Red-complex bacteria exhibit distinctly different interactions with human periodontal ligament stromal cells compared to Fusobacterium nucleatum.

The red-complex bacteria Porphyromonas gingivalis and Tannerella forsythia together with Fusobacterium nucleatum are essential players in periodontitis. This study investigated the bacterial interplay with human periodontal ligament mesenchymal stromal cells (hPDL-MSCs) which act in the acute phase of periodontal infection. The capability of the bacteria to induce an inflammatory response as well as their viability, cellular adhesion and invasion were analyzed upon mono- and co-infections of hPDL-MSCs to delineate potential synergistic or antagonistic effects. The expression level and concentration of interleukin (IL)−6, IL-8 and monocyte chemoattractant protein (MCP)−1 were measured using qRT-PCR and ELISA. Viability, invasion, and adhesion were determined quantitatively using agar plate culture and qualitatively by confocal microscopy. Viability of P. gingivalis and T. forsythia but not F. nucleatum was preserved in the presence of hPDL-MSCs, even in an oxygenated environment. F. nucleatum significantly increased the expression and concentration of IL-6, IL-8 and MCP-1 in hPDL-MSCs, while T. forsythia and P. gingivalis caused only a minimal inflammatory response. Co-infections in different combinations had no effect on the inflammatory response. Moreover, P. gingivalis mitigated the increase in cytokine levels elicited by F. nucleatum. Both red-complex bacteria adhered to and invaded hPDL-MSCs in greater numbers than F. nucleatum , with only a minor effect of co-infections. Oral bacteria of different pathogenicity status interact differently with hPDL-MSCs. The data support P. gingivalis' capability to manipulate the inflammatory host response. Further research is necessary to obtain a comprehensive picture of the role of hPDL-MSCs in more complex oral biofilms. • F. nucleatum induces significant cytokine release by hPDL-MSCs. • P. gingivalis-F. nucleatum co-infection antagonizes cytokine production. • hPDL-MSCs preserve viability of red-complex bacteria, but not F. nucleatum. • Red-complex bacteria are more adhesive/invasive to hPDL-MSCs than F. nucleatum. [ABSTRACT FROM AUTHOR]