While Mycoplasma gallisepticum (MG) is a major pathogen that causes chronic
respiratory diseases in chicken, the molecular mechanism of MG
infection is not clear. In this study, we investigated the roles of
Toll-like receptor 2 (TLR2) and 6 (TLR6) in MG
infection. We found that TLR2 type 2 (TLR2-2) and TLR6 had differential expressions in chicken embryo fibroblasts (DF-1 cells), where TLR6 was highly expressed, but TLR2-2 was barely expressed. Upon MG
infection, TLR6 expression was upregulated, followed by upregulation of downstream factors, MyD88, NF-κB,
IL2,
IL6, and TNF-α. Knockdown of TLR6 expression by
shRNA abolished the MG-induced inflammatory responses. More interestingly, in the presence of TLR6, TLR2-2 didn't respond to MG
infection in DF-1 cells. When TLR6 was knocked down by
shRNA, however, TLR2 was upregulated upon MG
infection, which was followed by upregulation of proinflammatory genes. Finally, we tested effects of the MG
infection on expression of TLR2-2 and TLR6 in the lungs and trachea tissues of chicken embryos. We found both TLR2-2 and TLR6 were upregulated upon MG
infection, followed by upregulation of the downstream NF-κB-mediated inflammatory responses. This study was the first to report the differential roles of TLR2-2 and TLR6 in MG-infected DF-1 cells and chicken embryos.