Porphyromonas gingivalis Differentially Modulates Apoptosome Apoptotic Peptidase Activating Factor 1 in Epithelial Cells and Fibroblasts.

Porphyromonas gingivalis is able to invade and modulate host-immune response to promote its survival. This bacterium modulates the cell cycle and programed cell death, contributing to periodontal lesion worsening. Several molecular pathways have been identified as key triggers of apoptosis, including apoptosome apoptotic peptidase activating factor 1 (APAF-1). Apaf-1 and X-linked inhibitor of apoptosis protein (Xiap) mRNA were differentially expressed between gingival samples harvested from human healthy and chronic periodontitis tissues (Apaf-1, 19.2-fold; caspase-9, 14.5-fold; caspase-3, 6.8-fold; Xiap: 2.5-fold in chronic periodontitis) (P < 0.05), highlighting their potential role in periodontitis. An increased proteic expression of APAF-1 was also observed in a murine experimental periodontitis model induced by P. gingivalis-soaked ligatures. In vitro, it was observed that P. gingivalis targets APAF-1, XIAP, caspase-3, and caspase-9, to inhibit epithelial cell death at both mRNA and protein levels. Opposite effect was observed in fibroblasts in which P. gingivalis increased cell death and apoptosis. To assess if the observed effects were associated to APAF-1, epithelial cells and fibroblasts were transfected with siRNA targeting Apaf-1. Herein, we confirmed that APAF-1 is targeted by P. gingivalis in both cell types. This study identified APAF-1 apoptosome and XIAP as intracellular targets of P. gingivalis, contributing to the deterioration of periodontal lesion through an increased persistence of the bacteria within tissues and the subversion of host-immune response.

Contribution of Statins towards Periodontal Treatment: A Review.

The pleiotropic effects of statins have been evaluated to assess their potential benefit in the treatment of various inflammatory and immune-mediated diseases including periodontitis. Herein, the adjunctive use of statins in periodontal therapy in vitro, in vivo, and in clinical trials was reviewed. Statins act through several pathways to modulate inflammation, immune response, bone metabolism, and bacterial clearance. They control periodontal inflammation through inhibition of proinflammatory cytokines and promotion of anti-inflammatory and/or proresolution molecule release, mainly, through the ERK, MAPK, PI3-Akt, and NF-κB pathways. Moreover, they are able to modulate the host response activated by bacterial challenge, to prevent inflammation-mediated bone resorption and to promote bone formation. Furthermore, they reduce bacterial growth, disrupt bacterial membrane stability, and increase bacterial clearance, thus averting the exacerbation of infection. Local statin delivery as adjunct to both nonsurgical and surgical periodontal therapies results in better periodontal treatment outcomes compared to systemic delivery. Moreover, combination of statin therapy with other regenerative agents improves periodontal healing response. Therefore, statins could be proposed as a potential adjuvant to periodontal therapy. However, optimization of the combination of their dose, type, and carrier could be instrumental in achieving the best treatment response.

Changes in lipopolysaccharide profile of Porphyromonas gingivalis clinical isolates correlate with changes in colony morphology and polymyxin B resistance.

Virulence factors on the surface of Porphyromonas gingivalis constitute the first line of interaction with host cells and contribute to immune modulation and periodontitis progression. In order to characterize surface virulence factors present on P. gingivalis, we obtained clinical isolates from healthy and periodontitis subjects and compared them with reference strains. Colony morphology, aggregation in liquid medium, surface charge, membrane permeability to bactericidal compounds, novobiocin and polymyxin B resistance, capsule presence and lipopolysaccharide (LPS) profiles were evaluated. By comparing isolates from healthy and periodontitis subjects, differences in colony morphology and aggregation in liquid culture were found; the latter being similar to two reference strains. These differences were not a consequence of variations in bacterial surface charge. Furthermore, isolates also presented differences in polymyxin B and novobiocin resistance; isolates from healthy subjects were susceptible to polymyxin B and resistant to novobiocin and, in contrast, isolates from periodontitis subjects were resistant to polymyxin B and susceptible to novobiocin. These changes in antimicrobial resistance levels correlate with variations in LPS profiles, since -unlike periodontitis isolates-isolates from healthy samples synthesize LPS molecules lacking both O-antigen moieties and anionic polysaccharide. Additionally, this phenotype correlated with the absence of O-antigen ligase activity. Altogether, our results reveal novel variations on surface components of P. gingivalis isolates obtained from healthy and periodontitis subjects that could be associated with differences in bacterial virulence and periodontitis progression.

Amelogenesis imperfecta: Next-generation sequencing sheds light on Witkop's classification.

Amelogenesis imperfecta (AI) is a heterogeneous group of genetic rare diseases disrupting enamel development (Smith et al., Front Physiol, 2017a, 8, 333). The clinical enamel phenotypes can be described as hypoplastic, hypomineralized or hypomature and serve as a basis, together with the mode of inheritance, to Witkop's classification (Witkop, J Oral Pathol, 1988, 17, 547-553). AI can be described in isolation or associated with others symptoms in syndromes. Its occurrence was estimated to range from 1/700 to 1/14,000. More than 70 genes have currently been identified as causative. Objectives: We analyzed using next-generation sequencing (NGS) a heterogeneous cohort of AI patients in order to determine the molecular etiology of AI and to improve diagnosis and disease management. Methods: Individuals presenting with so called "isolated" or syndromic AI were enrolled and examined at the Reference Centre for Rare Oral and Dental Diseases (O-Rares) using D4/phenodent protocol (www.phenodent.org). Families gave written informed consents for both phenotyping and molecular analysis and diagnosis using a dedicated NGS panel named GenoDENT. This panel explores currently simultaneously 567 genes. The study is registered under NCT01746121 and NCT02397824 (https://clinicaltrials.gov/). Results: GenoDENT obtained a 60% diagnostic rate. We reported genetics results for 221 persons divided between 115 AI index cases and their 106 associated relatives from a total of 111 families. From this index cohort, 73% were diagnosed with non-syndromic amelogenesis imperfecta and 27% with syndromic amelogenesis imperfecta. Each individual was classified according to the AI phenotype. Type I hypoplastic AI represented 61 individuals (53%), Type II hypomature AI affected 31 individuals (27%), Type III hypomineralized AI was diagnosed in 18 individuals (16%) and Type IV hypoplastic-hypomature AI with taurodontism concerned 5 individuals (4%). We validated the genetic diagnosis, with class 4 (likely pathogenic) or class 5 (pathogenic) variants, for 81% of the cohort, and identified candidate variants (variant of uncertain significance or VUS) for 19% of index cases. Among the 151 sequenced variants, 47 are newly reported and classified as class 4 or 5. The most frequently discovered genotypes were associated with MMP20 and FAM83H for isolated AI. FAM20A and LTBP3 genes were the most frequent genes identified for syndromic AI. Patients negative to the panel were resolved with exome sequencing elucidating for example the gene involved ie ACP4 or digenic inheritance. Conclusion: NGS GenoDENT panel is a validated and cost-efficient technique offering new perspectives to understand underlying molecular mechanisms of AI. Discovering variants in genes involved in syndromic AI (CNNM4, WDR72, FAM20A … ) transformed patient overall care. Unravelling the genetic basis of AI sheds light on Witkop's AI classification.

Implication of Toll/IL-1 receptor domain containing adapters in Porphyromonas gingivalis-induced inflammation.

Periodontitis is induced by periodontal dysbiosis characterized by the predominance of anaerobic species. TLRs constitute the classical pathway for cell activation by infection. Interestingly, the Toll/IL-1 receptor homology domain adapters initiate signaling events, leading to the activation of the expression of the genes involved in the host immune response. The aim of this study was to evaluate the effects of Porphyromonas gingivalis on the expression and protein-protein interactions among five TIR adapters (MAL, MyD88, TRIF, TRAM and SARM) in gingival epithelial cells and endothelial cells. It was observed that P. gingivalis is able to modulate the signaling cascades activated through its recognition by TLR4/2 in gingival epithelial cells and endothelial cells. Indeed, MAL-MyD88 protein-protein interactions associated with TLR4 was the main pathway activated by P. gingivalis infection. When transient siRNA inhibition was performed, cell viability, inflammation, and cell death induced by infection decreased and such deleterious effects were almost absent when MAL or TRAM were targeted. This study emphasizes the role of such TIR adapter proteins in P. gingivalis elicited inflammation and the precise evaluation of TIR adapter protein interactions may pave the way for future therapeutics in both periodontitis and systemic disease with a P. gingivalis involvement, such as atherothrombosis.

Experimental periodontitis in Msx2 mutant mice induces alveolar bone necrosis.

BACKGROUND: Msx2 homeoprotein is a key transcription factor of dental and periodontal tissue formation and is involved in many molecular pathways controlling mineralized tissue homeostasis such as Wnt/sclerostin pathway. This study evaluated the effect of Msx2-null mutation during experimental periodontitis in mice. METHODS: Experimental periodontitis was induced for 30 days in wild-type and Msx2 knock-in Swiss mice using Porphyromonas gingivalis infected ligatures. In knock-in mice, Msx2 gene was replaced by n-LacZ gene encoding ß-galactosidase. Periodontal tissue response was assessed by histomorphometry, tartrate-resistant acid phosphatase histoenzymology, ß-galactosidase, sclerostin immunochemistry, and terminal deoxynucleotidyl transferase-mediated dUTP nickend labeling assay. Expression of Msx2 gene expression was also evaluated in human gingival biopsies using RT-qPCR. RESULTS: During experimental periodontitis, osteonecrosis area and osteoclast number were significantly elevated in knock-in mice compared with wild-type mice. Epithelial downgrowth and bone loss was similar. Sclerostin expression in osteocytes appeared to be reduced during periodontitis in knock-in mice. Msx2 expression was detected in healthy and inflamed human gingival tissues. CONCLUSION: These data indicated that Msx2 pathway influenced periodontal tissue response to experimental periodontitis and appeared to be a protective factor against alveolar bone osteonecrosis. As shown in other inflammatory processes such as atherothrombosis, genes initially characterized in early development could also play an important role in human periodontal pathogenesis.

Porphyromonas gingivalis triggers the shedding of inflammatory endothelial microvesicles that act as autocrine effectors of endothelial dysfunction.

A link between periodontitis and atherothrombosis has been highlighted. The aim of this study was to determine the influence of Porphyromonas gingivalis on endothelial microvesicles (EMVPg) shedding and their contribution to endothelial inflammation. Endothelial cells (EC) were infected with P. gingivalis (MOI = 100) for 24 h. EMVPg were isolated and their concentration was evaluated by prothrombinase assay. EMVPg were significantly increased in comparison with EMVCtrl shedded by unstimulated cells. While EMVCtrl from untreated EC had no effect, whereas, the proportion of apoptotic EC was increased by 30 nM EMVPg and viability was decreased down to 25%, a value elicited by P. gingivalis alone. Moreover, high concentration of EMVPg (30 nM) induced a pro-inflammatory and pro-oxidative cell response including up-regulation of TNF-α, IL-6 and IL-8 as well as an altered expression of iNOS and eNOS at both mRNA and protein level. An increase of VCAM-1 and ICAM-1 mRNA expression (4.5 folds and 3 folds respectively (p < 0.05 vs untreated) was also observed after EMVPg (30 nM) stimulation whereas P. gingivalis infection was less effective, suggesting a specific triggering by EMVPg. Kinasome analysis demonstrated the specific effect induced by EMVPg on main pro-inflammatory pathways including JNK/AKT and STAT. EMVPg are effective pro-inflammatory effectors that may have detrimental effect on vascular homeostasis and should be considered as potential autocrine and paracrine effectors involved in the link between periodontitis and atherothrombosis.

In-situ forming implants loaded with chlorhexidine and ibuprofen for periodontal treatment: Proof of concept study in vivo.

Control of infection and inflammation is crucial for the success of periodontal treatment. In this study, in-situ forming implants (ISFI) loaded with chlorhexidine dihydrochloride (CHX) and ibuprofen (IBU) were developed and tested to optimize periodontal treatment outcomes. Release profiles were promising. Exposure to 1.5% and 5.3% CHX-IBU loaded ISFI's release media decreased significantly the P. gingivalis growth up to 20-fold and 35-fold, respectively, after 48 h (p < 0.05). The metabolic activity assay of gingival epithelial cells (EC) demonstrated 1.5% CHX-IBU-loaded ISFI to be non-toxic, therefore, it was selected for further experimentation. Furthermore, significant down-regulation of TNF-α release (34% at 6 h and 43% at 24 h, p < 0.05) in P. gingivalis lipopolysaccharide (Pg-LPS) stimulated EC exposed to 1.5% CHX-IBU ISFI release medium was demonstrated by ELISA. In vivo, 1.5% CHX-IBU ISFI was injected into the periodontal pocket in an experimental periodontitis mouse model and the reduction in inflammation and improvement in periodontal wound healing was evaluated through inflammatory cell scoring and histomorphometry at 7- and 15-days post-treatment. The results indicate that CHX-IBU loaded ISFI could be efficient as adjuvant to periodontal therapy for the control of infection and inflammation. Moreover, other (e.g., pro-regenerative) drugs could be incorporated into ISFI to further improve periodontal treatment outcomes.

IL-36γ is a pivotal inflammatory player in periodontitis-associated bone loss.

Periodontitis is a prevalent chronic inflammatory disease due to the host response (IL-1ß, IL-6, TNF-α and IL-17A) to oral bacteria such as Porphyromonas gingivalis. The newer members of the IL-1 family, IL-36s (IL-36α/IL-36ß/IL-36γ/IL-36Ra/IL-38) are known to be involved in host defense against P. gingivalis in oral epithelial cells (OECs) and are considered as key inflammatory mediators in chronic diseases. The aim of this study was to investigate the potential role of IL-36s in periodontitis. We showed here that IL-36γ mRNA gingival expression is higher in periodontitis patients, whereas IL-36ß and IL-36Ra mRNA expression are lower compared to healthy controls. Interestingly, the elevated IL-36γ expression in patients is positively correlated with the RANKL/OPG ratio, an index of bone resorption. In vitro, IL-36γ expression was induced through TLR2 activation in primary OECs infected with P. gingivalis but not in gingival fibroblasts, the most widespread cell type in gingival connective tissue. In OECs, recombinant IL-36γ enhanced the expression of inflammatory cytokines (IL-1ß, IL-6, TNF-α and IL-36γ), of TLR2 and importantly, the RANKL/OPG ratio. These findings suggest that IL-36γ could be a pivotal inflammatory player in periodontitis by perpetuating gingival inflammation and its associated alveolar bone resorption and could be a relevant therapeutic target.

Variability in Genomic and Virulent Properties of Porphyromonas gingivalis Strains Isolated From Healthy and Severe Chronic Periodontitis Individuals.

Porphyromonas gingivalis has been extensively associated with both the onset and progression of periodontitis. We previously isolated and characterized two P. gingivalis strains, one from a patient exhibiting severe chronic periodontitis (CP3) and another from a periodontally healthy individual (H3). We previously showed that CP3 and H3 exhibit differences in virulence since H3 showed a lower resistance to cationic peptides compared with CP3, and a lower ability to induce proliferation in gingival epithelial cells. Here, we aimed to determine whether differences in virulence between these two strains are associated with the presence or absence of specific genes encoding virulence factors. We sequenced the whole genomes of both P. gingivalis CP3 and H3 and conducted a comparative analysis regarding P. gingivalis virulence genetic determinants. To do so, we performed a homology search of predicted protein sequences in CP3 and H3 genomes against the most characterized virulence genes for P. gingivalis available in the literature. In addition, we performed a genomic comparison of CP3 and H3 with all the 62 genomes of P. gingivalis found in NCBI's RefSeq database. This approach allowed us to determine the evolutionary relationships of CP3 and H3 with other virulent and avirulent strains; and additionally, to detect variability in presence/absence of virulence genes among P. gingivalis genomes. Our results show genetic variability in the hemagglutinin genes. While CP3 possesses one copy of hagA and two of hagC, H3 has no hagA and only one copy of hagC. Experimentally, this finding is related to lower in vitro hemmaglutination ability of H3 compared to CP3. Moreover, while CP3 encodes a gene for a major fimbrium subunit FimA type 4 (CP3_00160), H3 possess a FimA type 1 (H3_01400). Such genetic differences are in agreement with both lower biofilm formation ability and less intracellular invasion to oral epithelial cells exhibited by H3, compared with the virulent strain CP3. Therefore, here we provide new results on the genome sequences, comparative genomics analyses, and phenotypic analyses of two P. gingivalis strains. The genomics comparison of these two strains with the other 62 genomes included in the analysis provided relevant results regarding genetic determinants and their association with P. gingivalis virulence.

Porphyromonas gingivalis bypasses epithelial barrier and modulates fibroblastic inflammatory response in an in vitro 3D spheroid model.

Porphyromonas gingivalis-induced inflammatory effects are mostly investigated in monolayer cultured cells. The aim of this study was to develop a 3D spheroid model of gingiva to take into account epithelio-fibroblastic interactions. Human gingival epithelial cells (ECs) and human oral fibroblasts (FBs) were cultured by hanging drop method to generate 3D microtissue (MT) whose structure was analyzed on histological sections and the cell-to-cell interactions were observed by scanning and transmission electron microscopy (SEM and TEM). MTs were infected by P. gingivalis and the impact on cell death (Apaf-1, caspase-3), inflammatory markers (TNF-α, IL-6, IL-8) and extracellular matrix components (Col-IV, E-cadherin, integrin ß1) was evaluated by immunohistochemistry and RT-qPCR. Results were compared to those observed in situ in experimental periodontitis and in human gingival biopsies. MTs exhibited a well-defined spatial organization where ECs were organized in an external cellular multilayer, while, FBs constituted the core. The infection of MT demonstrated the ability of P. gingivalis to bypass the epithelial barrier in order to reach the fibroblastic core and induce disorganization of the spheroid structure. An increased cell death was observed in fibroblastic core. The development of such 3D model may be useful to define the role of EC-FB interactions on periodontal host-immune response and to assess the efficacy of new therapeutics.

Periodontal Tissues, Maxillary Jaw Bone, and Tooth Regeneration Approaches: From Animal Models Analyses to Clinical Applications.

This review encompasses different pre-clinical bioengineering approaches for periodontal tissues, maxillary jaw bone, and the entire tooth. Moreover, it sheds light on their potential clinical therapeutic applications in the field of regenerative medicine. Herein, the electrospinning method for the synthesis of polycaprolactone (PCL) membranes, that are capable of mimicking the extracellular matrix (ECM), has been described. Furthermore, their functionalization with cyclosporine A (CsA), bone morphogenetic protein-2 (BMP-2), or anti-inflammatory drugs' nanoreservoirs has been demonstrated to induce a localized and targeted action of these molecules after implantation in the maxillary jaw bone. Firstly, periodontal wound healing has been studied in an induced periodontal lesion in mice using an ibuprofen-functionalized PCL membrane. Thereafter, the kinetics of maxillary bone regeneration in a pre-clinical mouse model of surgical bone lesion treated with BMP-2 or BMP-2/Ibuprofen functionalized PCL membranes have been analyzed by histology, immunology, and micro-computed tomography (micro-CT). Furthermore, the achievement of innervation in bioengineered teeth has also been demonstrated after the co-implantation of cultured dental cell reassociations with a trigeminal ganglia (TG) and the cyclosporine A (CsA)-loaded poly(lactic-co-glycolic acid) (PLGA) scaffold in the jaw bone. The prospective clinical applications of these different tissue engineering approaches could be instrumental in the treatment of various periodontal diseases, congenital dental or cranio-facial bone anomalies, and post-surgical complications.

Synthesis of a Novel Electrospun Polycaprolactone Scaffold Functionalized with Ibuprofen for Periodontal Regeneration: An In Vitro andIn Vivo Study.

Ibuprofen (IBU) has been shown to improve periodontal treatment outcomes. The aim of this study was to develop a new anti-inflammatory scaffold by functionalizing an electrospun nanofibrous poly-ε-caprolactone membrane with IBU (IBU-PCL) and to evaluate its impact on periodontal inflammation, wound healing and regeneration in vitro and in vivo. IBU-PCL was synthesized through electrospinning. The effects of IBU-PCL on the proliferation and migration of epithelial cells (EC) and fibroblasts (FB) exposed to Porphyromonas gingivlais lipopolysaccharide (Pg-LPS) were evaluated through the AlamarBlue test and scratch assay, respectively. Anti-inflammatory and remodeling properties were investigated through Real time qPCR. Finally, the in vivo efficacy of the IBU-PCL membrane was assessed in an experimental periodontitis mouse model through histomorphometric analysis. The results showed that the anti-inflammatory effects of IBU on gingival cells were effectively amplified using the functionalized membrane. IBU-PCL reduced the proliferation and migration of cells challenged by Pg-LPS, as well as the expression of fibronectin-1, collagen-IV, integrin α3ß1 and laminin-5. In vivo, the membranes significantly improved the clinical attachment and IBU-PCL also reduced inflammation-induced bone destruction. These data showed that the IBU-PCL membrane could efficiently and differentially control inflammatory and migratory gingival cell responses and potentially promote periodontal regeneration.

Porphyromonas gingivalis Differentially Modulates Cell Death Profile in Ox-LDL and TNF-α Pre-Treated Endothelial Cells.

OBJECTIVE: Clinical studies demonstrated a potential link between atherosclerosis and periodontitis. Porphyromonas gingivalis (Pg), one of the main periodontal pathogen, has been associated to atheromatous plaque worsening. However, synergism between infection and other endothelial stressors such as oxidized-LDL or TNF-α especially on endothelial cell (EC) death has not been investigated. This study aims to assess the role of Pg on EC death in an inflammatory context and to determine potential molecular pathways involved. METHODS: Human umbilical vein ECs (HUVECs) were infected with Pg (MOI 100) or stimulated by its lipopolysaccharide (Pg-LPS) (1µg/ml) for 24 to 48 hours. Cell viability was measured with AlamarBlue test, type of cell death induced was assessed using Annexin V/propidium iodide staining. mRNA expression regarding caspase-1, -3, -9, Bcl-2, Bax-1 and Apaf-1 has been evaluated with RT-qPCR. Caspases enzymatic activity and concentration of APAF-1 protein were evaluated to confirm mRNA results. RESULTS: Pg infection and Pg-LPS stimulation induced EC death. A cumulative effect has been observed in Ox-LDL pre-treated ECs infected or stimulated. This effect was not observed in TNF-α pre-treated cells. Pg infection promotes EC necrosis, however, in infected Ox-LDL pre-treated ECs, apoptosis was promoted. This effect was not observed in TNF-α pre-treated cells highlighting specificity of molecular pathways activated. Regarding mRNA expression, Pg increased expression of pro-apoptotic genes including caspases-1,-3,-9, Bax-1 and decreased expression of anti-apoptotic Bcl-2. In Ox-LDL pre-treated ECs, Pg increased significantly the expression of Apaf-1. These results were confirmed at the protein level. CONCLUSION: This study contributes to demonstrate that Pg and its Pg-LPS could exacerbate Ox-LDL and TNF-α induced endothelial injury through increase of EC death. Interestingly, molecular pathways are differentially modulated by the infection in function of the pre-stimulation.

Interleukin-33 and RANK-L Interplay in the Alveolar Bone Loss Associated to Periodontitis.

INTRODUCTION: Chronic Periodontitis (CP) is an inflammatory disease of bacterial origin that results in alveolar bone destruction. Porphyromonas gingivalis (Pg), one of the main periopathogens, initiates an inflammatory cascade by host immune cells thereby increasing recruitment and activity of osteoclasts, the bone resorbing cells, through enhanced production of the crucial osteoclastogenic factor, RANK-L. Antibodies directed against some cytokines (IL-1ß, IL-6 and TNF-α) failed to exhibit convincing therapeutic effect in CP. It has been suggested that IL-33, could be of interest in CP. OBJECTIVE: the present study aims to analyze whether and how IL-33 and RANK-L and/or their interplay are involved in the bone destruction associated to CP. MATERIAL AND METHODS: mRNAs and protein expressions of IL-33 and RANK-L were analyzed in healthy and CP human gingival samples by immunohistochemistry (IHC) and RT-qPCR. Murine experimental periodontitis (EP) was induced using Pg infected ligature and Pg free ligature around the first maxillary molar. Alveolar bone loss was recorded by µCT. Mouse gingival explants were stimulated for 24 hours with IL-33 and RANK-L mRNA expression investigated by RT-qPCR. Human oral epithelial cells were infected by Pg for 6, 12; 24 hours and IL-33 and RANK-L mRNA expressions were analyzed by RT-qPCR. RESULTS: IL-33 is overexpressed in gingival epithelial cells in human affected by CP as in the murine EP. In human as in murine gingival cells, RANK-L was independently induced by Pg and IL-33. We also showed that the Pg-dependent RANK-L expression in gingival epithelial cells occured earlier than that of IL-33. CONCLUSION: Our results evidence that IL-33 overexpression in gingival epithelial cells is associated with CP and may trigger RANK-L expression in addition to a direct effect of Pg. Finally, IL-33 may act as an extracellular alarmin (danger signal) showing proinflammatory properties in CP perpetuating bone resorption induced by Pg infection.