Th1 immune response promotes severe bone resorption caused by Porphyromonas gingivalis

TNFSF14 coordinately enhances CXCL10 and CXCL11 productions from IFN-gamma-stimulated human gingival fibroblasts

TNFSF14 is involved in the pathogenesis of some inflammatory diseases such as arthritis. CXCL10 and CXCL11 recruit Th1 cells, and the productions of these chemokines are related to the exacerbation of some inflammatory diseases including arthritis and periodontal disease. We examined in vitro effects of TNFSF14 on IFN-gamma-induced CXCL10 and CXCL11 production in human gingival fibroblasts (HGFs). HGFs constitutively expressed TNFSF14 receptors, LTbetaR and HVEM. TNFSF14 enhanced IFN-gamma-induced secretion of CXCL10 and CXCL11 from HGFs. IFN-gamma treatment increased HVEM expression on HGFs. TNFSF14 in combination with IFN-gamma resulted in increased activation of p38 MAPK, ERK and IkappaB-alpha compared with TNFSF14 or IFN-gamma alone. Moreover, inhibitors of p38 MAPK, ERK and NF-kappaB abolished the CXCL10 and CXCL11 productions from TNFSF14 with IFN-gamma-stimulated HGFs. These effects of TNFSF14 may promote the infiltration of Th1 cells into lesions with inflammatory diseases. TNFSF14 might act as a proinflammatory cytokine in some inflammatory diseases thus is a candidate therapeutic target.

Protective role of osteopontin in endodontic infection

Endodontic infections are polymicrobial infections resulting in bone destruction and tooth loss. The host response to these infections is complex, including both innate and adaptive mechanisms. Osteopontin (OPN), a secreted, integrin-binding protein, functions in the regulation of immune responses and enhancement of leucocyte migration. We have assessed the role of OPN in the host response to endodontic infection using a well-characterized mouse model. Periapical bone loss associated with endodontic infection was significantly more severe in OPN-deficient mice compared with wild-type 3 weeks after infection, and was associated with increased areas of inflammation. Expression of cytokines associated with bone loss, interleukin-1alpha (IL-1alpha) and RANKL, was increased 3 days after infection. There was little effect of OPN deficiency on the adaptive immune response to these infections, as there was no effect of genotype on the ratio of bacteria-specific immunoglobulin G1 and G2a in the serum of infected mice. Furthermore, there was no difference in the expression of cytokines associated with T helper type 1/type2 balance: IL-12, IL-10 and interferon-gamma. In infected tissues, neutrophil infiltration into the lesion area was slightly increased in OPN-deficient animals 3 days after infection: this was confirmed by a significant increase in expression of neutrophil elastase in OPN-deficient samples at this time-point. We conclude that OPN has a protective effect on polymicrobial infection, at least partially because of alterations in phagocyte recruitment and/or persistence at the sites of infection, and that this molecule has a potential therapeutic role in polymicrobial infections.

Kinin danger signals proteolytically released by gingipain induce Fimbriae-specific IFN-gamma- and IL-17-producing T cells in mice infected intramucosally with Porphyromonas gingivalis

Porphyromonas gingivalis, a Gram-negative bacterium that causes periodontitis, activates the kinin system via the cysteine protease R-gingipain. Using a model of buccal infection based on P. gingivalis inoculation in the anterior mandibular vestibule, we studied whether kinins released by gingipain may link mucosal inflammation to T cell-dependent immunity through the activation of bradykinin B(2) receptors (B(2)R). Our data show that P. gingivalis W83 (wild type), but not gingipain-deficient mutant or wild-type bacteria pretreated with gingipain inhibitors, elicited buccal edema and gingivitis in BALB/c or C57BL/6 mice. Studies in TLR2(-/-), B(2)R(-/-), and neutrophil-depleted C57BL/6 mice revealed that P. gingivalis induced edema through the sequential activation of TLR2/neutrophils, with the initial plasma leakage being amplified by gingipain-dependent release of vasoactive kinins from plasma-borne kininogens. We then used fimbriae (Fim) Ag as a readout to verify whether activation of the TLR2-->PMN-->B(2)R axis (where PMN is polymorphonuclear neutrophil) at early stages of mucosal infection had impact on adaptive immunity. Analyzes of T cell recall responses indicated that gingipain drives B(2)R-dependent generation of IFN-gamma-producing Fim T cells in submandibular draining lymph nodes of BALB/c and C57BL/6 mice, whereas IL-17-producing Fim T cells were generated only in BALB/c mice. In summary, our studies suggest that two virulence factors, LPS (an atypical TLR2 ligand) and gingipain, forge a trans-cellular cross-talk between TLR2 and B(2)R, thus forming an innate axis that guides the development of Fim-specific T cells in mice challenged intrabuccally by P. gingivalis. Ongoing research may clarify whether kinin-driven modulation of T cell responses may also influence the severity of chronic periodontitis.

Catechins inhibit CXCL10 production from oncostatin M-stimulated human gingival fibroblasts

CXC chemokine ligand 10 (CXCL10) plays a pivotal role in the recruitment of Th1 cells and, thus, in the development of periodontal disease. Epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), the major catechins derived from green tea, have multiple beneficial effects, but the effects of catechins on CXCL10 production from human gingival fibroblasts (HGFs) is not known. In this study, we investigated the mechanisms by which EGCG and ECG inhibit oncostatin M (OSM)-induced CXCL10 production in HGFs. HGFs constitutively expressed glycoprotein 130 and OSM receptor beta (OSMR beta), which are OSM receptors. OSM increased CXCL10 production in a concentration-dependent manner. EGCG and ECG prevented OSM-mediated CXCL10 production by HGFs. Inhibitors of p38 mitogen-activated protein kinase, c-Jun N-terminal kinase (JNK), phosphatidylinositol-3-OH kinase and signal transducer and activator of transcription (STAT)3 decreased OSM-induced CXCL10 production. EGCG significantly prevented OSM-induced phosphorylation of JNK, Akt (Ser473) and STAT3 (Tyr705 and Ser727). ECG prevented phosphorylation of JNK and Akt (Ser473). In addition, EGCG and ECG attenuated OSMR beta expression on HGFs. These data provide a novel mechanism through which the green tea flavonoids, catechins, can provide direct benefits in periodontal disease.

Radiolucency below the crown of mandibular horizontal incompletely impacted third molars and acute inflammation in men with diabetes

Although mandibular third molar has a high risk of infection extending any complications, the influence of diabetes on radiolucency and acute inflammation in pericoronitis remains unclear. The present study was to evaluate whether radiolucency below the crown is related to acute inflammation in mandibular horizontal incompletely impacted third molars and to review the records of 140 men more than 45 years with and without diabetes. The odds ratio of exhibiting acute inflammation was 3.38 (95% CI: 1.13-10.16, p < 0.05) and that of exhibiting severe acute inflammation was 15.38 (95% CI: 3.56-66.49, p < 0.0001), indicating an association of acute pericoronitis in diabetes. The frequency of radiolucency below the crown and below the root in diabetics was similar to that in nondiabetics. However, the odds ratio of exhibiting both radiolucency below the crown and acute inflammation under the diabetic condition was 4.85 (95% CI: 1.60-14.73, p < 0.01), whereas that of diabetics showing both radiolucency below the root and acute inflammation was 0.46 (95% CI: 0.06-3.74, p = 0.74). Radiolucency below the crown and acute inflammation were associated with diabetes, but that below root and acute inflammation were not associated with diabetes, indicating that the region below the crown carries susceptibility to acute pericoronitis, whereas the periodontium shows a protective effect against acute pericoronitis.

Porphyromonas gingivalis stimulates TACE production by T cells

INTRODUCTION

Tumour necrosis factor-alpha converting enzyme (TACE), also known as ADAM17, is a membrane-bound metalloprotease and disintegrin. It is produced by a number of host cells and is known to shed and release cell-bound cytokines, particularly members of the tumour necrosis factor family. The aim of this study was to investigate the effect of Porphyromonas gingivalis on TACE production by a human T-cell line, to identify putative virulence factors involved in this process, and to investigate the effect of doxycycline.

METHODS

P. gingivalis 6-day culture supernatants were used to challenge Jurkat T cells for 6 h. Secreted and cell-associated TACE levels were measured by enzyme-linked immunosorbent assay, whereas messenger RNA expression was investigated by quantitative real-time polymerase chain reaction. To investigate the involvement of cysteine proteases or proteinaceous components in general, P. gingivalis culture supernatants were treated with the specific chemical inhibitor TLCK or heat-inactivated, respectively. The effect of doxycycline on the regulation of TACE secretion by P. gingivalis was also investigated.

RESULTS

P. gingivalis challenge resulted in a concentration-dependent enhancement of TACE messenger RNA expression and protein release by Jurkat cells. TLCK treatment or heat treatment of P. gingivalis culture supernatants decreased TACE release to control levels. Doxycycline inhibited TACE secretion dose dependently.

CONCLUSION

The induction of TACE by T cells in response to P. gingivalis may in turn favour the shedding of host cell-bound cytokines into the local microenvironment, potentially amplifying the inflammatory response. In the present experimental system, P. gingivalis cysteine proteases are involved in TACE release by T cells.

The RgpA-Kgp proteinase-adhesin complexes of Porphyromonas gingivalis Inactivate the Th2 cytokines interleukin-4 and interleukin-5

The RgpA-Kgp proteinase-adhesin complexes are a primary virulence factor of Porphyromonas gingivalis, a major pathogen in the development of chronic periodontitis. The RgpA-Kgp complexes have been suggested to bias the immune response to a Th2 phenotype in disease by hydrolysis of Th1 cytokines. Here, we show that the RgpA-Kgp complexes hydrolyze and inactivate interleukin-4 (IL-4) and IL-5 under physiologically relevant conditions. Using the IL-4/IL-5-dependent TF1.8 T-cell line, it was found that at equimolar ratios of cytokine to RgpA-Kgp complexes, IL-4 and IL-5 were inactivated in the culture medium. The inactivation of IL-4 and IL-5 was RgpA-Kgp concentration dependent, as at an enzyme-to-cytokine molar ratio of 1:8, the bioactivity of the cytokines was greater than at the higher concentration of RgpA-Kgp of 1:1. Furthermore, inactivation of the cytokines by the RgpA-Kgp complexes was time dependent, as longer preincubation times resulted in lower cytokine activity. IL-5 was found to be slightly more resistant to inactivation than IL-4. Mass spectrometric analyses of IL-4 and IL-5 showed that hydrolysis by RgpA-Kgp complexes was C terminal to Arg and Lys residues of the cytokines. The peptides released indicated that the regions of IL-4 and IL-5 important for bioactivity were being hydrolyzed in the first 15 min of incubation. The ability of the RgpA-Kgp complexes to degrade Th2 cytokines may contribute to immune dysregulation and may play a role in the pathology of chronic periodontitis.

Bone resorption in incompletely impacted mandibular third molars and acute pericoronitis

Acute pericoronitis (AP) arises frequently in incompletely impacted mandibular third molars, but it remains unknown whether bone resorption in aging is associated with acute inflammation of the third molar. We conducted an experiment to compare the ratio of bone resorption to root length in the distal surface of the second molar (A), the proximal surface (B), and distal surface (C) in mesio-angular, incompletely impacted third molars in 27 young and 58 older adults with AP and 77 young and 79 older adults without a history of AP. Bone resorption in A, B, and C in older adults with AP demonstrated a significantly higher ratio when compared to those without AP, whereas there was no difference between those with and without AP in young adults except for B in women. However, there were no differences between bone resorption in B with AP in young and older women, and between bone resorption in C with AP in young and older adults. These indicate that AP and bone resorption are associated with incompletely impacted mandibular third molars in older adults.

Immune response and alveolar bone resorption in a mouse model of Treponema denticola infection

Treponema denticola is considered to be an agent strongly associated with periodontal disease. The lack of an animal infection model has hampered the understanding of T. denticola pathogenesis and the host's immune response to infection. In this study, we have established an oral infection model in mice, demonstrating that infection by oral inoculation is feasible. The presence of T. denticola in the oral cavities of the animals was confirmed by PCR. Mice given T. denticola developed a specific immune response to the bacterium. The antibodies generated from the infection were mainly of the immunoglobulin G1 subclass, indicating a Th2-tilted response. The antibodies recognized 11 T. denticola proteins, of which a 62-kDa and a 53-kDa protein were deemed immunodominant. The two proteins were identified, respectively, as dentilisin and the major outer sheath protein by mass spectrometry. Splenocytes cultured from the infected mice no longer produced interleukin-10 and produced markedly reduced levels of gamma interferon relative to those produced by naïve splenocytes upon stimulation with T. denticola. Mandibles of infected mice showed significantly greater bone resorption (P < 0.01) than those of mock-infected controls.

T lymphocyte activation and cytokine expression in periapical granulomas and radicular cysts

INTRODUCTION

Radicular cysts (RCs) are periapical lesions resulting in jaw bone destruction. The inflammatory dental periapical granuloma (PG) is considered to be the origin of RC formation; however the mechanism of RC development remains unclear.

METHODS

Cell suspension from the surgically extirpated tissue of 27 RCs and 25 PGs was obtained. Bacteriological analysis of the PG tissue samples was performed in order to define two major groups of PG according to the prevailing causative bacterial infection: the streptococcal PG (PG-S, n=10) and the anaerobe PG (PG-A, n=9) group. The inflammatory response of tissue infiltrating lymphocytes was assessed by following T lymphocyte activation (HLA-DR expression) as well as interferon gamma (IFN-gamma) and interleukin 4 (IL-4) production which were evaluated by the flow cytometry.

RESULTS

In comparison to RC both types of PG contained a higher proportion of activated T cells (HLA-DR) and lower proportion of IL-4 producing cells. PG-A tissue contained increased percentage of CD3 cells and increased percentage of T helper 1 (Th1) cells in comparison with PG-S. In RC the IFN-gamma production is higher than in streptococcal PG-S but similar as in PG-A.

DISCUSSION

Tissue infiltration by Th2 cells and IL-4 production is likely to play an etiopathogenic role in RC formation.

A new inflammatory cytokine on the block: re-thinking periodontal disease and the Th1/Th2 paradigm in the context of Th17 cells and IL-17

For almost two decades, the Th1/Th2 paradigm has offered a productive conceptual framework for investigating the pathogenesis of periodontitis. However, as with many other inflammatory diseases, the observed role of T-cell-mediated immunity in periodontitis did not readily fit this model. A new subset of CD4+ T-cells was recently discovered that explains many of the discrepancies in the classic Th1/Th2 model, and has been termed "Th17" based on its secretion of the novel pro-inflammatory cytokine IL-17. The identification of Th17 cells as a novel effector T-cell population compels re-examination of periodontitis in the context of the new subset and its signature cytokines. This review aims to offer a clarifying insight into periodontal pathogenesis under the extended Th1/Th2/Th17 paradigm, and is predicated on the principle that periodontal disease activity is determined by a complex interplay between the immune system and periodontal pathogens. The re-examination of existing periodontal literature and further studies in the light of these new discoveries may help explain how the inflammatory response results in damage to the periodontium while generally failing to control the pathogens. This knowledge is essential for the development of immunomodulatory intervention strategies for fine-tuning the host response to maximize the protective and minimize the destructive aspects of the periodontal host response. Moreover, with the advent of anti-cytokine biologic drugs that target the Th1 and Th17 pathways in autoimmunity, the potential consequences to periodontal disease susceptibility in humans need to be understood.

Analysis of the activity to induce toll-like receptor (TLR)2- and TLR4-mediated stimulation of supragingival plaque

BACKGROUND

The deleterious effects of the accumulation of supragingival plaque are well known, but the role of the proinflammatory property of supragingival plaque in periodontal diseases has not been completely elucidated. The aim of this study was to determine the relevance of Toll-like receptor (TLR)2- and TLR4-stimulating activity of supragingival plaque to periodontal parameters.

METHODS

We isolated 144 supragingival plaque samples and analyzed TLR2- and TLR4-stimulating activity using genetically engineered Chinese hamster ovary reporter cells that express a reporter molecule upon activation of nuclear factor-kappa B through TLR2 or TLR4. The numbers of Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), and Streptococcus mutans cells in each plaque sample were determined by real-time polymerase chain reaction.

RESULTS

The activity to induce TLR4-mediated stimulation, but not TLR2-mediated stimulation, was positively associated with the plaque score and bleeding on probing score of the teeth from which the plaque samples were taken. The activity to induce TLR2-mediated stimulation, but not TLR4-mediated stimulation, was negatively associated with probing depth and clinical attachment level. The ratio of TLR4-/TLR2-mediated stimulation was positively associated with all of those parameters. The number of P. gingivalis cells in each plaque sample was associated with the plaque score and clinical attachment level, but no strong association was observed between the ratio of examined bacteria in each plaque sample and the activity to induce TLR2- or TLR4-mediated stimulation, except for a weak correlation between the ratio of A. actinomycetemcomitans cells and the activity to induce TLR4-mediated stimulation.

CONCLUSION

The TLR2- and TLR4-stimulating activity of supragingival plaque is associated with clinical parameters for gingivitis and periodontitis.

Th1 biased response to a novel Porphyromonas gingivalis protein aggravates bone resorption caused by this oral pathogen

In previous studies we showed that biasing the immune response to Porphyromonas gingivalis antigens to the Th1 phenotype increases inflammatory bone resorption caused by this organism. Using a T cell screening strategy we identified eight P. gingivalis genes coding for proteins that appear to be involved in T-helper cell responses. In the present study, we characterized the protein encoded by the PG_1841 gene and evaluated its relevance in the bone resorption caused by P. gingivalis because subcutaneous infection of mice with this organism resulted in the induction of Th1 biased response to the recombinant PG1841 antigen molecule. Using an immunization regime that strongly biases toward the Th1 phenotype followed by challenge with P. gingivalis in dental pulp tissue, we demonstrate that mice pre-immunized with rPG1841 developed severe bone loss compared with control immunized mice. Pre-immunization of mice with the antigen using a Th2 biasing regime resulted in no exacerbation of the disease. These results support the notion that selected antigens of P. gingivalis are involved in a biased Th1 host response that leads to the severe bone loss caused by this oral pathogen.

Adrenomedullin suppresses tumour necrosis factor alpha-induced CXC chemokine ligand 10 production by human gingival fibroblasts

Periodontal disease is an inflammatory disorder characterized by the involvement of chemokines that are important for the recruitment of leucocytes. Several cytokines, including tumour necrosis factor alpha (TNF-alpha), are involved in regulating levels of chemokines in periodontal disease. CXC chemokine ligand 10 (CXCL10) is a chemokine related to the migration of T helper 1 cells. In this study, we examined CXCL10 expression in human gingival fibroblasts (HGFs). Moreover, we investigated the effects of adrenomedullin (AM), which is a multi-functional regulatory peptide, on the production of CXCL10 by HGFs. We revealed that TNF-alpha stimulation induced CXCL10 production by HGFs. HGFs expressed AM and AM receptors, calcitonin-receptor-like receptor (CRLR) and receptor-activity-modifying protein (RAMP) 2, mRNAs constitutively. AM treatment supressed CXCL10 production by TNF-alpha-stimulated HGFs. Moreover, we elucidated that AM produced by HGFs inhibited CXCL10 production by HGFs, because AM antagonist enhanced CXCL10 production by HGFs. TNF-alpha treatment enhanced CRLR and RAMP2 mRNA expression in HGFs. Furthermore, AM is expressed in human periodontal tissues, including both inflamed and clinically healthy tissues. These results suggest that the CXCL10 produced by HGFs may be involved in the migration of leucocytes into inflamed tissues and related to exacerbation of periodontal disease. AM might be a therapeutic target of periodontal disease, because AM can inhibit CXCL10 production by HGFs.

p38 MAPK signaling in oral-related diseases

Multiple dental diseases are characterized by chronic inflammation, due to the production of cytokines, chemokines, and prostanoids by immune and non-immune cells. Membrane-bound receptors provide a link between the extracellular environment and the initiation of intracellular signaling events that activate common signaling components, including p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and nuclear factor (NF)-kappaB. Although ERK pathways regulate cell survival and are responsive to extracellular mitogens, p38 MAPK, JNK, and NF-kappaB are involved in environmental stress responses, including inflammatory stimuli. Over the past decade, significant advances have been made relative to our understanding of the fundamental intracellular signaling mechanisms that govern inflammatory cytokine expression. The p38 MAPK pathway has been shown to play a pivotal role in inflammatory cytokine and chemokine gene regulation at both the transcriptional and the post-transcriptional levels. In this review, we present evidence for the significance of p38 MAPK signaling in diverse dental diseases, including chronic pain, desquamative disorders, and periodontal diseases. Additional information is presented on the molecular mechanisms whereby p38 signaling controls post-transcriptional gene expression in inflammatory states.