Differential Responses of Odontoblasts and Pulp Fibroblasts to Microbial Components

Odontoblasts and fibroblasts are suspected to influence innate immune response triggered in the dental pulp by micro-organisms that progressively invade the human tooth during the carious process. Objective: To determine whether both cell types differ in their response to pathogen-derived components, by performing a systematic comparative analysis of human odontoblast-like cell and pulp fibroblast responses to Toll-like receptor 2 (TLR2), TLR3 and TLR4 specific agonists (lipoteichoic acid [LTA], synthetic double-stranded RNA analog polyinosinedeoxycytidylic acid = [poly(I:C)] and lipopolysaccharide [LPS], respectively). Methods: Odontoblast-like cells and fibroblasts were obtained from twenty healthy non-erupted human third molars by culturing pulp explants (Couble et al., 2000). After 4 weeks, cells were stimulated with 1µg/mL highly purified Staphylococcus aureus LTA, 25µg/mL poly(I:C) or 1µg/mL ultra pure Escherichia coli LPS for 8hr. Unstimulated cells were used as controls. TLR2, TLR3 and TLR4 expression was assessed using real-time PCR and flow cytometry. Chemokine expression was determined using cDNA gene array, real-time PCR and antibody array. Culture supernatants were tested for their capacity to attract immature dendritic cells in Transwell migration assays. Results: Cells responded to TLR2 and TLR4 agonists by differential up-regulation of TLRs and chemokines. In particular, LTA increased TLR2 in odontoblast-like cells, but not in fibroblasts, whereas TLR4 expression remained unchanged. Conversely, LPS increased TLR4 in fibroblasts, but not in odontoblast-like cells, whereas TLR2 expression remained unchanged. CXCL2 and CXCL10 genes were increased by LTA only in odontoblast-like cells, while LPS increased CCL7, CCL26 and CXCL11 only in fibroblasts. Supernatants of stimulated cultures increased migration of immature dendritic cells compared to controls, odontoblast-like cells being more potent attractants than fibroblasts. Conclusion: Odontoblasts and pulp fibroblasts might differ in their immune responses to oral micro-organisms that invade the pulp tissue. Supported by the French Ministery of Higher Education and Research.