Chronic periodontitis is ail inflammatory disease affecting periodontal connective tissues and alveolar bone. Proinflammatory mediators induced by periodontal pathogens play vital roles in the initiation and progression of the disease. In this study, we examined whether Prevotella intermedia induces proinflammatory cytokines expression in human periodontal ligament cells (hPDLs). The mRNA expression and protein production were determined by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbant assay (ELISA) respectively. P. intermedia treatment dose- and time-dependently increased IL-6, IL-8 and M-CSF, but not IL-I beta and TNF alpha mRNA expression and protein secretion. Preincubation of hPDLs with extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38 kinase and phosphatidylinositol 3-kinase (PI3K) inhibitors PD98059, SP600125, SB203580 and LY294002 resulted in significant reduction in P. intermedia-induced IL-6, IL-8 and M-CSF expression. Blocking the synthesis of prostaglandin E-2 (PGE(2)) by indomethacin also abolished the stimulatory effects of P. intermedia oil cytokines expression. Our results indicate that P. intermedia induces proinflammatory cytokines through MAPKs and PI3K signaling pathways, and PGE2 is involved in the P. intermedia-induced proinflammatory cytokines upregulation. (C) 2009 Elsevier Inc. All rights reserved.