Interaction of Mycoplasma synoviae with chicken synovial sheath cells contributes to macrophage recruitment and inflammation

Mycoplasma synoviae (MS) is an important avian pathogen causing considerable economic hardship in the poultry industry. A major inflammation caused by MS is synovitis that occurs in the synovial tendon sheath and joint synovium. However, the overall appearance of pathological changes in the tendon sheath and surrounding tissues caused by MS infection at the level of pathological tissue sections was poor. Studies on the role of MS and synovial sheath cells (SSCs) interaction in the development of synovitis have not been carried out. Through histopathological observation, our study found that a major MS-induced pathological change of the tendon sheath synovium was extensive scattered and focal inflammatory cell infiltration of the tendon sheath synovial layer. In vitro research experiments revealed that the CFU numbers of MS adherent and invading SSC, the levels of expression of various pattern recognition receptors, inflammatory cytokines, and chemokines coding genes, such as IL-1β, IL-6, IL-8, CCL-20, RANTES, MIP-1β, TLR7, and TLR15 in SSCs, and chemotaxis of macrophages were significantly increased when the multiplicity of infection (MOI) of MS to SSC were increased tenfold. The expression level of IL-12p40 in SSC was significantly higher when the MOIs of MS to SSC were increased by a factor of 100. The interaction between MS and SSC can activate macrophages, which was manifested by a significant increase in the expression of IL-1β, IL-6, IL-8, CCL-20, RANTES, MIP-1β, and CXCL-13. This study systematically demonstrated that the interaction of MS with chicken SSC contributes to the inflammatory response caused by the robust expression of related cytokines and macrophage chemotaxis. These findings are helpful in elucidating the molecular mechanism of MS-induced synovitis in chickens.