Interleukin 4 (IL-4) and IL-6-producing memory T-cells in peripheral blood and gingival tissue in periodontitis patients with high serum antibody titers to Porphyromonas gingivalis

Inflammation indices in association with periodontitis and cancer

Inflammation is a complex physiological process that plays a pivotal role in many if not all pathological conditions, including infectious as well as inflammatory diseases, like periodontitis and autoimmune disorders. Inflammatory response to periodontal biofilms and tissue destruction in periodontitis is associated with the release of inflammatory mediators. Chronic inflammation can promote the development of cancer. Persistence of inflammatory mediators plays a crucial role in this process. Quantification and monitoring of the severity of inflammation in relation to cancer is essential. Periodontitis is mainly quantified based on the severity and extent of attachment loss and/or pocket probing depth, in addition with bleeding on probing. In recent years, studies started to investigate inflammation indices in association with periodontal diseases. To date, only few reviews have been published focusing on the relationship between blood cell count, inflammation indices, and periodontitis. This review presents a comprehensive overview of different systemic inflammation indices, their methods of measurement, and the clinical applications in relation to periodontitis and cancer. This review outlines the physiological basis of inflammation and the underlying cellular and molecular mechanisms of the parameters described. Key inflammation indices are commonly utilized in periodontology such as the neutrophil to lymphocyte ratio. Inflammation indices like the platelet to lymphocyte ratio, platelet distribution width, plateletcrit, red blood cell distribution width, lymphocyte to monocyte ratio, delta neutrophil index, and the systemic immune inflammation index are also used in hospital settings and will be discussed. The clinical roles and limitations, relationship to systemic diseases as well as their association to periodontitis and treatment response are described.

Artesunate-loaded thermosensitive chitosan hydrogel promotes osteogenesis of maxillary tooth extraction through regulating T lymphocytes in type 2 diabetic rats

BACKGROUND

Type 2 diabetes mellitus (T2DM) causes severe bone loss after tooth extraction as a hyperglycemic environment causes aberrant bone homeostasis. Artesunate (ART) is known to possess anti-inflammation and osteogenic properties. However, its osteogenesis property in alveolar bone remains unclear. This study aimed to explore the osteogenic and immunoregulatory effects of artesunate-loaded thermosensitive chitosan hydrogel (ART-loaded TCH) on maxilla tooth extraction in T2DM rats.

METHODS

T2DM rats were induced by a high-fat diet and streptozotocin. Different concentrations of ART-loaded TCH were applied in tooth extraction sockets. Bone loss and the expression of osteogenic regulatory factors (OPG, ALP, RANK) were evaluated. The immunoregulatory effects of ART-loaded TCH were observed through detecting the infiltration of T lymphocytes and their cytokines. The underlying mechanisms were explored.

RESULTS

Results showed that the 150 mg/ml ART-loaded TCH group significantly ameliorated maxilla bone height and bone mineral density when compared with the T2DM group (p < 0.05). It also improved the expression of OPG, ALP, and RANK. Although the alteration of CD4+ T, CD8+ T, and CD4+:CD8+ T ratio has no significant difference among groups, the release of Th1 and Th2 in the 150 mg/ml ART-loaded TCH group has been significantly regulated than in the T2DM group (p < 0.05). Besides, ART-loaded TCH treatment inhibited the expression of p38 MAPK and ERK1 in T2DM maxilla.

CONCLUSIONS

Therefore, the results indicated that 150 mg/ml ART-loaded TCH could be an effective method to prevent bone loss in T2DM tooth extraction rats by modulating the immunoregulation of Th1 and Th2 and the MAPK signaling pathway.

Oral microbiota-host interaction: the chief culprit of alveolar bone resorption

There exists a bidirectional relationship between oral health and general well-being, with an imbalance in oral symbiotic flora posing a threat to overall human health. Disruptions in the commensal flora can lead to oral diseases, while systemic illnesses can also impact the oral cavity, resulting in the development of oral diseases and disorders. Porphyromonas gingivalis and Fusobacterium nucleatum, known as pathogenic bacteria associated with periodontitis, play a crucial role in linking periodontitis to accompanying systemic diseases. In periodontal tissues, these bacteria, along with their virulence factors, can excessively activate the host immune system through local diffusion, lymphatic circulation, and blood transmission. This immune response disruption contributes to an imbalance in osteoimmune mechanisms, alveolar bone resorption, and potential systemic inflammation. To restore local homeostasis, a deeper understanding of microbiota-host interactions and the immune network phenotype in local tissues is imperative. Defining the immune network phenotype in periodontal tissues offers a promising avenue for investigating the complex characteristics of oral plaque biofilms and exploring the potential relationship between periodontitis and associated systemic diseases. This review aims to provide an overview of the mechanisms underlying Porphyromonas gingivalis- and Fusobacterium nucleatum-induced alveolar bone resorption, as well as the immunophenotypes observed in host periodontal tissues during pathological conditions.

Circulating inflammatory cell profiling and periodontitis: A systematic review and meta-analysis

Inflammation is a key driver of common noncommunicable diseases. Among common triggers of inflammation, chronic gingival inflammation (periodontitis) triggers a consistent humoral host inflammatory response, but little is known on its impact on circulating inflammatory cell profiles. We aimed to systematically appraise all the evidence linking periodontitis and its treatment to circulating inflammatory cell profiles. From 6 databases, 157 studies were eligible for qualitative synthesis and 29 studies for meta-analysis. Our meta-analysis showed that participants with periodontitis exhibited a significant mean increase in circulating CD4⁺ , CD4⁺ CD45RO⁺ , IFNγ-expressing CD4⁺ and CD8⁺ T cells, CD19⁺ CD27⁺ and CD5⁺ B cells, CD14⁺ CD16⁺ monocytes, and CD16⁺ neutrophils but decrease in CD8⁺ T and CD14⁺⁺ CD16^- monocytes. Our qualitative synthesis revealed that peripheral blood neutrophils of patients with periodontitis consistently showed elevated production of reactive oxygen species (ROS) when compared with those of healthy controls. Some evidence suggested that the treatment of periodontitis reversed the exaggerated ROS production, but limited and inconclusive data were found on several circulating inflammatory cell profiling. We conclude that periodontitis and its treatment are associated with minor but consistent alterations in circulating inflammatory cell profiles. These changes could represent key mechanisms explaining the association of periodontitis with other comorbidities such as cardiovascular disease, diabetes, and rheumatoid arthritis.

Maintaining homeostatic control of periodontal bone tissue

Alveolar bone is a unique osseous tissue due to the proximity of dental plaque biofilms. Periodontal health and homeostasis are mediated by a balanced host immune response to these polymicrobial biofilms. Dysbiotic shifts within dental plaque biofilms can drive a proinflammatory immune response state in the periodontal epithelial and gingival connective tissues, which leads to paracrine signaling to subjacent bone cells. Sustained chronic periodontal inflammation disrupts "coupled" osteoclast-osteoblast actions, which ultimately result in alveolar bone destruction. This chapter will provide an overview of alveolar bone physiology and will highlight why the oral microbiota is a critical regulator of alveolar bone remodeling. The ecology of dental plaque biofilms will be discussed in the context that periodontitis is a polymicrobial disruption of host homeostasis. The pathogenesis of periodontal bone loss will be explained from both a historical and current perspective, providing the opportunity to revisit the role of fibrosis in alveolar bone destruction. Periodontal immune cell interactions with bone cells will be reviewed based on our current understanding of osteoimmunological mechanisms influencing alveolar bone remodeling. Lastly, probiotic and prebiotic interventions in the oral microbiota will be evaluated as potential noninvasive therapies to support alveolar bone homeostasis and prevent periodontal bone loss.

Peripheral memory T-cell profile is modified in patients undergoing periodontal management

AIMS

T-cells are known to have a role in periodontitis, however, the effect of periodontal therapy on peripheral memory T-cells is unclear. This study evaluated variation in peripheral memory T-cells and red complex bacteria in sub-gingival plaque in patients undergoing periodontal management.

METHODS

Peripheral blood mononuclear cells and sub-gingival plaque were collected from 54 periodontitis patients at baseline, 3-, 6- and 12-months post-therapy and 40 healthy controls. Periodontitis patients were divided into treatment outcome (TxO) groups based on prevalence of sites with probing depth ≥5 mm as good (<10% of sites), moderate (10-20%) or poor (>20%) at study conclusion. Naïve (T_N -CCR7⁺ CD45RA⁺ ), central memory (T_CM -CCR7⁺ CD45RA^- ), effector memory (T_EM -CCR7^- CD45RA^- ) and effector memory T-cells re-expressing CD45RA (T_EMRA -CCR7^- CD45RA⁺ ) were phenotyped using flow cytometry in CD4⁺ , CD8⁺ , CD4⁺ CD8⁺ and CD4^- CD8^- T-cells and red complex bacteria were quantified using qPCR.

RESULTS

At baseline, periodontitis subjects had significantly greater mean probing depths and Porphyromonas gingivalis proportions, lower T_N but higher CD4⁺ T_CM , CD8⁺ T_CM , CD4⁺ CD8⁺ T_EM and CD4^- CD8^- T_EM cell proportions compared to health. Periodontal therapy decreased mean probing depths, P. gingivalis proportions, T_EM and CD4⁺ and CD8⁺ T_CM cells, but increased T_N and CD4⁺ and CD8⁺ T_EMRA cells. The T-cell profile in the good TxO group showed therapy-related changes in CD4⁺ T_EM , and CD8⁺ T_N and T_EM cells, whereas, no changes were observed in the poor TxO group.

CONCLUSION

Management and the reduction in red complex bacteria were associated with changes in peripheral memory T-cells in periodontitis.

Peripheral T helper cell profiles during management of periodontitis

AIM

Periodontitis has been associated with other systemic diseases with underlying inflammation responsible for the shared link. This study evaluated longitudinal variation in peripheral T helper cells in periodontitis patients undergoing management over 1 year.

MATERIALS AND METHODS

Periodontal parameters and peripheral blood mononuclear cells (PBMCs) were collected from 54 periodontitis patients at baseline, and 3-, 6- and 12-months post-treatment and 40 healthy controls. IFN-γ⁺ , IL-4⁺ , IL-17⁺ and Foxp3⁺ and their double-positive expression were identified in CD4⁺ and TCRαβ⁺ cells using flow cytometry. PBMCs were incubated with P. gingivalis, and IFN-γ, IL-4, IL-17 and IL-10 in cell supernatant were measured by ELISA. Cells and cytokines were also assessed based on clinical response to treatment where good (<10% of sites), moderate (10-20%) and poor (>20%) treatment outcome (TxO) groups had probing depths of ≥5 mm at study conclusion.

RESULTS

IFN-γ⁺ cells were lower at baseline, and 3- and 6-months compared to health, whereas Foxp3⁺ cells were increased at 12-months compared to all preceding timepoints and health. The good TxO group showed treatment-related variation in IFN-γ⁺ and Foxp3⁺ cells, whereas the poor TxO group did not. IFN-γ and IL-17 cytokine expression in cell supernatants was significantly lower at baseline compared to health, and IFN-γ and IL-10 showed treatment-related decrease.

CONCLUSION

This study suggests that IFN-γ⁺ and Foxp3⁺ cells may have a role in the systemic compartment in periodontitis. Periodontal management has local and systemic effects, and thus, assessment and management of periodontitis should form an integral part of overall systemic health.

Roles of Porphyromonas gingivalis and its virulence factors in periodontitis

Periodontitis is an infection-driven inflammatory disease, which is characterized by gingival inflammation and bone loss. Periodontitis is associated with various systemic diseases, including cardiovascular, respiratory, musculoskeletal, and reproductive system related abnormalities. Recent theory attributes the pathogenesis of periodontitis to oral microbial dysbiosis, in which Porphyromonas gingivalis acts as a critical agent by disrupting host immune homeostasis. Lipopolysaccharide, proteases, fimbriae, and some other virulence factors are among the strategies exploited by P. gingivalis to promote the bacterial colonization and facilitate the outgrowth of the surrounding microbial community. Virulence factors promote the coaggregation of P. gingivalis with other bacteria and the formation of dental biofilm. These virulence factors also modulate a variety of host immune components and subvert the immune response to evade bacterial clearance or induce an inflammatory environment. In this chapter, our focus is to discuss the virulence factors of periodontal pathogens, especially P. gingivalis, and their roles in regulating immune responses during periodontitis progression.

Epigenetic biomarkers: a step forward for understanding periodontitis

Periodontitis is a common oral disease that is characterized by infection and inflammation of the tooth supporting tissues. While its incidence is highly associated with outgrowth of the pathogenic microbiome, some patients show signs of predisposition and quickly fall into recurrence after treatment. Recent research using genetic associations of candidates as well as genome-wide analysis highlights that variations in genes related to the inflammatory response are associated with an increased risk of periodontitis. Intriguingly, some of the genes are regulated by epigenetic modifications, supposedly established and reprogrammed in response to environmental stimuli. In addition, the treatment with epigenetic drugs improves treatment of periodontitis in a mouse model. In this review, we highlight some of the recent progress identifying genetic factors associated with periodontitis and point to promising approaches in epigenetic research that may contribute to the understanding of molecular mechanisms involving different responses in individuals and the early detection of predispositions that may guide in future oral treatment and disease prevention.

Blocking proinflammatory cytokine release modulates peripheral blood mononuclear cell response to Porphyromonas gingivalis

BACKGROUND

Chronic periodontitis (CP) is an inflammatory disease in which cytokines play a major role in the progression of disease. Anti-inflammatory cytokines (interleukin 4 [IL-4] and IL-10) were reported to be absent or reduced in diseased periodontal tissues, suggesting an imbalance between the proinflammatory and anti-inflammatory mediators. This study tests the hypothesis that there is cellular crosstalk mediated by proinflammatory and anti-inflammatory cytokines and that blocking proinflammatory cytokine (tumor necrosis factor-α [TNF-α] and IL-1) production will enhance anti-inflammatory cytokine (IL-4 and IL-10) production from peripheral blood mononuclear cells (PBMCs) in response to Porphyromonas gingivalis.

METHODS

PBMCs were isolated from individuals diagnosed with CP or healthy individuals and cultured for 24 hours. Concanavalin A (ConA) was used as an activator of lymphocyte function. Live and heat-killed P. gingivalis or lipopolysaccharide from P. gingivalis were used as the bacterial stimulants. TNF-α and IL-1 production was neutralized by specific antibodies against TNF-α and IL-1α or IL-β. Culture supernatants were evaluated by enzyme-linked immunosorbent assay for TNF-α, IL-1β, IL-4, and IL-10 production.

RESULTS

Live P. gingivalis did not result in any significant IL-10 or IL-4 release, whereas heat-killed P. gingivalis led to a significant increase in IL-10 levels compared with unstimulated or live P. gingivalis-stimulated cells from both healthy individuals or those with CP. Overall, PBMCs from patients with CP produced significantly lower IL-10 in response to ConA and P. gingivalis, suggesting chronic suppression of the anti-inflammatory cytokine production. Blocking the proinflammatory cytokine response did not result in any substantial change in IL-10 or IL-4 response to live P. gingivalis. Blocking the proinflammatory cytokine response restored IL-10 production by cells from CP in response to P. gingivalis lipopolysaccharide.

CONCLUSIONS

These findings suggest that PBMCs from patients with CP have suppressed anti-inflammatory cytokine production that can, in part, be restored by neutralizing proinflammatory cytokines. Monocytes are an important source of IL-10 production, and monocyte-derived IL-10 might play a regulatory role in the pathogenesis of CP.

Effect of non-surgical periodontal therapy on the levels of Th17/Th1/Th2 cytokines and their transcription factors in Chinese chronic periodontitis patients

AIM

A new subset of CD4(+) T cells, Th17, has been recently discovered independent from Th1/Th2 paradigm. The aim of this study was to investigate the effects of non-surgical periodontal therapy on the expression of Th17/Th1/Th2 cytokines and transcription factors, and Th17 cell vibration in Chinese chronic periodontitis patients.

MATERIALS AND METHODS

The levels of Th17/Th1/Th2 cytokines (IL-17, IL-21/IFN-γ/IL-4) in gingival crevicular fluid from 30 chronic periodontitis patients before and after treatment were determined by ELISA. The expression of transcription factors (RORC, T-bet and GATA-3) in peripheral blood was measured by real-time PCR, and the levels of Th17 cells in CD4(+) T cells were determined by flow cytometry.

RESULTS

After treatment, the levels of IL-17 and IL-21 were down-regulated (P<0.05), and IL-4 was increased (P<0.05), but there were no differences in the level of IFN-γ (P>0.05). Correspondingly, the expression of RORC was decreased 1.99-fold (P<0.05), and GATA-3 was increased 1.76-fold (P<0.05). However, there were no differences in the level of T-bet (P>0.05). Moreover, the quantity of Th17 cells in peripheral blood was decreased (P<0.05), especially IL-17(+) IFN-γ(+) subgroup.

CONCLUSIONS

These results suggest that Th17 cells play a destructive role in the immune balance of periodontitis, and the effect of Th1 cells is not significant, while Th2 cells have a protective effect.

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.

Destructive periodontitis lesions are determined by the nature of the lymphocytic response

It is now 35 years since Brandtzaeg and Kraus (1965) published their seminal work entitled "Autoimmunity and periodontal disease". Initially, this work led to the concept that destructive periodontitis was a localized hypersensitivity reaction involving immune complex formation within the tissues. In 1970, Ivanyi and Lehner highlighted a possible role for cell-mediated immunity, which stimulated a flurry of activity centered on the role of lymphokines such as osteoclast-activating factor (OAF), macrophage-activating factor (MAF), macrophage migration inhibition factor (MIF), and myriad others. In the late 1970s and early 1980s, attention focused on the role of polymorphonuclear neutrophils, and it was thought that periodontal destruction occurred as a series of acute exacerbations. As well, at this stage doubt was being cast on the concept that there was a neutrophil chemotactic defect in periodontitis patients. Once it was realized that neutrophils were primarily protective and that severe periodontal destruction occurred in the absence of these cells, attention swung back to the role of lymphocytes and in particular the regulatory role of T-cells. By this time in the early 1990s, while the roles of interleukin (IL)-1, prostaglandin (PG) E(2), and metalloproteinases as the destructive mediators in periodontal disease were largely understood, the control and regulation of these cytokines remained controversial. With the widespread acceptance of the Th1/Th2 paradigm, the regulatory role of T-cells became the main focus of attention. Two apparently conflicting theories have emerged. One is based on direct observations of human lesions, while the other is based on animal model experiments and the inability to demonstrate IL-4 mRNA in gingival extracts. As part of the "Controversy" series, this review is intended to stimulate debate and hence may appear in some places provocative. In this context, this review will present the case that destructive periodontitis is due to the nature of the lymphocytic infiltrate and is not due to periodic acute exacerbations, nor is it due to the so-called virulence factors of putative periodontal pathogens.

Single-nucleotide polymorphisms in the IL-4 and IL-13 promoter region in aggressive periodontitis

INTRODUCTION

IL-4 and IL-13 polymorphisms have been shown to influence the susceptibility to systemic diseases. In this study, possible associations between the IL-4 -590 C-->T, IL-4 -34 C-->T, IL-13 -1112 C-->T and IL-13 -1512 A-->C promoter polymorphisms were investigated in subjects with generalized aggressive periodontitis (AgP) compared with healthy individuals.

MATERIAL AND METHODS

Fifty-eight patients with diagnosis of generalized AgP and 51 matched healthy controls participated in the study. Blood samples were collected and DNA isolated. Molecular analyses were performed by PCR-RFLP in a blind fashion. Genotype and allele frequencies among study groups were compared using Fisher's exact test (alpha value: 0.05). Pearson's chi(2) test was used for analysis of Hardy-Weinberg equilibrium.

RESULTS

The frequency of the IL-4 -590 T/T and IL-4 -34 T/T genotypes differed significantly between groups (p=0.05, 0.02, respectively), although the allele frequencies were similar. There was a higher frequency of the IL-4 -590 T/T and IL-4 -34 T/T genotypes in patients with AgP compared with controls. The genotype and allele frequencies of the IL-13 polymorphisms did not differ between groups.

CONCLUSIONS

This study demonstrated an association between the IL-4 -590 T/T and IL-4 -34 T/T genotypes and AgP. Further research is necessary to prove if there is an association of these polymorphisms with AgP, and if the polymorphisms have a functional effect.

Changes in Gingival Crevicular Fluid Interleukin-4 and Interferon-gamma in Patients with Chronic Periodontitis Before and After Periodontal Initial Therapy

Cytokines are pivotal to the immune response of chronic periodontitis. The present study investigated the changes of gingival crevicular fluid (GCF) interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) in patients with chronic periodontitis before and after initial nonsurgical periodontal therapy (NSPT). GCF was collected from 17 patients by means of Periopaper at baseline and 1 month after NSPT. IL-4 and IFN-gamma were measured by enzyme-linked immunoabsorbent assay. NSPT resulted in decreased total amount of IFN-gamma, increased concentration of IL-4, and increased ratio of IL-4 to IFN-gamma levels. We suggest that a low ratio of IL-4 to IFN-gamma levels might be involved in the destruction (diseased sites) of periodontal tissue, whereas an increased ratio of IL-4 to IFN-gamma levels could be related to the improvement of clinical periodontal health.

Binding of Porphyromonas gingivalis gingipains to human CD4(+) T cells preferentially down-regulates surface CD2 and CD4 with little affect on co-stimulatory molecule expression

The role of Porphyromonas gingivalis cysteine proteinases (gingipains) in the evasion of host cell-mediated immunity has not been fully determined. In this study, modulation by gingipains of accessory and co-stimulatory molecule expression on human CD4(+) T cells was evaluated. Arg-gingipain rather than Lys-gingipain binds to resting CD4(+) T cells in the presence of serum. The constitutive expression of CD28 on T cells was slightly up-regulated following challenge with gingipains, whereas CD45 and CD3 were not affected. Binding of anti-CD2 and anti-CD4 monoclonal antibodies (mAbs) was reduced after challenge of T cells with gingipains, but restored to 50 and 100%, respectively, of control levels, after 48h of incubation in medium depleted of gingipains. The induced expression, by anti-CD3 mAb, of CTLA-4, CD25, and CD40 ligand (CD40L) was decreased following incubation of T cells with gingipains which also led to decreased response to anti-CD3 and anti-CD28 mAbs as shown by reduction of interleukin-2 (IL-2) production. Cumulatively, these results indicate that activated gingipains attach to T cells and preferentially cleave CD2 and CD4 molecules, with potential to impair T cell responses at periodontal sites.

Immune processes in periodontal disease: a review

The inflammatory and immune processes in periodontitis are complex and, although a great deal of information is available, many questions remain. Variation in human susceptibility to periodontitis has long been accepted, but the pathological basis of this is poorly understood. Similarly, we know little of the differences, if any, between the pathology of chronic and aggressive periodontitis. Genetics and environmental influences play a role in the susceptibility process, but if and how that translates through the immune and inflammatory processes to produce the plasma cell-dominated lesions seen in periodontitis remain to be elucidated. This review will focus on immunological aspects of the inflammatory changes seen in gingivitis and periodontitis, addressing both humoral and cellular responses to the microbial insult from dental plaque. A tendency for an individual or site to form an extensive plasma cell infiltrate may indicate an inability to defend against periodontopathogens and thus a predisposition to periodontitis. The issues to be considered include: 1) homing of immune and inflammatory cells to target tissues; 2) their local proliferation and synthetic activity; 3) the cytokine profile of the leukocytes; 4) the immunoglobulin subclasses of locally produced antibodies; 5) mucosal and systemic immune characteristics of the response; 6) the humoral immune response in periodontal health and disease states; and 7) the antigenic target of the immune response in periodontal lesions.

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.

Generation of gingival T cell lines/clones specific with Porphyromonas gingivalis pulsed dendritic cells from periodontitis patients

OBJECTIVES AND BACKGROUND

It is well documented that in periodontitis lesions, most infiltrated gingival T cells are antigen-specific memory T cells. These cells play an important role as regulators and effector cells in the pathogenesis of periodontitis. In this study, we used dendritic cells (DCs) as antigen-presenting cells to generate human gingival T cell lines and clones specific for Porphyromonas gingivalis from periodontitis patients.

METHODS

Autologous DCs were derived from the patients' adherent monocytes using granulocyte-macrophage colony-stimulating factor and interleukin (IL)-4. Lymphocytes were isolated from gingival biopsies using collagenase enzyme digestion and the number was increased by subsequent culturing in IL-2-containing medium. T cells were then negatively sorted using flow cytometry, cocultured with P. gingivalis-pulsed DCs and subsequently expanded in the culture medium containing IL-2. T cells were kept viable and active by periodic exposure to antigen-pulsed DCs. The specificity of the T cell lines was tested against four plaque bacteria: P. gingivalis, Actinobacillus actinomycetemcomitans, Prevotella intermedia and Actinomyces viscosus. The established T cell lines were then cloned. Three P. gingivalis-specific T cell lines and 12 gingival T cell clones were generated. They all showed good specificity against P. gingivalis but not to other plaque bacteria.

RESULTS

All T cell clones were positive for CD4 and the majority of them produced interferon gamma, but a minimal or negligible amount of IL-5.

CONCLUSIONS

The data obtained clearly showed that monocyte-derived DCs could be used as powerful antigen-presenting cells to generate antigen-specific T cells from periodontitis tissues.

Prostaglandin E2 downregulates interleukin-12 production through EP4 receptors in human monocytes stimulated with lipopolysaccharide from Actinobacillus actinomycetemcomitans and interferon-gamma

In the present study, we examined the effect of prostaglandin (PG) E2 on interleukin (IL) -12 production in monocytes stimulated with a combination of lipopolysaccharide (LPS) from Actinobacillus actinomycetemcomitans and interferon-gamma (A. actinomycetemcomitans-LPS/IFN-gamma). Indomethacin, a cyclooxygenase inhibitor, enhanced IL-12 production, but inhibited PGE2 generation in A. actinomycetemcomitans-LPS/IFN-gamma-stimulated monocytes. Exogenous PGE2 inhibited IL-12 release in the cells. EP2, EP3 and EP4 receptor mRNA expression was detected in monocytes by reverse transcription-polymerase chain reaction. 11-deoxy-PGE1 (an EP2/EP4 agonist) inhibited IL-12 production in A. actinomycetemcomitans-LPS/IFN-gamma-challenged monocytes, whereas butaprost (an EP2 agonist) or ONO-AP-324 (an EP3 agonist) had no effect on IL-12 production. Dibutyryl cAMP, a cAMP analogue, and forskolin, an adenylate cyclase activator, mimicked depression of IL-12 production by PGE2. From these results, we suggest that PGE2 inhibits IL-12 production via EP4 receptors by cAMP-dependent pathways in A. actinomycetemcomitans-LPS/IFN-gamma-challenged monocytes.

Porphyromonas gingivalis antigen preferentially stimulates T cells to express IL-17 but not receptor activator of NF-kappaB ligand in vitro

Although T cells have been implicated in the pathogenesis and are considered to be central to both their progression and control of chronic inflammatory periodontal diseases, the precise contribution of T cells to tissue destruction has not been fully clarified. Recently, interleukin (IL)-17 and receptor activator of Nuclear factor kappaB NF-kappaB ligand (RANKL) have received much attention as a result of their proinflammatory and bone metabolic roles, respectively. We therefore investigated the effect of outer membrane protein (OMP) from Porphyromonas gingivalis (P. gingivalis) on the expression of IL-17 and RANKL in peripheral blood mononuclear cells (PBMCs) and compared these between gingivitis and periodontitis, which are representative of stable and progressive lesions, respectively. The in situ expression of these molecules was also examined. P. gingivalis OMP stimulated PBMCs to express IL-17 at both the mRNA and protein level. Although the mean expression of mRNA was not different between the two groups, the mean level of IL-17 in the culture supernatants was higher in gingivitis patients than in periodontitis patients. However, the frequency of IL-17-positive samples was higher in the periodontitis patients. This stimulatory effect was not evident for RANKL expression in either periodontitis or gingivitis patients. In gingival tissue samples, IL-17 mRNA was detected in gingivitis more frequently than in periodontitis. The expression of RANKL mRNA was much lower than that of IL-17 in terms of both level and frequency. These results suggest that IL-17 but not RANKL may be involved in the pathogenesis of periodontal diseases. However, there may be negative regulatory mechanisms for IL-17 in gingivitis.

Antigen-presenting cells in human periodontal disease tissues

T cells are present in the inflammatory infiltrates of periodontal disease lesions and require antigen presentation by antigen-presenting cells (APCs). While it is still not known whether Th1 or Th2 cells predominate in these lesions, it has been reported that different APCs may induce activation of different T-cell subsets. An immunoperoxidase technique was used to investigate the presence of CD1a+, CMRF-44+, CMRF-58+ and CD83+ dendritic cells, CD14+ macrophages or dendritic cell precursors and CD19+ B cells in gingival biopsies from 21 healthy or gingivitis and 25 periodontitis subjects. The samples were divided into three groups according to the size of infiltrate (group 1, small infiltrates; group 2, medium infiltrates; group 3, extensive infiltrates). The presence of numerous CD1a+ Langerhans cells was noted in the epithelium with no differences between the healthy/gingivitis and periodontitis groups. The percentage of CD83+ dendritic cells in the infiltrates was higher than the percentage of CD1a+, CMRF-44+ or CMRF-58+ dendritic cells. Endothelial cells positive for CD83 were found predominantly in areas adjacent to infiltrating cells, CD83+ dendritic cells being noted in the region of CD83+ endothelium. The percentage of CD14+ cells in the inflammatory infiltrates was similar to that of CD83+ dendritic cells. B cells were the predominant APC in group 2 and 3 tissues. The percentage of B cells in group 3 periodontitis lesions was increased in comparison with group 1 periodontitis tissues and also in comparison with group 3 healthy/gingivitis sections. Functional studies are required to determine the roles of different APC subpopulations in periodontal disease.

The role of CD4+ cells in vivo on the induction of the immune response to Porphyromonas gingivalis in mice

BACKGROUND

It has previously been suggested that CD4+ T cells play a pivotal role in regulating the immune response to periodontal pathogens. The aim of the present study therefore was to determine delayed type hypersensitivity (DTH), spleen cell proliferation, serum and splenic anti-Porphyromonas gingivalis antibody levels, and lesion sizes following challenge with viable P. gingivalis in CD4-depleted BALB/c mice immunized with P. gingivalis outer membrane proteins (OMP).

METHODS

Four groups of BALB/c mice were used. Groups 1 and 2 were injected intraperitoneally (ip) with saline for 3 consecutive days and then weekly throughout the experiment. Groups 3 and 4 were injected ip with rat immunoglobulin and a monoclonal rat anti-mouse CD4 antibody, respectively. Two days later, group 1 mice were injected ip with saline only, while all the other groups were immunized ip with P gingivalis OMP weekly for 3 weeks. One week later following the last immunization of OMP, 3 separate experiments were conducted to determine: 1) the DTH response to P gingivalis OMP by measuring footpad swelling; 2) the levels of antibodies to P gingivalis in serum samples and spleen cell cultures using an enzyme-linked immunosorbent assay, as well as spleen cell proliferation after stimulation with OMP; and 3) the lesion sizes after a subcutaneous challenge with viable P. gingivalis cells.

RESULTS

In CD4+ T-cell-depleted mice (group 4), the DTH response and antigen-stimulated cell proliferation were significantly suppressed when compared to groups 2 and 3. Similarly, the levels of serum and splenic IgM, IgG, and all IgG subclass antibodies to P. gingivalis OMP were depressed. Delayed healing of P gingivalis-induced lesions was also observed in the CD4+ T-cell-depleted group.

CONCLUSIONS

This study has shown that depletion of CD4+ T cells prior to immunization with P gingivalis OMP led to the suppression of both the humoral and cell-mediated immune response to this microorganism and that this was associated with delayed healing. These results suggest that the induction of the immune response to P. gingivalis is a CD4+ T-cell-dependent mechanism and that CD4+ T cells are important in the healing process.

T cell knockout mice have diminished alveolar bone loss after oral infection with Porphyromonas gingivalis

Periodontal diseases are chronic inflammatory diseases that can result in resorption of the alveolar bone of the jaw. We have developed a murine model in which alveolar bone loss is induced by oral infection with Porphyromonas gingivalis, an oral anaerobic bacterium associated with periodontal disease in humans. Here we compared a strain of immunocompetent mice (C57BL/6J) to the same strain of mice made T cell deficient by genetic deletion of the alpha chain of their T cell receptors (C57BL/6J-Tcra). T cell deficiency did not affect the ability of P. gingivalis to implant in the oral cavity. The two strains of mice had equal percentages of P. gingivalis among their cultivable anaerobes 7 weeks after infection. The same bacterial load led to much less bone resorption in the T cell deficient mice than in the immune normal mice, measured as either the number of sites with significant loss, or as the total amount of bone resorbed. T cell deficient mice lost bone at only three out of 14 measurement sites, compared with eight out of 14 sites in the wild-type mice. The total amount of bone lost was 70% less in the T cell deficient mice. T cell deficient mice had lower titers of P. gingivalis-specific IgG than the wild-type mice after oral infection did, but the same titers of specific IgA. Lower titers did not correlate with greater bone loss. Antigen-activated T lymphocytes are known to induce osteoclastogenesis; here we demonstrate that T cell deletion decreases the amount of alveolar bone loss induced by infection of the murine oral cavity.

P. gingivalis-specific T-cell lines produce Th1 and Th2 cytokines

Cytokines produced by T-cells in periodontal lesions may determine the nature of the adaptive immune response. Since different antigen-presenting cells (APC) may direct the Th1/Th2 response, P. gingivalis-specific T-cell lines were established by different APC subpopulations, and their cytokine profiles were determined. Peripheral blood mononuclear cells induced similar percentages of IL-4+ and IFN-gamma+ T-cells and lower percentages of IL-10+ T-cells. Epstein-Barr virus-transformed B-cells (LCL) induced higher percentages of IL-4+ cells than IFN-gamma+ cells, with lower percentages of IL-10+ cells. Peripheral blood mononuclear cells induced a higher percent of IFN-gamma+ CD8 cells than LCL (p = 0.004). Purified B-cells, monocytes, and dendritic cells induced similar percentages of IL-4+ and IFN-gamma+ cells, although again, the percentage of IL-10+ cells was lower. The results of the present study have demonstrated that, as measured by FACS analysis of intracytoplasmic cytokines, P. gingivalis-specific T-cells produce both Th1 and Th2 cytokines, regardless of the APC population.

Proteolysis of interleukin-6 receptor (IL-6R) by Porphyromonas gingivalis cysteine proteinases (gingipains) inhibits interleukin-6-mediated cell activation

Current consensus is that periodontitis is an infectious disease in which a deregulated chronic inflammatory reaction not only may lead to periodontal tissue damage but also eventually may cause tooth loss. In controlling the inflammatory state the interplay between a network of cytokines and their receptors plays an important role. Here we show that the interleukin-6 receptor (IL-6R) is rapidly and efficiently inactivated by gingipains, the arginine- (HRgpA and RgpB) and lysine- (Kgp) specific cysteine proteinases from Porphyromonas gingivalis. Preincubation of HepG2 cells with active gingipains results in the loss of gp80 (CD126) from the cell surface. This also correlates with a decreased responsiveness to stimulation by interleukin-6 (IL-6), as determined by measurement of the status of IL-6R-mediated STAT 3 (Signal Transducer and Activator of Transcription 3) activation by this cytokine. Significantly, incubation of cells with gingipains was not accompanied by release of the soluble receptor, indicating its degradation, and this was confirmed by susceptibility of the recombinant, soluble receptor to proteolytic digestion by these enzymes. With the exception of the degradation of soluble IL-6R (sIL-6R) by Kgp, all of these reactions were also observed in the presence of serum suggesting that receptor inactivation may occur in vivo. Interestingly, Kgp, although less effective in cleaving sIL-6R, was able to decrease cell responsiveness to IL-6, possibly through degradation/inactivation of the signal transducing component (gp130) associated with IL-6R. These data, together with previous observation that IL-6 itself is inactivated by gingipains, suggest that at periodontitis sites infected by P. gingivalis the inflammatory reactions dependent on IL-6 could be severely hindered contributing to both tissue damage and periodontopathogen survival.

Clinical, pathological and immunological aspects of periodontal disease

The inflammatory and immune responses during the development and progression of periodontitis are reviewed. Susceptibility to periodontitis may be related to whether plasma cells predominate in the tissues of an individual, or a site, in response to the microbial insult from dental plaque. The tendency for an individual or site to form an extensive plasma cell infiltrate may indicate an inability to defend against periodontopathogenic bacteria and thus a predisposition to periodontitis. Selected pertinent areas of current interest in cellular and humoral immunology are considered within the periodontal context. These topical issues include (a) homing of immune and inflammatory cells to target tissues; (b) the local proliferation and synthetic activity of immune and inflammatory cells; (c) the cytokine profile of the inflammatory and immune cells; and (d) the immunoglobulin subclasses of locally produced antibodies.

Cytokines in periodontal disease: where to from here?

Numerous studies have attempted to elucidate the cytokine networks involved in chronic periodontitis, often with conflicting results. A variety of techniques were used to study cells in situ, cells extracted from gingival tissues, peripheral blood mononuclear cells, purified cell populations, and T cell lines and clones. Bacterial components, including sonicates, killed cells, outer membrane components, and purified antigens, have all been used to stimulate cells in vitro, making comparisons of cytokine profiles difficult. As it is likely that different cells are present at different disease stages, the inability to determine disease activity clinically is a major limitation of all these studies. In the Context of tissue destruction, cytokines such as IL-1, IL-6 and IL-18 are likely to be important, as are their regulating cytokines IL-10 and IL-11. In terms of the nature of the inflammatory infiltrate, two apparently conflicting hypotheses have emerged: one based on direct observations of human lesions, the other based on animal experimentation and the inability to demonstrate IL-4 mRNA in gingival extracts. In the first of these, Th1 responses are responsible for the stable lesion, while in the second Th2 responses are considered protective. Using Porphyromonas gingivalis-specific T cell lines we have shown a tendency for IFN-gamma production rather than IL-4 or IL-10 when antigen is presented with peripheral blood mononuclear cells which may contain dendritic cells. It is likely that the nature of the antigen-presenting cell is fundamental in determining the nature of the cytokine profile, which may in turn open up possibilities for new therapeutic modalities.

Anti-inflammatory cytokine IL-10 and T cell cytokine profile in periodontitis granulation tissue

Th2 cells are more abundant than Th1 cells in periodontitis lesions, but the relative importance of the Th1 and Th2 subsets in periodontal disease is not understood. In addition, the role of proinflammatory and anti-inflammatory cytokines in this disease process is unclear. Biopsies were obtained from 10 patients with early onset periodontitis (EOP) and 10 patients with adult periodontitis (AP). From all of the patients in the AP group we were able to obtain and section the gingival tissue to serve as controls. We used polyclonal monospecific antibodies to detect cells expressing IL-2, IL-4, IL-6, IL-10 and IL-15, tumour necrosis factor (TNF-alpha) and interferon-gamma (IFN-gamma) in formalin-fixed, paraffin-embedded sections of granulation tissue from periodontitis lesions. We also employed a series of oligonucleotide probes to detect cells expressing the cytokine transcripts in the same tissue biopsies. Cells that expressed IL-4 or IL-6 were more numerous than cells expressing either IL-2 or IFN-gamma. Th2 cells were more numerous in EOP and AP tissues. IL-15 substitutes for IL-2 in a number of biological activities related to the Th1 immune response, and interestingly, in periodontal lesions the IL-15-expressing cells outnumbered IL-2-expressing cells, suggesting that this is the pattern of immune regulation by T cells in the periodontium. The functional balance in the T cell subsets detected by their cytokine profiles underlies the importance of the anti-inflammatory mechanisms taking place in the diseased tissue. The numbers of inflammatory leucocytes that express the anti-inflammatory cytokine IL-10 are much more widely distributed than those that express the proinflammatory cytokines IL-6 and TNF-alpha. This study suggests that large numbers of infiltrating inflammatory cells as well as accessory cells are involved in the down-regulation of the inflammatory and immune response in periodontitis.

CD26 Immuno-Expression and Periodontal Disease Progression

Immunological mechanisms participate in the pathogenesis of human chronic inflammatory periodontal disease (CIPD). Human CD4(+) lymphocytes express functionally heterogeneous profiles of cytokine production. CD26 is an integral membrane glycoprotein, that is, a marker of Th1-like cytokine development. The purpose of the present study was to compare the immuno-expression of CD26 receptor in periodontal sites with and without clinical attachment loss (CAL). Five patients with rapidly progressing periodontitis and one with juvenile periodontitis were investigated. Each patient presented at least one site with and without CAL. Ten sites with CAL and nine without any CAL were biopsied, followed by the immunohistochemical identification of the CD26 receptor using the MIB-DS2/7 antibody. The results demonstrated that the percentage of positive cells for this antigen in the periodontal sites with CAL was not significantly different from those without attachment loss. Therefore, Th1 cell impairment may not be directly involved with periodontal attachment loss.

Elevated CTLA-4 expression on CD4 T cells from periodontitis patients stimulated with Porphyromonas gingivalis outer membrane antigen

To characterize the T cell response to Porphyromonas gingivalis, we examined the expression of costimulatory molecules on T cells derived from adult periodontitis patients with high serum antibody titre to P. gingivalis. The expression of CD28, CTLA-4, CD40 ligand (CD40L) on CD4+ T cells was analysed by flow cytometry. IL-10 and transforming growth factor-beta (TGF-beta) mRNA expression were determined by reverse transcription-polymerase chain reaction (RT-PCR) and subsequent image analysis. Peripheral blood mononuclear cells (PBMC) derived from periodontitis patients showed higher proliferative responses to P. gingivalis outer membrane (OM) than those from healthy controls (P < 0.05). The percentage of CTLA-4+ cells within CD4+ T cells of patients was significantly higher than that of healthy controls after P. gingivalis OM stimulation (33.0% versus 11.9%, P < 0.01). There was no significant difference in the percentages of CD28+ cells and CD40L+ cells, and the percentage of CD40L+ cells was low in both groups even after stimulation. Stimulation of PBMC with P. gingivalis OM induced significantly higher IL-10 mRNA expression in periodontitis patients than in healthy controls (P < 0.05). The level of TGF-beta mRNA expression of patients tended to be higher than that of healthy controls, but there was no significant difference. To elucidate the functional role of CTLA-4, we further investigated the secondary proliferative response to P. gingivalis OM. Interestingly, P. gingivalis OM stimulation did not enhance antigen-specific secondary response. Anti-CTLA-4 MoAb had no effect on proliferation in the presence of P. gingivalis OM. CTLA-4Ig suppressed the proliferative response significantly (P < 0.01). These results suggest that T cell responses to P. gingivalis OM may be regulated by CTLA-4 that is expressed at the late phase of T cell activation, and, in part, immunosuppressive cytokines. Taken together, CTLA-4 may play a crucial role in the pathogenesis of chronic inflammatory periodontal disease.

Th1 and Th2 cytokine profile in patients with early onset periodontitis and their healthy siblings

Early onset periodontitis (EOP) is a chronic inflammatory periodontal disease with a strong genetic link affecting individuals aged 17 to 25. In the familial studies we tested the hypothesis about the role of Th1 and Th2 cytokines in the pathogenesis of EOP disease. The study involved 6 individuals with EOP disease and their 6 siblings with healthy periodontium. Actinobacillus actinomycetemcomitans (A. a), a bacterium typical for EOP, was detected in all people studied. Th1 and Th2 cytokine production was measured after in vitro stimulation. Peripheral blood mononuclear cells (PBMC) were isolated and cultivated for 24 h and 7 days with PWM, A. a. or Escherichia coli. The levels of IL-4, IFN-gamma, IgA, IgG and IgM were measured by ELISA methods. After in vitro stimulation of PBMC, a significantly higher production of IL-4 and significantly lower production of IFN-gamma were found in the group of patients compared with their healthy siblings. The increased level of IL-4 in patients was in good agreement with an increased level of IgM after stimulation of lymphocytes with E. coli. These results support Seymour's hypothesis according to which patients with progressive disease primarily activate Th2 lymphocytes while non-susceptible individuals activate Th1 lymphocytes.

The proportion of interleukin-4, interferon-gamma and interleukin-10-positive cells in Porphyromonas gingivalis--specific T-cell lines established from P. gingivalis-positive subjects

T-cell cytokine profiles in ten adult periodontitis and seven age-matched healthy or gingivitis subjects were determined. Porphyromonas gingivalis-specific T-cell lines were established from the peripheral blood of these individuals all of whom had past or present evidence of P. gingivalis infection. FACS analysis was used to determine the percentage of CD4- and CD8-positive cells in each line staining for cytoplasmic interleukin (IL)-4, interferon-gamma and IL-10. There were no differences in the mean percentage of IL-4-, interferon-gamma- or IL-10-positive T cells between the two groups. However, the individual profiles showed that the CD4 cells in five of the seven healthy or gingivitis lines had a higher proportion of interferon-gamma-positive cells, with two lines demonstrating higher percentages of IL-10- and/or IL-4-positive CD4 cells. Five of the ten adult periodontitis lines demonstrated either equal or higher percentages of IL-4-positive and/or IL-10-positive CD4 cells. With respect to the CD8 cells, two of the seven lines established from the healthy or gingivitis subjects and six of the ten adult periodontitis lines showed profiles with a higher percentage IL-4- and/or IL-10-positive cells. When the total T-cell contribution (CD4 plus CD8) for each T-cell line was determined from the individual CD4:CD8 ratios, only one of the healthy or gingivitis lines showed a profile with a higher proportion of IL-10-positive cells, while the results for the adult periodontitis lines were the same as indicated for the CD4 cell profiles, with five lines showing a higher percentage of IL-4- and/or IL-10-positive cells. In conclusion, this study has shown that in P. gingivalis-responsive T-cell lines established from adult periodontitis and healthy or gingivitis subjects, there was a predominant trend towards a higher percentage of interferon-gamma positive cells than either IL-4- or IL-10-positive cells. However, there were variations from this trend, although whether these variations indicate true susceptibility to progressive disease has yet to be determined.

Rapid and efficient inactivation of IL-6 gingipains, lysine- and arginine-specific proteinases from Porphyromonas gingivalis

Deregulation of the cytokine network is an important adaptation of pathogenic bacteria to modulate and evade a host immune response. Here we describe that IL-6 is rapidly and efficiently cleaved and inactivated by the arginine- and lysine-specific proteinases from Porphyromonas gingivalis, referred to as RGP-A, RGP-B, and KGP. One of the primary cleavage sites for RGPs has been mapped between R18 and Q19 within the N-terminal region of the IL-6 polypeptide chain; however, both KGP and RGPs cleave IL-6 within the C-terminal region of the polypeptide chain. After these initial proteolytic cleavages, IL-6 is further degraded by each of the enzymes tested. Although KGP is the most potent IL-6-degrading proteinase, the initial C-terminal cleavage of IL-6 mediated by all gingipains is already sufficient to inactivate this cytokine. Our data are consistent with the observation that in periodontitis the IL-6 concentration is lowest in the gingival tissue adjacent to bacterial plaque, whereas significantly elevated concentrations of this cytokine are detected around the infected area. Degradation of IL-6 by gingipains may, therefore, represent an additional mechanism which influences the balance between pro- and anti-inflammatory reactions at distal versus proximal sites from the periodontal plaque.