Toll-like receptor 2 activation by lipoteichoic acid induces differential production of pro-inflammatory cytokines in human odontoblasts, dental pulp fibroblasts and immature dendritic cells

Odontoblasts, dental pulp fibroblasts and immature dendritic cells (DCs) have been involved in the human dental pulp immune response to oral pathogens that invade dentine during the caries process. How they regulate the inflammatory response to Gram-positive bacteria remains nevertheless largely unknown. In this study we investigated the production of the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β) and interleukin-8 (CXCL8) in these three cell types upon stimulation with lipoteichoic acid (LTA), a cell wall component of Gram-positive bacteria that activates the pattern recognition molecule Toll-like receptor 2 (TLR2). We observed that TNF-α gene expression was up-regulated in all LTA-stimulated cell types. IL-1β gene expression was not or barely detectable in odontoblast-like cells and pulp fibroblasts when stimulated or not, but was expressed in immature DCs and increased upon stimulation. TNF-α and IL-1β proteins were detected in DC culture supernatants but not in odontoblast-like cell and pulp fibroblast ones. CXCL8 gene and protein were clearly expressed and increased in the three cell types upon LTA stimulation. These data indicate that LTA-dependent TLR2 activation in odontoblasts and pulp fibroblasts, in contrast to immature DCs, does not lead to significant TNF-α and IL-1β production, but that all three cell types influence the pulp inflammatory/immune response through CXCL8 synthesis and secretion.