Glaesserella parasuis induces IL-17 production might through PKC-ERK/MAPK and IκB/NF-κB signaling pathways

In our previous study, the outer membrane protein P2 of Glaesserella parasuis (G. parasuis) induced the production of interleukin-17A (IL-17A) in host cells. However, how the G. parasuis infection produces IL-17A in the host is unknown. In this study, at 48 hpi in piglets, the proportion of Th17 cells in the peripheral blood significantly increased as determined by flow cytometry, but the overall proportion was low. IL-17 mRNA and protein levels significantly increased in the lungs and spleens of infected piglets. Histopathological examination staining, immunohistochemistry and viability counts, revealed that IL-17 expression might be positively correlated with bacterial content and the degree of pathological injury in lung and spleen tissues. Furthermore, when infected with the G. parasuis Nagasaki strain compared with avirulent strain C5, the primary porcine alveolar macrophages (PAMs) significantly produced IL-17 in a time-dose dependent manner. In addition, we demonstrated that PKC, MEK and NF-κB signaling pathways were essential for G. parasuis-induced IL-17 production because the addition of corresponding inhibitors dramatically reduced IL-17 mRNA production. The phosphorylation levels of PKC, ERK1/2 and IκB in G. parasuis-infected primary PAMs also increased significantly as the infection dose increased as assessed by western blotting. Thus, these finding imply that IL-17 induced by G. parasuis infection is dependent on activation of PKC-ERK/MAPK and IκB/NF-κB signaling pathways.