Porphyromonas gingivalis with either Tannerella forsythia or Treponema denticola induces synergistic IL-6 production by murine macrophage-like J774.1 cells

The intriguing strategies of Tannerella forsythia's host interaction

Tannerella forsythia, a member of the "red complex" bacteria implicated in severe periodontitis, employs various survival strategies and virulence factors to interact with the host. It thrives as a late colonizer in the oral biofilm, relying on its unique adaptation mechanisms for persistence. Essential to its survival are the type 9 protein secretion system and O-glycosylation of proteins, crucial for host interaction and immune evasion. Virulence factors of T. forsythia, including sialidase and proteases, facilitate its pathogenicity by degrading host glycoproteins and proteins, respectively. Moreover, cell surface glycoproteins like the S-layer and BspA modulate host responses and bacterial adherence, influencing colonization and tissue invasion. Outer membrane vesicles and lipopolysaccharides further induce inflammatory responses, contributing to periodontal tissue destruction. Interactions with specific host cell types, including epithelial cells, polymorphonuclear leukocytes macrophages, and mesenchymal stromal cells, highlight the multifaceted nature of T. forsythia's pathogenicity. Notably, it can invade epithelial cells and impair PMN function, promoting dysregulated inflammation and bacterial survival. Comparative studies with periodontitis-associated Porphyromonas gingivalis reveal differences in protease activity and immune modulation, suggesting distinct roles in disease progression. T. forsythia's potential to influence oral antimicrobial defense through protease-mediated degradation and interactions with other bacteria underscores its significance in periodontal disease pathogenesis. However, understanding T. forsythia's precise role in host-microbiome interactions and its classification as a keystone pathogen requires further investigation. Challenges in translating research data stem from the complexity of the oral microbiome and biofilm dynamics, necessitating comprehensive studies to elucidate its clinical relevance and therapeutic implications in periodontitis management.

Volatile sulfide compounds and oral microorganisms on the inner surface of masks in individuals with halitosis during COVID-19 pandemic

Mask-wearing is still recommended owing to the continuing impact of the COVID-19 pandemic. Within the closed chamber created by the mask, people are increasingly self-aware of their oral malodor. In this prospective and cross-sectional study, we aimed to measure volatile sulfide compound (VSC) levels in patients with halitosis and investigate the oral microbiome profile on the inner surface of their KF94 masks. We also investigated which oral microbiota increases VSC levels and whether the oral microbiomes of oral saliva and mask are correlated. A total of 50 subjects (41 women, average age 38.12 ± 12.58 years old) were included in the study, 25 healthy subjects and 25 patients with halitosis who wore masks for more than 3 h. The dominant bacterial species, bacterial profile, and Shannon diversity index of whole unstimulated saliva and the inner surface of the mask were investigated. The bacterial 16S ribosomal RNA genes of the major oral bacterial species were analyzed using real-time PCR. Gas chromatography was used to measure hydrogen sulfide (H₂S) and methyl mercaptan (CH₃SH), which are representative VSCs. The total bacterial DNA copy number was significantly higher in the saliva sample than in the mask sample (p < 0.001), and the average value was 276 times greater. Shannon diversity index was also significantly higher in saliva than in the inner surface of the mask (2.62 ± 0.81 vs. 1.15 ± 1.52, p < 0.001). The most common Gram-negative and Gram-positive species in the masks were Porphyromonas gingivalis (Pg) and Lactobacillus casei (Lc), respectively. The bacterial species with significant positive correlations between saliva and mask samples were Prevotella intermedia (Pi) (r = 0.324, p = 0.022), Eikenella corrodens (r = 0.309, p = 0.029), Lc (r = 0.293, p = 0.039), and Parvimonas micra (Pm) (r = 0.366, p = 0.009). The mean value of CH₃SH was significantly higher in the halitosis group than in the non-halitosis group (17.84 ± 29.00 vs. 3.84 ± 10.57 ppb, p = 0.031). In the halitosis group, the DNA copy numbers and VSC levels showed highly positive correlation coefficients in the order Pg, Treponema denticola (Td), Tannerella forsythia (Tf), Pi, and Prevotella nigrescens (Pn) (all p < 0.05). Regarding bacterial profiles of the mask, Td was strongly correlated with CH₃SH (r = 0.414, p = 0.040) and total VSCs (r = 0.374, p = 0.033) only in halitosis group. Mask-wearing time was strongly correlated with total VSCs, H₂S, and CH₃SH (all r > 0.8, p < 0.001). Oral bacteria, whose association with halitosis has been identified, increased VSC levels in mask-wearing subjects during the COVID-19 pandemic, particularly the number of Gram-negative anaerobes such as Pg and Td. Mask-wearing time was a major factor in increasing VSC levels. The study results suggest that people with halitosis could control these Gram-negative bacteria by improving oral hygiene and regularly changing masks.

Oral Dysbiosis in Severe Forms of Periodontitis Is Associated With Gut Dysbiosis and Correlated With Salivary Inflammatory Mediators: A Preliminary Study

Inflammation is a driven force in modulating microbial communities, but little is known about the interplay between colonizing microorganisms and the immune response in periodontitis. Since local and systemic inflammation may play a whole role in disease, we aimed to evaluate the oral and fecal microbiome of patients with periodontitis and to correlate the oral microbiome data with levels of inflammatory mediator in saliva. Methods: Nine patients with periodontitis (P) in Stage 3/Grade B and nine age-matched non-affected controls (H) were evaluated. Microbial communities of oral biofilms (the supra and subgingival from affected and non-affected sites) and feces were determined by sequencing analysis of the 16SrRNA V3-V4 region. Salivary levels of 40 chemokines and cytokines were correlated with oral microbiome data. Results: Supragingival microbial communities of P differed from H (Pielou's evenness index, and Beta diversity, and weighted UniFrac), since relative abundance (RA) of Defluviitaleaceae, Desulfobulbaceae, Mycoplasmataceae, Peptostreococcales-Tissierellales, and Campylobacteraceae was higher in P, whereas Muribaculaceae and Streptococcaceae were more abundant in H. Subgingival non-affected sites of P did not differ from H, except for a lower abundance of Gemellaceae. The microbiome of affected periodontitis sites (PD ≥ 4 mm) clustered apart from the subgingival sites of H. Oral pathobionts was more abundant in sub and supragingival biofilms of P than H. Fecal samples of P were enriched with Acidaminococcus, Clostridium, Lactobacillus, Bifidobacterium, Megasphaera, and Romboutsia when compared to H. The salivary levels of interleukin 6 (IL-6) and inflammatory chemokines were positively correlated with the RA of several recognized and putative pathobionts, whereas the RA of beneficial species, such as Rothia aeria and Haemophilus parainfluenzae was negatively correlated with the levels of Chemokine C-C motif Ligand 2 (CCL2), which is considered protective. Dysbiosis in patients with periodontitis was not restricted to periodontal pockets but was also seen in the supragingival and subgingival non-affected sites and feces. Subgingival dysbiosis revealed microbial signatures characteristic of different immune profiles, suggesting a role for candidate pathogens and beneficial organisms in the inflammatory process of periodontitis.

The Th17/Treg cell balance: crosstalk among the immune system, bone and microbes in periodontitis

Periodontopathic bacteria constantly stimulate the host, which causes an immune response, leading to host-induced periodontal tissue damage. The complex interaction and imbalance between Th17 and Treg cells may be critical in the pathogenesis of periodontitis. Furthermore, the RANKL/RANK/OPG system plays a significant role in periodontitis bone metabolism, and its relationship with the Th17/Treg cell imbalance may be a bridge between periodontal bone metabolism and the immune system. This article reviews the literature related to the Th17/Treg cell imbalance mediated by pathogenic periodontal microbes, and its mechanism involving RANKL/RANK/OPG in periodontitis bone metabolism, in an effort to provide new ideas for the study of the immunopathological mechanism of periodontitis.

Compositional Data Analysis of Periodontal Disease Microbial Communities

Periodontal disease (PD) is a chronic, progressive polymicrobial disease that induces a strong host immune response. Culture-independent methods, such as next-generation sequencing (NGS) of bacteria 16S amplicon and shotgun metagenomic libraries, have greatly expanded our understanding of PD biodiversity, identified novel PD microbial associations, and shown that PD biodiversity increases with pocket depth. NGS studies have also found PD communities to be highly host-specific in terms of both biodiversity and the response of microbial communities to periodontal treatment. As with most microbiome work, the majority of PD microbiome studies use standard data normalization procedures that do not account for the compositional nature of NGS microbiome data. Here, we apply recently developed compositional data analysis (CoDA) approaches and software tools to reanalyze multiomics (16S, metagenomics, and metabolomics) data generated from previously published periodontal disease studies. CoDA methods, such as centered log-ratio (clr) transformation, compensate for the compositional nature of these data, which can not only remove spurious correlations but also allows for the identification of novel associations between microbial features and disease conditions. We validated many of the studies’ original findings, but also identified new features associated with periodontal disease, including the genera Schwartzia and Aerococcus and the cytokine C-reactive protein (CRP). Furthermore, our network analysis revealed a lower connectivity among taxa in deeper periodontal pockets, potentially indicative of a more “random” microbiome. Our findings illustrate the utility of CoDA techniques in multiomics compositional data analysis of the oral microbiome.

Heat-killed Candida albicans augments synthetic bacterial component-induced proinflammatory cytokine production

Candida albicans can enhance the invasion of oral epithelial cells by Porphyromonas gingivalis, although the fungus is not a periodontal pathogen. In this study, we investigated whether C. albicans augments proinflammatory cytokine production by mouse macrophage-like J774.1 cells incubated with synthetic bacterial components. Mouse macrophage-like J774.1 cells, mouse primary splenocytes, human THP-1 cells, and A549 cells were pretreated with or without heat-killed C. albicans (HKCA) or substitutes for C. albicans cell wall components in 96-well flat-bottomed plates. Cells were then washed and incubated with Pam₃CSK₄, a Toll-like receptor (TLR) 2 ligand, or lipid A, a TLR4 ligand. Culture supernatants were analyzed by ELISA for secreted IL-6, MCP-1, TNF-α, and IL-8. HKCA augmented TLR ligand-induced proinflammatory cytokine production by J774.1 cells, mouse splenocytes, and THP-1 cells, but not A549 cells. However, IL-6, MCP-1, and TNF-α production induced by Pam₃CSK₄ or lipid A was not augmented when cells were pretreated with curdlan, a dectin-1 ligand, or mannan, a dectin-2 ligand. In contrast, pretreatment of cells with TLR ligands upregulated the production of IL-6 and TNF-α, but not MCP-1, induced by Pam₃CSK₄ or lipid A. The results suggest that C. albicans augments synthetic bacterial component-induced cytokine production by J774.1 cells via the TLR pathway, but not the dectin-1 or dectin-2 pathway.

In vivo expression of proteases and protease inhibitor, a serpin, by periodontal pathogens at teeth and implants

Porphyromonas gingivalis and Tannerella forsythia secrete proteases, gingipains and KLIKK-proteases. In addition, T. forsythia produces a serpin (miropin) with broad inhibitory spectrum. The aim of this pilot study was to determine the level of expression of miropin and individual proteases in vivo in periodontal and peri-implant health and disease conditions. Biofilm and gingival crevicular fluid (GCF)/ peri-implant sulcular fluid (PISF) samples were taken from healthy tooth and implant sites (n = 10), gingivitis and mucositis sites (n = 12), and periodontitis and peri-implantitis sites (n = 10). Concentration of interleukin-8 (IL-8), IL-1β and IL-10 in GCF was determined by enzyme-linked immunosorbent assay. Loads of P. gingivalis and T. forsythia and the presence of proteases and miropin genes were assessed in biofilm by quantitative PCR, whereas gene expression was estimated by quantitative RT-PCR. The presence of P. gingivalis and T. forsythia, as well as the level of IL-8 and IL-1β, were associated with disease severity in the periodontal and peri-implant tissues. In biofilm samples harboring T. forsythia, genes encoding proteases were found to be present at 72.4% for karilysin and 100% for other KLIKK-protease genes and miropin. At the same time, detectable mRNA expression of individual genes ranged from 20.7% to 58.6% of samples (for forsylisin and miropsin-1, respectively). In comparison with the T. forsythia proteases, miropin and the gingipains were highly expressed. The level of expression of gingipains was associated with those of miropin and certain T. forsythia proteases around teeth but not implants. Cumulatively, KLIKK-proteases and especially miropin, might play a role in pathogenesis of both periodontal and peri-implant diseases.

Extracellular galectin-1 enhances adhesion to and invasion of oral epithelial cells by Porphyromonas gingivalis

Galectin-1 and galectin-3 are C-type lectin receptors that bind to lipopolysaccharide in the cell wall of gram-negative bacteria. In this study, we investigated the effects of galectin-1 and galectin-3 on adhesion to and invasion of the human gingival epithelial cell line Ca9-22 by Porphyromonas gingivalis, a periodontal pathogenic gram-negative bacterium. Recombinant galectin-1, but not galectin-3, enhanced P. gingivalis adhesion and invasion, although both galectins bound similarly to P. gingivalis. Flow cytometry also revealed that Ca9-22 cells express low levels of galectin-1 and moderate levels of galectin-3. Ca9-22 cells in which galectin-3 was knocked-down did not exhibit enhanced P. gingivalis adhesion and invasion. Similarly, specific antibodies to galectin-1 and galectin-3 did not inhibit P. gingivalis adhesion and invasion. These results suggest that soluble galectin-1, but not galectin-3, may exacerbate periodontal disease by enhancing the adhesion to and invasion of host cells by periodontal pathogenic bacteria.

Etidronate down-regulates Toll-like receptor (TLR) 2 ligand-induced proinflammatory cytokine production by inhibiting NF-κB activation

BACKGROUND

Etidronate is a non-nitrogen-containing bisphosphonate (non-NBP) used for anti-bone resorptive therapy as well as having inhibitory effects on atherosclerotic plaques. The present study examined the effects of etidronate on the production of proinflammatory cytokines and chemokines by the macrophage-like cell line, J774.1, incubated with Pam₃Cys-Ser-(Lys)₄ (Pam₃CSK₄, a Toll-like receptor (TLR) 2 agonist) and lipid A (a TLR4 agonist).

METHODS

J774.1 cells and human monocytic THP-1 cells were pretreated with or without etidronate for 5min, and then incubated with or without Pam₃CSK₄ or lipid A for 24h. Levels of secreted interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and macrophage inflammatory protein-1α (MIP-1α) in culture supernatants were measured by enzyme-linked immunosorbent assay (ELISA). Cytotoxicity was determined by LDH activity in the supernatants. We also examined the effects of etidronate on the activation of nuclear factor-κB (NF-κB) and p38 mitogen-activated protein kinase (MAPK) in J774.1 cells by ELISA and Western blotting.

RESULTS

Treatment of J774.1 cells with etidronate down-regulated TLR2 ligand-induced production of IL-6, TNF-α, MCP-1, and MIP-1α. Etidronate also inhibited Pam₃CSK₄-induced MCP-1 and TNF-α production by THP-1 cells. However, etidronate did not induce cytotoxicity and reduced lipid A-induced cytotoxicity in J774.1 cells. In addition, this agent did not down-regulate TLR4 ligand-induced proinflammatory cytokine production. Furthermore, etidronate inhibited the translocation of NF-κB but not p38 MAPK in J774.1 cells stimulated with Pam₃CSK₄ or lipid A.

CONCLUSION

Etidronate likely inhibits proinflammatory cytokine production in J774.1 cells by suppressing NF-κB activation in the TLR2 and not the TLR4 pathway.

Relationship between periodontitis-associated subgingival microbiota and clinical inflammation by 16S pyrosequencing

AIM

To analyse the relationship between the chronic periodontitis-associated subgingival microbiota and clinical inflammation.

MATERIAL AND METHODS

Sixty subjects with generalized chronic periodontitis participated in this study. Patients were divided into two groups according to their bleeding on probing (BOP) scores: BOP-1 group (mean scores ≤50% in sampled sites) and BOP-2 group (mean scores >50%). Subgingival bacterial samples from periodontal patients were studied by pyrosequencing PCR products of the 16S rRNA gene and by real-time PCR.

RESULTS

In all the analysed subgingival samples, 102 bacterial genera and 203 species (from 41 genera of interest) were identified. Rarefaction curves showed a greater number of bacterial species in samples from BOP-2 group compared to BOP-1 group. The BOP-1 group had significantly higher abundance percentages of Anaeroglobus (especifically, A. geminatus), Capnocytophaga (especifically C. gingivalis), TM7 and Veillonella. The BOP-2 had significantly higher abundance percentages of Desulfobulbus (especially D. propionicus), Eubacterium (especially E. saphenum), Filifactor alocis, Streptococcus constellatus, Tannerella (especially, T. forsythia) and Treponema.

CONCLUSION

16S pyrosequencing revealed that increased inflammation, at sites with periodontitis, is associated with a more diverse subgingival microbiota and specific changes in the bacterial composition, involving "established" periopathogens, symbionts and novel low-abundance pathobionts.

Gingipain-dependent augmentation by Porphyromonas gingivalis of phagocytosis of Tannerella forsythia

In the pathogenesis of periodontitis, Porphyromonas gingivalis plays a role as a keystone pathogen that manipulates host immune responses leading to dysbiotic oral microbial communities. Arg-gingipains (RgpA and RgpB) and Lys-gingipain (Kgp) are responsible for the majority of bacterial proteolytic activity and play essential roles in bacterial virulence. Therefore, gingipains are often considered as therapeutic targets. This study investigated the role of gingipains in the modulation by P. gingivalis of phagocytosis of Tannerella forsythia by macrophages. Phagocytosis of T. forsythia was significantly enhanced by coinfection with P. gingivalis in a multiplicity of infection-dependent and gingipain-dependent manner. Mutation of either Kgp or Rgp in the coinfecting P. gingivalis resulted in attenuated enhancement of T. forsythia phagocytosis. Inhibition of coaggregation between the two bacterial species reduced phagocytosis of T. forsythia in mixed infection, and this coaggregation was dependent on gingipains. Inhibition of gingipain protease activities in coinfecting P. gingivalis abated the coaggregation and the enhancement of T. forsythia phagocytosis. However, the direct effect of protease activities of gingipains on T. forsythia seemed to be minimal. Although most of the phagocytosed T. forsythia were cleared in infected macrophages, more T. forsythia remained in cells coinfected with gingipain-expressing P. gingivalis than in cells coinfected with the gingipain-null mutant or infected only with T. forsythia at 24 and 48 h post-infection. Collectively, these results suggest that P. gingivalis, mainly via its gingipains, alters the clearance of T. forsythia, and provide some insights into the role of P. gingivalis as a keystone pathogen.

Characterization of Treponema denticola mutants defective in the major antigenic proteins, Msp and TmpC

Treponema denticola, a gram-negative and anaerobic spirochete, is associated with advancing severity of chronic periodontitis. In this study, we confirmed that two major antigenic proteinswere Msp and TmpC, and examined their physiological and pathological roles using gene-deletion mutants. Msp formed a large complex that localized to the outer membrane, while TmpC existed as a monomer and largely localized to the inner membrane. However, TmpC was also detected in the outer membrane fraction, but its cell-surface exposure was not detected. Msp defects increased cell-surface hydrophobicity and secretion of TNF-α from macrophage-like cells, whereas TmpC defects decreased autoagglutination and chymotrypsin-like protease activities. Both mutants adhered to gingival epithelial cells similarly to the wild-type and showed slightly decreased motility. In addition, in Msp-defective mutants, the TDE1072 protein, which is a major membrane protein, was abolished; therefore, phenotypic changes in the mutant can be, at least in part, attributed to the loss of the TDE1072 protein. Thus, the major antigenic proteins, Msp and TmpC, have significant and diverse impacts on the characteristics of T. denticola, especially cell surface properties.

Transcriptional responses of Treponema denticola to other oral bacterial species

The classic organization by Socransky and coworkers categorized the oral bacteria of the subgingival plaque into different complexes. Treponema denticola, Porphyromonas gingivalis and Tannerella forsythia are grouped into the red complex that is highly correlated with periodontal disease. Socransky's work closely associates red with orange complex species such as Fusobacterium nucleatum and Prevotella intermedia but not with members of the other complexes. While the relationship between species contained by these complexes is in part supported by their ability to physically attach to each other, the physiological consequences of these interactions and associations are less clear. In this study, we employed T. denticola as a model organism to analyze contact-dependent responses to interactions with species belonging to the same complex (P. gingivalis and T. forsythia), the closely associated orange complex (using F. nucleatum and P. intermedia as representatives) and the unconnected yellow complex (using Streptococcus sanguinis and S. gordonii as representatives). RNA was extracted from T. denticola alone as well as after pairwise co-incubation for 5 hrs with representatives of the different complexes, and the respective gene expression profiles were determined using microarrays. Numerous genes related to motility, metabolism, transport, outer membrane and hypothetical proteins were differentially regulated in T. denticola in the presence of the tested partner species. Further analysis revealed a significant overlap in the affected genes and we identified a general response to the presence of other species, those specific to two of the three complexes as well as individual complexes. Most interestingly, many predicted major antigens (e.g. flagella, Msp, CTLP) were suppressed in responses that included red complex species indicating that the presence of the most closely associated species induces immune-evasive strategies. In summary, the data presented here provide an in-depth understanding of the transcriptional responses triggered by contact-dependent interactions between microorganisms inhabiting the periodontal pocket.

Candida albicans enhances invasion of human gingival epithelial cells and gingival fibroblasts by Porphyromonas gingivalis

Although Candida albicans has been isolated from periodontal pockets, its relationship to periodontitis is unclear. In this study, we investigated the effect of C. albicans on the adhesion and invasion of Ca9-22, a human gingival epithelial cell line, and human gingival fibroblasts by Porphyromonas gingivalis. Heat-killed C. albicans and water-soluble mannoprotein-β-glucan complex from C. albicans (CAWS) did not enhance P. gingivalis adhesion or upregulate the expression of β1 integrin and ICAM-1, which are required for P. gingivalis invasion; both the epithelial cells and fibroblasts expressed dectin-1, which recognizes components of the C. albicans cell wall. However, pretreatment of Ca9-22 cells and human gingival fibroblasts with heat-killed C. albicans or CAWS significantly enhanced P. gingivalis invasion. These results suggest that C. albicans may exacerbate infectious disease by enhancing the invasion of host cells by anaerobic bacteria.

Virulence of major periodontal pathogens and lack of humoral immune protection in a rat model of periodontal disease

OBJECTIVE

This study was designed to test the hypothesis that periodontal pathogens Tannerella forsythia and Porphyromonas gingivalis are synergistic in terms of virulence potential using a model of mixed-microbial infection in rats.

MATERIALS AND METHODS

Three groups of rats were infected orally with either T. forsythia or P. gingivalis in mono-bacterial infections or as mixed-microbial infections for 12 weeks and a sham-infected group were used as a control. This study examined bacterial infection, inflammation, immunity, and alveolar bone loss changes with disease progression.

RESULTS

Tannerella forsythia and P. gingivalis genomic DNA was detected in microbial samples from infected rats by PCR indicating their colonization in the rat oral cavity. Primary infection induced significantly high IgG, IgG2b, IgG1, and IgG2a antibody levels indicating activation of mixed Th1 and Th2 immune responses. Rats infected with the mixed-microbial consortium exhibited significantly increased palatal horizontal and interproximal alveolar bone loss. Histological examinations indicated significant hyperplasia of the gingival epithelium with moderate inflammatory infiltration and apical migration of junctional epithelium. The results observed differ compared to uninfected controls.

CONCLUSION

Our results indicated that T. forsythia and P. gingivalis exhibit virulence, but not virulence synergy, resulting in the immuno-inflammatory responses and lack of humoral immune protection during periodontitis in rats.

Treponema denticola suppresses expression of human {beta}-defensin-3 in gingival epithelial cells through inhibition of the toll-like receptor 2 axis

We reported previously that Treponema denticola, one of the periodontal pathogens, suppresses the expression of human beta-defensins (HBDs) in human gingival epithelial cells. To identify the mechanisms involved in this suppression, immortalized and normal human gingival epithelial cells were infected with live or heat-killed T. denticola for 24 h, and then the expression of HBDs was examined by real-time RT-PCR. Live T. denticola suppressed the expression of HBD-3 substantially and also suppressed the expression of HBD-1 and HBD-2. However, heat-killed bacteria did not produce a suppressive effect but instead slightly upregulated the levels of HBD-2 and HBD-3. In contrast to live T. denticola, which reduced the activation of mitogen-activated protein kinase (MAPK) and NF-kappaB within an hour of infection, heat-killed bacteria did not show any inhibitory effect on the MAPK and NF-kappaB signaling pathways. Knockdown of Toll-like receptor 2 (TLR2) via RNA interference abolished the suppressive effect of T. denticola on the expression of HBD-3. Heat-killed T. denticola but not live bacteria could activate TLR2 in CHO/CD14/TLR2 reporter cells, suggesting that T. denticola contains a heat-labile inhibitor(s) of TLR2 in addition to ligands recognized by TLR2. Indeed, live T. denticola was able to inhibit TLR2 activation by Pam(3)CSK. In conclusion, T. denticola suppressed the expression of HBD-3 by inhibiting the TLR2 axis in gingival epithelial cells. These results may provide new insight into the pathogenesis of periodontitis caused by T. denticola.