Prior reports have shown that IL-8 mRNA is up-regulated in epithelial cells challenged with Fusobacterium nucleatum (Fn), whereas IL-8 mRNA is simultaneously up-and down-regulated by Porphyromonas gingivalis (Pg) (Darveau et al, 1998; Huang et al, 2001). Objectives: To investigated the underlying mechanisms of these regulations. Methods: Experimental approaches included bacterial stimulation of gingival epithelial cells by either a brief challenge (2 h) or a continuous co-culture throughout the incubation period (4 h). Based on our previous report, the brief challenge resulted in IL-8 mRNA up-regulation by Pg, and the continuous co-culture is required for IL-8 mRNA down-regulation by Pg. In both approaches, epithelial cells were harvested at 4 h for analysis. Viable or nonviable (heat- or formalin-treated) Fn 12230 and Pg ATCC 33277 were used for the studies. Results: We found that nonviable Fn (heat-treated) up-regulated IL-8 mRNA less than its viable counterpart, whereas the ability of nonviable Pg (heat- or formalin-treated) to down-regulate IL-8 mRNA was lost. However, the nonviable Pg remained capable of up-regulating IL-8 mRNA. Treatment of epithelial cells with protein synthesis inhibitor cycloheximide did not affect the viable Fn to up-regulate IL-8 mRNA while it disabled the viable Pg to down-regulate IL-8 mRNA. Conclusions: Our data indicate that IL-8 mRNA up-regulation by Fn relies largely on heat sensitive bacterial factor(s) and this up-regulation does not require de novo protein synthesis in gingival epithelial cells; whereas IL-8 mRNA up-regulation by Pg is heat resistant and IL-8 mRNA down-regulation by Pg relies on heat sensitive bacterial factor(s). Furthermore, this IL-8 mRNA down-regulation by Pg appears in large part dependent on de novo protein synthesis in gingival epithelial cells. (Supported in part by a UCLA Academic Senate Research Grant and a UCLA School of Dentistry Research Opportunity Grant)

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