Abstract
Prevotella nigrescens is a gram-negative anaerobic rod that is frequently isolated from patients with periodontitis and other oral infectious diseases. We previously isolated exopolysaccharide (EPS)-producing P. nigrescens strains 22 and 23 from a chronic periodontitis patient and purified the EPS of each strain. In this study, we investigated the biological effects of EPS on human periodontal ligament fibroblasts (PDL cells) and human peripheral blood mononuclear cells (PBMCs) in order to understand how these organisms establish their biofilm scaffold in periodontal tissue. PDL cells and PBMCs were exposed to purified EPS (1-100 μg/ml) to determine the effect of EPS on proliferation, alkaline phosphatase (ALP) activity, and cytokine production by PDL cells and PBMCs. These cells were also cultured with purified EPS and Escherichia coli lipopolysaccharide (LPS) to determine whether EPS increases or inhibits the effects of LPS. Both the EPS from strain 22 and the EPS from strain 23 displayed a slightly inhibitory effect on proliferation by PDL cells and modestly increased the ALP activity of PDL cells. EPS did not induce IL-6, IL-8, or GM-CSF production by PDL cells, nor did EPS induce IL-1β, IL-6, IL-8, or TNF-α production by PBMCs. Pre-incubation of PBMCs with EPS for 24 hours diminished the effect of LPS stimulation on IL-6 and IL-8 production by PBMCs. EPS did not increase inflammatory cytokine production by PDL cells or PBMCs, and EPS pretreatment reduced LPS-induced cytokine production by PBMCs. These results suggest that the role of EPS may be to enable P. nigrescens to escape from host immune responses when the organism invades periodontal tissues and allow it to cause persistent oral infection.
