Response of epithelial cells to invasion by Treponema denticola

Treponema denticola is a major pathogen of chronic periodontitis and has several virulence factors such as a surface protease, dentilisin, and the major outer sheath protein Msp. Invasion of gingival epithelial cells by periodontopathogens may play an important role in the development of periodontitis. The aim of this study was to investigate the effects of the virulence factors of T. denticola on epithelial cell response. Rat epithelial cells (Res) collected from oral mucosa and porcine epithelial rests of Malassez cells (ERMs) were cultured until confluent. Each type of cell was infected with T. denticola ATCC 35405 (wild type), K1 (dentilisin-deficient mutant), or DMSP-3 (Msp-deficient mutant) at a multiplicity of infection of 1:100. After infection, infected Res were observed by scanning electron microscopy (SEM). Expression of proteins in Res was also investigated by confocal laser scanning microscopy (CLSM) and staining with antibodies for interleukin-6 (IL-6), IL-1 beta, beta-defensin 2, and heat shock protein 70 (HSP-70). The mRNA expression of these proteins was also investigated by RT-PCR. Observation by SEM revealed that T. denticola adhered to REs and that some of the cells invaded Res in a polar manner. This pattern of invasion was also observed by CSLM. Expression of IL-6, IL-1beta, and HSP-70 mRNA showed an increase in T. denticola wild-type infected cells. While peak expression of IL-1beta and IL-6 mRNA was observed at 1 hr after infection, that of HSP-70 mRNA was seen at 24 hr; the same pattern of increase was also observed in both the dentilisin- and Msp-deficient mutants. This pattern of expression was also observed by CLSM. Expression of beta-defensin 2 in cells infected by T. denticola wild-type strain was higher than that in cells infected by T. denticola K1 or DMSP-3. These results suggest that dentilisin and Msp induce production of beta-defensin 2 in epithelial cells.