Mycoplasma gallisepticum induced inflammation-mediated Th1/Th2 immune imbalance via JAK/STAT signaling pathway in chicken trachea: Involvement of respiratory microbiota

The respiratory microbiota plays a significant role in the host defense against Mycoplasma gallisepticum (MG) infection. The results showed that MG infection changed respiratory microbiota composition, which lead to the tracheal inflammation injury and oxidative stress. MG infection significantly induced immunosuppression in chickens at day 3 and 5 post-infection. In addition, MG infection increased the expressions of pro-inflammatory cytokines in tracheal tissues and activated TLR4 mediated JAK/STAT signaling pathway at day 3 post-infection compared to the control group. Meanwhile, the expressions of pro-inflammatory cytokines were decreased and the expressions of JAK/STAT signaling pathway were decreased at day 5 and day 7 post-infection. On the contrary, the expressions of anti-inflammatory cytokines were significantly decreased at day 3 post-infection and were increased at day 5 and day 7 post-infection in the MG infection group. The antibiotic cocktail group received the respiratory microbiota from the MG infection group, which induced inflammatory injury and oxidative stress, induced mucosal barrier damage by down regulating tight junction-related genes and altered the expressions of mucin, which could be the possible causes of dysregulated immune responses. Importantly, the expressions of pro-inflammatory cytokines were significantly decreased and TLR4 mediated JAK/STAT signaling pathway was downregulated at day 1 and 3 post-transplantation. While, respiratory microbiota transplanted from MG infection significantly increased the expressions of pro-inflammatory cytokines and activated JAK/STAT signaling at day 7 post-transplantation. These results highlighted the role of respiratory microbiota in MG-induced tracheal inflammation injury, and offered a new strategy for the preventive intervention of this disease.