Successive active phases observed in periodontal diseases may be explained either by a sudden activation of the pro-forms of tissue-stored degradative enzymes such as metalloproteinases (MMPs) or by an imbalance between metalloproteinases and their tissue inhibitors (TIMPs). To discriminate between these two hypotheses, we quantified the levels, the percentage of active form, and the activities of four metalloproteinases (MMPs -1, -2, -3, and -9), as well as the levels of two tissue inhibitors of metalloproteinases (TIMP-1 and -2) and the activity of cathepsin C in tissue extract supernatants and their corresponding gingival crevicular fluid samples collected from periodontitis-affected and healthy patients. Our results supported evidence that tissue destruction results from an imbalance of metalloproteinases over their tissue inhibitors rather than from a sudden activation of the pro-forms of these enzymes. A significant reduction in the activity of cathepsin C also contributed to the degradative process.

Our results did not reveal significant differences in the expression of mRNAs encoding for the MMPs between healthy and periodontitis-affected patients, reflecting the great heterogeneity in the periodontal status of individuals. However, they indicate that gingival fibroblasts are an active source of MMP-2 production in response to a periopathogen.

In order to examine the possible implication of human epithelial and endothelial cells in the pathogenesis of various diseases associated with oral viridans streptococci, we tested the immunomodulatory effects of 11 representative strains of oral viridans streptococci on human epithelial KB cells and endothelial cells. We then examined the possible role of two major adhesins from oral viridans streptococci, protein I/II and rhamnoseglucose polymers (RGPs), in this process. In this study we demonstrate that oral viridans streptococci are potent stimulators of interleukin-8 (IL-8) production from KB cells and of IL-6 and IL-8 production from endothelial cells. The ability of protein I/II and RGPs to contribute to these effects was then examined. Using biotinylated protein I/IIf and RGPs from Streptococcus mutans OMZ 175, we showed that these adhesins bind to KB and endothelial cells through specific interactions and that the binding of these molecules initiates the release of IL-8 from KB cells and of IL-6 and IL-8 from endothelial cells. These results suggest that protein I/IIf and RGPs play an important role in the interactions between bacteria and KB and endothelial cells in that similar cytokine profiles are obtained when cells are stimulated with bacteria or surface components. We also provide evidence that protein I/IIf binds to and stimulates KB and endothelial cells through lectin interactions and that N-acetyl neuraminic acid (NANA) and fucose present on cell surface glycoproteins may form the recognition site since binding and cytokine release can be inhibited by dispase and periodate treatment of cells and by NANA and fucose. These results demonstrate that oral viridans streptococci, probably by engaging two cell surface adhesins, exert immunomodulatory effects on human KB and endothelial cells.

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