Oral treponemes and their outer membrane extracts activate human gingival epithelial cells through toll-like receptor 2

Oral treponemes are considered to be important in the development and progression of periodontal diseases. We investigated the mechanisms of recognition and activation of human gingival epithelial cells (HGEC) with the oral treponemes Treponema denticola, Treponema vincentii, and Treponema medium and their outer membrane extracts (OMEs). T. vincentii and T. medium but not T. denticola produced interleukin 8 (IL-8) in an HGEC culture. Further, all three treponemes induced IL-8 mRNA expression and NF-kappaB activation in HGEC. Among them, T. denticola especially exhibited trypsin- and chymotrypsin-like protease activities, and the addition of chymostatin, a chymotrypsin protease inhibitor, resulted in detectable IL-8 production by HGEC cultured with T. denticola. Additionally, IL-8 mRNA expression in HGEC cultured with the three treponemes and their OMEs was definitely inhibited by the mouse anti-human Toll-like receptor 2 (TLR2) monoclonal antibody TL2.1. These findings suggest that oral treponemes and their OMEs activate HGEC through TLR2.