The interplay of lipopolysaccharide-binding protein and cytokines in periodontal health and disease

Aim: Periodontal pathogenesis is characterized by Gram-negative bacteria activation of series of pro- and anti-inflammatory cytokines from host cells through the pathway of lipopolysaccharide (LPS), LPS-binding protein (LBP) and CD14. The present study investigated the expression profiles of interleukin (IL)-1 β and IL-10 in periodontal health and disease, and examined the effects of Escherichia coli LPS and LBP interaction on the expression of IL-1 β and IL-10 by human gingival fibroblasts (HGF).
Material and Methods: Gingival biopsies were collected from 44 subjects with chronic periodontitis and 15 periodontally healthy subjects. The expression of IL-1 β and IL-10 was detected by immunohistochemistry. The mRNA expression of IL-1 β and IL-10 in HGF was detected by RT-PCR with or without recombinant human LBP (rhLBP), while the peptides were analysed by an enzyme-linked immunosorbent assay.
Results: IL-1 β was detected in both oral sulcular epithelia of healthy controls and periodontal pocket epithelia of patients. IL-10 was mainly expressed in the intercellular spaces of connective tissues. IL-1 β displayed a reverse pattern of expression levels with reference to IL-10, and a negative correlation existed between LBP and the ratio of IL-1 β /IL-10. rhLBP suppressed E. coli LPS-induced IL-1 β expression by HGF.
Conclusion: An appropriate interplay of LBP and cytokines may have a beneficial effect on innate host defence, thereby contributing to periodontal homeostasis.     

Interferon-γ stimulates CD14, TLR2 and TLR4 mRNA expression in gingival fibroblasts increasing responsiveness to bacterial challenge

ObjectiveTo investigate the potential effects of IFN-03A5 on the responsiveness of human gingival fibroblasts to bacterial challenge.DesignmRNA and protein expression of CD14, TLR2 and TLR4 in human gingival fibroblasts was detected by quantitative polymerase chain reaction (Q-PCR) and flow cytometry. The effect of preincubation with IFN-03A5 on subsequent bacterial LPS-induced expression of IL-6 and IL-8 by gingival fibroblasts was determined by ELISA. Bacterial LPS-induced IκBα degradation in human gingival fibroblasts was investigated by western blot.ResultsHuman gingival fibroblasts express CD14, TLR2 and TLR4 mRNAs. IFN-03A5, but not IL-103B2, induced mRNA expression of all three receptors and the expression of membrane bound CD14 protein. Pre-incubation of fibroblasts with IFN-03A5 and subsequent stimulation with Escherichia coli LPS or Porphyromonas gingivalis LPS led to increased production of IL-6 and IL-8. LPS-induced pro-inflammatory cytokine production was abrogated by a blocking antibody to CD14. Both E. coli LPS and P. gingivalis LPS induced IκBα degradation in human gingival fibroblasts.ConclusionOur data indicate that IFN-03A5 primes human gingival fibroblasts, through the upregulation of CD14 expression, which results in increased responsiveness to bacterial LPS challenge, as determined by pro-inflammatory cytokine production.     

LPS刺激牙龈成纤维细胞IL-6、IL-8的产生和膜表面受体CD14的表达

目的：观察牙龈卟啉菌和中间普氏菌LPS刺激人牙龈成纤维细胞合成IL-6、IL-8的能力，并了解LPS是否通过细胞表面膜受体mCD14介导信号传导。方法：4种浓度的LPS在不同时间段。分别作用于体外培养的人牙龈成纤维细胞。采用ELISA检测IL-6、IL-8含量的变化，同时利用逆转录聚合酶链反应，进一步观察IL-6、IL-8，CD14在mRNA水平的表达特征。结果：ELISA和RT-PCR的反应结果证实，受LPS的刺激，细胞合成和分泌细胞因子IL-6、IL-8的能力明显增强，但未检测到细胞表面膜受体mCD14mRNA的表达。结论：LPS用于牙龈成纤维细胞合成和分泌细胞因子没有通过膜受体mCD14的介导。     

Actinobacillus actinomycetemcomitans lipopolysaccharide stimulates collagen phagocytosis by human gingival fibroblasts

Introduction:  Collagen phagocytosis by fibroblasts is involved in the intracellular pathway related to collagen breakdown in soft connective tissues. The possible role of lipopolysaccharide (LPS) in regulating this fibroblast function has not been elucidated so we investigated the effect of LPS from Actinobacillus actinomycetemcomitans , a periodontopathic bacterium, on collagen phagocytic activity in human gingival fibroblasts and associated regulatory mechanisms.
Methods:  LPS pretreatment stimulated binding of collagen-coated beads to cells and, subsequently, their internalization.
Results:  The LPS-activated collagen phagocytic process was enhanced in the presence of the soluble form of CD14 (sCD14) or LPS-binding protein (LBP), while the LPS/LBP treatment activated Akt and induced actin reorganization. Furthermore, these LPS/LBP-induced effects were partially suppressed by adding phosphatidyl-inositol-3 kinase (PI3K) inhibitors.
Conclusion:  These results suggest that A. actinomycetemcomitans LPS disturbs the homeostasis of collagen metabolism within gingival tissue by facilitating collagen phagocytosis by gingival fibroblasts, and serum sCD14 and LBP positively regulate the action of LPS. In addition, the PI3K/Akt signaling is thought to partially mediate the LPS/LBP-stimulated collagen phagocytic pathway, which may be dependent on actin cytoskeletal rearrangement.     

Immunochemical detection of CD14 on human gingival fibroblasts in vitro

The activation of monocytes and macrophages induced by lipopolysaccharide has been shown to contribute to the binding of lipopolysaccharide and lipopolysaccharide-binding protein complex to the cell surface CD14 molecule. To clarify the mechanism of the lipopolysaccharide-induced modulation of the function of gingival fibroblasts, we investigated the effect of anti-CD14 on interleukin 6 (IL-6) production on human gingival fibroblasts in vitro. Immunochemical staining revealed weak positivity for CD14 on fibroblasts from healthy gingiva, while strong positivity for CD14 was found on fibroblasts from inflamed gingiva. Western blot profiles of the fibroblasts and monocytes showed a CD14-positive reaction at 55 kDa. Fluorescein isothiocyanate-conjugated Escherichia coli lipopolysaccharide bound to fibroblasts more strongly in the presence of 10% fetal bovine serum than without serum. This binding, as well as IL-6 production, was blocked by anti-CD14 monoclonal antibody. The results showed that CD14 was present on human gingival fibroblasts, which suggests that lipopolysaccharide modulation of gingival fibroblast function depends on CD14.     

Soluble CD14-dependent intercellular adhesion molecular-1 induction by Porphyromonas gingivalis lipopolysaccharide in human gingival fibroblasts.

BACKGROUND: Intercellular adhesion molecule-1 (ICAM-1) is involved in the accumulation and activation of leukocytes in inflammatory sites through binding to beta2 integrins expressed on leukocytes. We investigated whether or not lipopolysaccharide (LPS) derived from the periodontopathic bacterium Porphyromonas gingiualis affects ICAM-1 expression on human gingival fibroblasts (HGF). CD14 is a receptor for LPS on monocytes and macrophages and is also present in serum as a soluble protein. We further examined the effects of serum and soluble CD14 (sCD14) on ICAM-1 expression in HGF stimulated with P. gingivalis LPS. METHODS: HGF were prepared from explants of human gingival tissues and incubated in 96-well culture plates before LPS stimulation. LPS derived from Escherichia coli O55:B5 and P. gingivalis ATCC 33277 LPS were employed. sCD14 was purified from normal human serum (NHS) by affinity chromatography using an anti-CD14 monoclonal antibody. ICAM-1 expression on HGF was measured by a cell enzyme-linked immunosorbent assay. RESULTS: P. gingivalis LPS induced ICAM-1 on HGF in a dose-dependent manner in the presence of either 10% fetal calf serum or 2% NHS. The ability of P. gingivalis LPS to induce ICAM-1 was comparable to that of LPS from E. coli at high LPS concentrations. In the absence of NHS, ICAM-1 induction was negligible in HGF stimulated with P. gingivalis LPS, reaching a maximum at 2% NHS. The ICAM-1 expression induced by P. gingivalis LPS was inhibited by a monoclonal antibody to CD14. Supplementation of serum-free medium with sCD14 alone restored the capacity of HGF to respond to P. gingivalis LPS. CONCLUSIONS: These results indicate that P. gingivalis LPS induces ICAM-1 expression in HGF in an sCD14-dependent manner. The overexpression of ICAM-1 on fibroblasts in gingiva induced by P. gingivalis LPS seems to be involved in the retention of inflammatory cells in periodontitis lesions.     

Contrasting responses of human gingival and periodontal ligament fibroblasts to bacterial cell-surface components through the CD14/Toll-like receptor system

We compared human periodontal ligament fibroblasts with human gingival fibroblasts isolated from the same donor to examine interleukin-8 (IL-8) responses of the cells to Salmonella lipopolysaccharide, a water-soluble peptidoglycan from Staphylococcus epidermidis and the synthetic muramyldipeptide, with special reference to the possible involvement of the CD14/Toll-like receptor (TLR) system of the cells in the responses. Human gingival fibroblasts expressed CD14 on their surfaces and strongly expressed CD14 mRNA, while human periodontal ligament fibroblasts showed considerably lower levels of expression in both respects. Both cells expressed mRNA of TLR-related molecules, i.e. TLR2, TLR4, MD-2 and MyD88, although human periodontal ligament fibroblasts expressed TLR2 more strongly than human gingival fibroblasts. Human gingival fibroblasts exhibited a stronger IL-8 response than human periodontal ligament fibroblasts to lipopolysaccharide, while human periodontal ligament fibroblasts exhibited a response comparable to, or slightly stronger than, that of human gingival fibroblasts to S. epidermidis peptidoglycan and muramyldipeptide. The IL-8 responses of both cells to lipopolysaccharide and S. epidermidis peptidoglycan were completely inhibited by antihuman CD14 monoclonal antibody (MAb). The responses of both cells to lipopolysaccaride were significantly inhibited by antihuman TLR4 MAb, while those to S. epidermidis peptidoglycan were inhibited by antihuman TLR2 MAb. In contrast, muramyldipeptide activated both types of cells in a TLR2- and TLR4-independent manner, although the activities of muramyldipeptide on human gingival fibroblasts, but not human periodontal ligament fibroblasts, were significantly inhibited by anti-CD14 MAb.     

Retinoic acid-inducible gene-I is induced in gingival fibroblasts by lipopolysaccharide or poly IC: possible roles in interleukin-1beta, -6 and -8 expression

Retinoic acid-inducible gene-I (RIG-I) is a member of the DExH family of proteins, and little is known of its biological function in the oral region. We previously reported that interleukin 1beta (IL-1beta) induced RIG-I expression in gingival fibroblasts. In this study, we studied the mechanism of RIG-I expression induced by lipopolysaccharide (LPS) or double-stranded RNA (dsRNA) in gingival fibroblasts. We also addressed the role of RIG-I in the expression of IL-1beta, IL-6 and IL-8 in gingival fibroblasts stimulated with LPS or dsRNA. We stimulated cultured human gingival fibroblasts with LPS or dsRNA, and examined the expression of RIG-I mRNA and protein. The effect of cycloheximide, a protein synthesis inhibitor, on RIG-I induction by these stimuli was examined. The expression of IL-1beta, IL-6 and IL-8 in gingival fibroblasts transfected with RIG-I cDNA stimulated with LPS or dsRNA was examined. LPS or dsRNA induced the expression of mRNA and protein for RIG-I in concentration- and time-dependent manners. We also examined the localization of RIG-I, and found that it was expressed in cytoplasm. Cycloheximide did not suppress the LPS or dsRNA-induced RIG-I expression. Introduction of RIG-I cDNA into gingival fibroblasts resulted in enhanced expression of IL-1beta, IL-6 and IL-8; moreover, overexpression of RIG-I stimulated with LPS or dsRNA synergistically increased expression of IL-1beta, IL-6 and IL-8. RIG-I may have important roles in the innate immune response in the regulation of IL-1beta, IL-6 and IL-8 expression in gingival fibroblasts in response to LPS and dsRNA.     

Porphyromonas gingivalis induction of mediator and cytokine secretion by human gingival fibroblasts

We hypothesized that bacterial viability and strain characteristics of Porphyromonas gingivalis could affect the induction of pro-inflammatory mediator secretion by human gingival fibroblast cultures. Both killed and viable P. gingivalis elicited production of prostaglandin E2, interleukin-1 beta (IL-1 beta), IL-6 and IL-8, although killed P. gingivalis induced generally higher levels, particularly IL-6 and IL-8, compared with the viable bacteria. P. gingivalis strains, which exhibited wild-type levels of trypsin-like protease activity, stimulated human gingival fibroblasts to secrete increased levels of prostaglandin E2 and IL-1 beta, although minimal levels of IL-6 and IL-8 were noted in supernatants from the gingival fibroblast cells. P. gingivalis strains BEI and NG4B19, which have either decreased or undetectable levels of trypsin-like protease, respectively, induced significantly greater IL-6 and IL-8 levels in gingival fibroblast cultures compared with the other strains. The ability of antibody to P. gingivalis to alter human gingival fibroblast production of pro-inflammatory mediators was tested using nonhuman primate antisera. Both immune and nonimmune sera altered the P. gingivalis-generated pattern of mediators from the gingival fibroblasts. We conclude that: (i) viable and killed P. gingivalis were capable of inducing various pro-inflammatory cytokines from human gingival fibroblasts; (ii) strain differences in cytokine induction were noted, and the expression of a trypsin-like protease activity was related to decreased extracellular levels of IL-6 and IL-8; and (iii) the presence of serum, particularly with specific antibody to P. gingivalis, significantly altered human gingival fibroblast cytokine production compared with P. gingivalis alone.     

Regulation of cytokine production in human gingival fibroblasts following treatment with nicotine and lipopolysaccharide

BACKGROUND: Patients who smoke are at increased risk for chronic periodontitis (CP). Most studies suggest that the microbial flora in these patients is similar to that found in non-smoking CP patients. Thus, the increased risk for development of CP is not dependent on an altered microbial profile, but rather to some change in the host response to these periopathogens. There is evidence that human gingival fibroblasts (HGF) derived from diseased sites produce greater amounts of interleukin (IL)-6 and IL-8 in vitro than cells derived from healthy sites. This suggests that HGF subpopulations may be selected based upon the inflammatory milieu in which they reside. The hypothesis to be tested was that the combination of nicotine and lipopolysaccharide (LPS) could regulate HGF inflammatory mediator production. METHODS: HGF cell cultures were established from explants derived from 10 patients with CP. HGF cell cultures were stimulated with 1 mM, 1 microM, or 1 nM nicotine +/- Escherichia coli or Porphyromonas gingivalis LPS. At 12, 24, or 48-hour time points, the cells were counted and the supernatant was collected for subsequent IL-6 and IL-8 determination in an enzyme-linked immunosorbent assay. RESULTS: At the 24-hour time point, 1 nM nicotine stimulated IL-6 production compared to control (P=0.02). E. coli LPS alone caused a 3- to 4-fold increase in IL-6 and IL-8 production, whereas P gingivalis LPS did not augment IL-6 or IL-8. A synergistic effect upregulating IL-6 was observed with combined treatment of 1 mM nicotine and E. coli LPS or P gingivalis LPS at the 24-hour time point (P<0.0005 and P=0.002, respectively). Similar effects were seen when IL-8 production was evaluated following HGF stimulation with high doses of nicotine and E. coli LPS or P gingivalis LPS. CONCLUSIONS: These results demonstrate that nicotine by itself can stimulate HGF IL-6 and IL-8 production. Moreover, the combination of high doses of nicotine and either E. coli or P gingivalis LPS can synergistically upregulate cytokine production. These findings support the hypothesis that a proinflammatory fibroblast phenotype may be elicited in an environment enriched with bacterial LPS and nicotine.     

Keratinocyte growth factor (KGF)-1 and -2 protein and gene expression in human gingival fibroblasts

The onset and progression of periodontal disease is associated with significant changes in the epithelial component of the attachment complex. From the early to the advanced stages of periodontal disease increased epithelial cell proliferation, migration and invasion into the surrounding connective tissue takes place. Concomitantly there is a significant increase in proinflammatory cytokine expression in periodontal tissue and quantitative and qualitative changes in the subgingival microflora, including an increase in gram-negative microorganisms. One of the most significant virulence factors of these bacteria is lipopolysaccharide (LPS) connected to the outer membrane. Two important growth factors controlling epithelial behavior are Keratinocyte Growth Factor-1 (KGF-1) and -2 (KGF-2). Connective tissue cells express these growth factors, but only epithelial cells respond to them. We studied the effect of proinflammatory cytokines and LPS on gingival fibroblast expression of KGF-1 and KGF-2 in vitro. Gingival fibroblasts were found to express KGF-1 and -2 in culture but only KGF-1 protein and gene expression was stimulated by serum, in a concentration-dependent manner by proinflammatory cytokines IL-1alpha, IL-1beta, TNF-alpha and IL-6 and LPS isolated from Porphyromonas gingivalis and Escherichia coli. The local increase in proinflammatory cytokine expression and the accumulation of LPS in disease sites may therefore stimulate gingival fibroblast expression of KGF-1. We hypothesize that this local increase in KGF-1 expression may, via a paracrine mechanism, stimulate local epithelial cell proliferation, migration and invasion during the onset and progression of periodontitis.     

Cranberry components inhibit interleukin-6, interleukin-8, and prostaglandin E production by lipopolysaccharide-activated gingival fibroblasts

Periodontitis is a chronic inflammatory disease that affects the tooth supporting tissues. Gingival fibroblasts are the most abundant cells in periodontal tissues and participate actively in the host inflammatory response to periodontopathogens, which is known to mediate local tissue destruction in periodontitis. The aim of this study was to investigate the effect of a proanthocyanidin-enriched cranberry fraction, prepared from cranberry juice concentrate, on inflammatory mediator production by gingival fibroblasts stimulated by the lipopolysaccharide (LPS) of Aggregatibacter actinomycetemcomitans. Interleukin (IL)-6, IL-8, and prostaglandin E(2) (PGE(2)) production by fibroblasts treated with the cranberry fraction and stimulated by A. actinomycetemcomitans LPS was evaluated by enzyme-linked immunosorbent assay. Changes induced by A. actinomycetemcomitans LPS and the cranberry fraction in the expression and phosphorylation state of fibroblast intracellular signaling proteins were characterized by antibody microarrays. The LPS-induced IL-6, IL-8, and PGE(2) responses of gingival fibroblasts were inhibited by treatment with the cranberry fraction. This fraction was found to inhibit fibroblast intracellular signaling proteins, a phenomenon that may lead to a down-regulation of activating protein-1 activity. Cranberry components also reduced cyclooxygenase 2 expression. This study suggests that cranberry juice contains molecules with interesting properties for the development of new host-modulating therapeutic strategies in the adjunctive treatment of periodontitis.     

CD-14和Tool样受体在牙髓卟啉单胞菌脂多糖诱导成骨细胞白细胞介素6表达中的作用

目的 探讨CD-14和Tool样受体（Toll like receptors,TLR）在牙髓卟啉单胞菌（Porphyromonas endodontalis,Pe）脂多糖诱导小鼠成骨细胞白细胞介素6(IL-6)表达中的作用。方法用10 mg/L的Pe-脂多糖分别作用于小鼠成骨细胞MC3T3-E1不同时间,未加Pe-脂多糖的MC3T3-E1为空白对照组。反转录聚合酶链反应(RT-PCR)和酶联免疫吸附试验检测细胞IL-6基因和蛋白的表达,RT-PCR和流式细胞术检测细胞表面CD-14、TLR-2及TLR-4基因和蛋白的表达变化。抗小鼠CD-14、TLR-2及TLR-4抗体预处理细胞后,采用RT-PCR法检测Pe-脂多糖诱导细胞IL-6mRNA表达的变化。应用SPSS 11.0统计软件对结果进行单因素方差分析Dunnett-t检验。结果Pe-脂多糖作用于细胞后,与空白对照组比较细胞IL-6 mRNA和蛋白的表达明显增加,6h时IL-6表达[(36.534±0.574) ng/L]显著高于空白对照组[(11.696±0.672)ng/L)],P＜O.01;空白对照组中CD-14和TLR-4 mRNA呈弱表达,CD-14和TLR-4的阳性细胞率分别为(39.038±3.131)％和( 11.438±0.385)％,加入Pe-脂多糖后CD-14和TLR-4 mRNA表达明显增加,CD-14和TLR-4的阳性细胞率分别增加至(62.407±1.800)％和(21.367±2.271)％,但TLR-2的表达未见明显变化;中和抗体实验证明CD-14或TLR-4抗体均可部分抑制细胞IL-6 mRNA的表达,TLR-2抗体则无此作用。结论Pe-脂多糖作用于成骨细胞MC3T3-E1诱导其炎症因子IL-6的产生依赖于CD-14和TLR-4受体,与TLR-2无关。     

内毒素耐受对人牙龈上皮细胞分泌IL-1β、IL-6和IL-8的影响

目的:观察脂多糖(lipopolysaccharides,LPS)反复刺激细胞,诱导产生的内毒素耐受对人牙龈上皮细胞(human gingival epithelial cells,HGECs)分泌细胞因子IL-1β、IL-6和IL-8的影响。方法:采用1mg/L牙龈卟啉单胞菌(Porphyromonas gingivalis,P.gingivalis)LPS或1mg/L大肠杆菌(Escherichia coli,E.coli)LPS刺激HGECs 24h,洗涤细胞后,分别采用相同的LPS再次刺激24h,构建内毒素耐受模型。采用ELISA技术检测细胞条件培养液中IL-1β、IL-6和IL-8分泌水平的变化。结果:P.gingivalis LPS或E.coli LPS刺激HGECs 24h后,3种细胞因子的分泌水平均较刺激前明显增高(P<0.05)。2种LPS重复刺激,诱导细胞耐受后,IL-6和IL-8的分泌水平较第1次刺激后明显降低(P<0.05),但P.gingivalis LPS重复刺激后,IL-1β的分泌水平与第1次刺激后无明显差别。结论:内毒素耐受能抑制HGECs分泌细胞因子IL-6和IL-8,进而可能影响牙周组织的炎症和免疫反应。     

Differential expression of Class II (DR & DQ) antigens by human gingival Langerhans' cells and keratinocytes in vitro

The expression of the Class II products DR and DQ on human gingival epithelium was examined using immunofluorescence and immunoperoxidase staining. Differential expression of Class II antigens was seen in chronic gingivitis in adults, with T6(+) DR(+) cells being more numerous than T6(+) DQ(+) cells. The periodontopathic organism Fusobacterium nucleatum (FN) induced DQ expression on Langerhans' cells (LC) during in vitro explant culture of gingival tissue. This effect was mimicked by endotoxin (LPS) from F. nucleatum and by E. coli LPS. These results indicate that differential expression of Class II products, a feature of chronic gingival inflammation, may result from the action of LPS on gingival LC.     

Differential expression of Class II (DR & DQ) antigens by human gingival Langerhans' cells and keratinocytes in vitro

The expression of the Class II products DR and DQ on human gingival epithelium was examined using immunofluorescence and immunoperoxidase staining. Differential expression of Class II antigens was seen in chronic gingivitis in adults, with T6(+) DR(+) cells being more numerous than T6(+) DQ(+) cells. The periodontopathic organism Fusobacterium nucleatum (FN) induced DQ expression on Langerhans' cells (LC) during in vitro explain culture of gingival tissue. This effect was mimicked by endotoxin (LPS) from F. nucleatum and by E. coli LPS. These results indicate that differential expression of Class II products, a feature of chronic gingival inflammation, may result from the action of LPS on gingival LC.     

Direct and indirect effects of Porphyromonas gingivalis lipopolysaccharide on interleukin-6 production by human gingival fibroblasts

We examined the production of interleukin-6 (IL-6) by human gingival fibroblasts (ATCC CRL 1292) stimulated with lipopolysaccharide (LPS) from Porphyromonas gingivalis and Escherichia coli, or supernatant of human peripheral blood adherent cell culture medium incubated in the presence of IL-1 and the same two LPS. Confluent monolayers of gingival fibroblasts were incubated with stimulants for 6 h at 37 degrees C in 5% CO2 and air. After removal of stimulants, the cell cultures were incubated for an additional 2 or 24 h in the same environment. At the end of the culture period, supernatants were collected and assayed for IL-6 activity by stimulatory IgG production with the human B-lymphoblastoid cell line CESS. The direct effect of LPS on IL-6 production by gingival fibroblasts was much weaker than the indirect one via IL-1 production by adherent cells. The stimulating effect of culture supernatants of adherent cells stimulated with LPS on IL-6 production by gingival fibroblasts was as effective as that of recombinant IL-1, when this latter was added at a concentration equivalent to that contained in the culture supernatant of adherent cells. These results suggest that, although gingival fibroblasts may be involved in the pathogenesis of chronic periodontal disease by the production of cytokines, such a role may not result from a direct stimulation by periodontopathic bacteria. The phenomenon is more likely to be mediated indirectly by IL-1 produced by infiltrating inflammatory cells.