Interleukin-1 and interleukin-1 inhibitor production by human adherent cells stimulated with periodontopathic bacteria

Abundant secretion of bioactive interleukin-1beta by human macrophages induced by Actinobacillus actinomycetemcomitans leukotoxin

Actinobacillus actinomycetemcomitans produces a leukotoxin that selectively kills human leukocytes. Recently, we reported that macrophages are highly sensitive to leukotoxin and that their lysis involves activation of caspase 1. In this study, we show that leukotoxin also induces the production and release of proinflammatory cytokines from human macrophages. The macrophages were challenged with leukotoxin or lipopolysaccharide (LPS) from A. actinomycetemcomitans or LPS from Escherichia coli, and the production and secretion of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor alpha (TNF-alpha) were determined at the mRNA and protein levels by reverse transcription-PCR and enzyme-linked immunosorbent assay, respectively. Leukotoxin (1 to 30 ng/ml) induced abundant production and secretion of IL-1beta, while the effects on IL-6 and TNF-alpha production were limited. Leukotoxin (1 ng/ml) caused a 10-times-higher release of IL-1beta than did LPS (100 ng/ml). The secreted IL-1beta was mainly the bioactive 17-kDa protein. At higher concentrations (>30 ng/ml), leukotoxin caused secretion of mainly inactive cytokine, the 31-kDa pro-IL-1beta. The presence of specific antibodies to IL-1beta or of a caspase 1 inhibitor blocked the secretion and production of the cytokine. Supernatants of leukotoxin-challenged macrophages stimulated bone resorption when tested in a mouse calvarial model. The activity could be blocked by an IL-1 receptor antagonist or specific antibodies to IL-1beta. We concluded that A. actinomycetemcomitans leukotoxin can trigger abundant production and secretion of bioactive IL-1beta by human macrophages, which is mediated by activation of caspase 1.

Caspase 1 involvement in human monocyte lysis induced by Actinobacillus actinomycetemcomitans leukotoxin

Actinobacillus actinomycetemcomitans, an oral bacterium implicated in the etiology of periodontal diseases, produces a leukotoxin that selectively lyses primate neutrophils and monocytes, the major populations of defense cells in the periodontium. Though lysis requires expression of the receptor lymphocyte function-associated molecule 1 (LFA-1) on the cell surface, not all LFA-1-expressing leukocyte populations are equally susceptible to the toxin. In this study, the susceptibility of human leukocytes to leukotoxin-induced lysis is compared to their expression of LFA-1 and the activity of caspase 1. Cytolysis was determined by the activity of lactate dehydrogenase released from peripheral human leukocytes after 1-h exposure to leukotoxin. Monocytes were lysed at leukotoxin concentrations of > or = 5 ng/ml, while the corresponding values for neutrophils and lymphocytes were approximately 10 times greater. Similar LFA-1 expression was found in all susceptible cell populations irrespective of their degree of sensitivity to the toxin. Exposure of monocytes to leukotoxin increased their caspase 1 activity about fivefold within 10 to 20 min. Presence of the caspase 1 inhibitor Ac-YVAD-CMK significantly blocked the leukotoxin-induced lysis of monocytes only. At sublytic concentrations, leukotoxin induced no apoptotic activity in monocytes, as revealed by the lack of caspase 3 activation and DNA fragmentation. Monocytes are the most lysis-sensitive leukocytes for A. actinomycetemcomitans leukotoxin. Their lysis by this toxin depends on caspase 1 activation and proceeds through a process that differs from classical apoptosis.

Mast cells and oral inflammation

Mast cells are mobile granule-containing secretory cells that are distributed preferentially about the microvascular endothelium in oral mucosa and dental pulp. The enzyme profile of mast cells in oral tissues resembles that of skin, with most mast cells expressing the serine proteases tryptase and chymase. Mast cells in oral tissues contain the pro-inflammatory cytokine tumour necrosis factor-alpha in their granules, and release of this promotes leukocyte infiltration during evolving inflammation in several conditions, including lichen planus, gingivitis, pulpitis, and periapical inflammation, through induction of endothelial-leukocyte adhesion molecules. Mast cell synthesis and release of other mediators exerts potent immunoregulatory effects on other cell types, while several T-lymphocyte-derived cytokines influence mast cell migration and mediator release. Mast cell proteases may contribute to alterations in basement membranes in inflammation in the oral cavity, such as the disruptions that allow cytotoxic lymphocytes to enter the epithelium in oral lichen planus. A close relationship exists among mast cells, neural elements, and laminin, and this explains the preferential distribution of mast cells in tissues. Mast cells are responsive to neuropeptides and, through their interaction with neural elements, form a neural immune network with Langerhans cells in mucosal tissues. This facilitates mast cell degranulation in response to a range of immunological and non-immunological stimuli. Because mast cells play a pivotal role in inflammation, therapies that target mast cell functions could have value in the treatment of chronic inflammatory disorders in the oral cavity.

Isolation and properties of a tripeptidyl peptidase from a periodontal pathogen Prevotella nigrescens

Prolyltripeptidyl amino peptidase activity was found in a crude extract of Prevotella nigrescens and this enzyme was purified by procedures including concentration with ammonium sulfate, ion exchange chromatography, gel filtration, and isoelectric focusing. This peptidase hydrolyzed Ala-Ala-Pro-p-nitroanilide as well as Ala-Phe-Pro-p-nitroanilide. Furthermore, several p-nitroanilide derivatives of dipeptides with a proline residue in the second position from the amino-terminal end (Xaa-Pro) were also cleaved detectably. The molecular mass of this tripeptidase was calculated as 56 kDa and its isoelectric point was 5.8. The enzyme was inactivated completely by heating at 60 degrees C for 5 min and inhibited significantly by specific serine enzyme inhibitors.

Cytokine expression in periodontal health and disease

Soluble proteins that serve as mediators of cell function and are produced by various cell types, such as structural and inflammatory cells, are collectively called cytokines. Several lines of evidence have revealed that cytokines play important roles not only in tissue homeostasis but also in the pathogenesis of many infectious diseases. Recent research on biological activities in normal periodontium and the pathogenesis of periodontal diseases has clarified the involvement of various cytokines in the biological activities observed in the sites. Cytokines play crucial roles in the maintenance of tissue homeostasis, a process which requires a delicate balance between anabolic and catabolic activities. In particular, growth factors--such as fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF), transforming growth factor-beta (TGF-beta)--are thought to play important roles in modulating the proliferation and/or migration of structural cells in the periodontium and the production of various extracellular matrices by these cells. On the other hand, there is little doubt that excessive and/or continuous production of cytokines in inflamed periodontal tissues is responsible for the progress of periodontitis and periodontal tissue destruction. Particularly, inflammatory cytokines--such as IL-1 alpha, IL-1 beta, IL-6, and IL-8--are present in the diseased periodontal tissues, and their unrestricted production seems to play a role in chronic leukocyte recruitment and tissue destruction. It is possible that monitoring cytokine production or its profile may allow us to diagnose an individual's periodontal disease status and/or susceptibility to the disease. In addition, although the hypothesis is still controversial, it has been suggested that discrete T-cell subsets (Th1 and Th2) with different cytokine profiles play specific roles in the immunopathogenesis of periodontal diseases.

Factors affecting IL-1-mediated collagen metabolism by fibroblasts and the pathogenesis of periodontal disease: a review of the literature

Fibroblasts have been studied extensively for their contribution to connective tissue destruction in diseases where the metabolism of extracellular matrix components plays an essential part in their pathogenesis. A considerable dissolution, especially of collagen fibrils, is a well-known characteristic of the periodontal ligament and the gingival connective tissue in microbial-induced periodontal disease. Fibroblasts, responsible for the assembly of the extracellular matrix, are capable of responding directly to oral microbial challenges or indirectly, following activation of the host immune response, and can alter the composition of connective tissue in several ways: synthesis of inflammatory mediators, their receptors and antagonists; fibroblast proliferation; collagen synthesis; phagocytosis of collagen fibrils; and synthesis of proteolytic enzymes, including matrix metalloproteinases and their corresponding inhibitors. The contributions of these cellular fibroblastic properties to the pathogenesis of periodontal disease are reviewed in the context of the cytokine, interleukin-1, as the inflammatory regulator.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Cytokine-inducing components of periodontopathogenic bacteria

Pro-inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8 and tumour necrosis factor (TNF) are believed to be the major pathological mediators of inflammatory diseases ranging from arthritis to the periodontal diseases. The stimuli inducing proinflammatory cytokine induction in the former disease is unclear but in the periodontal diseases it is obvious that the stimulus is the accumulation of bacteria in the subgingival region. As these bacteria do not invade the lesional tissues in large numbers, it is believed that their soluble components or products interact with host tissues to induce cytokine gene transcription. The paradigm is that lipopolysaccharide is the key bacterial component inducing pro-inflammatory cytokine gene expression. However, over the past decade a growing number of reports on non-oral bacteria have established that many other bacterial components, as well as secretory products, have the capacity to induce cytokine synthesis. Some of these, such as the protein pneumolysin from Streptococcus pneumoniae, are incredibly potent (in this case inducing cytokine synthesis at femtomolar concentrations). This review surveys the range of bacterial components and products which have been shown to stimulate cytokine synthesis with particular emphasis on the hypothesis that these components play a role in the pathology of the periodontal diseases.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Induction of the CD1a Langerhans cell marker on human monocytes

Monocytes have recently been recognized as a precursor of Langerhans cells. This study examined the regulatory influence of the epithelial environment on the putative first step of the transition towards a Langerhans cell phenotype--the induction of CD1a antigen. The keratinocyte-derived cytokines granulocyte-macrophage-colony-stimulating factor, tumour necrosis factor-alpha, interleukin-6, and interleukin-1 beta induced CD1a expression, as did supernatants of keratinocytes extracted from inflammatory sites (periodontitis). Induction was abrogated by transforming growth factor-beta and a keratinocyte-derived interleukin-1 inhibitor. The optimal temperature for induction was 34 degrees C, not 37 degrees C. These results demonstrate that the components of the epithelial environment (cytokines and lower temperature) exert important influences, which may be part of local regulation of Langerhans cell development.

Marginal periodontitis and cytokines: a review of the literature

Recent research on the immunopathogenesis of marginal periodontitis has focused on cytokines, because these mediators govern biological activities in inflammatory tissue destruction. Several studies have been carried out to elucidate the involvement of cytokines in periodontitis, including cytokine measurements in samples from gingival tissue, gingival crevicular fluid, and in supernatants of stimulated in vitro grown cells from gingival tissue and peripheral blood. The results, summarized in this review, suggest that cytokines are involved in the progress of periodontitis. Furthermore, cytokines may be valuable as markers of tissue breakdown. At the present stage, however, there are difficulties in detecting and quantifying cytokines by immunochemical methods and, in particular, by bioassays. Increased knowledge of the cytokine network may open new pathways of periodontitis treatment by controlling processes involved in tissue breakdown.

Interleukin 1, interleukin 6 and transforming growth factor-beta production by human gingival mononuclear cells following stimulation with Porphyromonas gingivalis and Fusobacterium nucleatum

Gingival mononuclear cell production of interleukin 1 (IL-1), interleukin 6 (IL-6) and transforming growth factor-beta (TGF-beta) after stimulation with the putative periodontopathic bacteria, Porphyromonas gingivalis and Fusobacterium nucleatum was investigated. Using an ELISA method, gingival mononuclear cells extracted from 18 adult periodontitis subjects were found to be producing IL-1. However, IL-1 activity could only be detected in 5 out of these 18 cases when tested using a thymocyte proliferation bio-assay, suggesting the presence of IL-1 inhibitors. Depletion of monocytes from peripheral blood cultures resulted in a significant decrease in IL-1 activity following P. gingivalis stimulation while there was no effect in the level of IL-1 activity following stimulation with F. nucleatum. This suggests that P. gingivalis and F. nucleatum stimulate different cell types to produce IL-1. Like IL-1, IL-6 production by gingival mononuclear cells was significantly greater than that produced by the control peripheral blood mononuclear cells. Following P. gingivalis and F. nucleatum stimulation, higher levels of IL-6 could be detected; however, both organisms stimulated similar levels. Intracytoplasmic immunofluorescence staining demonstrated a lower percent TGF-beta+ cells in bacterial stimulated peripheral blood mononuclear cell cultures compared with cells in medium alone. In the gingival mononuclear cell cultures, the percentage TGF-beta+ cells peaked at day 1 in F. nucleatum-stimulated, whereas in P. gingivalis-stimulated cultures the peak TGF-beta+ cells occurred at day 3, again suggesting stimulation of different cell subsets. These results illustrate that different periodontopathic bacteria may stimulate different cell types to produce cytokines which may have synergistic or antagonistic effects.

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.

Bacteroides (Porphyromonas) gingivalis fimbriae activate mouse peritoneal macrophages and induce gene expression and production of interleukin-1

The purpose of this study was to examine whether Bacteroides (Porphyromonas) gingivalis fimbriae, an important structure involved in attachment of the bacteria to periodontal tissues, activate macrophages and subsequently induce gene expression and production of interleukin-1 (IL-1) in the cells. The fimbriae increased glucose consumption and lysozyme activity in BALB/c macrophages, both criteria of macrophage activation of peritoneal macrophages, in a dose-dependent fashion. A marked increase in the mRNA level of the c-myc gene, an oncogene, in the cells was observed after a 1-h treatment with the fimbriae, and the level decreased rapidly after 3 h. The fimbriae (4 micrograms of protein per ml) markedly induced IL-1 alpha and IL-1 beta gene expression in the cells and IL-1 production. The expression of IL-1 alpha and IL-1 beta genes measured in terms of specific mRNA increased 1 h after the start of treatment and peaked at 6 h. Such increased expression of IL-1 beta was also observed in C3H/HeJ mice, a lipopolysaccharide low-responder strain. The fimbriae stimulated transcriptional activity of IL-1 beta in the cells, but not that of IL-1 alpha. We also observed that fimbriae-induced IL-1 gene expression was not regulated by endogenous prostaglandin triggered by the fimbriae. Therefore, these observations suggest that B. gingivalis fimbriae may be involved in the pathogenesis of adult periodontal disease via triggering of IL-1 production by monocytes/macrophages in periodontal diseases.

Human dermal mast cells contain and release tumor necrosis factor alpha, which induces endothelial leukocyte adhesion molecule 1

Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine that mediates endothelial leukocyte interactions by inducing expression of adhesion molecules. In this report, we demonstrate that human dermal mast cells contain sizeable stores of immunoreactive and biologically active TNF-alpha within granules, which can be released rapidly into the extracellular space upon degranulation. Among normal human dermal cells, mast cells are the predominant cell type that expresses both TNF-alpha protein and TNF-alpha mRNA. Moreover, induction of endothelial leukocyte adhesion molecule 1 expression is a direct consequence of release of mast cell-derived TNF-alpha. These findings establish a role for human mast cells as "gatekeepers" of the dermal microvasculature and indicate that mast cell products other than vasoactive amines influence endothelium in a proinflammatory fashion.

Human gingival Langerhans cells stimulate allogeneic lymphocytes: requirement for MHC class II antigens

Langerhans cells (LC) are antigen-presenting cells which express high levels of Class II MHC antigens on their plasma membranes. While the expression of these antigens on gingival LC has been documented, their functional significance is unclear. In this study, the mixed epithelial cell-lymphocyte culture reaction (MECLR) between stimulator cells (LC) and allogenic lymphocytes was used as an in vitro model for investigating the role of the MHC Class II antigens HLA-DR, -DQ, and -DP in alloantigen presentation by gingival LC. In epithelial cell suspensions prepared from human gingiva, MHC Class II antigen expression (HLA-DR, -DP, -DQ) was confined to CD1a-positive LC. Depletion of Class II antigen-bearing LC from epithelial cells using monoclonal antibodies (L243, B7/21, and SK10) and complement inhibited the ability of epithelial cells to stimulate proliferation in the MECLR. Pre-treatment of epithelial cell suspensions with the same monoclonal antibodies suppressed proliferation in the MECLR, as did direct addition of these antibodies to co-cultures of epithelial cells and lymphocytes. These results indicate that HLA-DQ and -DP, together with DR antigens on gingival LC, are involved in LC-lymphocyte interactions. Since LC are potent antigen presenting cells, alterations in the expression of MHC Class II antigens on the surface of these cells will influence their ability to stimulate lymphocytes during the initiation of the cellular immune response to the accumulation of dental plaque.

Immunohistologic analysis of epithelial cell populations in oral lichen planus

Previous studies have demonstrated heterogeneity within lesional lymphocytes in drug-related oral lichen planus (D-LP) and idiopathic lichen planus (I-LP). This study examined the phenotype of Langerhans cells (LC) and keratinocytes in non-erosive D-LP and I-LP. In I-LP, keratinocytes expressed HLA-DR antigens whilst LC co-expressed CDIa, MHC Class II and CD4 antigens. The high levels of expression of MHC Class II antigens by LC were maintained during short term organ culture. In I-LP, the epithelium contained occasional CD25+ dendritic cells (putative activated LC). These cell phenotypes are suggestive of cell activation and likely result from local production of gamma interferon. In D-LP, expression of MHC Class II antigens on LC was reduced and no CD25+ cells were detected. The epithelium contained an increased number of CD45RA+ dendritic cells. While no differences between the production of interleukin-1 and interleukin-1 inhibitors by tissue samples could be detected, it is likely that the variations in epithelial cell phenotypes in I-LP and D-LP reflect altered cytokine production.