Saliva influences interaction of periodontopathic bacteria with KB-cells

Objectives: Most in vitro studies focusing on interaction of periodontopathic bacteria with epithelial cells used only single infections, moreover the possible influence of saliva is not included. Here, the influence of saliva and mixed infections were studied.

Methods: KB-cells were infected with A. actinomycetemcomitans Y4 (A.a.), P. gingivalis ATCC 33277 (P.g.ref.) and P.g. M5-1-2 (clinical isolate, P.g.cli.), T. forsythia ATCC 43037 (T.f.), T. denticola ATCC 35405 (T.d.) separately or in combination with F. nucleatum ATCC 25586 (F.n.) with and without the addition of artificial saliva. After 1, 6 and 18 h the numbers of adherent and internalized bacteria were counted and the levels of IL-6 and IL-8 in the supernatants were determined by means of ELISA.

Results: Saliva did not change the numbers of adherent bacteria but reduced the numbers of invasive A.a. and P.g.cli. Only single bacteria attached to KB cells were visible in SEM-photographs. Saliva promoted the release of IL-6 and IL-8 (after 18 h non infected KB-cells with saliva 37.4 pg/ml, without 20.6 pg/ml). Compared to non infected cells only the mono-infection with A.a. and F.n. increased the levels of IL-6 and IL-8 (F.n.: IL-6 25.5 pg/ml; IL-8 135 pg/ml after 18 h). Mixed infections had synergistic and antagonistic effects. After infection with P.g.ref. and F.n. up to 233 pg/ml IL-6 and 102.4 pg/ml IL-8 were measured. Non of the both cytokines was detectable, if P.g.cli. even in combination with F.n. effected on KB-cells. After a mixed infection with P.g.ref., T.d., T.f. and F.n. initial 3 pg/ml IL-6 were measured, after 18 h only 0.45 pg/ml; IL-8 was never found. Conclusions: Saliva acts immunomodulatoric and influences interaction of bacteria with host cells. A complex biofilm like on solid surfaces is not formed on KB-cells. Results obtained in experiments using single strains cannot be transferred onto mixed infections.