Treponema denticola invasion of human gingival epithelial cells

Objective: Adherence to and invasion of host cells by pathogens play an important role in the development of inflammatory diseases. Treponema denticola has been detected from gingival tissue in recurrent periodontitis. Invasion into host cells is a strategy for evading host defenses. The present study investigated the adherence and invasion of T. denticola in human gingival epithelial cells focusing on the surface protease dentilisin.

Methods: To observe interaction of T. denticola with human gingival epithelial cell line Ca9-22, confocal scanning laser microscopy (CSLM) was performed following dual labeling. 3H-uridine-labeled T. denticola 35405 (wild type) and its isogenic mutant, K1, which lacks dentilisin, were also used. The epithelial cells were exposed to T. denticola at a multiplicity of infection of 1:100. After 2-hour incubation, non-adherent T. denticola cells were washed out and adherent cells were counted. For invasion assay, adherent T. denticola were killed with antibiotics, and internalized T. denticola were counted using a liquid scintillation counter.

Results:, CSLM clearly revealed adherence and internalization of T. denticola ATCC35405 in the gingival epithelial cells. Invasion assay using 3H-uridine-labeling confirmed adherence and invasion by T. denticola ATCC35405 (adherence efficiencies: 5.8%, and invasion efficiencies: 2.7%). Adherence and invasion efficiencies of dentilisin-deficient mutant K1 were statistically significantly lower (adherence: 1.6%, invasion: 0.6%, p < 0.01) than those of the wild type strain. Adherence and invasion by T. denticola wild-type strain were also partially inhibited by addition of phenylmethylsulfonyl fluoride (adherence: 3.2%, invasion: 1.8%).

Conclusion: The results suggest that T. denticola has the ability to invade into gingival epithelial cells and that dentilisin is required for the invasion.