Blockade of sympathetic β-receptors inhibits Porphyromonas gingivalis-induced alveolar bone loss in an experimental rat periodontitis model

Introduction

Periodontal disease is characterised by alveolar bone loss. Some studies have suggested the involvement of sympathetic nervous system in the deterioration of periodontal disease. Noradrenaline, released from sympathetic nerve terminals due to various stimuli, binds to specific adrenergic receptors on immune cells. Recently, we reported that restraint stress augmented the alveolar bone loss induced by Porphyromonas gingivalis infection. In this study, we investigated the effects of the β-blocker (propranolol) on alveolar bone loss induced by P. gingivalis infection to examine the involvement of sympathetic nerves in periodontal breakdown.

Methods

Sprague-Dawley rats were treated as follows: saline injection (Group A), propranolol injection (Group B), saline injection and oral challenge with P. gingivalis (Group C), and propranolol injection and oral challenge with P. gingivalis (Group D). Horizontal alveolar bone loss was evaluated by measuring the distance between the cemento-enamel junction and the alveolar bone crest. Specimens from periodontal tissue were evaluated by staining with hematoxylin-eosin and tartrate-resistant acid phosphatase.

Results

Blockade of β-receptors in periodontal tissue by propranolol inhibited osteoclast differentiation and prevented alveolar bone loss induced by P. gingivalis infection. Histological study revealed that the number of osteoclasts detected was proportional to the level of bone loss.

Conclusions

These results indicate that the sympathetic nervous system is involved in the development of periodontitis and suggest that sympathetic signal modulation with β-blockers enables the control of alveolar bone mass metabolism.     

Streptococcus cristatus ArcA interferes with Porphyromonas gingivalis pathogenicity in mice

Xie H, Hong J, Sharma A, Wang B‐Y. Streptococcus cristatus ArcA interferes with Porphyromonas gingivalis pathogenicity in mice. J Periodont Res 2012; 47: 578–583. © 2012 John Wiley & Sons A/S Background and Objective: Porphyromonas gingivalis has been implicated as one of the major pathogens in chronic periodontitis, an infectious disease affecting the majority of the adult population. We have previously demonstrated that a surface protein, arginine deiminase (ArcA), of Streptococcus cristatus represses production of P. gingivalis long fimbriae and interrupts the formation of P. gingivalis biofilms in vitro. Our in vivo studies have also shown that the distribution of P. gingivalis and S. cristatus in human subgingival plaque is negatively correlated. The objective of this study was to determine if S. cristatus ArcA inhibits P. gingivalis colonization and attenuates its subsequent pathogenesis in alveolar bone loss in the murine oral cavity. Material and Methods: A wild‐type strain of S. cristatus (CC5A) and its arcA knockout mutant (ArcAE) were used as initial colonizers in the oral cavity of BALB/cByJ mice. Colonization of P. gingivalis on the existing S. cristatus biofilms was assessed by quantitative PCR, and P. gingivalis‐induced alveolar bone loss was measured 6 wk after P. gingivalis infection. Results: The presence of S. cristatus CC5A, but not its arcA mutant, attenuated P. gingivalis colonization in the murine oral cavity. In addition, P. gingivalis‐induced alveolar bone loss was significantly lower in mice initially infected with S. cristatus CC5A than in those infected with the arcA mutant. Conclusion: This study provides direct evidence that S. cristatus ArcA has an inhibitory effect on P. gingivalis colonization, which may in turn attenuate the pathogenicity of P. gingivalis.     

Deficiency of iNOS contributes to Porphyromonas gingivalis‐induced tissue damage

Periodontitis is a chronic inflammatory disease that results in extensive soft and hard tissue destruction of the periodontium. Porphyromonas gingivalis possesses an array of virulence factors and has been shown to induce expression of inducible nitric oxide synthase (iNOS) in inflammatory cells. The aim of this study was to investigate the effect of eliminating iNOS in a murine model of P. gingivalis infection. This was achieved by utilizing a P. gingivalis‐induced skin abscess model, and an alveolar bone loss model employing an oral infection of P. gingivalis in iNOS knockout mice. The results indicated that iNOS knockout mice exhibit more extensive soft tissue damage and alveolar bone loss in response to P. gingivalis infection compared to wild‐type mice. The local immune response to P. gingivalis in iNOS knockout mice was characterized by increased numbers of polymorphonuclear monocytes, while the systemic immune response was characterized by high levels of interleukin‐12. The iNOS is required for an appropriate response to P. gingivalis infection.     

Therapeutic effect of a topical CCR2 antagonist on induced alveolar bone loss in mice

Barros SP, Arce RM, Galloway P, Lawter JR, Offenbacher S. Therapeutic effect of a topical CCR2 antagonist on induced alveolar bone loss in mice. J Periodont Res 2011; 46: 246–251. © 2011 John Wiley & Sons A/S Background and Objective: Chemokines are known to regulate leukocyte trafficking, recruitment and infiltration in periodontal diseases. The study objective was to determine the effect of an experimental oral/topical chemokine (C‐C motif) receptor 2 (CCR2)‐antagonist treatment on alveolar bone loss in a mouse model of Porphyromonas gingivalis‐induced periodontitis. Material and Methods: Balb/C mice (n = 41) were randomly assigned to four groups. Group 1 was infected by P. gingivalis applied orally/topically for 5 wk. Group 2 was also infected and then treated with vehicle (aqueous methylcellulose) for an additional 4 wk. Group 3 was infected and orally/topically treated with CCR2 antagonist (10 mg/kg). Group 4 served as a noninfected, nontreated control group. Mice received intraperitoneal injections of Alizarin (30 mg/kg) and calcein (20 mg/kg) three times from the last day of infection to determine mineral deposition, reflecting bone dynamics. Mandibles were analysed by morphometry and confocal fluorescence microscopy. Results: Alveolar bone loss was compared among groups using Tukey’s test, and bone formation was qualitatively observed. Infected mice showed significantly greater alveolar bone loss than noninfected control animals (group 1 vs. 4, p < 0.01). Vehicle‐treated mice (group 2) showed the largest area of alveolar bone loss (p < 0.01), while mice treated with the CCR2 antagonist showed the smallest area of alveolar bone loss and were similar to the control group (group 3 vs. 4, p = 0.14). Qualitative analysis of fluorescent dye uptake indicated increased bone formation in CCR2‐antagonist‐treated mice, suggesting an improved bone repairing process. Conclusion: The results suggested that treatment with CCR2 antagonist inhibited alveolar bone loss and improved bone formation in this model. These data support further evaluation of CCR2 antagonist as a therapeutic target for the development of new treatment modalities on bacterially induced alveolar bone resorption.     

Liver X receptors contribute to periodontal pathogen‐elicited inflammation and oral bone loss

Periodontal diseases are chronic oral inflammatory diseases that are polymicrobial in nature. The presence of specific bacteria in subgingival plaque such as Porphyromonas gingivalis is associated with microbial dysbiosis and the modulation of host immune response. Bacterially elicited innate immune activation and inflammation are key elements implicated in the destruction of soft and hard tissues supporting the teeth. Liver X receptors (LXRs) are nuclear hormone receptors with important function in lipid homeostasis, inflammation, and host response to infection; however, their contribution to chronic inflammatory diseases such as periodontal disease is not understood. The aim of this study was to define the contribution of LXRs in the development of immune response to P. gingivalis and to assess the roles that LXRs play in infection‐elicited oral bone loss. Employing macrophages, we observed that P. gingivalis challenge led to reduced LXRα and LXRβ gene expression compared with that observed with unchallenged wild‐type cells. Myeloid differentiation primary response gene 88 (MyD88)‐independent, Toll/interleukin‐1 receptor‐domain‐containing adapter‐inducing interferon‐β (TRIF)‐dependent signaling affected P. gingivalis‐mediated reduction in LXRα expression, whereas neither pathway influenced the P. gingivalis effect on LXRβ expression. Employing LXR agonist and mice deficient in LXRs, we observed functional effects of LXRs in the development of a P. gingivalis‐elicited cytokine response at the level of the macrophage, and participation of LXRs in P. gingivalis‐elicited oral bone loss. These findings identify novel importance for LXRs in the pathogenesis of P. gingivalis infection‐elicited inflammation and oral bone loss.     

Divergence of the systemic immune response following oral infection with distinct strains of Porphyromonas gingivalis

Periodontitis is a polymicrobial oral infection characterized by the destruction of tooth‐supporting structures that can be linked to systemic diseases such as cardiovascular disease, diabetes or rheumatoid arthritis. Porphyromonas gingivalis, a bacterium implicated in the etiology of periodontitis, has shown variation in inducing T‐cell responses among different strains. Therefore, in this study we investigated the strain‐specific immune response using a murine experimental model of periodontitis. Periodontitis was induced by P. gingivalis strains A7A1‐28, W83 and W50, and later confirmed by the presence of P. gingivalis in the oral microflora and by alveolar bone resorption. Splenocytes were evaluated for gene expression, cellular proteins and cytokine expression. Dendritic cells were stimulated in vitro for T helper cell–cytokine profiling. Results showed that P. gingivalis had the ability to alter the systemic immune response after bacterial exposure. Strains W50 and W83 were shown to induce alveolar bone loss, whereas the A7A1‐28 strain did not significantly promote bone resorption in mice. Splenocytes derived from mice infected with strains W50 and W83 induced expression of high levels of interleukin‐4 (IL‐4) but A7A1‐28 stimulated increased IL‐10. Stimulation of dendritic cells in vitro showed a similar pattern of cytokine expression of IL‐12p40, IL‐6 and transforming growth factor‐β among strains. A distinct systemic response in vivo was observed among different strains of P. gingivalis, with IL‐10 associated with the least amount of alveolar bone loss. Evaluation of pathogen‐driven systemic immune responses associated with periodontal disease pathogenesis may assist in defining how periodontitis may impact other diseases.     

In Vivo Inhibition of Porphyromonas gingivalis Growth and Prevention of Periodontitis With Quorum‐Sensing Inhibitors

Background: Autoinducer (AI)‐2 has an important role in biofilm formation in the oral environment. Mature biofilms formed as a result of the cell‐to‐cell communication make it difficult to overcome periodontitis with the use of antibiotics. Previous in vitro studies suggest that quorum‐sensing inhibitors (QSIs) interfere with AI‐2. This study compares the QSI effects resulting from an oral inoculation of Porphyromonas gingivalis in an experimental animal model. Methods: Forty‐five male mice were divided into three groups (n = 15 each): 1) infection; 2) QSI; and 3) control. Infection and QSI groups received oral inoculation of P. gingivalis, whereas treatment with QSIs (furane compound and d ‐ribose) was only performed in the QSIs group. The control group was a negative control not receiving manipulation. After 42 days, mice were sacrificed, and the distance from the alveolar bone crest (ABC) to the cemento‐enamel junction (CEJ) was measured by microcomputed tomography. P. gingivalis DNA was quantified in the soft and hard tissues around the molar teeth by real‐time polymerase chain reaction. Results: Distance from ABC to CEJ was significantly increased in the P. gingivalis infection group compared with the control group (P = 0.02) and significantly decreased in the QSI group compared with the infection group (P = 0.02). The QSI group contained 31.64% of the bacterial DNA count of the infection group. Conclusion: Use of QSIs in the mice infection model showed a reduction of bone breakdown and a decrease in the number of bacteria in vivo, suggesting that QSIs can be a new approach to prevention and treatment of periodontitis.     

Periodontitis in the absence of B cells and specific anti‐bacterial antibody

Periodontitis (PD) results from complex interactions between a dysbiotic oral microbiota and a dysregulated host immune response. The inflammatory infiltrate in the gingiva of PD patients includes an abundance of B cells, implicating these cells in the immunopathology. We sought to investigate the role of B cells in PD using a murine model. Wild‐type or B‐cell‐deficient (μMT) mice were orally infected with Porphyromonas gingivalis. One or six weeks following infection, lymphocyte populations in the gingiva and cervical draining lymph nodes (dLN) were analysed by flow cytometry; serum anti‐P. gingivalis IgG antibody titers were measured by enzyme‐linked immunosorbent assay, and alveolar bone loss was determined. In wild‐type mice, the percentage of gingival B cells expressing receptor activator of nuclear factor‐κB ligand (RANKL) was significantly increased 1 week post‐infection (5.36% control versus 11% PD, P < 0.01). The percentage of Fas⁺ GL7⁺ germinal centre B cells in the dLN was significantly increased at both 1 week (2.03% control versus 6.90% PD, P < 0.01) and 6 weeks (4.45% control versus 8.77% PD, P < 0.05) post‐infection. B‐cell‐deficient mice were protected from P. gingivalis‐induced alveolar bone loss, with a lack of B‐cell proliferation and lack of CD4⁺ CD44⁺ CD62L^? T‐cell generation in the dLN, and absence of serum anti‐P. gingivalis antibodies. Our data imply a pathological role for B cells in PD, and that selective targeting of this immune axis may have a role in treating severe periodontal disease.     

In vivo and ex vivo actions of a novel P. gingivalis inhibitor on multi‐species biofilm,inflammatory response,and periodontal bone loss

Chronic periodontitis is one of the most common infectious inflammatory diseases worldwide. Current therapeutic options for the disease are only partially and temporarily successful due to periodontal re‐emergence of pathogens such as Porphyromonas gingivalis, a keystone bacterium in the oral microbial communities, which elicits a dysbiosis between the microbiota and the host. Previously, we reported a peptide inhibitor of P. gingivalis (SAPP) that specifically targets P. gingivalis and reduces its virulence potential in vitro. Here, we show that SAPP can modulate the ability of P. gingivalis to suppress the host innate immune system. Using a cytokine array analysis, we found that the levels of several cytokines including IL‐6, IL‐8, and MCP‐1 in the culture media of human oral keratinocytes (HOKs) were significantly diminished in the presence of P. gingivalis. Whereas the levels of these cytokines were restored, at least partially, in the culture media of HOKs by SAPP treatment. Furthermore, we also observed in an ex vivo assay that SAPP efficiently inhibited biofilm primed formation by mixed‐species oral bacteria, and significantly dampened the abnormally innate immune responses induced by these bacteria. We also demonstrated, using a mouse model, that SAPP could prevent alveolar bone loss induced by P. gingivalis. Our results suggest that SAPP specifically targets P. gingivalis and its associated bacterial communities and could be envisioned as an emerging therapy for periodontitis.     

Oral immunization with Porphyromonas gingivalis outer membrane protein and CpG oligodeoxynucleotides elicits T helper 1 and 2 cytokines for enhanced protective immunity

The aim of this study was to evaluate the efficacy of an oral vaccine containing the 40‐kDa outer membrane protein of Porphyromonas gingivalis (40K‐OMP) and synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN) to control oral infection by P. gingivalis. Oral immunization with 40K‐OMP plus CpG ODN induced significant 40K‐OMP‐specific serum immunoglobulin G (IgG), IgA, and saliva IgA antibody responses. The 40K‐OMP‐specific CD4⁺ T cells induced by oral 40K‐OMP plus CpG ODN produced both T helper type 1 (Th1; interferon‐γ) and Th2 (interleukin‐4) cytokines. Furthermore, increased frequencies of CD11c⁺ B220⁺ dendritic cells (DCs) and CD11c⁺ CD11b⁺ DCs with upregulated expression of CD80, CD86, CD40, and major histocompatibility complex class II molecules were noted in spleen, Peyer’s patches, and cervical lymph nodes. Immunized mice were then infected orally with P. gingivalis to determine whether the immune responses induced by oral 40K‐OMP plus CpG ODN were capable of suppressing the bone resorption caused by P. gingivalis infection. Mice given 40K‐OMP plus CpG ODN showed significantly reduced bone loss associated with oral infection by P. gingivalis. Oral administration of 40K‐OMP together with CpG ODN induces Th1‐type and Th2‐type cells, which provide help for protective immunity against P. gingivalis infection. This may be an important tool for the prevention of chronic periodontitis.     

Reduced expression of lipopolysaccharide‐induced CXC chemokine in Porphyromonas gingivalis‐induced experimental periodontitis in matrix metalloproteinase‐8 null mice

Hernández M, Gamonal J, Salo T, Tervahartiala T, Hukkanen M, Tjäderhane L, Sorsa T. Reduced expression of LIX/CXCL5 in Porphyromonas gingivalis‐induced experimental periodontitis in matrix metalloproteinase‐8 null mice. J Periodont Res 2011; 46: 58–66. © 2010 John Wiley & Sons A/S Background and Objective: Matrix metalloproteinase‐8 (MMP‐8) is a central mediator in chronic periodontitis. Recently developed MMP‐8‐deficient mice show an impaired polymorphonuclear neutrophil response and more severe alveolar bone loss in Porphyromonas gingivalis‐induced experimental periodontitis. The main mediators involved in neutrophil and monocyte/macrophage recruitment and in bone loss include lipopolysaccharide‐induced CXC chemokine (LIX/CXCL5), stromal‐derived factor‐1/CXC chemokine ligand 12 (SDF1/CXCL12) and RANKL. Therefore, the aim of this study was to characterize the expression of LIX/CXCL5, SDF1/CXCL12 and RANKL in Porphyromonas gingivalis‐induced experimental periodontitis in MMP‐8^?/^? (knockout) and wild‐type mice. Material and methods:  MMP‐8 null and WT P. gingivalis‐infected and uninfected mice were included. Histopathological changes were assessed and LIX/CXCL5, SDF1/CXCL12 and RANKL were immunodetected and quantified. Results: Typical histopathological features of chronic periodontitis were seen in P. gingivalis‐infected groups. LIX/CXCL5 expression was restricted to the gingival papilla in all four groups. Significantly lower expression of LIX/CXCL5 was seen in the knockout group compared with the wild‐type infected group (p < 0.05). SDF1/CXCL12 and RANKL expression was mainly localized to the alveolar crest, including inflammatory leukocytes, vascular endothelium, osteoblasts and osteoclasts. Significant increases of SDF1/CXCL12 and RANKL were seen in both knockout and wild‐type P. gingivalis‐infected groups compared with uninfected groups (p < 0.05). Conclusion: RANKL and SDF1/CXCL12 are up‐regulated in P. gingivalis‐induced periodontitis and they appear to be associated with the pathogenesis of the disease. MMP‐8 is associated with a reduced expression of LIX/CXCL5 in the P. gingivalis‐induced experimental periodontitis model.     

Serum antibody response to oral infection precedes but does not prevent Porphyromonas gingivalis–induced alveolar bone loss in mice

The purpose of this study was to determine whether humoral immunity prevents bacterially induced alveolar bone loss. BALB/cByJ mice were orally infected with the human periodontopathic bacterium Porphyromonas gingivalis, and were compared with sham-infected mice. Specific serum antibody titers to P. gingivalis were measured by enzyme-linked immunosorbent assay. Alveolar bone levels were measured as the distance from the cementoenamel junction to the alveolar bone crest and bone loss was defined as a change in bone levels over time or between infected and sham-infected animals. The specific humoral response was predominantly of the IgG isotype, although low levels of specific serum IgA were also present. Antibody titers in the infected animals were significantly different from those in the sham-infected animals by 18 days and remained at maximal levels at 47 days. Bone loss became significant by 26 days and continued to progress at 47 days. Thus the serum antibody response to oral infection with P. gingivalis preceded detectable bone loss and remained elevated while bone loss increased. The presence of specific antibody did not prevent the onset or progression of bone loss.     

Tetracyclines inhibit Porphyromonas gingivalis-induced alveolar bone loss in rats by a non-antimicrobial mechanism

Tetracyclines have been widely used as adjuncts in periodontal therapy due to the antimicrobial efficacy of these drugs. Recently, their ability to inhibit host-derived matrix metalloproteinases (collagenase and gelatinase) and bone resorption in organ culture has also been invoked as a therapeutic rationale. The current study was undertaken to determine whether tetracyclines can inhibit alveolar bone loss in vivo due to a non-antimicrobial action of these drugs. Experimental periodontitis was induced by inoculating adult, male Sprague-Dawley rats with P. gingivalis (strain 381) following kanamycin/ampicillin pretreatment. Doxycycline, non-antimicrobial chemically-modified tetracycline (CMT-1) and vehicle alone were administered daily to 3 infected groups of rats (n=6 rats per group; each group housed in a sterilized inflatable isolator) beginning 10 days after P. gingivalis inoculation. The control group (n = 6; non-infected rats) received only vehicle. After 5 weeks of daily drug administration by gastric intubation, the experiment was terminated and blood samples were taken from each animal to determine antibody levels against P. gingivalis. Plaque samples were collected from each group of animals before and after P. gingivalis inoculation and at the end of the experiment for microbiological examination. The jaws were removed from each rat, defleshed and then analyzed morphometrically and radiographically to assess bone loss. Serum antibody levels against P. gingivalis were significantly elevated in the 3 infected groups compared to the non-infected controls. This, together with the microbiologic findings, indicated that these groups of rats were infected with P. gingivalis. Significantly greater bone loss was observed in the untreated P. gingivalis-infected group compared to the controls based on both morphometric and radiographic measurements. Oral administration of doxycycline or CMT-1 to the P. gingivalis-infected rats completely inhibited this bone loss. As expected, CMT-1 did not exhibit an antimicrobial effect against P. gingivalis. Therefore, this study indicates that tetracyclines can inhibit alveolar bone loss in vivo by a mechanism which is independent of the antimicrobial efficacy of these drugs.     

Impact of Porphyromonas gingivalis inoculation on ligature-induced alveolar bone loss. A pilot study in rats

Meulman T, Peruzzo DC, Stipp RN, Gonçalves PF, Sallum EA, Casati MZ, Goncalves RB, Nociti FH Jr. Impact of Porphyromonas gingivalis inoculation on ligature‐induced alveolar bone loss. A pilot study in rats. J Periodont Res 2011; 46: 629–636.©2011 John Wiley & Sons A/S Background and Objective: Periodontitis is a polymicrobial infection characterized by the loss of connective tissue attachment, periodontal ligament and alveolar bone. The aim of this study was to evaluate the impact of Porphyromonas gingivalis inoculation on the ligature‐induced alveolar bone loss (ABL) model in rats. Material and Methods: Forty male Wistar rats were randomly assigned to the following groups: G1, control (n = 10); G2, ligature‐induced ABL (n = 15); and G3, ligature‐induced ABL + P. gingivalis inoculation (n = 15). Rats in G2 and G3 were killed 15, 21 and 30 d after ligature placement, and the following parameters were assessed: microbiological load; ABL; and interleukin (IL)‐1β (Il1beta)/Il1ra, Il6/Il10 and Rankl/osteoprotegerin (Opg) mRNA ratios in the gingival tissues, as determined by quantitative PCR. Results: Microbiological analyses demonstrated that rats in G1, G2 and G3 were positive for the presence of bacteria (determined using PCR amplification of the 16S gene), but that only the treatment sites of rats in G3 were positive for P. gingivalis at all time‐points investigated. Histometrically, significant bone loss (p < 0.001) was observed for both ligated groups (G2 and G3) compared with the nonligated group (G1), with higher ABL observed for G2 at all the experimental time‐points. Furthermore, gene‐expression analysis demonstrated that the presence of P. gingivalis in the dentogingival area significantly decreased the Il1β/Il1ra, Il6/Il10 and Rankl/Opg mRNA ratios compared with ligature alone. Conclusion: Within the limits of this pilot study, it was concluded that inoculation of P. gingivalis affected the ligature‐induced ABL model by the induction of an anti‐inflammatory and antiresorptive host response.     

Immunoprotective effects of a hemin‐binding peptide derived from hemagglutinin‐2 against infection with Porphyromonas gingivalis

The principal etiologic agent in periodontal disease, Porphyromonas gingivalis, generates cysteine proteases that bind heme with domains such as hemagglutinin‐2 (HA2). High‐affinity HA2–hemin binding supplies the porphyrin and ferric iron needed for growth and virulence. The DHYAVMISK peptide, recently identified at the hemin‐binding site of HA2, inhibits hemin binding. We now evaluate the protective effect of vaccination with DGFPGDHYAVMISK (termed DK) against P. gingivalis using a rat infection model. Rats immunized with DK generated anti‐peptide serum IgGs and salivary sIgAs (as measured by ELISA). In a subcutaneous abscess model, the protective effect of immunization was then investigated by measuring abscess size following subcutaneous injection with P. gingivalis. In an oral infection model, a ligature inoculated with P. gingivalis was used to induce periodontitis. The degree of bone erosion, ordinarily provoked by infection, was then evaluated by micro‐computed tomography. We found that anti‐peptide antibody titers of serum IgGs and salivary sIgAs for rats immunized with DK and adjuvant were significantly higher than for sham‐immunized rats (injected with adjuvant/PBS alone; P < .05). In the subcutaneous abscess model, the DK + adjuvant‐vaccinated rats recovered faster than sham‐vaccinated animals, with their abscess sizes significantly smaller (P < .05). Further, in the experimental periodontitis model, bone loss at the molar palatal side for DK + adjuvant‐vaccinated rats was significantly lower than for sham‐vaccinated animals (P < .05). Collectively, these data demonstrate the potential of (DK) peptide immunization in terms of eliciting an immunoprotective effect against infection with P. gingivalis.     

Porphyromonas gingivalis-specific IgG subclass antibody levels as immunological risk indicators of periodontal bone loss

Background: It has been well demonstrated a positive association between the magnitude of host antibody response and periodontal disease status. Previous studies also reported that Porphyromonas gingivalis‐specific IgG subclass antibodies were elevated in sera from adult periodontitis patients. However, the rôle and the association of these IgG subclass antibodies to the development of periodontal diseases are poorly understood. Aim: The aim of present investigation was to examine the relation of serum IgG subclass antibody levels and alveolar bone loss in treated and untreated periodontitis patients. Methods: Serum samples were taken from 20 treated and maintained periodontitis patients (SPT patients), 30 untreated patients and 19 periodontally healthy subjects. We determined the IgG subclass antibody titers to P. gingivalis whole cells using an enzyme‐linked immunosorbent assay (ELISA). Subgingival plaque samples were taken from the mesio‐buccal surface of 6 randomly selected teeth of SPT patients and evaluated for the presence of P. gingivalis by immunofluorescence microscopy. Clinical measurements were also taken including full mouth intraoral radiographs to measure interproximal alveolar bone loss at baseline (BLS1) and at a 5‐year recall visit in the SPT patients (BLS2). Results: Our results indicated that both patient groups had detectable levels of IgG1, IgG2, and IgG4. Significantly higher IgG1 was observed in both patient groups compared to the healthy subjects. The untreated patients also exhibited significantly elevated IgG2 response (p<0.05). The mean IgG4 level of the SPT patients was significantly higher compared to the other subject group (p<0.05). A statistically significant positive correlation between IgG2 levels and changes in bone levels (ΔBLS: BLS2‐BLS1) was seen in the SPT patients (p<0.001). SPT patients with high IgG2 and low IgG4 showed greater bone loss than those with low IgG2 and high IgG4 (p<0.05), although the mean prevalence of P. gingivalis in the 2 groups did not differ significantly. Conclusion: Our data suggest that the prolonged IgG2 response after periodontal treatment may be indicative of recurrent or persistent periodontal destruction.     

Immunologic environment influences macrophage response to Porphyromonas gingivalis

Macrophages adapt both phenotypically and functionally to the cytokine balance in host tissue microenvironments. Recent studies established that macrophages contribute an important yet poorly understood role in the development of infection‐elicited oral bone loss. We hypothesized that macrophage adaptation to inflammatory signals encountered before pathogen interaction would significantly influence the subsequent immune response of these cells to the keystone oral pathobiont Porphyromonas gingivalis. Employing classically activated (M1) and alternatively activated (M2) murine bone‐marrow‐derived macrophage (BMDMø), we observed that immunologic activation of macrophages before P. gingivalis challenge dictated phenotype‐specific changes in the expression of inflammation‐associated molecules important to sensing and tuning host response to bacterial infection including Toll‐like receptors 2 and 4, CD14, CD18 and CD11b (together comprising CR3), major histocompatibility complex class II, CD80, and CD86. M2 cells responded to P. gingivalis with higher expression of tumor necrosis factor‐α, interleukin‐6, monocyte chemoattractant protein‐1, macrophage inflammatory protein‐1α, regulated on activation normal T cell expressed and secreted, and KC than M1 cells. M1 BMDMø expressed higher levels of interleukin‐10 to P. gingivalis than M2 BMDMø. Functionally, we observed that M2 BMDMø bound P. gingivalis more robustly than M1 BMDMø. These data describe an important contribution of macrophage skewing in the subsequent development of the cellular immune response to P. gingivalis.