In vivo exposure to Porphyromonas gingivalis up-regulates nitric oxide but suppresses tumour necrosis factor-alpha production by cultured macrophages

Is the oral microbiome a source to enhance mucosal immunity against infectious diseases?

Mucosal tissues act as a barrier throughout the oral, nasopharyngeal, lung, and intestinal systems, offering first-line protection against potential pathogens. Conventionally, vaccines are applied parenterally to induce serotype-dependent humoral response but fail to drive adequate mucosal immune protection for viral infections such as influenza, HIV, and coronaviruses. Oral mucosa, however, provides a vast immune repertoire against specific microbial pathogens and yet is shaped by an ever-present microbiome community that has co-evolved with the host over thousands of years. Adjuvants targeting mucosal T-cells abundant in oral tissues can promote soluble-IgA (sIgA)-specific protection to confer increased vaccine efficacy. Th17 cells, for example, are at the center of cell-mediated immunity and evidence demonstrates that protection against heterologous pathogen serotypes is achieved with components from the oral microbiome. At the point of entry where pathogens are first encountered, typically the oral or nasal cavity, the mucosal surfaces are layered with bacterial cohabitants that continually shape the host immune profile. Constituents of the oral microbiome including their lipids, outer membrane vesicles, and specific proteins, have been found to modulate the Th17 response in the oral mucosa, playing important roles in vaccine and adjuvant designs. Currently, there are no approved adjuvants for the induction of Th17 protection, and it is critical that this research is included in the preparedness for the current and future pandemics. Here, we discuss the potential of oral commensals, and molecules derived thereof, to induce Th17 activity and provide safer and more predictable options in adjuvant engineering to prevent emerging infectious diseases.

Receptor-interacting protein kinase 2 contributes to host innate immune responses against Fusobacterium nucleatum in macrophages and decidual stromal cells

PROBLEM

Chorioamnionitis is caused by a bacterial infection that ascends from the vagina and can cause adverse pregnancy outcomes (APOs). Fusobacterium nucleatum (F. nucleatum) is a periodontal pathogen associated with the occurrence of APOs. In this study, we evaluated whether receptor-interacting protein kinase 2 (Ripk2), an adaptor protein of the cytosolic receptors nucleotide-binding oligomerization domain (NOD)1 and NOD2, in macrophages and human decidual stromal cells (hDSCs) contributes to immune responses against F. nucleatum.

METHOD OF STUDY

Bone marrow-derived macrophages (BMDMs) isolated from wild-type (WT) and Ripk2-deficient mice and hDSCs were cultured with F. nucleatum (MOI 1, 10, 100). BMDMs and hDSCs were assessed using enzyme-linked immunosorbent assay, Western blot analysis, real-time PCR, and nitrite assay.

RESULTS

Fusobacterium nucleatum-induced production of IL-6, but not of TNF-α and IL-10, was lower in Ripk2-deficient BMDMs than in WT cells. Western blotting revealed a decrease in F. nucleatum-induced p65 phosphorylation in Ripk2-deficient macrophages, whereas mitogen-activated protein kinases activation was comparable between WT and Ripk2-deficient cells. The production of nitric oxide (NO) in response to F. nucleatum and the gene and protein expression of inducible NO synthase was impaired in Ripk2-deficient BMDMs. In hDSCs, F. nucleatum upregulated the gene and protein expression of NOD1, NOD2, and Ripk2 in a time-dependent manner. F. nucleatum also increased the production of IL-6, CXCL8, and CCL2, whereas this production was decreased by the Ripk2 inhibitors SB203580 and PP2.

CONCLUSIONS

In conclusion, Ripk2 signaling appears to contribute to the F. nucleatum-induced immune response and can be a preventive and therapeutic target against APOs.

Withaferin A inhibits inflammatory responses induced by Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans in macrophages

Periodontitis is a progressive chronic inflammatory disease and a major cause of tooth loss in humans. As a withanolides, withaferin A (WA) is known to exhibit strong anti‑inflammatory activity. The present study examined whether WA inhibited inflammatory responses in macrophages in response to two representative periodontal pathogens, Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans. Murine bone marrow‑derived macrophages (BMDMs) were used in this study and cytokine production in culture supernatants was measured by enzyme‑linked immunosorbent assays. Western blot analysis was performed to determine the activation of nuclear factor‑κB and mitogen‑activated protein kinases (MAPKs) and the expression of inducible nitric oxide synthase (iNOS), toll‑like receptor (TLR) 2 and TLR4. The production of nitric oxide (NO) was determined by the Griess reaction. WA treatment was shown to decrease interleukin (IL)‑6 and tumor necrosis factor (TNF)‑α production in BMDMs in response to F. nucleatum and A. actinomycetemcomitans in a dose‑dependent manner. The phosphorylation of IκB‑α and MAPKs (p38, extracellular signal‑regulated kinases and c‑Jun N‑terminal kinases) induced by F. nucleatum and A. actinomycetemcomitans was also inhibited by WA. F. nucleatum and A. actinomycetemcomitans induced iNOS expression and NO production in BMDMs, which was inhibited by WA in a dose‑dependent manner. WA also reduced endogenous and induced expression of TLR2 and TLR4 in these cells. These results suggest that WA may be a potential therapeutic agent or preventive additive for periodontitis control.

Anti-biofilm properties of wound dressing incorporating nonrelease polycationic antimicrobials

Polycationic nanoparticles show biocompatible, broad-spectrum bactericidal properties in vitro and in vivo when incorporated in denture lining material post-maxillectomy in head and neck cancer patients. In the present study, the synthesized Crosslinked quaternary ammonium polyethylenimine nanoparticles were found to have a strong bactericidal activity against a wide variety of microorganisms rapidly killing bacterial cells when incorporated at small concentrations into soft lining materials without compromising mechanical and biocompatibility properties. This appears advantageous over conventional released antimicrobials with regard to in vivo efficacy and safety, and may provide a convenient platform for the development of non-released antimicrobials. This is a crucial issue when it comes to giving an answer to the serious and life-threatening problems of contaminations in immunocompromised patients such as orofacial cancer patient.

Direct recognition of Fusobacterium nucleatum by the NK cell natural cytotoxicity receptor NKp46 aggravates periodontal disease

Periodontitis is a common human chronic inflammatory disease that results in the destruction of the tooth attachment apparatus and tooth loss. Although infections with periopathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) are essential for inducing periodontitis, the nature and magnitude of the disease is determined by the host's immune response. Here, we investigate the role played by the NK killer receptor NKp46 (NCR1 in mice), in the pathogenesis of periodontitis. Using an oral infection periodontitis model we demonstrate that following F. nucleatum infection no alveolar bone loss is observed in mice deficient for NCR1 expression, whereas around 20% bone loss is observed in wild type mice and in mice infected with P. gingivalis. By using subcutaneous chambers inoculated with F. nucleatum we demonstrate that immune cells, including NK cells, rapidly accumulate in the chambers and that this leads to a fast and transient, NCR1-dependant TNF-α secretion. We further show that both the mouse NCR1 and the human NKp46 bind directly to F. nucleatum and we demonstrate that this binding is sensitive to heat, to proteinase K and to pronase treatments. Finally, we show in vitro that the interaction of NK cells with F. nucleatum leads to an NCR1-dependent secretion of TNF-α. Thus, the present study provides the first evidence that NCR1 and NKp46 directly recognize a periodontal pathogen and that this interaction influences the outcome of F. nucleatum-mediated periodontitis.

Visible light promotes interleukin-10 secretion by sublethal fluences

OBJECTIVE

To determine the effect of blue light on cultured splenocyte viability and secretion of cytokines involved in the regulation of immune responses in the inflammatory process.

BACKGROUND DATA

Previous studies showed that red light has various effects on lymphocyte proliferation and production of cytokines.

MATERIALS AND METHODS

Cultured mouse splenocytes were exposed to visible light (wavelengths, 450-490 nm) using 2-108 J/cm(2), with and without scavengers of reactive oxygen species (ROS). One half of the samples were stimulated by the heat-killed periopathogenic bacterium Porphyromonas gingivalis. Following incubation for 48 h, the levels of the cytokines interleukin-10 (IL-10), tumor necrosis factor alpha (TNFα), and interferon gamma (IFNγ) were analyzed, and the viability of the cells was tested using the XTT assay. The total oxidant-scavenging capacity of the nonexposed and exposed splenocytes to light was determined by a chemiluminescence assay, and the temperature of the cell culture medium was measured after light exposure.

RESULTS

Exposure to blue light at fluences of 27-108 J/cm(2) caused a decrease in splenocyte viability. Lower fluences increased the secretion of cytokine IL-10, which was abolished by ROS scavengers. Exposure to light had no effect on the secretion of cytokines TNFα and IFNγ. Following exposure to light, more ROS were detected and the temperature measured did not exceed 30.7°C.

CONCLUSIONS

Blue light had a stimulatory effect on cell secretion of IL-10, mediated by ROS. Therefore, an increase in IL-10 might be a potential method for modulating the inflammatory processes of local disorders, such as periodontitis and arthritis.

Enhanced monocyte migration and pro-inflammatory cytokine production by Porphyromonas gingivalis infection

BACKGROUND AND OBJECTIVE

Porphyromonas gingivalis, a major periodontal pathogen, has been reported to be involved in atherogenesis. In order to further understand this pathogen's link with systemic inflammation and vascular disease, we investigated its influence on murine monocytes and macrophages from three different sources.

MATERIAL AND METHODS

Concanavalin A-elicited peritoneal macrophages, peripheral blood monocyte-derived macrophages and WEHI 274.1 monocytes were infected with either P. gingivalis 381 or its non-invasive fimbriae-deficient mutant, DPG3.

RESULTS

Infection with P. gingivalis 381 markedly induced monocyte migration and significantly enhanced production of the pro-inflammatory cytokines, tumor necrosis factor-alpha and interleukin-6. Consistent with a role for this pathogen's major fimbriae and/or its invasive capacity, infection with DPG3 had a minimal effect on both monocyte attraction and pro-inflammatory cytokine production.

CONCLUSION

Since monocyte recruitment and activation are important steps in the development of vascular inflammation and atherosclerosis, these results suggest that P. gingivalis infection may be involved in these processes.

Pathophysiological mechanism of the developing maxillofacial radicular cyst

The radicular cysts are result of inflammatory process in the periapical tissues associated with necrotic and infected pulps. Humoral and cellular immune responses play a central role in the pathogenesis of these lesions. The most important role in the growth of these lesion have proinflammatore cytokine TNF-?, IL-1 and IL-6. Cytokine can be secreted by macrophages, monocytes and other cells of the immune system and can participate in skeletal homeostasis including osteoclastic formation, and bone resorption in maxillofacial region. The aim of this study is to give a concise review for mechanism of growth of maxilofacial radicular cysts, indicated of clinical aspect, as well as explained role of cytokine in this pathophysiology process.

TCR zeta down-regulation under chronic inflammation is mediated by myeloid suppressor cells differentially distributed between various lymphatic organs

T cell AgR zeta chain down-regulation associated with T cell dysfunction has been described in cancer, infectious, and autoimmune diseases. We have previously shown that chronic inflammation is mandatory for the induction of an immunosuppressive environment leading to this phenomenon. To identify the key immunosuppressive components, we used an in vivo mouse model exhibiting chronic inflammation-induced immunosuppression. Herein, we demonstrate that: 1) under chronic inflammation secondary lymphatic organs display various immunological milieus; zeta chain down-regulation and T cell dysfunction are induced in the spleen, peripheral blood, and bone marrow, but not in lymph nodes, correlating with elevated levels of Gr1(+)Mac-1(+) myeloid suppressor cells (MSC); 2) MSC are responsible for the induction of such an immunosuppression under both normal and inflammatory conditions; and 3) normal T cells administered into mice exhibiting an immunosuppressive environment down-regulate their zeta expression. Such an environment is anticipated to limit the success of immunotherapeutic strategies based on vaccination and T cell transfer, which are currently under investigation for immunotherapy of cancer.

Proinflammatory and antimicrobial nitric oxide in gingival fluid of diabetic patients with periodontal disease

Abnormal nitric oxide (NO) synthesis has been implicated in the pathogenesis of both periodontal disease and diabetes mellitus. In diabetic patients, increased inducible NO synthase in inflamed gingiva correlated with NO in gingival crevicular fluid. Although increased NO reflected more-severe inflammation, it was associated with reductions in CFU of Prevotella intermedia, a major periodontopathogen, highlighting dual roles for NO.

Citrus oil and MgCl2 as antibacterial and anti-inflammatory agents

BACKGROUND

The antibacterial and anti-inflammatory properties of Dead Sea magnesium chloride (MgCl(2)), citrus oil, and their combination were investigated. Citrus oil is composed of monoterpenes, in particular D-limonene, which is known to inhibit growth of bacteria, fungi, and certain parasites.

METHODS

Inhibition of Porphyromonas gingivalis in vitro was used to evaluate the antibacterial effect of a mixture of Dead Sea magnesium chloride and citrus oil and of each of the components. A subcutaneous chamber model in mice was used to assess the anti-inflammatory effect of the mixture and the individual components. Leukocyte migration, tumor necrosis factor-alpha (TNF-alpha) secretion, and interleukin (IL)-10 secretion were determined. Hydrocortisone was used as a positive control.

RESULTS

Citrus oil had an antibacterial effect with a minimal inhibitory concentration (MIC) of 1 mg/ml, whereas MgCl(2) at concentrations up to 10 mg/ml did not exhibit any antibacterial activity. However, a mixture of 10 mg/ml MgCl(2) and 0.25 mg/ml citrus oil dramatically increased inhibition of bacterial growth. The combination of MgCl(2) and the citrus oil resulted in lower levels of TNF-alpha and leukocyte migration while maintaining the levels of IL-10 compared to the control.

CONCLUSION

These findings suggest that a mixture of citrus oil and MgCl(2) could be used as a natural antibacterial and anti-inflammatory agent.

Inhibition of Experimental Gingivitis in Beagle Dogs With Topical Mercaptoalkylguanidines

BACKGROUND

Nitric oxide is a free radical produced in host tissues by constitutive and inducible forms of the enzyme nitric oxide synthase. Nitric oxide plays physiological roles, but it is also involved in the pathophysiology of several inflammatory conditions, including arthritis, ulcerative colitis, and circulatory shock. Local increases in inducible nitric oxide synthase (iNOS) and reactive nitrogen products have also been demonstrated in humans and animals with periodontal disease. This masked, randomized, placebo-controlled preclinical investigation examined the effect of two mercaptoalkylguanidines, mercaptoethylguanidine (MEG) and guanidinoethyldisulfide (GED), which are iNOS inhibitors and reactive nitrogen scavenging compounds, on the development of experimental gingivitis in beagle dogs.

METHODS

Fifteen female, 1-year-old beagles first completed a 2-week dose-escalation experiment during which a maximum tolerated dose was determined for MEG and GED gels. Thereafter, all animals were brought to optimal gingival health by mechanical scaling, followed by rigorous daily toothbrushing over a 4-week washout period. Experimental gingivitis was then induced, with cessation of plaque control and institution of a soft diet over 8 weeks. Beagles randomly received 0.3% MEG, 0.3% GED, or placebo (vehicle) gels, topically applied twice daily to premolar teeth. Gingival inflammation, bleeding tendency, and supragingival plaque were clinically measured at baseline and at 2, 3, 4, 6, and 8 weeks. Comparisons among groups and between group pairs (active versus placebo) were made using Kruskal-Wallis tests.

RESULTS

From baseline to day 7, all groups expressed similar indices. Thereafter, significant and time-dependent increases in the plaque index (PI), gingival index (GI), and percentage of bleeding on probing (%BOP) were observed in placebo-treated beagles. Mean GI scores for beagles treated with GED or MEG gels remained at or below baseline levels for the entire treatment period. At weeks 2, 3, 4, and 8, GI scores were significantly lower for MEG and GED groups compared to the placebo group (P<0.05). In addition, MEG and GED gels significantly reduced gingival bleeding responses by 8 weeks (P<0.05). Although placebo-treated beagles demonstrated %BOP scores of 43% at week 8, GED- and MEG-treated beagles exhibited %BOP scores of 21% and 26%, respectively. Since no statistical difference among PI scores was noted for any of the time points, neither mercaptoalkylguanidine appeared to affect supragingival plaque levels.

CONCLUSION

The data from this preclinical study indicate that mercaptoalkylguanidines, topically administered, may significantly reduce experimental gingivitis in the beagle dog.

The effect of immunization on the response to P. gingivalis infection in mice is adjuvant-dependent

AIM

Studies on vaccines against the periodontal pathogen Porphyromonas gingivalis have produced conflicting results, but no consideration has been given to the role of different adjuvants in these vaccines. We have previously shown that an intra-chamber challenge with heat-killed P. gingivalis was modified by immunization with different adjuvants. This study tested the hypothesis that different adjuvants in P. gingivalis vaccines would differentially modify the host response to a live P. gingivalis infection.

RESULTS

Using P. gingivalis-infected subcutaneous chambers in mice, we show that vaccination with P. gingivalis in alum attenuated the pro-inflammatory cytokine levels at the site of infection, while the vaccine containing incomplete Freund's adjuvant did the opposite. Although both vaccines induced a similar humoral IgG response, P. gingivalis-induced abscesses were significantly smaller in the alum-adjuvant group.

CONCLUSIONS

The results suggest that the immune response and the resultant protection to a P. gingivalis infection, in P. gingivalis-vaccinated mice, are adjuvant-dependent.

Nitric oxide synthase inhibition prevents alveolar bone resorption in experimental periodontitis in rats

BACKGROUND

Periodontitis is the most frequent cause of tooth loss in adults. Nitric oxide (NO) has been linked to bone resorption mechanisms during inflammation processes. The aim of this study was to investigate the effect of NOS (NO synthase) inhibitors in the alveolar bone loss in an experimental periodontitis disease (EPD) model.

METHODS

Wistar rats were subjected to a ligature placement around the second upper left molars and were sacrificed at 11 days. Alveolar bone loss was evaluated by the sum of distances between the cusp tips and the alveolar bone along the axis of each molar root, subtracting from the contralateral side. Histopathological analysis was based on cell influx, alveolar bone, and cementum integrity. Leukogram was performed at 6 hours and 1, 7, and 11 days after the EPD induction. Groups were treated with the NOS inhibitors, aminoguanidine (AG) (2.5 to 10 mg/kg/d), or L-arginine methyl ester (L-NAME, 5 to 20 mg/kg/d) intraperitoneally (i.p.), 1 hour before the EPD induction and daily for 11 days. Controls received only saline (EPD group). As controls for L-NAME specificity, groups were co-treated with either L-arginine (150 to 600 mg/kg/d) or D-arginine (600 mg/kg/d) and L-NAME (20 mg/kg/d). Different groups were used for morphometric and histopathological analysis.

RESULTS

Both L-NAME and AG significantly and dose-dependently inhibited the alveolar bone loss as compared to EPD group. L-NAME (20 mg/kg/d) reduced the alveolar bone loss by 50%, whereas AG (5 mg/kg/d) reduced it by 47% compared to EPD. This result was coupled to a significant reduction of cell influx to the periodontium, as well as to the preservation of alveolar bone and cementum, seen at histopathology, for both compounds. The co-administration of L-arginine, but not of D-arginine reversed L-NAME effects.

CONCLUSION

These data provide evidence that NOS inhibitors prevent inflammatory bone resorption in experimental periodontitis.

L-arginine-dependent nitric oxide production of a murine macrophage-like RAW 264.7 cell line stimulated with Porphyromonas gingivalis lipopolysaccharide

The aim of this study was to determine nitric oxide (NO) production of a murine macrophage cell line (RAW 264.7 cells) when stimulated with Porphyromonas gingivalis lipopolysaccharides (Pg-LPS). RAW 264.7 cells were incubated with i) various concentrations of Pg-LPS or Salmonella typhosa LPS (St-LPS), ii) Pg-LPS with or without L-arginine and/or NG-monomethyl-L-arginine (NMMA), an arginine analog or iii) Pg-LPS and interferon-gamma (IFN-gamma) with or without anti-IFN-gamma antibodies or interleukin-10 (IL-10). Tissue culture supernatants were assayed for NO levels after 24 h in culture. NO was not observed in tissue culture supernatants of RAW 264.7 cells following stimulation with Pg-LPS, but was observed after stimulation with St-LPS. Exogenous L-arginine restored the ability of Pg-LPS to induce NO production; however, the increase in NO levels of cells stimulated with Pg-LPS with exogenous L-arginine was abolished by NMMA. IFN-gamma induced independent NO production by Pg-LPS-stimulated macrophages and this stimulatory effect of IFN-gamma could be completely suppressed by anti-IFN-gamma antibodies and IL-10. These results suggest that Pg-LPS is able to stimulate NO production in the RAW 264.7 macrophage cell model in an L-arginine-dependent mechanism which is itself independent of the action of IFN-gamma.

Sustained exposure to bacterial antigen induces interferon-γ-dependent T cell receptor ζ down-regulation and impaired T cell function

T cell antigen receptor zeta chain down-regulation and impaired in vitro T cell function have been described in cancer and autoimmune and infectious diseases. However, the immunological basis for this phenomenon is unknown. Sustained exposure to antigen and chronic systemic inflammation, factors shared by the various pathologies, might account for this phenomenon. We developed an in vivo experimental system that mimics these conditions and show that sustained exposure of mice to bacterial antigens was sufficient to induce T cell antigen receptor zeta chain down-regulation and impair T cell function, provided an interferon-gamma-dependent T helper type 1 immune response developed. This indicates zeta chain down-regulation could be a physiological response that attenuates an exacerbated immune response. However, it can act as a 'double-edged sword', impairing immune responses to chronic diseases.

Interferon-gamma deficiency attenuates local P. gingivalis-induced inflammation

Infection with the periodontal pathogen Porphyromonas gingivalis causes a strong local inflammatory reaction. Using IFNgamma-deficient mice, we tested the hypothesis that the absence of IFNgamma would result in a reduction of the local pro-inflammatory response to P. gingivalis. Cytokine secretion by macrophages from IFNgamma(-/-) animals was significantly attenuated. Addition of IFNgamma restored cytokine secretion. In vivo injection of P. gingivalis into subcutaneous chambers increased the intra-chamber leukocyte counts and TNFalpha and IL-1beta levels. This increase was significantly lower in the IFNgamma(-/-) mice. Local reconstitution of IFNgamma(-/-) mice at the site of inflammation with the IFNgamma gene increased the levels of TNFalpha and decreased the IL-10 levels. Anti-P. gingivalis IgG1 levels, a marker of Th2 response, were higher in immunized IFNgamma(-/-) than in IFNgamma(+/+) mice. The results suggest that lack of IFNgamma reduced the amplitude of the local pro-inflammatory response without decreasing the humoral protective response. The higher IgG1/IgG2a ratio observed supports the possibility of a Th2-dominant response in IFNgamma-deficient animals.

Immunization to Porphyromonas gingivalis enhances the local pro-inflammatory response to subcutaneous bacterial challenge

BACKGROUND, AIMS

Human and animal studies have suggested that immunization to P. gingivalis might be beneficial for controlling periodontitis, by the induction of protective antibody response. The present study was designed to examine the effect of immunization on the local cellular, cytokine and antibody response to P. gingivalis in mice.

METHODS

Subcutaneous chambers were implanted in 3 groups of mice. 2 groups were then immunized with P. gingivalis in either incomplete Freund's (IFA) or an Alum-based adjuvant. The 3rd group served as the control. At baseline, all mice were challenged with an intra-chamber injection of P. gingivalis. Chamber exudates were sampled at baseline, 1 and 7 days post-challenge, following by determination of leukocyte counts and the cytokines TNF-alpha, IFNgamma (pro-inflammatory) and IL-10 (anti-inflammatory). IgG levels to P. gingivalis were analyzed in both the exudates and serum.

RESULTS

Leukocyte accumulation increased in the chambers over the study period and was more marked in the immunized groups. P. gingivalis challenge induced the expression of the tested cytokines in all groups. Levels of IFNgamma showed a significantly greater increase in the immunized groups on day 1 post-challenge. By day 7, the levels in the controls had reached those of the immunized groups. IL-10 levels were significantly higher in the control group compared to the immunized groups on day 1 and by day 7 they were reduced significantly in all groups to barely detectable levels. While there were no significant differences in TNF-alpha levels between IFA and control groups, they were significantly higher in the Alum group on day 0 and 7. Both immunization protocols induced anti-P. gingivalis IgG. The Alum group achieved the highest antibody levels, which were due to the increased expression of IgG1, a marker of a Th2-response.

CONCLUSIONS

The results suggest that immunization to P. gingivalis results in enhanced expression of pro-inflammatory, tissue-destructive cytokines in the inflammatory site. The nature of the adjuvant used for immunization allows manipulation of the T-cell response, and alum was more effective in reducing the inflammatory response than IFA.

Expression of cytokines and inducible nitric oxide synthase in inflamed gingival tissue

BACKGROUND

Periodontopathic bacteria induce inflammation of periodontal tissues. The cytokines and nitric oxide released in periodontal lesions have been reported to play a protective role in bacterial infection and to relate to the process of inflammation. To clarify the relationship between colonization of periodontopathic bacteria and cytokines, we evaluated profiles of inflammatory cytokines, chemokine, anti-inflammatory cytokines, and inducible nitric oxide synthase (iNOS) and colonization by Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans, which are major pathogens of periodontitis.

METHODS

mRNA expression of cytokines and iNOS in inflamed and healthy gingival tissue was determined using reverse transcription-polymerase chain reaction (RT-PCR), and the relationship between their profiles and the detection of specific bacteria was analyzed.

RESULTS

The relative expression of interleukin (IL)-6 and iNOS mRNAs in periodontal lesions was significantly higher than those in healthy individuals. IL-6 mRNA expression was also significantly higher at bleeding on probing (BOP)-positive sites than at BOP-negative sites. The expressions of IL-1alpha and IL-8 increased, but IL-10 expression decreased at sites where A. actinomycetemcomitans was detected. We found no correlation between the expression of cytokine and iNOS mRNA and infection by P. gingivalis.

CONCLUSIONS

The expression of IL-6 may reflect inflammation in gingival tissue, and iNOS may be involved in the inflammatory process in periodontitis. The presence of A. actinomycetemcomitans or P. gingivalis might relate to the different cytokine profiles of IL-1alpha, IL-8, and IL-10.

Evidence for reactive nitrogen species formation in the gingivomucosal tissue

An increase in nitric oxide production has been demonstrated in periodontitis. Here we investigated the potential role of nitric-oxide-derived nitrating species (such as peroxynitrite) in a rat model of ligature-induced periodontitis. Formation of 3-nitrotyrosine, the stable product formed from tyrosine reacting with nitric-oxide-derived nitrating species, was detected in the gingivomucosal tissue. 3-Nitrotyrosine immunohistochemical analysis revealed a significant elevation in the number of immunopositive leukocytes, and higher immunoreactivity of the gingival ligaments and epithelium in the ligated than in the contralateral (control) side. On both sides, several 3-nitrotyrosine-positive bands and, on the ligated side, a unique 52-kDa 3-nitrotyrosine-positive band were detected by Western blot. However, in the sterile gingivomucosal tissue of rat pups, no 3-nitrotyrosine or inducible nitric oxide synthase immunoreactivity was found. Analysis of these data suggests that resident bacteria of the gingivomucosal tissue induce an increase in reactive nitrogen species, which is greatly enhanced by plaque formation in periodontitis.

The role of immune responses in bone loss during periodontal disease

A network of cytokines and other soluble mediators unites the immune system and bone; bacterial infections induce immune responses which may perturb this network. Periodontal diseases are Gram-negative infections resulting in bone loss in the jaw. Evidence is presented that immune responses to these infections produces net resorption of bone.

Experimental stress suppresses recruitment of macrophages but enhanced their P. gingivalis LPS-stimulated secretion of nitric oxide

BACKGROUND

Epidemiological studies have suggested that stress can alter the onset and progression of periodontal disease. However, the mechanisms involved are not clear. The present study was designed to examine whether the functional response of mouse macrophages stimulated by Porphyromonas gingivalis lipopolysaccharide (LPS) is affected by experimental stress, and to investigate the role of corticosterone (CS) in the stress-related effects.

METHODS

Two models of stress were used: emotional (isolation) and physical (cold). We measured thioglycollate-induced macrophage recruitment in vivo, and LPS-induced nitric oxide (NO) secretion by the macrophages in vitro. Two groups of mice were exposed to the stress conditions: isolation or cold. A third group was injected daily with CS, and a fourth group was used as a control (no stress). After 3 days of stress conditions, thioglycollate was injected into the peritoneal cavity. Four days later, peritoneal macrophages were isolated, counted, and cultured. The secretion of NO by the cultured cells was evaluated with and without P. gingivalis LPS stimulation.

RESULTS

The number of cells in the peritoneal lavage of stressed mice was significantly reduced in comparison to macrophages isolated from non-stressed animals. The number of macrophages from CS-treated mice did not differ from controls. NO secretion from unstimulated macrophages did not differ between the stressed and control groups. Stimulation of the macrophages with P. gingivalis LPS significantly enhanced NO secretion by macrophages from the control and stressed animals, but not by the CS-treated group. NO levels secreted by P. gingivalis-stimulated cells from the two stressed groups were significantly higher than the levels secreted by controls, and the isolation group released significantly higher levels than the cold group. Stimulation of the macrophages with P. gingivalis LPS and interferon (IFN)-gamma resulted in enhanced NO secretion in the 4 groups compared to LPS alone, with no significant differences between the groups.

CONCLUSIONS

The results suggest that experimental stress modulates the response of macrophages to inflammatory stimulants, and that CS is not the sole mediator involved. The presence of IFN-gamma in the culture may mask the functional differences induced by stress. The stress-induced upregulation of NO secretion might be involved in the accelerated periodontal destruction in stressed subjects.

Repeat bacterial challenge in a subcutaneous chamber model results in augmented tumour necrosis factor-alpha and interferon-gamma response, and suppression of interleukin-10

The present study compared the effect of a single or a repeat challenge with the Gram-negative pathogen Porphyromonas gingivalis on the local inflammatory response within subcutaneous chamber model in mice. Subcutaneous chambers were implanted 2 weeks prior to the final challenge. The repeat-challenge (REP) group received two intrachamber bacterial injections 14 days apart, while the single-injection group (SIN) received only a single bacterial challenge. Injection of saline was used as the control. The cellular contents of the chamber exudates were used for differential cell counts, and the supernatants were analysed for tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin (IL)-10 levels. Immunoglobulin G1 (IgG1) and IgG2a levels to P. gingivalis in the exudates were also determined. The results showed that the leucocyte counts increased significantly post-challenge, and the REP group showed the highest number of lymphocytes and neutrophils. Both P. gingivalis-challenged groups exhibited significant increase in TNF-alpha and IL-10 levels at day 1 post-challenge. TNF-alpha levels in the chamber exudate were threefold higher in the REP group compared with the SIN group on day 1 post-challenge (P < 0.05). In contrast, IL-10 levels were significantly lower in the REP group 1 day post-challenge compared with the SIN group. The REP group had significantly higher levels of IFN-gamma at baseline, and this difference remained significant 1 day post-challenge. Analysis of antibody levels to P. gingivalis showed that while the control and the SIN groups had no anti-P. gingivalis IgG in the chamber exudate during the 7-day study period, the REP group showed high anti-P. gingivalis IgG levels. In addition, the titres of IgG2a were fivefold higher than the IgG1 titres. The results showed that a repeat local challenge with P. gingivalis augmented the proinflammatory cytokines TNF-alpha and IFN-gamma, while inhibiting the accumulation of the anti-inflammatory cytokine IL-10. This shift towards a T helper 1 (Th1)-dominant response was reflected in the relatively high anti-P. gingivalis IgG2a titres in the local inflammatory environment 7 days post-challenge.

Biological activities of lipopolysaccharides extracted from porcine vaccine strains

Lipopolysaccharides (LPSs) were purified from Actinobacillus pleuropneumoniae serotype 2, Bordetella bronchiseptica and Haemophilus parasuis serotype 5, which were used for vaccine production in Japan, by the phenol-water procedure. In SDS-PAGE analysis, A. pleuropneumoniae LPS, as well as Escherichia coli LPS, demonstrated a typical ladder profile of a smooth-type LPS. On the other hand, B. bronchiseptica and H. parasuis LPSs lacked the ladder profiles. It was found that the biological activity of these LPSs was comparable to those of E. coli LPS in terms of activation of the clotting enzyme of Limulus amoebocyte lysate, mitogenic activity of mouse spleen cells, stimulation of TNF-alpha and nitric oxide production, but IL-6 production could hardly be observed in any LPS.

Antigen activation of THP-1 human monocytic cells after stimulation with lipopolysaccharide from oral microorganisms and granulocyte-macrophage colony-stimulating factor

A human THP-1 monocyte cell line culture system has been utilized to evaluate the morphological changes in THP-1 cells and to measure expression of activation antigens (CD-11b, CD-11c, CD-14, CD-35, CD-68, CD-71 and HLA-DR) as evidence of maturation of THP-1 cells in response to stimulation by lipopolysaccharide (LPS) from the oral microorganisms, Fusobacterium nucleatum and Porphyromonas gingivalis, and granulocyte-macrophage colony-stimulating factor. THP-1 cells were stimulated with LPS (1 microgram/ml) of P. gingivalis or F. nucleatum for different time periods (1, 2, 4 and 7 d). Detection of different activation antigens on THP-1 cells was performed by indirect immunohistochemical staining followed by light microscopy. Confirmational studies were performed in parallel using indirect immunofluorescence and immunogold electron microscopy for detection of the corresponding activation antigens. Expression of different activation antigens by resting THP-1 cells revealed HLA-DR to be on 3% of the cells; CD-11b, 9%; CD-11c, 8%; CD-14, 22%; CD-35, 9% and CD-68, 7%. The CD-71 activation antigen was not expressed in untreated THP-1 cells. LPS stimulation increased expression of all activation antigens. A significant (p < 0.05) increase in expression of CD-11b, CD-11c, CD-14, CD-35, CD-68 and CD-71 was observed when GM-CSF (50 IU/ml) was supplemented during the treatment of THP-1 cells with LPS of F. nucleatum or P. gingivalis. Activation and differentiation of THP-1 cells by LPS from oral microorganisms in the presence of GM-CSF supports a role for human macrophages in acute and chronic periodontal diseases and may explain the clinically observable periodontal exacerbations in some patients after GM-CSF therapy.