Keynote Lecture: LBP modulation of LTA-induced TLR2 signalling in human odontoblasts

Previous studies have suggested that human odontoblasts are involved in the dental pulp immune and inflammatory response to oral pathogens that invade dentin during the caries process. However, how odontoblasts regulate the early pulp response to Gram-positive bacteria, which predominate in shallow and moderate dentin caries, is not completely understood. We previously showed that activation of Toll-like receptor (TLR)2, a pattern recognition molecule activated by lipoteichoic acid (LTA) from Gram-positive bacteria, triggers TLR2 up-regulation, NF-κB nuclear translocation, and production of pro-inflammatory chemokines and cytokines, including CXCL8 and IL-6, by odontoblasts in vitro. Objective: To determine whether odontoblast activation by LTA is modulated by the lipopolysaccharide-binding protein (LBP), an acute-phase protein over-expressed in inflamed pulps which has been shown to interact with LTA. Methods: Human teeth were collected with the informed consent of the patients, in accordance with the Declaration of Helsinki and following a protocol approved by the local ethics committee. Odontoblast-like cells were differentiated from pulp explant cultures derived from non-erupted healthy third molars. Cells were stimulated for 4 h with various concentrations of LTA, alone or in association with LBP. Gene expression of the pro-inflammatory chemokine CXCL8, the cytokine interleukin-6 (IL-6), and the LTA receptor TLR2 was assessed using real-time PCR. Results were expressed as mean values ± SD and statistical analysis was determined with Student's t test. Results: CXCL8, IL-6 and TLR2 genes were significantly up-regulated by LTA, but this increase was reduced when LBP was added together with LTA in the culture medium. Conclusion: These data demonstrate that LBP negatively regulates TLR2 signalling induced by LTA in human odontoblasts and might play a role in protecting human dental pulp from excessive immune response to cariogenic Gram-positive bacteria. Supported by University Lyon 1, CNRS, IFRO and Région Rhone-Alpes.