Lipopolysaccharide-binding protein inhibits toll-like receptor 2 activation by lipoteichoic acid in human odontoblast-like cells

Abstract

Introduction: Previous studies have suggested that odontoblasts sense gram-positive bacteria components through Toll-like receptor 2 (TLR2) and trigger dental pulp immunity by producing proinflammatory cytokines. Currently, the factors that modulate odontoblast TLR2 activation are unknown. Our aim was to investigate lipopolysaccharide-binding protein (LBP) effects on the TLR2-mediated odontoblast response.

Methods: Human odontoblast-like cells were stimulated with lipoteichoic acid (LTA) (a TLR2 ligand), LBP, CD14 (a TLR2 cofactor), or various combinations of LTA/LBP, LTA/CD14, or LTA/CD14/LBP. CXCL8, IL6, and TLR2 gene expression was assessed by real-time polymerase chain reaction. CXCL8 and interleukin (IL)-6 production was determined by enzyme-linked immunosorbent assay in culture supernatants of cells stimulated with LTA, LTA/CD14, or LTA/CD14/LBP. LBP effects on nuclear factor kappa B (NF-κB), p38, JNK, ERK, STAT3, and p70S6 signaling pathways were determined in LTA-stimulated odontoblast-like cells with a multiplex biometric immunoassay. LBP effects were compared with specific inhibitors of these signaling pathways. LBP transcript and protein were investigated in vivo in healthy and inflamed dental pulps by real-time polymerase chain reaction and immunohistochemistry.

Results: Activation of CXCL8, IL6, and TLR2 gene expression and CXCL8 and IL-6 secretion in LTA- and LTA/CD14-stimulated odontoblast-like cells was significantly decreased by LBP. LBP inhibited NF-κB and p38 signaling pathways in LTA-stimulated cells in a similar way to NF-κB and p38 inhibitors. LBP transcript and protein were detected in vivo in inflamed dental pulps but not in healthy ones.

Conclusions: These results demonstrate that LBP reduces TLR2-dependent production of inflammatory cytokines by odontoblast-like cells. We suggest that in this way it could modulate host defense in human dental pulp.

Keywords: CD14; CXCL8; IL-6; LBP; NF-κB; Toll-like receptor; human dental pulp; innate immunity; p38; pathogen-associated molecular pattern.