Two Commensal Bacteria Induced Differential Gingival Innate Immune Response

Objectives: Gingival epithelial cells are a central component of the barrier between oral microflora and internal tissues. Host response to bacteria and surface components are thought to be important in the maintain of periodontal homeostasis. Innate immunity confers non specific protection against a large number of oral bacteria. Toll-Like Receptors 2 and 4 and antimicrobial peptides such as human beta-defensins 2 and 3 have been identified as key elements in innate immunity response against microbial infection. We studied the specific host response to commensal S. sanguinis, and the opportunistic F. nucleatum bacteria, which are respectively Gram-positive and Gram-negative. Methods: Ca9-22 cell line and stably transfected Ca9-22/TLR2 clone, were challenged with proinflammatory cytokines, wall membrane bacterial extracts or live bacteria. The expression of TLR-2 and 4, hBD-2 and 3, and IL-8 respective mRNA was assayed with quantitative PCR. Released HBD-2, hBD-3 and IL-8 were quantified by ELISA. Results: Firstly, Ca9-22 cell line react differentially to live bacteria compared with bacterial extracts, by producing greater beta-defensin and IL-8 responses for F. nucleatum. Opposite data were obtained for S. sanguinis. When using Ca9-22/TLR2, S. sanguinis behaved like F. nucleatum. Furthermore, small interference RNA-mediated specific down-regulation of the TLR2 expression in Ca9-22/TLR2 resulted in a reversion of the response. Secondly, whereas beta-defensins were inhibited in Ca9-22 after challenge with S. sanguinis, they were strongly activated in Ca9-22/TLR2, without promoting inflammation. Conclusion: Together our data showed that a regular commensal bacteria like S. sanguinis and the opportunistic F. nucleatum considered as the bridge for pathogenous bacteria colonization, regulated differentially oral innate immunity defence and homeostasis, in particular through the TLR2 receptor signaling.