Smoking modulates human gingival epithelial cell responses

Objectives: We investigated a critical role of human gingival epithelial cells (HGECs) in orchestrating the innate immune responses of periodontal tissues via Toll-like receptor (TLR) signaling and evaluated the immune modulating effect of cigarette smoke extract (CSE)on these HGEC responses.

Methods: Primary HGEC culture was establsihed from health gingival biopsies and their TLR expression was analyzed by RT PCR. The responses of HGECs to specific-purified TLR ligand and/or tumor necrosis factor(TNF)-alpha were measured by the expression of anti-microbial peptide human beta defensin 2 (HBD-2)(RT-PCR) and pro-inflammatory cytokine IL-8 (ELISA). The effect of CSE and nicotine on stimulated HGECs was also evaluated.

Results: HGECs expressed mRNA of TLRs 1,2,3,5,6,9,10, and minimally of TLR4, but not of TLRs7 or 8. Stimulation of HGECs with highly purified TLR2 ligand (LPS derived from a key periodontal pathogen Porphyromonas gingivalis, TLR3 ligand (poly(I:C)), and TLR5 ligand (Samonella typhimurium flagellin) led to expression of HBD-2 as well as of IL-8. A potent TLR9 ligand, CpGODN2006 had no such effect despite detectable TLR9 expression. Enhancement of HBD-2 and IL-8 was observed in HGECs after combined stimulation with P. gingivalis LPS and TNF-alpha, as compared with single stimulation. When CSE was added into the stimulated HGEC culture, HBD-2 was markedly reduced, whereas IL-8 was markely increased. These effects were also observed, but markedly attenuated, upon treatment with nicotine, a major component of cigarette smoke.

Conclusions: Cigarette smoke exposure could modulate the HGEC responses by suppressing HBD-2 and enhancing IL-8 production, therefore disrupting the homeostasis and increasing susceptibility to periodontal disease. This work was supported by Thai Health Grant, Government Research Budget (GRB02503202), and the 90th anniversary of Chulalongkorn University.