Interaction of Treponema denticola TD-4, GM-1, and MS25 with human gingival fibroblasts

The adherence of Treponema denticola GM-1, TD-4, and MS25 to human gingival fibroblasts (HGFs) was studied to serve as an introduction to investigations into the interactions of these oral bacteria with human host cells. Under both aerobic (5% CO2) and anaerobic (85% N2 plus 10% H2 plus 5% CO2) environments, the interactions with the HGFs were such that strains GM-1 and MS25 were consistently more adherent than strain TD-4. Polyclonal antibodies to GM-1 inhibited GM-1 adherence by 70%, while MS25 and TD-4 showed differing degrees of cross-reactive inhibition, indicative of common but not identical epitopes on the surface of the three T. denticola strains. Pretreatment of the three strains with trypsin did not inhibit adherence; proteinase K did, however, inhibit this interaction by 80%. Trypsin pretreatment of the HGFs resulted in increases in adherence of 50 and 86% for GM-1 and MS25, respectively, while a decrease of 41% was noted for TD-4. Exposure of the T. denticola strains to sugars and lectin pretreatment of the HGFs implicated adherence mediation by mannose and galactose residues on the HGF surface. Periodate treatment of HGFs resulted in a 50% drop in adherence for GM-1 and MS25, but did not decrease that of TD-4. Addition of fetal bovine serum inhibited adherence of the three strains to differing degrees, with TD-4 being the most susceptible. Addition of purified fibronectin (100 micrograms/ml) resulted in greater than 50% inhibition in GM-1 and MS25 adherence, while a 25% increase occurred with TD-4. While strain differences were noted in some of the parameters studied, the results indicate two possibilities for T. denticola-HGF adherence: a lectinlike adhesin(s) on the T. denticola surface with affinity for galactose and mannose on the HGF surface, and a serum host factor(s) bridging T. denticola and HGFs.