Human periodontal ligament cells exhibit no endotoxin tolerance upon stimulation with Porphyromonas gingivalis...

Endotoxin tolerance is characterized by a state of hyporesponsiveness after confrontation with endotoxins such as lipopolysaccharides (LPS) at low concentrations. The aim of this study was to investigate, whether pretreatment with Porphyromonas gingivalis leads to endotoxin tolerance induction and possible alterations in toll-like receptor (TLR) 2- and 4-induced response in human periodontal ligament cells (hPDLCs).

Primary hPDLCs were pretreated with P. gingivalis (0.1 or 0.3 μg/mL) LPS for 24 hours and afterwards treated with one of the following stimuli: P. gingivalis LPS (1 μg/mL); TLR4 agonist Escherichia coli LPS (0.1 μg/mL; 1 μg/mL); TLR2 agonist Pam3CSK4 (0.1 μg/mL; 1 μg/mL). The protein expression of interleukin (IL)-6, IL-8 and monocyte chemotactic protein-1 was analyzed with quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Gene expression levels of TLR2 and TLR4 were determined by quantitative polymerase chain reaction.

Pretreatment of cells with low concentrations of P. gingivalis LPS did not result in lower production of IL-6, IL-8 and monocyte chemotactic protein-1 compared to control group. In some cases, pretreated cells exhibited lower gene expression levels of TLR2 and TLR4 compared to non-pretreated cells.

The results of this study implicate that hPDLCs do not develop endotoxin tolerance. Furthermore, the amplitude of the inflammatory response shows no significant dependency on TLR2 and TLR4 expression levels.