Mechanisms of Actinobacillus actinomycetemcomitans-induced expression of interleukin-8 in gingival epithelial cells.
BACKGROUND
Gingival epithelial cells (GEC) are the first cells of the periodontium to encounter known periodontal pathogens, such as Actinobacillus actinomycetemcomitans (A.a.) and, therefore, the role of this pathogen in the initiation of the inflammatory response is critical. However, little is known about the interactions of A.a. with GEC. In the present study, the mechanisms by which extracts from A.a. induced expression of the chemotactic cytokine interleukin-8 (IL-8) in GEC, in vitro, were examined.


METHODS
An established GEC line, PP, was co-cultured with sonicated extracts of A.a. under various in vitro experimental conditions, and the IL-8 secretion was determined with enzyme-linked immunosorbent assay.


RESULTS
A.a. extracts induced a time- and dose-dependent expression of IL-8 from the cells. Dose-response studies indicated that the highest IL-8 secretion (7-fold, P < 0.01) was at the level of 50 micrograms/ml of A.a. extract. Time-course studies revealed a dramatic increase of IL-8 expression after 12 hours of continuous stimulation. Pretreatment with polymyxin B (lipopolysaccharide [LPS] inhibitor) did not reduce the IL-8 expression induced by A.a. extracts (P > 0.10). The introduction of p38 mitogen-activated protein kinase (MAPK) inhibitor SB 203580 markedly inhibited (> 75%, P < 0.01) A.a.-induced expression of IL-8. It is concluded that A.a. extracts upregulated the basal IL-8 expression in GEC.


CONCLUSIONS
The effect was LPS-independent and involved a p38 MAPK signal transducing pathway. Understanding mechanisms of proinflammatory cytokine induction is important in periodontal pathology as it may lead to novel therapeutic approaches for periodontitis, thus controlling host inflammatory responses.
Sfakianakis
A
A
Department of Periodontology, School of Dental Medicine, University of Connecticut, Farmington, CT, USA.
Barr
C E
CE
Kreutzer
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D
D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002460:Cell Line; D004396:Coloring Agents; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D004847:Epithelial Cells / Q000276:immunology / Q000382:microbiology; D004926:Escherichia coli; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D005881:Gingiva / Q000276:immunology* / Q000382:microbiology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D016209:Interleukin-8 / Q000235:genetics* / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000276:immunology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000276:immunology; D011112:Polymyxin B / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D015398:Signal Transduction; D013223:Statistics as Topic; D013997:Time Factors; D015854:Up-Regulation; D048051:p38 Mitogen-Activated Protein Kinases
D000900:Anti-Bacterial Agents; D004396:Coloring Agents; D004791:Enzyme Inhibitors; D007093:Imidazoles; D016209:Interleukin-8; D008070:Lipopolysaccharides; D011725:Pyridines; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D011112:Polymyxin B; C093642:SB 203580