title: Involvement of Toll-like receptor 2 in apoptosis of Aggregatibacter actinomycetemcomitans-infected THP-1 cells.
abstract: OBJECTIVE
  Aggregatibacter (Actinobacillus) actinomycetemcomitans is a gram-negative bacterium that has been associated with aggressive periodontitis. A actinomycetemcomitans infection induces apoptosis in the human monocytic cell line THP-1, and p38 mitogen-activated protein kinase (p38) activity and tumor necrosis factor-α (TNF-α) production are enhanced by A actinomycetemcomitans infection. However, mechanisms governing the recognition of A actinomycetemcomitans by monocytes during apoptosis have not been elucidated. A actinomycetemcomitans cell wall components stimulate Toll-like receptor (TLR)2 and/or TLR4. The authors examined whether TLR2 and/or TLR4 were involved in the apoptosis of A actinomycetemcomitans-infected THP-1 cells.
  
  
  METHODS
  A actinomycetemcomitans-infected THP-1 cells were transferred to six-well culture plates and incubated for 0 to 6 hours. In some experiments, THP-1 cells were incubated with anti-TLR2, anti-TLR4, or isotype control antibody (10 μg/mL) for 30 minutes prior to A actinomycetemcomitans infection. Expression of messenger RNA (mRNA) was examined by reverse transcription-polymerase chain reaction. Intracellular bacteria recovered from A actinomycetemcomitans-infected cells and apoptotic cells were detected by APOPercentage dye (Biocolor Ltd, Northern Ireland, UK) staining. Cellular p38 activity and TNF-α production were assessed with enzyme-linked immunosorbent assay.
  
  
  RESULTS
  The expression of TLR2 mRNA was increased by A actinomycetemcomitans infection. Phagocytosis and apoptosis in A actinomycetemcomitans-infected THP-1 cells were inhibited by the addition of anti-TLR2 antibody. Also, anti-TLR2 antibody suppressed the activation of p38 and production of TNF-α in A actinomycetemcomitans-infected THP-1 cells.
  
  
  CONCLUSIONS
  These results suggest that A actinomycetemcomitans induces increased expression of TLR2, leading to phagocytosis and apoptosis of THP-1 cells via p38 activation and TNF-α production.
authors.affiliation: Division of Periodontology and Endodontology, Department of Oral Rehabilitation, School of Dentistry, Health Sciences University of Hokkaido, 1757 Kanazawa, Ishikari-Tobetsu, Hokkaido 061-0293, Japan. satsuki@hoku-iryo-u.ac.jp
authors.forename: Satsuki
authors.initials: S
authors.lastname: Kato
authors.forename: Keisuke
authors.initials: K
authors.lastname: Nakashima
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Nagasawa
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Abiko
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Furuichi
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000276:immunology* / Q000472:pathogenicity*; D017209:Apoptosis; D002460:Cell Line; D020869:Gene Expression Profiling; D006801:Humans; D009000:Monocytes / Q000276:immunology* / Q000382:microbiology* / Q000502:physiology; D051195:Toll-Like Receptor 2 / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D048051:p38 Mitogen-Activated Protein Kinases / Q000096:biosynthesis
chemical_list: C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases