Expression of TLR4 co-factors in healthy and inflammatory dental pulps

Human dental pulp has been shown to express the ten pattern recognition molecules of the Toll-like receptor (TLR) family and is thus well equipped to detect pathogens invading the tissue. Among them, TLR4, the lipopolysaccharide sensing receptor, requires co-factors to initiate intracellular signaling pathways that trigger innate and/or adaptive immune responses. These co-factors include lipopolysaccharide-binding protein (LBP), CD14 and MD2, which are involved in LPS sensing by TLR4, and the cytoplasmic TLR4-binding adaptor MyD88. How these molecules are modulated in human dental pulp challenged by cariogenic bacteria remains unknown. Objective: To determine whether LBP, CD14, MD2 and MyD88 are differentially expressed in inflamed dental pulps under carious lesions compared to healthy ones. Methods: Healthy and carious human molars were collected with informed consent of the patients, in accordance with the Declaration of Helsinki and following a protocol approved by the local ethics committee. Inflammatory pulps were taken from teeth with clinical features of irreversible acute pulpitis. LBP, CD14, MD2 and MyD88 gene expression was assessed in six healthy and six inflammatory pulp samples using real-time PCR. Results were expressed as mean values ± SD and statistical analysis was determined with Student's t test. LBP gene expression was also assessed by conventional PCR. Results: Gene expression was significantly increased in inflammatory pulps for CD14 (7.27-fold, p = 0.001), MD2 (3.08-fold, p = 0.001) and MyD88 (3.48-fold, p = 0.047). LBP gene expression was not detected in healthy pulps, but detected in inflammatory ones. Conclusion: These data suggest that up-regulation of TLR4 co-factors is part of the dental pulp immune response to cariogenic bacteria and likely important in protecting the human pulp tissue from the deleterious effects of these pathogens. Supported by the French Ministery of Higher Education and Research and Région Rhone-Alpes.