Haemophilus parasuis infection activates the NF-κB pathway in PK-15 cells through IκB degradation.

Haemophilus parasuis is the causative agent inducing a severe inflammation of the serous membranes in pigs, which contribute to the great economic losses in the pig industry in China in the recent years. In this study, it was demonstrated that H. parasuis could activate the inflammatory transcription factor nuclear factor-kappaB (NF-κB) in a bacteria time- and dose-dependent manner in PK-15 cells, and inactivated H. parasuis significantly reduced the level of NF-κB activation in PK-15 cells compared with the counterpart especially in the later stage. After H. parasuis infection, the degradation of IκBα and phosphorylation of p65 was detected in PK-15 cells. Furthermore, the subcellular localization analyzed using confocal laser microscopy showed that p65-GFP rapidly translocated to the nucleus when PK-15 cells were stimulated with H. parasuis. In addition, real-time RT-PCR showed that the key inflammatory mediators including IL-8, CCL4 and CCL5, regulated by nuclear factor-kappaB (NF-κB) were up-regulated dramatically by the infection of H. parasuis in PK-15 cells. This was the first time to report that H. parasuis infection activated the NF-κB pathway in vitro through IκB degradation.