The response of human gingival epithelial cells to toll-like receptor ligands and nicotine

Abstract

Human gingival epithelial cells (HGECs) are strategically placed cells of periodontium. They continually expose to oral commensal, pathogenic bacteria as well as harmful agents and their response is important for keeping homeostasis. Human β-defensin 2 (HBD-2) is recognized as an important anti-microbial peptide and the major source is HGECs. In the present study, we demonstrated that HGECs from healthy periodontal tissues clearly expressed mRNA of TLRs 1, 2, 3, 5, 9, 10 and minimally expressed TLR4, but did not express TLRs 7 and 8. Stimulation of HGECs with highly purified TLR2 ligand (P. gingivalis LPS), TLR3 ligand (poly I:C), and TLR5 ligand (Salmonella typhimurium flagellin) led to expression of HBD-2 as measured by RT-PCR. A potent TLR 9 ligand, CpG ODN 2006 had no effect, although HGECs showed a detectable TLR9 mRNA expression. Combination of key periodontopathic: P. gingivalis LPS and pro-inflammatory cytokine: TNF- α significantly enhanced HBD-2 expression in HGECs as compared to a single-stimulation. Cigarette smoking has a strong association with periodontitis. Nicotine, a major component of cigarette smoke, is known to have several biologic effects in suppressing immunological defense mechanism. Our study is the first to report the effect of nicotine on an innate immune response of HGECs. Treatment of nicotine at a non-toxic dose led to significantly down-regulated HBD-2 expression by HGECs in response to P. gingivalis LPS and TNF- α as compared to the non-treatment (p<0.05). Overall our results suggest a critical role of HGECs in orchestrating the innate immune responses of periodontal tissue via TLR signaling. The response of HGECs specifically, in HBD-2 production could be suppressed by nicotine, therefore well supporting the concept of smoking as an important risk factor in periodontitis.