Haemophilus parasuis modulates cellular invasion via TGF-β1 signaling.

TGF-β1 plays an important role during the invasion of some bacteria into cells by regulating the expression of integrins, fibronectin, and other extracellular matrix proteins. We postulated that TGF-β1 levels could affect the invasion of Haemophilus parasuis into PK-15 cells. After infection by H. parasuis, PK-15 cells had elevated levels of TGF-β1 expression. Treatment of PK-15 cells with TGF-β1 prior to infection significantly decreased invasion by H. parasuis. Both TGF-β1 treatment and H. parasuis infection resulted in significant induction of fibronectin (Fn) and α5 integrin. Although pretreatment of PK-15 cells with siRNA fragments targeting Fn and α5 integrin resulted in enhanced H. parasuis invasion, H. parasuis attachment was elevated only on cells treated with the α5 integrin siRNA, there was no corresponding increase in attachment to cells treated with Fn siRNA. Our results firstly demonstrated that expression of TGF-β1, Fn and α5 integrin inhibited invasion of H. parasuis in PK-15 cells.