Bacteria interfere with A. actinomycetemcomitans colonization.

It is known that beneficial bacteria can suppress the emergence of pathogenic bacteria, particularly in the gastrointestinal tract. This study examined the potential for a similar suppression of Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans colonization of epithelial cells, due to its potential relevance in periodontal diseases. Seven presumed beneficial bacteria were examined for their ability to interfere, exclude, or displace A. actinomycetemcomitans from epithelial cells in vitro. Streptococcus sanguinis, Streptococcus mitis, and Streptococcus salivarius showed prominent inhibitory effects on either A. actinomycetemcomitans recovery or colonization. These results confirmed the hypothesis that bacterial interactions interfere with A. actinomycetemcomitans colonization of epithelial cells in vitro, and demonstrated the potential beneficial effects of S. mitis, S. salivarius, and S. sanguinis.

Interactions between periodontal bacteria and human oral epithelial cells: Fusobacterium nucleatum adheres to and invades epithelial cells.

Bacteria are causative agents of periodontal diseases. Interactions between oral bacteria and gingival epithelial cells are essential aspects of periodontal infections. Using an in vitro tissue culture model, a selected group of gram-negative anaerobic bacteria frequently associated with periodontal diseases, including Bacteroides forsythus, Campylobacter curvus, Eikenella corrodens, Fusobacterium nucleatum, Porphyromonas gingivalis, and Prevotella intermedia, were examined for their ability to adhere to and invade primary cultures of human gingival epithelial cells (HGEC). The effects of these bacteria on the production of interleukin-8 (IL-8), a proinflammatory chemokine, were also measured. These studies provided an initial demonstration that F. nucleatum adhered to and invaded HGEC and that this was accompanied by high levels of IL-8 secretion from the epithelial cells. The attachment and invasion characteristics of F. nucleatum were also tested using KB cells, an oral epithelial cell line. The invasion was verified by transmission electron microscopy and with metabolic inhibitors. Invasion appeared to occur via a "zipping" mechanism and required the involvement of actins, microtubules, signal transduction, protein synthesis, and energy metabolism of the epithelial cell, as well as protein synthesis by F. nucleatum. A spontaneous mutant, lam, of F. nucleatum, isolated as defective in autoagglutination, was unable to attach to or invade HGEC or KB cells, further indicating the requirement of bacterial components in these processes. Sugar inhibition assays indicated that lectin-like interactions were involved in the attachment of F. nucleatum to KB cells. Investigation of these new virulence phenotypes should improve our understanding of the role of F. nucleatum in periodontal infections.

Fusobacterium nucleatum T18 aggregates human mononuclear cells and inhibits their PHA-stimulated proliferation.

In previous studies Fusobacterium nucleatum has been shown to induce either stimulatory or inhibitory effects on human mononuclear cells. We examined the interaction of human mononuclear cells with human and cynomolgus monkey strains of F. nucleatum. Peripheral blood mononuclear cells (PBMCs) isolated from normal donors were aggregated in the presence of cells of F. nucleatum but not control bacteria. The aggregation of PBMCs and F. nucleatum T18 was inhibited by either L-arginine, L-lysine, or pretreatment of the bacterial cells with heat, but was unaffected by the presence of sugars or normal human serum. Strain T18 aggregated purified T-cells and monocytes at approximately equal concentrations. When F. nucleatum T18 was incubated with PHA-stimulated PBMCs, DNA synthesis in the PBMCs was significantly inhibited and detection of IL-2R alpha on the PBMCs was reduced. These studies indicate that F. nucleatum aggregates PBMCs, and that this interaction is associated with both an inhibition of PBMC proliferation and a decrease in IL-2 receptor expression. The ability of F. nucleatum to inhibit mononuclear cell proliferation may be significant in the pathogenesis of periodontal diseases.

Effect of oral bacteria on peripheral blood leukocyte interleukin-6 and soluble interleukin-6 receptor production.

To determine the effect of pathogenic oral bacteria on interleukin 6 (IL-6) and soluble IL-6 receptor production, we measured their release by human peripheral blood mononuclear cells in vitro. Unseparated peripheral blood mononuclear cells, peripheral blood lymphocytes (monocyte depleted), pure T cells, or monocytes were cultured with Actinobacillus actinomycetemcomitans, Capnocytophaga gingivalis, Capnocytophaga ochracea, Fusobacterium nucleatum or Porphyromonas gingivalis for 24 h. Supernatants were tested for IL-6 and soluble IL-6 receptor by enzyme-linked immunosorbent assay. Only monocytes and peripheral blood mononuclear cells responded with significant IL-6 release in the presence of all bacteria tested. However, peripheral blood lymphocytes were capable of producing IL-6 when activated by phytohemagglutinin or IL-2 followed by bacteria, though substantially less than cultures containing monocytes. No bacteria tested increased soluble IL-6 receptor release over spontaneous soluble IL-6 receptor release. We conclude that monocytes release IL-6 after contact with oral pathogens; however, soluble IL-6 receptor from T cells and monocytes is constitutively produced and may modulate IL-6 actions.