cells after PPV infection and reached the peak level at 48 h. In addition, the transcript profile of nuclear factor kappa B (NF-κB) signal pathway relating genes (MyD88, IRAK1, TRAF6, TAK1α, IκBκB and NF-κB) expression levels increased at different times. Furthermore, to verify the IL-6 expression was specific with the TLR9 expression and then by activating the NF-κB signal pathway, TLR9 and NF-κB specific inhibitors were applied during PPV infection, separately, the result indicated that the expression of IL-6 was decreased after inhibitor treatment. Taken together, PPV infection significantly induced IL-6 expression and this induction depended on NF-κB activation and TLR9 signaling pathways in PK-15 cell.