Periodontal disease is the major cause of adult tooth loss and is commonly characterized by a chronic inflammation caused by infection of oral bacteria. Porphyromonas gingivalis ( P. gingivalis ) is one of the suspected periodontopathic bacteria and is frequently isolated from the periodontal pockets of patients with chronic periodontal disease. The lipopolysaccharide (LPS) of P. gingivalis is a key factor in the development of periodontitis. Gingival fibroblasts, which are the major constituents of gingival connective tissue, may directly interact with bacteria and bacterial products, including LPS, in periodontitis lesions. It is suggested that gingival fibroblasts play an important role in the host responses to LPS in periodontal disease. P. gingivalis LPS enhances the production of inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8, and tumor necrosis factor alpha (TNF-␣ ) in gingival fibroblasts. However, the receptor that binds with P. gingivalisLPS on gingival fibroblasts remained unknown for many years. Recently, it was demonstrated that P. gingivalis LPS binds to gingival fibroblasts. It was also found that gingival fibroblasts express CD14, Toll-like receptor 4 (TLR4), and myeloid differentiation primary response gene 88 (MyD88). P. gingivalis LPS treatment of gingival fibroblasts activates several intracellular proteins, including protein tyrosine kinases, and up-regulates the expression of monocyte chemoattractant protein-1 (MCP-1), extracellular signal-regulated kinase 1 (ERK1), and signal-regulated kinase 2 (ERK2), IL-1 receptor-associated kinase (IRAK), nuclear factor-B (NF-B), and activating protein-1 (AP-1). These results suggest that the binding of P. gingivalis LPS to CD14 and TLR4 on gingival fibroblasts activates various second-messenger systems. In this article, we review recent findings on the signaling pathways induced by the binding of P. gingivalis LPS to CD14 and Toll-like receptors (TLRs) in gingival fibroblasts.

Transforming growth factor /3 (TGF (3),t originally isolated from platelets as a 25-kD peptide (1, 2), has been shown to be a product of other inflammatory cells, including lymphocytes (3, 4) and macrophages (5, 6), and to have potent immunomodulatory effects (7). Although five different forms of TGFJ3 have now been characterized (1), only TGF01 and its homologue, TGF02 (8, 9), have thus far been identified in hemopoietic cells (6). Each ofthese peptides has been cloned, demonstrating that TGF01 is encoded as a 390 amino acid precursor (10), TGFs2 as a 412 amino acid precursor (11,12), and that both have a signal peptide of 20-23 amino acids at the NH2 terminus . The processed 112 amino acid chains of the two peptides share 72% sequence homology and appear to bind equally well to TGFS class III receptors (13), although TGFS1 binds with greater affinity than TGF02 to class I and II receptors (14, 15). Interestingly, lymphoid cells appear to possess only class I and II TGF,6 receptors (16), although in vitro, lymphocyte and monocyte responses to TGF01 and 02 appear comparable (6,17,18). The secretion of TGFa peptides by lymphocytes and monocytes only after activation (3-6) implicates these polypeptides in the evolution of immunologic processes, and in recent studies TGFR has been identified in chronic inflammatory tissues (19)(20)(21)(22), including the synovium of rheumatoid arthritis patients (7,22) and in experimentally induced arthritis in rodents (22). To define the role of TGFS in such lesions, we injected natural or recombinant TGF0 directly into the joint cavity of Lewis rats and monitored its effect on cellular recruitment and activation, and on its potential modulation of pathogenic effects. TGF01 and TGF02 were both found to induce synovial erythema, swelling, and leukocyte infiltration . The infiltrating mononuclear cells, activated to express growth factors, likely regulated the pronounced synovial hyperplasia that was apparent within 2-3 d. Based on these observations, it appears that TGF0, released by platelets and inflammatory cells in the arthritic synovium, may directly contribute to the events associated with inflammatory arthropathies.

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Dental implant surgery commonly proceeds in two stages. It is generally accepted that bone loss around implants does not occur at stage-II surgery because implants do not receive mechanical loading. However, early marginal bone loss around implants occasionally does occur during the healing period. Genetic polymorphisms in the interleukin-1 (IL-1) gene have been reported to be important for bone homeostasis and susceptibility to bone disease. We therefore investigated whether the idiopathic early marginal bone loss around implants is related to polymorphisms in the IL-1 gene. We performed a case-control study. Patients demonstrating marginal bone loss around implants at stage-II surgery were designated as the 'marginal bone loss (+)' group and those without bone loss as the 'marginal bone loss (-)' group. Polymorphisms of the IL-1alpha and IL-1beta genes (IL-1A-889, IL-1B-511 and IL-1B+3954) were detected by restriction fragment length polymorphism using NcoI, AvaI and TaqI after polymerase chain reactions. A total of 251 implants were placed in 39 patients. Marginal bone loss was observed in 36 implants. The patients with IL-1B-511 2/2 genotype exhibited a significantly higher occurrence of marginal bone loss than those with IL-1B-511 1/1 or 1/2 genotypes (OR=5.63; 95% CI=1.20-26.42; P=0.033). Multiple logistic regression analyses showed a markedly increased odds ratio (OR=10.86; 95% CI=1.64-71.90) in IL-1B-511 2/2 genotype carriers, while ORs of the other risk factors for bone loss, such as age, smoking status, post-menopausal women and bone quality, remained between 0.44 and 6.20. There was no significant difference in the distributions of the IL-1B+3954 and IL-1 A-889 genotypes between cases and controls. These data suggest that the IL-1B-511 2/2 genotype has a significant association with the incidence of early marginal bone loss around endosseous implants.