title: Mechanisms of IL-8 suppression by Treponema denticola in gingival epithelial cells.
abstract: The purpose of this study was to investigate the mechanism(s) of interleukin (IL)-8 suppression by Treponema denticola, one of the major periodontal pathogens, in gingival epithelial cells. Immortalized human gingival epithelial HOK-16B cells were infected with wild-type (WT), dentilisin-deficient (K1) or flagellin-deficient (flgE) T. denticola in the presence or absence of 2% human serum for 24 h. The levels of IL-8 expression were measured with real-time reverse transcription PCR and ELISA. In the absence of human serum, the WT and flgE, but not K1, substantially reduced not only the levels of IL-8 protein but also of IL-8 mRNA. Such downregulation of IL-8 mRNA was independent of bacterial invasion. Degradation of cytokine mixture by the WT, K1 and flgE revealed dentilisin-dependent preferential degradation of tumor necrosis factor (TNF)-α, an IL-8-inducing cytokine. WT and flgE significantly decreased the levels of TNFα secreted by HOK-16B cells, suggesting modulation of IL-8 through dentilisin-mediated degradation of TNFα. The addition of human serum to the culture potentiated the suppressive effect of T. denticola, resulting in substantial reductions of IL-8 and TNFα levels, even by K1. The serum-dependent effects of T. denticola were attributed to its ability to suppress the accumulation of intracellular reactive-oxygen species (ROS), a group of ubiquitous signaling molecules. Pretreatment with an antioxidant suppressed TNFα-induced IL-8 expression, confirming the role of ROS in TNFα signaling. Collectively, T. denticola targeted a key inflammatory cytokine and its signaling molecule to modulate the host innate immune response, which provides a new insight into modulation of host immunity by a periodontal pathogen.
authors.affiliation: Department of Immunology and Molecular Microbiology, BK21 CLS, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea.
authors.forename: Ah-ram
authors.initials: AR
authors.lastname: Jo
authors.affiliation: Department of Immunology and Molecular Microbiology, BK21 CLS, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea.
authors.forename: Keum Jin
authors.initials: KJ
authors.lastname: Baek
authors.affiliation: Department of Immunology and Molecular Microbiology, BK21 CLS, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea.
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Shin
authors.affiliation: Department of Immunology and Molecular Microbiology, BK21 CLS, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Republic of Korea.
authors.forename: Youngnim
authors.initials: Y
authors.lastname: Choi
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D002918:Chymotrypsin / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000276:immunology*; D005881:Gingiva / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D016209:Interleukin-8 / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D015603:Keratinocytes / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D010447:Peptide Hydrolases; D059748:Proteolysis; D017382:Reactive Oxygen Species / Q000276:immunology / Q000378:metabolism; D048373:Treponema denticola / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D014211:Treponemal Infections / Q000235:genetics / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C508606:CXCL8 protein, human; C097681:FlgE protein, Bacteria; D016209:Interleukin-8; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; D010447:Peptide Hydrolases; C102570:dentilisin; D002918:Chymotrypsin