Periodontitis is the inflammatory response in periodontal tissues elicited by bacterial colonization in periodontal pockets. In this response, pocket epithelial cells are the first cells to come into contact with bacteria. To elucidate this mechanism, we determined the adherence of the periodontopathic bacterium Eikenella corrodens 1073, which has a GalNAc-sensitive lectin-like adhesin (EcLS), to a human oral epithelial carcinoma cell line (KB) and the induction of proinflammatory cytokine production in the cells following exposure to this bacterium in vitro. In the adherence assay, EcLS played a role as the adhesin of this bacterium in adherence to KB cells. In a reverse transcriptase PCR, significant interleukin-8 (IL-8) and IL-6 mRNA levels were induced in response to exposure to this bacterium. In an enzyme-linked immunosorbent assay after an 8-h bacterial exposure, the IL-8 and IL-6 protein levels were 13.5- and 8.3-fold higher than those in the nonexposed controls, respectively. These protein responses were time dependent. Interestingly, whenE. corrodens was separated from KB cells by cell culture inserts, a slight stimulation of the IL-6 and IL-8 mRNA and secreted protein levels was seen. These results imply that the direct contact ofE. corrodens 1073 with oral epithelial cells is not necessarily required for the stimulation of IL-6 and IL-8 secretion. We suggest that E. corrodens induces the epithelial cells to secrete proinflammatory cytokines which serve as an early signaling system to host immune and inflammatory cells in underlying connective tissues.

In the inflammatory response elicited by bacterial colonization in periodontal pockets, pocket epithelial cells not only serve as a barrier to isolate the pocket microenvironment from external stimuli but also regulate the functions of neighboring cells including fibroblasts and inflammatory cells. To elucidate this mechanism, we characterized the effects of periodontopathic bacterium Eikenella corrodens 1073 components on the production of some inflammatory mediators in a human oral epithelial cell line (KB). In enzyme-linked immunosorbent assay (ELISA), the E. corrodens supernatant induced interleukin-6 (IL-6), IL-8 and prostaglandin E2 but not interferon-gamma (IFN-gamma) production by KB cells. After incubation with E. corrodens supernatant, KB cells showed a marked increase in the levels of IL-6, IL-8 and PG G/H synthase (cyclooxygenase)-2, but not IFN-gamma, gene expression by reverse-transcriptase polymerase chain reaction. All these E. corrodens products responsible for production of these inflammatory mediators resisted freezing and boiling and were present in a 10-kDa filtrate. These results imply that these soluble small-molecular-mass products from E. corrodens stimulate various inflammatory mediator productions by human oral epithelial cells and may play a role in the initiation of periodontal inflammation and subsequently perpetuate the inflammatory response during chronic infection.

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