Prevention of Porphyromonas gingivalis-induced oral bone loss following immunization with gingipain R1

Advances and challenges in the development of periodontitis vaccines: A comprehensive review

Periodontitis is a prevalent polymicrobial disease. It damages soft tissues and alveolar bone, and causes a significant public-health burden. Development of an advanced therapeutic approach and exploration of vaccines against periodontitis hold promise as potential treatment avenues. Clinical trials for a periodontitis vaccine are lacking. Therefore, it is crucial to address the urgent need for developing strategies to implement vaccines at the primary level of prevention in public health. A deep understanding of the principles and mechanisms of action of vaccines plays a crucial role in the successful development of vaccines and their clinical translation. This review aims to provide a comprehensive summary of potential directions for the development of highly efficacious periodontitis vaccines. In addition, we address the limitations of these endeavors and explore future possibilities for the development of an efficacious vaccine against periodontitis.

Arginine-specific gingipains (RgpA/RgpB) knockdown modulates neutrophil machinery

Background

Gingipains are important virulence factors present in Porphyromonas gingivalis. Arginine-specific gingipains (RgpA and RgpB) are critically associated with increased proteolytic activity and immune system dysfunction, including neutrophilic activity. In this study, we assessed the impact of gingipains (RgpA and RgpB) on neutrophil function.

Methods

Peripheral blood samples were obtained; neutrophils were isolated and incubated with P. gingivalis A7436, W50, and the double RgpA/RgpB double knockout mutant E8 at MOI 20 for 2 hours. Neutrophil viability was assessed by Sytox staining. Phagocytic capacity and apoptosis were measured by flow cytometry. Superoxide release was measured by superoxide dismutase and cytochrome c reduction assay. Gene expression of TLR2, p47-phox, p67-phox, and P2 × 7was measured by qPCR. Inflammatory cytokine and chemokine production was measured by IL-1β, IL-8, RANTES, and TNF-α in cell supernatants.

Results

Neutrophil TLR2 gene expression was reduced in the absence of RgpA/RgpB (p < 0.05), while superoxide production was not significantly impacted. RgpA/RgpB-/- significantly impaired neutrophil phagocytic function (p < 0.05) and increased TNF-α production when compared with the wild-type control (p < 0.05). Neutrophil apoptosis was not altered when exposed to RgpA/RgpB-/- E8 (p > 0.05).

Conclusion

These data suggest that arginine-specific gingipains (RgpA/RgpB) can modulate neutrophil responses against P. gingivalis infection.

Porphyromonas gingivalis Vaccine: Antigens and Mucosal Adjuvants

Porphyromonas gingivalis (Pg), a Gram-negative anaerobic bacterium found in dental plaque biofilm within periodontal pockets, is the primary pathogenic microorganism responsible for chronic periodontitis. Infection by Pg significantly impacts the development and progression of various diseases, underscoring the importance of eliminating this bacterium for effective clinical treatment. While antibiotics are commonly used to combat Pg, the rise of antibiotic resistance poses a challenge to complete eradication. Thus, the prevention of Pg infection is paramount. Research suggests that surface antigens of Pg, such as fimbriae, outer membrane proteins, and gingipains, can potentially be utilized as vaccine antigens to trigger protective immune responses. This article overviews these antigens, discusses advancements in mucosal adjuvants (including immunostimulant adjuvants and vaccine-delivery adjuvants), and their application in Pg vaccine development. Furthermore, the review examines the advantages and disadvantages of different immune pathways and common routes of Pg vaccine immunization. By summarizing the current landscape of Pg vaccines, addressing existing challenges, and highlighting the potential of mucosal vaccines, this review offers new insights for the advancement and clinical implementation of Pg vaccines.

Alzheimer's Disease: A Systems View Provides a Unifying Explanation of Its Development

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder affecting 50 million people globally. It is characterized by the presence of extracellular senile plaques and intracellular neurofibrillary tangles, consisting of amyloid-β and hyperphosphorylated tau proteins, respectively. Despite global research efforts, there is currently no cure available, due in part to an incomplete understanding of the disease pathogenesis. Numerous possible mechanisms, or hypotheses, explaining the origins of sporadic or late-onset AD have been proposed, including the amyloid-β, inflammatory, vascular, and infectious hypotheses. However, despite ample evidence, the failure of multiple trial drugs at the clinical stage illuminates the possible pitfalls of these hypotheses. Systems biology is a strategy which aims to elucidate the interactions between parts of a whole. Using this approach, the current paper shows how the four previously mentioned hypotheses of AD pathogenesis can be intricately connected. This approach allows for seemingly contradictory evidence to be unified in a system-focused explanation of sporadic AD development. Within this view, it is seen that infectious agents, such as P. gingivalis, may play a central role. The data presented here shows that when present, P. gingivalis or its virulence factors, such as gingipains, may induce or exacerbate pathologies underlying sporadic AD. This evidence supports the view that infectious agents, and specifically P. gingivalis, may be suitable treatment targets in AD.

Pan-Genome Analysis of Oral Bacterial Pathogens to Predict a Potential Novel Multi-Epitopes Vaccine Candidate

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium, mainly present in the oral cavity and causes periodontal infections. Currently, no licensed vaccine is available against P. gingivalis and other oral bacterial pathogens. To develop a vaccine against P. gingivalis, herein, we applied a bacterial pan-genome analysis (BPGA) on the bacterial genomes that retrieved a total number of 4908 core proteins, which were further utilized for the identification of good vaccine candidates. After several vaccine candidacy analyses, three proteins, namely lytic transglycosylase domain-containing protein, FKBP-type peptidyl-propyl cis-trans isomerase and superoxide dismutase, were shortlisted for epitopes prediction. In the epitopes prediction phase, different types of B and T-cell epitopes were predicted and only those with an antigenic, immunogenic, non-allergenic, and non-toxic profile were selected. Moreover, all the predicted epitopes were joined with each other to make a multi-epitopes vaccine construct, which was linked further to the cholera toxin B-subunit to enhance the antigenicity of the vaccine. For downward analysis, a three dimensional structure of the designed vaccine was modeled. The modeled structure was checked for binding potency with major histocompatibility complex I (MHC-I), major histocompatibility complex II (MHC-II), and Toll-like receptor 4 (TLR-4) immune cell receptors which revealed that the designed vaccine performed proper binding with respect to immune cell receptors. Additionally, the binding efficacy of the vaccine was validated through a molecular dynamic simulation that interpreted strong intermolecular vaccine-receptor binding and confirmed the exposed situation of vaccine epitopes to the host immune system. In conclusion, the study suggested that the model vaccine construct has the potency to generate protective host immune responses and that it might be a good vaccine candidate for experimental in vivo and in vitro studies.

Future Drug Targets in Periodontal Personalised Medicine-A Narrative Review

Periodontal disease is an infection-driven inflammatory disease characterized by the destruction of tooth-supporting tissues. The establishment of chronic inflammation will result in progressive destruction of bone and soft tissue changes. Severe periodontitis can lead to tooth loss. The disease has complex pathogenesis with an interplay between genetic, environmental, and host factors and pathogens. Effective management consists of plaque control and non-surgical interventions, along with adjuvant strategies to control inflammation and disrupt the pathogenic subgingival biofilms. Recent studies have examined novel approaches for managing periodontal diseases such as modulating microbial signaling mechanisms, tissue engineering, and molecular targeting of host inflammatory substances. Mounting evidence suggests the need to integrate omics-based approaches with traditional therapy to address the disease. This article discusses the various evolving and future drug targets, including proteomics, gene therapeutics, vaccines, and nanotechnology in personalized periodontal medicine for the effective management of periodontal diseases.

Computational Design of a Multi-Epitope Vaccine Against Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative pathogenic bacterium associated with chronic periodontitis. The development of a chimeric peptide-based vaccine targeting this pathogen could be highly beneficial in preventing oral bone loss as well as other severe gum diseases. We applied a computational framework to design a multi-epitope-based vaccine candidate against P. gingivalis. The vaccine comprises epitopes from subunit proteins prioritized from the P. gingivalis reference strain (P. gingivalis ATCC 33277) using several reported vaccine properties. Protein-based subunit vaccines were prioritized through genomics techniques. Epitope prediction was performed using immunoinformatic servers and tools. Molecular modeling approaches were used to build a putative three-dimensional structure of the vaccine to understand its interactions with host immune cells through biophysical techniques such as molecular docking simulation studies and binding free energy methods. Genome subtraction identified 18 vaccine targets: six outer-membrane, nine cytoplasmic membrane-, one periplasmic, and two extracellular proteins. These proteins passed different vaccine checks required for the successful development of a vaccine candidate. The shortlisted proteins were subjected to immunoinformatic analysis to map B-cell derived T-cell epitopes, and antigenic, water-soluble, non-toxic, and good binders of DRB1*0101 were selected. The epitopes were then modeled into a multi-epitope peptide vaccine construct (linked epitopes plus adjuvant) to enhance immunogenicity and effectively engage both innate and adaptive immunity. Further, the molecular docking approach was used to determine the binding conformation of the vaccine to TLR2 innate immune receptor. Molecular dynamics simulations and binding free energy calculations of the vaccine-TLR2 complex were performed to highlight key intermolecular binding energies. Findings of this study will be useful for vaccine developers to design an effective vaccine for chronic periodontitis pathogens, specifically P. gingivalis.

The effect of local application of thymoquinone, Nigella sativa’s bioactive component, on bone healing in experimental bone defects infected with Porphyromonas gingivalis

Purpose

This study was performed to evaluate the influence of local application of thymoquinone (TQ) on bone healing in experimental bone defects infected with Porphyromonas gingivalis (PG).

Methods

Forty-two female rats were randomly divided into 6 groups. A bone defect was created on the right tibia of all animals. The PG, PG/collagen membrane (COL) and PG/TQ/COL groups were infected with PG. In the COL and PG/COL groups, the defects were covered with a COL; in the TQ/COL and PG/TQ/COL groups, the defects were covered with a TQ-containing COL. After 28 days, all animals were sacrificed. Quantitative measurements of new bone formation and osteoblast lining, as well as semiquantitative measurements of capillary density and tissue response, were analyzed. Furthermore, the presence of bacterial infections in defect areas was evaluated.

Results

The new bone formation, osteoblast number, and capillary density were significantly higher in the TQ groups than in the control groups (P<0.001, P<0.001, and P<0.01, respectively). In a comparison between the TQ/COL group, with a TQ-containing COL (TQ/COL), and the PG–infected TQ-containing COL (PG/TQ/COL) group, the newly formed bone and capillary density were higher in the TQ/COL group (P<0.01). When the control group was compared to the PG, PG/COL, and PG/TQ/COL groups in terms of tissue response, the differences were statistically significant (P<0.001, P=0.02, and P=0.041, respectively). The intensity of the inflammatory cell reaction was higher in the PG, PG/COL, and PG/TQ/COL groups (P<0.05).

Conclusions

Within the limitations of this study, the local application of a TQ-containing COL positively affected bone healing even if the bone defects were infected. The results suggest that TQ increased angiogenesis and showed promise for accelerating bone defect healing. Further research is warranted to support these findings and reach more definitive conclusions.

Oral infection with a periodontal pathogen alters oral and gut microbiomes

Periodontal disease, an inflammatory bone disease of the oral cavity, affects more than 50% of the United States population over the age of 30. The Gram-negative, anaerobic bacterium Porphyromonas gingivalis, the etiological agent of periodontal disease, is known to induce dysbiosis of the oral microbiome while promoting inflammatory bone loss. We have recently reported that P. gingivalis can also alter the gut microbiota of mice prone to develop inflammatory atherosclerosis. However, it is still unknown whether P. gingivalis induces similar changes to the gut microbiome as it does to oral microbiome. In this study, we demonstrate that P. gingivalis infection increases the diversity of the oral microbiome, allowing for colonization of potentially opportunistic species in the oral microbiome and overgrowth of commensal species in both the oral and gut microbiomes. Since periodontal disease treatment in humans typically involves antibiotic treatment, we also examined the combined effect of P. gingivalis infection on mice pretreated with oral antibiotics. By correlating the oral and cecal microbiota of P. gingivalis-infected mice fed a normal chow diet, we identified blooms of the Gram-negative genera Barnesiella and Bacteroides and imbalances of mucin-degrading bacteria. These disrupted community structures were predicted to have increased detrimental functional capacities including increased flavonoid degradation and l-histidine fermentation. Though antibiotic pretreatment (without P. gingivlais) had a dominant impact on the cecal microbiome, P. gingivalis infection of mice with or without antibiotic pretreatment increased the abundance of the phylum Firmicutes and the Porphyromonadaceae family in the cecum. Collectively, our study demonstrates that P. gingivalis oral infection disrupted the oral and cecal microbiomes of otherwise unperturbed mice, altering their community membership and functional potential.

A Porphyromonas gingivalis Capsule-Conjugate Vaccine Protects From Experimental Oral Bone Loss

Periodontal diseases are chronic inflammatory diseases of the periodontium that result in progressive destruction of the soft and hard tissues supporting the teeth, and it is the most common cause of tooth loss among adults. In the US alone, over 100 million individuals are estimated to have periodontal disease. Subgingival bacteria initiate and sustain inflammation, and, although several bacteria have been associated with periodontitis, Porphyromonas gingivalis has emerged as the key etiological organism significantly contributing to the disease. Currently, intensive clinical maintenance strategies are deployed to mitigate the further progression of disease in afflicted individuals; however, these treatments often fail to stop disease progression, and, as such, the development of an effective vaccine for periodontal disease is highly desirable. We generated a conjugate vaccine, comprising of the purified capsular polysaccharide of P. gingivalis conjugated to eCRM®, a proprietary and enhanced version of the CRM197 carrier protein with predetermined conjugation sites (Pg-CV). Mice immunized with alum adjuvanted Pg-CV developed robust serum levels of whole organism-specific IgG in comparison to animals immunized with unconjugated capsular polysaccharide alone. Using the murine oral bone loss model, we observed that mice immunized with the capsule-conjugate vaccine were significantly protected from the effects of P. gingivalis-elicited oral bone loss. Employing a preclinical model of infection-elicited oral bone loss, our data support that a conjugate vaccine incorporating capsular polysaccharide antigen is effective in reducing the main clinical endpoint of periodontal disease-oral bone destruction. Further development of a P. gingivalis capsule-based conjugate vaccine for preventing periodontal diseases is supported.

Salivary IgA antibody to malondialdehyde-acetaldehyde associates with mild periodontal pocket depth

OBJECTIVE

Oxidized epitopes such as malondialdehyde-acetaldehyde (MAA) play a crucial role in the progression of atherosclerosis through activation of the humoral immune response. The exact mechanism of the association between atherosclerosis and periodontal diseases is not fully understood. The aim of the current study is to evaluate the association of oral humoral immune response to oxidized epitopes with parameters of periodontal disease.

MATERIALS AND METHODS

The Parogene cohort consist of patients who have undergone coronary angiography due to cardiac symptoms. In this study, 423 patients were randomly selected for an extensive oral examination. Salivary Immunoglobulin A to oxidized epitopes and bacterial antigens was determined by chemiluminescence immunoassay.

RESULTS

In a binary logistic regression model adjusted with periodontal disease confounders, periodontal pocket depth (PPD) 4-5 mm associated with salivary IgA antibodies to MAA-LDL (p = 0.034), heat shock protein 60 of Aggregatibacter actinomycetemcomitans (p = 0.045), Porphyromonas gingivalis (p = 0.045), A. actinomycetemcomitans (p = 0.005), P. intermedia (p = 0.020), and total IgA (p = 0.003).

CONCLUSIONS

The current study shows the association of salivary IgA to MAA-LDL with PPD 4-5 mm in a cohort of patients with chronic coronary artery disease. Humoral immune cross-reactivation to oxidized epitopes such MAA-LDL could partly explain the link of periodontitis with systemic diseases.

Current understanding of periodontal disease pathogenesis and targets for host-modulation therapy

Recent advances indicate that periodontitis is driven by reciprocally reinforced interactions between a dysbiotic microbiome and dysregulated inflammation. Inflammation is not only a consequence of dysbiosis but, via mediating tissue dysfunction and damage, fuels further growth of selectively dysbiotic communities of bacteria (inflammophiles), thereby generating a self-sustained feed-forward loop that perpetuates the disease. These considerations provide a strong rationale for developing adjunctive host-modulation therapies for the treatment of periodontitis. Such host-modulation approaches aim to inhibit harmful inflammation and promote its resolution or to interfere directly with downstream effectors of connective tissue and bone destruction. This paper reviews diverse strategies targeted to modulate the host periodontal response and discusses their mechanisms of action, perceived safety, and potential for clinical application.

Targeting a cysteine protease from a pathobiont alleviates experimental arthritis

Background

Several lines of evidence suggest that the pathobiont Porphyromonas gingivalis is involved in the development and/or progression of auto-inflammatory diseases. This bacterium produces cysteine proteases, such as gingipain RgpA, endowed with the potential to induce significant bone loss in model systems and in patients.

Objective

We sought to gain further insight into the role of this pathobiont in rheumatoid arthritis (RA) and to identify novel therapeutic targets for auto-inflammatory diseases.

Methods

We profiled the antibody response to RgPA-specific domains in patient sera. We also tested the potential protective effects of RgpA domains in an experimental arthritis model.

Results

Pre-immunization of rats with purified recombinant RgpA domains alleviated arthritis in the joints of the rodents and reduced bone erosion. Using a functional genomics approach at both the mRNA and protein levels, we report that the pre-immunizations reduced arthritis severity by impacting a matrix metalloprotease characteristic of articular injury, a chemokine known to be involved in recruiting inflammatory cells, and three inflammatory cytokines. Finally, we identified an amino acid motif in the RgpA catalytic domain of P. gingivalis that shares sequence homology with type II collagen.

Conclusion

We conclude that pre-immunization against gingipain domains can reduce the severity of experimentally induced arthritis. We suggest that targeting gingipain domains by pre-immunization, or, possibly, by small-molecule inhibitors, could reduce the potential of P. gingivalis to translocate to remote tissues and instigate and/or exacerbate pathology in RA, but also in other chronic inflammatory diseases.

PerioVax3, a key antigenic determinant with immunoprotective potential against periodontal pathogen

Treponema (T.) denticola is one of the key etiological agents in the development of periodontitis. The major outer sheath protein (Msp) of T. denticola has been shown to mediate pathogenesis and to facilitate adhesion of T. denticola to mucosal surfaces. This study aimed to find short polypeptides in the amino acid sequence of Msp which may be immunogenic and might elicit protective antisera against T. denticola. The complete msp sequence was divided into six fragments and the corresponding genes were cloned and expressed. Antisera against the polypeptides were raised in rabbits and fragment 3 (F3), hereinafter called PerioVax3 was the most potent fragment of the Msp in terms of yielding high titer antiserum. An adhesion assay was done to examine the inhibitory effects of antisera on the attachment of T. denticola to human gingival fibroblasts (HGFs) and human fibronectin. Antiserum against PerioVax3 significantly inhibited attachment of T. denticola to the substratum. Also, antiserum against PerioVax3 inhibited detachment of HGFs upon T. denticola exposure. To begin examining the clinical relevance of this work, blood samples from 12 sever periodontitis patients were collected and the sera were used in western blotting against the recombinant polypeptides. Periodontitis patient antisera exclusively detected PerioVax3 in western blotting. The data suggest that PerioVax3 carries epitopes that may trigger humoral immunity against T. denticola, which may protect against its adhesion functions. The complexity of periodontitis suggests that PerioVax3 may be considered for testing as a component of an experimental multivalent periodontal vaccine in further preclinical and clinical studies.

Immunization with cell-free-generated vaccine protects from Porphyromonas gingivalis-induced alveolar bone loss

Introduction

Periodontal diseases (PD) are complex oral inflammatory diseases initiated by keystone bacteria such as Porphyromonas gingivalis. A vaccine for PD is desirable as clinical treatment involves protracted maintenance strategies aimed to retain dentition. Although prior immunization approaches targeting P. gingivalis have reported variable success in limiting facets of disease such as oral bone loss, it remains that a vaccine for this disease may be attainable.

Aim

To investigate cell‐free protein synthesis (CFPS) as a platform to produce vaccinable targets suitable for efficacy testing in a P. gingivalis‐induced murine oral bone loss model.

Materials and Methods

Recombinantly generated P. gingivalis minor fimbriae protein (Mfa1), RgpA gingipain hemagglutinin domain 1 (HA1), and RgpA gingipain hemagglutinin domain 2 (HA2) were combined in equivalent doses in adjuvants and injected intramuscularly to immunize mice. Serum levels of protein‐specific antibody were measured by ELISA, and oral bone levels were defined by morphometrics.

Results

Recombinantly generated P. gingivalis proteins possessed high fidelity to predicted size and elicited protein‐specific IgG following immunization. Importantly, immunization with the vaccine cocktail protected from P. gingivalis elicited oral bone loss.

Conclusion

These data verify the utility of the CFPS technology to synthesize proteins that have the capacity to serve as novel vaccines.

Revisiting the Page & Schroeder model: the good, the bad and the unknowns in the periodontal host response 40 years later

In their classic 1976 paper, Page & Schroeder described the histopathologic events and the types of myeloid cells and lymphocytes involved in the initiation and progression of inflammatory periodontal disease. The staging of periodontal disease pathogenesis as 'initial', 'early', 'established' and 'advanced' lesions productively guided subsequent research in the field and remains fundamentally valid. However, major advances regarding the cellular and molecular mechanisms underlying the induction, regulation and effector functions of immune and inflammatory responses necessitate a reassessment of their work and its integration with emerging new concepts. We now know that each type of leukocyte is actually represented by functionally distinct subsets with different, or even conflicting, roles in immunity and inflammation. Unexpectedly, neutrophils, traditionally regarded as merely antimicrobial effectors in acute conditions and protagonists of the 'initial' lesion, are currently appreciated for their functional versatility and critical roles in chronic inflammation. Moreover, an entirely new field of study, osteoimmunology, has emerged and sheds light on the impact of immunoinflammatory events on the skeletal system. These developments and the molecular dissection of crosstalk interactions between innate and adaptive leukocytes, as well as between the immune system and local homeostatic mechanisms, offer a more nuanced understanding of the host response in periodontitis, with profound implications for treatment. At the same time, deeper insights have generated new questions, many of which remain unanswered. In this review, 40 years after Page & Schroeder proposed their model, we summarize enduring and emerging advances in periodontal disease pathogenesis.

[Experimental research on Arginine-gingipain A gene vaccine from Porphyromonas gingivalis that prevents peri-implantitis in Beagle dogs]

OBJECTIVE

This study aims to use Arginine-gingipain A gene vaccine (pVAX1-rgpA) to immunize adult Beagle dogs and to evaluate its effect during peri-implantitis progression and development.

METHODS

Plasmid pVAX1-rgpA was constructed. The second and third bilateral mandible premolars of 15 adult Beagle dogs were extracted, and the implants were placed immediately. After 3 months, the animals were randomly divided into groups A, B, and C. Afterward, the animals were immunized thrice with plasmid pVAX1-rgpA, with heat-killed Porphyromonas gingivalis, or pVAX1, respectively. IgG in the serum and secretory IgA (sIgA) in saliva were quantitatively analyzed by enzyme-linked immunosorbent assay before and after 2 weeks of immunization. Peri-implantitis was induced with cotton ligatures fixed around the neck of implants. Probing depth (PD) and bleeding on probing were recorded. All animals were sacrificed after ligaturation for 6 weeks. Decalcified sections with thickness of 50 μm were prepared and dyed with methylene blue to observe the bone phenotype around implants.

RESULTS

Levels of serum IgG and sIgA in saliva were higher in groups A and B after immunization than before the process (P<0.05) and higher than those in group C (P<0.05). However, no difference was observed between groups A and B (P>0.05). At 4 and 6 weeks after ligaturation, PD of the ligatured side in group C was higher than that in groups A and B (P<0.05). On the other hand, no difference was identified between groups A and B (P>0.05). Bone loss in group A was significantly lower than that of the other groups (P<0.05). Abundant inflammatory cells and bacteria were present in the bone loss area around the implants in the three groups, as identified through hard tissue section observation. However, group C presented the most number of inflammatory cells and bacteria in the bone loss area around the implants.

CONCLUSIONS

IgG and sIgA can be generated by immunity with rgpA DNA vaccine, which can significantly slow down bone loss during experimental peri-implantitis in dogs.

Mucosal immunization with a flagellin-adjuvanted Hgp44 vaccine enhances protective immune responses in a murine Porphyromonas gingivalis infection model

Chronic periodontitis is caused by interactions between the oral polymicrobial community and host factors. Periodontal diseases are associated with dysbiotic shift in oral microbiota. Vaccination against periodontopathic bacteria could be a fundamental therapeutic to modulate polymicrobial biofilms. Because oral cavity is the site of periodontopathic bacterial colonization, mucosal vaccines should provide better protection than vaccines administered systemically. We previously reported that bacterial flagellin is an excellent mucosal adjuvant. In this study, we investigated whether mucosal immunization with a flagellin-adjuvanted polypeptide vaccine induces protective immune responses using a Porphyromonas gingivalis infection model. We used the Hgp44 domain polypeptide of Arg-gingipain A (RgpA) as a mucosal antigen. Intranasal (IN) immunization induced a significantly higher Hgp44-specific IgG titer in the serum of mice than sublingual (SL) administration. The co-administration of flagellin potentiated serum IgG responses for both the IN and SL vaccinations. On the other hand, the anti-Hgp44-specific IgA titer in the saliva was comparable between IN and SL vaccinations, suggesting SL administration as more compliant vaccination route for periodontal vaccines. The co-administration of flagellin significantly potentiated the secretory IgA response in saliva also. Furthermore, mice administered a mixture of Hgp44 and flagellin via the IN and SL routes exhibited significant reductions in alveolar bone loss induced by live P. gingivalis infections. An intranasally administered Hgp44-flagellin fusion protein induced a comparable level of Hgp44-specific antibody responses to the mixture of Hgp44 and flagellin. Overall, a flagellin-adjuvanted Hgp44 antigen would serve an important component for a multivalent mucosal vaccine against polymicrobial periodontitis.

Protective and Destructive Immunity in the Periodontium: Part 2—T-cell-mediated Immunity in the Periodontium

Based on the results of recent research in the field and Part 1 of this article (in this issue), the present paper will discuss the protective and destructive aspects of the T-cell-mediated adaptive immunity associated with the bacterial virulent factors or antigenic determinants during periodontal pathogenesis. Attention will be focused on: (i) osteoimmunology and periodontal disease; (ii) some molecular techniques developed and applied to identify critical microbial virulence factors or antigens associated with host immunity (with Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis as the model species); and (iii) summarizing the identified virulence factors/antigens associated with periodontal immunity. Thus, further understanding of the molecular mechanisms of the host’s T-cell-mediated immune responses and the critical microbial antigens related to disease pathogenesis will facilitate the development of novel therapeutics or protocols for future periodontal treatments. Abbreviations used in the paper are as follows: A. actinomycetemcomitans ( Aa), Actinobacillus actinomycetemcomitans; Ab, antibody; DC, dendritic cells; mAb, monoclonal antibody; pAb, polyclonal antibody; OC, osteoclast; PAMP, pathogen-associated molecular patterns; P. gingivalis ( Pg), Porphyromonas gingivalis; RANK, receptor activator of NF-κB; RANKL, receptor activator of NF-κB ligand; OPG, osteoprotegerin; TCR, T-cell-receptors; TLR, Toll-like receptors.

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.

Effects of Bio-Oss® and Cerasorb® dental M on the expression of bone-remodeling mediators in human monocytes

In contribution to diverse techniques of bone reconstruction involving biomaterials in contemporary dentistry, this study aimed to evaluate the effect of the bone-grafting materials Bio-Oss^® and Cerasorb^® Dental M on the expression of cytokines associated with bone remodeling by human monocytes in vitro. Bio-Oss^® and Cerasorb^® Dental M were incubated in separate culture media, and their supernatants were added to mononuclear cells of human peripheral blood, some of which had been stimulated with Porphyromonas gingivalis. The frequency of total monocytes and CD14⁺ monocytes producing cytokines interleukin 6 (IL-6), IL-8, IL-10, IL-12, and tumor necrosis factor alpha (TNF-α) were determined by flow cytometry. One-way analysis of variance with repeated measures, followed by Tukey's post hoc test, revealed that stimulation with P. gingivalis increased the expression of IL-6 and IL-8 and reduced the expression of TNF-α compared to effects demonstrated in the control group (p < 0.05). Adding biomaterial supernatants did not significantly affect the expression of any cytokine evaluated, however, either in the absence or in the presence of bacterial stimulation. Our data suggest that Bio-Oss^® and Cerasorb^® Dental M neither stimulate cytokine production in human monocytes nor interfere with mechanisms of cell communication mediated by cytokines evaluated during stimulation with P. gingivalis. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2066-2073, 2017.

Vaccination with recombinant RgpA peptide protects against Porphyromonas gingivalis-induced bone loss

OBJECTIVE

Following Porphyromonas gingivalis infection in mice, the efficacy of vaccination by recombinant and native RgpA in modulating the early local anti-inflammatory and immune responses and periodontal bone loss were examined.

MATERIAL AND METHODS

Using the subcutaneous chamber model, exudates were analyzed for cytokines after treatment with native RgpA and adjuvant (test), or adjuvant and saline alone (controls). Mice were also immunized with recombinant RgpA after being orally infected with P. gingivalis. After 6 wk, serum was examined for anti-P. gingivalis IgG1 and IgG2a titers and for alveolar bone resorption.

RESULTS

Immunization with native RgpA shifted the immune response toward an anti-inflammatory response as demonstrated by decreased proinflammatory cytokine IL-1β production and greater anti-inflammatory cytokine IL-4 in chamber exudates. Systemically, immunization with recombinant RgpA peptide prevented alveolar bone loss by 50%, similar to immunization with heat-killed whole bacteria. Furthermore, recombinant RgpA shifted the humoral response toward high IgG1 and low IgG2a titers, representing an in vivo anti-inflammatory response.

CONCLUSIONS

The present study demonstrates the potential of RgpA to shift the early local immune response toward an anti-inflammatory response while vaccination with recRgpA protected against P. gingivalis-induced periodontitis.

The enduring importance of animal models in understanding periodontal disease

Whereas no single animal model can reproduce the complexity of periodontitis, different aspects of the disease can be addressed by distinct models. Despite their limitations, animal models are essential for testing the biological significance of in vitro findings and for establishing cause-and-effect relationships relevant to clinical observations, which are typically correlative. We provide evidence that animal-based studies have generated a durable framework for dissecting the mechanistic basis of periodontitis. These studies have solidified the etiologic role of bacteria in initiating the inflammatory response that leads to periodontal bone loss and have identified key mediators (IL-1, TNF, prostaglandins, complement, RANKL) that induce inflammatory breakdown. Moreover, animal studies suggest that dysbiosis, rather than individual bacterial species, are important in initiating periodontal bone loss and have introduced the concept that organisms previously considered commensals can play important roles as accessory pathogens or pathobionts. These studies have also provided insight as to how systemic conditions, such as diabetes or leukocyte adhesion deficiency, contribute to tissue destruction. In addition, animal studies have identified and been useful in testing therapeutic targets.

Defining the role of Porphyromonas gingivalis peptidylarginine deiminase (PPAD) in rheumatoid arthritis through the study of PPAD biology

BACKGROUND

Antibodies to citrullinated proteins are a hallmark of rheumatoid arthritis (RA). Porphyromonas gingivalis peptidylarginine deiminase (PPAD) has been implicated in the initiation of RA by generating citrullinated neoantigens and due to its ability to autocitrullinate.

OBJECTIVES

To define the citrullination status and biology of PPAD in P gingivalis and to characterise the anti-PPAD antibody response in RA and associated periodontal disease (PD).

METHODS

PPAD in P gingivalis cells and culture supernatant were analysed by immunoblotting and mass spectrometry to detect citrullination. Recombinant PPAD (rPPAD), inactive mutant PPAD (rPPAD(C351S)), and N-terminal truncated PPAD (rPPAD(Ntx)) were cloned and expressed in Escherichia coli. Patients with RA and healthy controls were assayed for IgG antibodies to citrullinated rPPAD and unmodified rPPAD(C351S) by ELISA. Anti-PPAD antibodies were correlated with anti-cyclic citrullinated peptide (third-generation) antibody levels, RA disease activity and PD status.

RESULTS

PPAD from P gingivalis is truncated at the N-terminal and C-terminal domains and not citrullinated. Only when artificially expressed in E coli, full-length rPPAD, but not truncated (fully active) rPPAD(Ntx), is autocitrullinated. Anti-PPAD antibodies show no heightened reactivity to citrullinated rPPAD, but are exclusively directed against the unmodified enzyme. Antibodies against PPAD do not correlate with anti-cyclic citrullinated peptide levels and disease activity in RA. By contrast, anti-PPAD antibody levels are significantly decreased in RA patients with PD.

CONCLUSIONS

PPAD autocitrullination is not the underlying mechanism linking PD and RA. N-terminal processing protects PPAD from autocitrullination and enhances enzyme activity. Anti-PPAD antibodies may have a protective role for the development of PD in patients with RA.

Subcutaneous vaccination with Porphyromonas gingivalis ameliorates periodontitis by modulating Th17/Treg imbalance in a murine model

To date, Porphyromonas gingivalis (P. gingivalis) vaccination has been studied only in animals, and no effective prophylactic human periodontal vaccine has been developed, with the reason for the failure of prophylactic human periodontal vaccines unknown. T helper 17 cell (Th17)/regulatory T (Treg) cell responses play an important role in the development of periodontitis, and a Th17/Treg imbalance causes the pathogenesis of periodontitis. However, whether vaccination with P. gingivalis can prevent periodontitis through modulation of the Th17/Treg imbalance remains unknown. In this study, mice were subcutaneously vaccinated with formalin-killed P. gingivalis and then orally challenged with P. gingivalis. The vaccination protected the mice from alveolar bone resorption and inflammation. These protective effects might be ascribed to downregulation of Th17 cells and interleukin (IL)-17A production, upregulation of Treg and receptor activator of nuclear factor-kappa B ligand (RANKL)(+)CD4(+)T cells, and IL-10 and transforming growth factor-β1 production, and inhibition of lymphocyte proliferation. Our findings may provide a direction for the development of a vaccine or therapy against periodontitis by alteration of the Th17/Treg imbalance.

Strategies for the inhibition of gingipains for the potential treatment of periodontitis and associated systemic diseases

Gingipains are the major virulence factors of Porphyromonas gingivalis, the main periodontopathogen. It is expected that inhibition of gingipain activity in vivo could prevent or slow down the progression of adult periodontitis. To date, several classes of gingipain inhibitors have been recognized. These include gingipain N-terminal prodomains, synthetic compounds, inhibitors from natural sources, antibiotics, antiseptics, antibodies, and bacteria. Several synthetic compounds are potent gingipain inhibitors but inhibit a broad spectrum of host proteases and have undesirable side effects. Synthetic compounds with high specificity for gingipains have unknown toxicity effects, making natural inhibitors more promising as therapeutic gingipain blockers. Cranberry and rice extracts interfere with gingipain activity and prevent the growth and biofilm formation of periodontopathogens. Although the ideal gingipain inhibitor has yet to be discovered, gingipain inhibition represents a novel approach to treat and prevent periodontitis. Gingipain inhibitors may also help treat systemic disorders that are associated with periodontitis, including cardiovascular disease, rheumatoid arthritis, aspiration pneumonia, pre-term birth, and low birth weight.

kgp, rgpA, and rgpB DNA vaccines induce antibody responses in experimental peri-implantitis

BACKGROUND

Peri-implantitis is the key factor for implant failure. This study aims to evaluate kgp, rgpA, and rgpB DNA vaccines to induce an immune response and prevent peri-implantitis.

METHODS

The kgp, rgpA, and rgpB genes were amplified by polymerase chain reaction (PCR) from Porphyromonas gingivalis (Pg) ATCC 33277 and cloned into the pVAX1 vector. Titanium implants were placed into the mandibular bone of dogs. Three months later, the animals were divided into four groups, immunized with pVAX1-kgp, pVAX1-rgpA, pVAX1-rgpB, or pVAX1. Cotton ligatures infiltrated with Pg were tied around the neck of the implants. Immunoglobulin (Ig)G and IgA antibodies were detected by enzyme-linked immunosorbent assay before and after immunization.

RESULTS

The kgp, rgpA, and rgpB genes were successfully cloned into the pVAX1 plasmid. Animals immunized with pVAX1-kgp and pVAX1-rgpA showed higher titers of IgG and IgA antibodies compared to those before immunization (P <0.05) and compared to those that were immunized with pVAX1 and pVAX1-rgpB, whereas there were no significant differences in the animals treated with pVAX1 and pVAX1-rgpB. Furthermore, among these, the kgp DNA vaccine was more effective. The bone losses of the groups with pVAX1-kgp and pVAX1-rgpA were significantly attenuated.

CONCLUSION

pVAX1-kgp and pVAX1-rgpA DNA vaccines enhanced immunity responses and significantly retarded bone loss in experimental peri-implantitis animal models, whereas pVAX1-rgpB was ineffective.

Emerging roles of immunostimulatory oral bacteria in periodontitis development

Periodontitis is a common dental disease which results in irreversible alveolar bone loss around teeth, and subsequent tooth loss. Previous studies have focused on bacteria that damage the host and the roles of commensals to facilitate their colonization. Although some immune responses targeting oral bacteria protect the host from alveolar bone loss, recent studies show that particular host defense responses to oral bacteria can induce alveolar bone loss. Host-damaging and immunostimulatory oral bacteria cooperatively induce bone loss by inducing gingival damage followed by immunostimulation. In mouse models of experimental periodontitis induced by either Porphyromonas gingivalis or ligature, γ-proteobacteria accumulate and stimulate host immune responses to induce host damage. Here we review the differential roles of individual bacterial groups in promoting bone loss through the induction of host damage and immunostimulation.

The lysine gingipain adhesin domains from Porphyromonas gingivalis interact with erythrocytes and albumin: Structures correlate to function

The crystal structure of the K1 domain, an adhesin module of the lysine gingipain (Kgp) expressed on the cell surface by the periodontopathic anaerobic bacterium, Porphyromonas gingivalis W83, is compared to the previously determined structures of homologues K2 and K3, all three being representative members of the cleaved adhesin domain family. In the structure of K1, the conformation of the most extensive surface loop is unexpectedly perturbed, perhaps by crystal packing, and is displaced from a previously reported arginine-anchored position observed in K2 and K3. This displacement allows the loop to become free to interact with other proteins; the alternate flipped-out loop conformation is a novel mechanism for interacting with target host proteins, other bacteria, or other gingipain protein domains. Further, the K1 adhesin module, like others, is found to be haemolytic in vitro, and so, functions in erythrocyte recognition thereby contributing to the haemolytic function of Kgp. K1 was also observed to selectively bind to haem-albumin with high affinity, suggesting this domain may be involved in gingipain-mediated haem acquisition from haem-albumin. Therefore, it is most likely that all cleaved adhesin domains of Kgp contribute to the pathogenicity of P. gingivalis in more complex ways than simply mediating bacterial adherence.

Prevalence of Porphyromonas gingivalis four rag locus genotypes in patients of orthodontic gingivitis and periodontitis

Porphyromonas gingivalis is considered as a major etiological agent in periodontal diseases and implied to result in gingival inflammation under orthodontic appliance. rag locus is a pathogenicity island found in Porphyromonas gingivalis. Four rag locus variants are different in pathogenicity of Porphyromonas gingivalis. Moreover, there are different racial and geographic differences in distribution of rag locus genotypes. In this study, we assessed the prevalence of Porphyromonas gingivalis and rag locus genotypes in 102 gingival crevicular fluid samples from 57 cases of gingivitis patients with orthodontic appliances, 25 cases of periodontitis patients and 20 cases of periodontally healthy people through a 16S rRNA-based PCR and a multiplex PCR. The correlations between Porphyromona.gingivalis/rag locus and clinical indices were analyzed. The prevalence of Porphyromonas gingivalis and rag locus genes in periodontitis group was the highest among three groups and higher in orthodontic gingivitis than healthy people (p<0.01). An obviously positive correlation was observed between the prevalence of Porphyromonas gingivalis/rag locus and gingival index. rag-3 and rag-4 were the predominant genotypes in the patients of orthodontic gingivitis and mild-to-moderate periodontitis in Shandong. Porphyromonas.gingivalis carrying rag-1 has the strong virulence and could be associated with severe periodontitis.

Porphyromonas gingivalis infection-associated periodontal bone resorption is dependent on receptor activator of NF-κB ligand

Porphyromonas gingivalis is one of the oral microorganisms associated with human chronic periodontitis. The purpose of this study is to determine the role of the receptor activator of nuclear factor-κB ligand (RANKL) in P. gingivalis infection-associated periodontal bone resorption. Inbred female Rowett rats were infected orally on four consecutive days (days 0 to 3) with 1 × 10(9) P. gingivalis bacteria (strain ATCC 33277). Separate groups of rats also received an injection of anti-RANKL antibody, osteoprotegerin fusion protein (OPG-Fc), or a control fusion protein (L6-Fc) into gingival papillae in addition to P. gingivalis infection. Robust serum IgG and salivary IgA antibody (P < 0.01) and T cell proliferation (P < 0.05) responses to P. gingivalis were detected at day 7 and peaked at day 28 in P. gingivalis-infected rats. Both the concentration of soluble RANKL (sRANKL) in rat gingival tissues (P < 0.01) and periodontal bone resorption (P < 0.05) were significantly elevated at day 28 in the P. gingivalis-infected group compared to levels in the uninfected group. Correspondingly, RANKL-expressing T and B cells in rat gingival tissues were significantly increased at day 28 in the P. gingivalis-infected group compared to the levels in the uninfected group (P < 0.01). Injection of anti-RANKL antibody (P < 0.05) or OPG-Fc (P < 0.01), but not L6-Fc, into rat gingival papillae after P. gingivalis infection resulted in significantly reduced periodontal bone resorption. This study suggests that P. gingivalis infection-associated periodontal bone resorption is RANKL dependent and is accompanied by increased local infiltration of RANKL-expressing T and B cells.

rgpA DNA vaccine induces antibody response and prevents alveolar bone loss in experimental peri-implantitis

BACKGROUND

Peri-implantitis is one of many reasons for dental implant failure. This study is designed to prevent experimental peri-implantitis by arginine-specific gingipain A (rgpA) DNA vaccine.

METHODS

The bilateral mandibular second and third premolars from 15 male beagle dogs were extracted, and 60 implants were immediately implanted. Three months after implantation, the animals were randomly divided into groups A, B, and C and immunized with plasmid vector-rgpA, heat-killed Porphyromonas gingivalis, and plasmid vector, respectively. Cotton ligatures infiltrated with P. gingivalis were placed in the submarginal position around the neck of the implants to induce peri-implantitis. Clinical measurements, including probing depth (PD) and bleeding on probing, were recorded every 2 weeks postoperatively, and P. gingivalis-specific immunoglobulin G (IgG) in serum and secretory IgA (sIgA) in saliva were quantitatively analyzed by enzyme-linked immunosorbent assay at the same time. Animals were sacrificed after 6 weeks, 50-μm undecalcified histologic sections were prepared using methylene blue dye, and bone loss around implants was measured.

RESULTS

Higher levels of IgG in serum and sIgA in saliva could be measured in groups A and B but not in group C after immunization. There were statistical differences (P <0.05) between, before, and after immunization, but no difference was found between groups A and B (P >0.05). Both peri-implant PD and bone loss in group A were significantly less than in groups B and C.

CONCLUSIONS

IgG and sIgA could be generated by immunization with rgpA DNA vaccine, which could significantly slow down bone loss in the experimental peri-implantitis canine model.

Recognition of Porphyromonas gingivalis gingipain epitopes by natural IgM binding to malondialdehyde modified low-density lipoprotein

Objective

Increased risk for atherosclerosis is associated with infectious diseases including periodontitis. Natural IgM antibodies recognize pathogen-associated molecular patterns on bacteria, and oxidized lipid and protein epitopes on low-density lipoprotein (LDL) and apoptotic cells. We aimed to identify epitopes on periodontal pathogen Porphyromonas gingivalis recognized by natural IgM binding to malondialdehyde (MDA) modified LDL.

Methods and Results

Mouse monoclonal IgM (MDmAb) specific for MDA-LDL recognized epitopes on P. gingivalis on flow cytometry and chemiluminescence immunoassays. Immunization of C57BL/6 mice with P. gingivalis induced IgM, but not IgG, immune response to MDA-LDL and apoptotic cells. Immunization of LDLR^−/− mice with P. gingivalis induced IgM, but not IgG, immune response to MDA-LDL and diminished aortic lipid deposition. On Western blot MDmAb bound to P. gingivalis fragments identified as arginine-specific gingipain (Rgp) by mass spectrometry. Recombinant domains of Rgp produced in E. coli were devoid of phosphocholine epitopes but contained epitopes recognized by MDmAb and human serum IgM. Serum IgM levels to P. gingivalis were associated with anti-MDA-LDL levels in humans.

Conclusion

Gingipain of P. gingivalis is recognized by natural IgM and shares molecular identity with epitopes on MDA-LDL. These findings suggest a role for natural antibodies in the pathogenesis of two related inflammatory diseases, atherosclerosis and periodontitis.

Animal models to study host-bacteria interactions involved in periodontitis

Animal models have distinct advantages because they can mimic cellular complexities that occur in humans in vivo and are often more accurate than in vitro studies that take place on plastic surfaces with limited numbers of cell types present. Furthermore, cause and effect relationships can be established by applying inhibitors or activators or through the use of genetically modified animals. Such gain or loss of function studies are often difficult to achieve in human clinical studies, particularly in obtaining target tissue due to important ethical considerations. Animal models in periodontal disease are particularly important at this point in the development of the scientific basis for understanding the predominant pathological processes. Periodontal disease can be broken down into discrete steps, each of which may be studied separately depending upon the animal model. These steps involve the development of a pathogenic biofilm, invasion of connective tissue by bacteria or their products, induction of a destructive host response in connective tissue and limitation of are pair process that follows tissue breakdown. Animal studies can test hypotheses related to each of these steps, and should be evaluated by their capacity to test a specific hypothesis rather than recapitulating all aspects of periodontal disease. Thus, each of the models described below can be adapted to test discrete components of the pathological process of periodontal disease, but not necessarily all of them.

Cloning and characterization of heavy and light chain genes encoding the FimA-specific monoclonal antibodies that inhibit Porphyromonas gingivalis adhesion

FimA of Porphyromonas gingivalis, a major pathogen in periodontitis, is known to be closely related to the virulence of these bacteria and has been suggested as a candidate for development of a vaccine against periodontal disease. In order to develop a passive immunization method for inhibiting the establishment of periodontal disease, B hybridoma clones 123-123-10 and 256-265-9, which produce monoclonal antibodies (Mabs) specific to purified fimbriae, were established. Both mAbs reacted with the conformational epitopes displayed by partially dissociated oligomers of FimA, but not with the 43 kDa FimA monomer. Gene sequence analyses of full-length cDNAs encoding heavy and light chain immunoglobulins enabled classification of the genes of mAb 123-123-10 as members of the mVh II (A) and mVκ I subgroups, and those of mAb 256-265-9 as members of the mVh III (D) and mVκ I subgroups. More importantly, 50 ng/mL of antibodies purified from the culture supernatant of antibody gene-transfected CHO cells inhibited, by approximately 50%, binding of P. gingivalis to saliva-coated hydroxyapatite bead surfaces. It is expected that these mAbs could be used as a basis for passive immunization against P. gingivalis-mediated periodontitis.

HGP44 induces protection against Porphyromonas gingivalis-Induced alveolar bone loss in mice

The protective effect of DNA vaccines expressing the Arg-gingipain A domain against bone loss induced by Porphyromonas gingivalis infection was investigated in a murine model. phgp44, which expresses the 44-kDa adhesion/hemagglutinin domain of Arg-gingipain A, prevented P. gingivalis-induced alveolar bone loss. The results indicate that phgp44 could be a candidate antigen for a vaccine against P. gingivalis infection.

Porphyromonas gingivalis accelerates inflammatory atherosclerosis in the innominate artery of ApoE deficient mice

OBJECTIVE

Studies in humans support a role for the oral pathogen Porphyromonas gingivalis in the development of inflammatory atherosclerosis. The goal of this study was to determine if P. gingivalis infection accelerates inflammation and atherosclerosis in the innominate artery of mice, an artery which has been reported to exhibit many features of human atherosclerotic disease, including plaque rupture.

METHODS AND RESULTS

Apolipoprotein E-deficient (ApoE-/-) mice were orally infected with P. gingivalis, and magnetic resonance imaging (MRI) was used to monitor the progression of atherosclerosis in live mice. P. gingivalis infected mice exhibited a statistically significant increase in atherosclerotic plaque in the innominate artery as compared to uninfected mice. Polarized light microscopy and immunohistochemistry revealed that the innominate arteries of infected mice had increased lipids, macrophages and T cells as compared to uninfected mice. Increases in plaque, total cholesterol esters and cholesterol monohydrate crystals, macrophages, and T cells were prevented by immunization with heat-killed P. gingivalis prior to pathogen exposure.

CONCLUSIONS

These are the first studies to demonstrate progression of inflammatory plaque accumulation in the innominate arteries by in vivo MRI analysis following pathogen exposure, and to document protection from plaque progression in the innominate artery via immunization.

Porphyromonas gingivalis accelerates inflammatory atherosclerosis in the innominate artery of ApoE deficient mice

OBJECTIVE

Studies in humans support a role for the oral pathogen Porphyromonas gingivalis in the development of inflammatory atherosclerosis. The goal of this study was to determine if P. gingivalis infection accelerates inflammation and atherosclerosis in the innominate artery of mice, an artery which has been reported to exhibit many features of human atherosclerotic disease, including plaque rupture.

METHODS AND RESULTS

Apolipoprotein E-deficient (ApoE-/-) mice were orally infected with P. gingivalis, and magnetic resonance imaging (MRI) was used to monitor the progression of atherosclerosis in live mice. P. gingivalis infected mice exhibited a statistically significant increase in atherosclerotic plaque in the innominate artery as compared to uninfected mice. Polarized light microscopy and immunohistochemistry revealed that the innominate arteries of infected mice had increased lipids, macrophages and T cells as compared to uninfected mice. Increases in plaque, total cholesterol esters and cholesterol monohydrate crystals, macrophages, and T cells were prevented by immunization with heat-killed P. gingivalis prior to pathogen exposure.

CONCLUSIONS

These are the first studies to demonstrate progression of inflammatory plaque accumulation in the innominate arteries by in vivo MRI analysis following pathogen exposure, and to document protection from plaque progression in the innominate artery via immunization.

Porphyromonas gingivalis-host interactions in a Drosophila melanogaster model

Porphyromonas gingivalis is a Gram-negative obligate anaerobe that has been implicated in the etiology of adult periodontitis. We recently introduced a Drosophila melanogaster killing model for examination of P. gingivalis-host interactions. In the current study, the Drosophila killing model was used to characterize the host response to P. gingivalis infection by identifying host components that play a role during infection. Drosophila immune response gene mutants were screened for altered susceptibility to killing by P. gingivalis. The Imd signaling pathway was shown to be important for the survival of Drosophila infected by nonencapsulated P. gingivalis strains but was dispensable for the survival of Drosophila infected by encapsulated P. gingivalis strains. The P. gingivalis capsule was shown to mediate resistance to killing by Drosophila antimicrobial peptides (Imd pathway-regulated cecropinA and drosocin) and human beta-defensin 3. Drosophila thiol-ester protein II (Tep II) and Tep IV and the tumor necrosis factor (TNF) homolog Eiger were also involved in the immune response against P. gingivalis infection, while the scavenger receptors Eater and Croquemort played no roles in the response to P. gingivalis infection. This study demonstrates that the Drosophila killing model is a useful high-throughput model for characterizing the host response to P. gingivalis infection and uncovering novel interactions between the bacterium and the host.

Porphyromonas gingivalis virulence in a Drosophila melanogaster model

Porphyromonas gingivalis has been implicated in the etiology of adult periodontitis. In this study, we examined the viability of Drosophila melanogaster as a new model for examining P. gingivalis-host interactions. P. gingivalis (W83) infection of Drosophila resulted in a systemic infection that killed in a dose-dependent manner. Differences in the virulence of several clinically prevalent P. gingivalis strains were observed in the Drosophila killing model, and the results correlated well with studies in mammalian infection models and human epidemiologic studies. P. gingivalis pathobiology in Drosophila did not result from uncontrolled growth of the bacterium in the Drosophila hemolymph (blood) or overt damage to Drosophila tissues. P. gingivalis killing of Drosophila was multifactorial, involving several bacterial factors that are also involved in virulence in mammals. The results from this study suggest that many aspects of P. gingivalis pathogenesis in mammals are conserved in Drosophila, and thus the Drosophila killing model should be useful for characterizing P. gingivalis-host interactions and, potentially, polymicrobe-host interactions.

Vaccines against periodontitis: a forward-looking review

Periodontal disease, as a polymicrobial disease, is globally endemic as well as being a global epidemic. It is the leading cause for tooth loss in the adult population and has been positively related to life-threatening systemic diseases such as atherosclerosis and diabetes. As a result, it is clear that more sophisticated therapeutic modalities need to be developed, which may include vaccines. Up to now, however, no periodontal vaccine trial has been successful in satisfying all the requirements; to prevent the colonization of a multiple pathogenic biofilm in the subgingival area, to elicit a high level of effector molecules such as immunoglobulin sufficient to opsonize and phagocytose the invading organisms, to suppress the induced alveolar bone loss, or to stimulate helper T-cell polarization that exerts cytokine functions optimal for protection against bacteria and tissue destruction. This article reviews all the vaccine trials so as to construct a more sophisticated strategy which may be relevant in the future. As an innovative strategy to circumvent these barriers, vaccine trials to stimulate antigen-specific T-cells polarized toward helper T-cells with a regulatory phenotype (Tregs, CD4+, CD25+, FoxP3+) have also been introduced. Targeting not only a single pathogen, but polymicrobial organisms, and targeting not only periodontal disease, but also periodontal disease-triggered systemic disease could be a feasible goal.

Pathogen-mediated inflammatory atherosclerosis is mediated in part via Toll-like receptor 2-induced inflammatory responses

Studies in humans have established that polymorphisms in genes encoding the innate immune Toll-like receptors (TLRs) are associated with inflammatory atherosclerosis. In hyperlipidemic mice, TLR2 and TLR4 have been reported to contribute to atherosclerosis progression. Human and mouse studies support a role for the oral pathogen Porphyromonas gingivalis in atherosclerosis, although the mechanisms by which this pathogen stimulates inflammatory atherosclerosis via innate immune system activation is not known. Using a genetically defined apolipoprotein E-deficient (ApoE(-/-)) mouse model we demonstrate that pathogen-mediated inflammatory atherosclerosis occurs via both TLR2-dependent and TLR2-independent mechanisms. P. gingivalis infection in mice possessing functional TLR2 induced the accumulation of macrophages as well as inflammatory mediators including CD40, IFN-gamma and the pro-inflammatory cytokines IL-1 beta, IL-6 and tumor necrosis factor-alpha in atherosclerotic lesions. The expression of these inflammatory mediators was reduced in atherosclerotic lesions from P. gingivalis-infected TLR2-deficient (TLR2(-/-)) mice. These studies provide a mechanistic link between an innate immune receptor and pathogen-accelerated atherosclerosis by a clinically and biologically relevant bacterial pathogen.