Bacterial AB toxins and host-microbe interactions

AB toxins are protein virulence factors secreted by many bacterial pathogens, contributing to the pathogenicity of the cognate bacteria. AB toxins consist of two functionally distinct components: the enzymatic "A" component for pathogenicity and the receptor-binding "B" component for toxin delivery. Consistently, unlike other virulence factors such as effectors, AB toxins do not require additional systems to deliver them to the target host cells. Target host cells are located in the infection site and/or located distantly from infected host cells. The first part of this review discusses the structural and functional features of single-peptide and multiprotein AB toxins in the context of host-microbe interactions, using several well-characterized examples. The second part of this review discusses toxin neutralization strategies, as well as applications of AB toxins relevant to developing intervention strategies against diseases.

Sublingual immunization with recombinant GroEL plus CpG-ODN inhibits Porphyromonas gingivalis-induced inflammation and alveolar bone loss

It has been reported that GroEL, a heat shock protein (HSP) produced by the representative periodontopathogenic bacterium, Porphyromonas gingivalis, induces inflammation-induced osteoclastogenesis and promotes alveolar bone resorption. In this study, we demonstrated the efficacy of a mucosal vaccine targeting GroEL against bone resorption induced by P. gingivalis. Female BALB/c mice received sublingual CpG oligodeoxynucleotide as an adjuvant with recombinant GroEL (rGroEL) prior to P. gingivalis exposure. Animals were euthanized 30 days after P. gingivalis inoculation. Sublingual immunization (SLI) with rGroEL elicited significant rGroEL-specific serum immunoglobulin (Ig)G and salivary IgA antibody (Ab) responses, and these responses were sustained for approximately 1 year. Interestingly, 10-fold more GroEL-specific IgA Ab-producing cells were detected in the submandibular glands (SMGs) than in the spleen. Antigen (Ag)-specific cells isolated from the spleen and SMGs induced significantly higher levels of IFN-γ expression after Ag restimulation in vitro. Flow cytometry illustrated that the frequency of CD11b⁺ dendritic cells with enhanced expression of CD80, CD86, CD40, and major histocompatibility complex II molecules was significantly increased in the SMGs. Furthermore, SLI with rGroEL significantly suppressed P. gingivalis-induced alveolar bone resorption and P. gingivalis-stimulated tumor necrosis factor-α, interleukin-6, and HSP60 expression in the gingiva. These findings suggest that SLI with rGroEL and CpG oligodeoxynucleotide is a beneficial strategy for preventing periodontal disease, mainly by presenting Ags in the oral region and inducing antibody production in the mucosal and systemic systems.

Mucosal Vaccination Against Periodontal Disease: Current Status and Opportunities

Approximately 9 out of 10 adults have some form of periodontal disease, an infection-induced inflammatory disease of the tooth-supporting tissues. The initial form, gingivitis, often remains asymptomatic, but this can evolve into periodontitis, which is typically associated with halitosis, oral pain or discomfort, and tooth loss. Furthermore, periodontitis may contribute to systemic disorders like cardiovascular disease and type 2 diabetes mellitus. Control options remain nonspecific, time-consuming, and costly; largely relying on the removal of dental plaque and calculus by mechanical debridement. However, while dental plaque bacteria trigger periodontal disease, it is the host-specific inflammatory response that acts as main driver of tissue destruction and disease progression. Therefore, periodontal disease control should aim to alter the host's inflammatory response as well as to reduce the bacterial triggers. Vaccines may provide a potent adjunct to mechanical debridement for periodontal disease prevention and treatment. However, the immunopathogenic complexity and polymicrobial aspect of PD appear to complicate the development of periodontal vaccines. Moreover, a successful periodontal vaccine should induce protective immunity in the oral cavity, which proves difficult with traditional vaccination methods. Recent advances in mucosal vaccination may bridge the gap in periodontal vaccine development. In this review, we offer a comprehensive overview of mucosal vaccination strategies to induce protective immunity in the oral cavity for periodontal disease control. Furthermore, we highlight the need for additional research with appropriate and clinically relevant animal models. Finally, we discuss several opportunities in periodontal vaccine development such as multivalency, vaccine formulations, and delivery systems.

Adjuvants: friends in vaccine formulations against infectious diseases

Infectious diseases represent a major cause of deaths worldwide. No vaccine or effective treatment exists nowadays, especially against intracellular pathogens. The increase in multiple drug and superbug antibiotic resistance strains, excessive medication, or misuse of drugs has prompted the search for other safe and effective alternatives. Consistent with this, adjuvants (Latin word "adjuvare": "help or aid") co-administered (Exo) in vaccines have emerged as a promising alternative to initiate and boost an innate, downstream signal that led to adaptative immune response. Nowadays, a promising model of strong immunogens and adjuvants at mucosal sites are the microbial bacterial toxins. Other adjuvants that are also used and might successfully replace aluminum salts in combination with nanotechnology are CpG-ODN, poly IC, type I IFNs, mRNA platforms. Therefore, in the present review, we focused to revisit the old to the new adjuvants compounds, the properties that make them friends in vaccine formulations against infectious diseases.

Atheroprotective nasal immunization with a heat shock protein 60 peptide from Porphyromonas gingivalis

Purpose

Immunization with Porphyromonas gingivalis heat shock protein 60 (PgHSP60) may have an immunoregulatory effect on atherogenesis. The aim of this study was to determine whether nasal immunization with a PgHSP60 peptide could reduce atherosclerotic plaque formation in apolipoprotein E knockout (ApoE KO) mice.

Methods

Seven-week-old male ApoE KO mice were assigned to receive a normal diet, a Western diet, a Western diet and challenge with PgHSP60-derived peptide 14 (Pep14) or peptide 19 (Pep19), or a Western diet and immunization with Pep14 or Pep19 before challenge with Pep14 or Pep19.

Results

Atherosclerotic plaques were significantly smaller in mice that received a Western diet with Pep14 nasal immunization than in mice that received a Western diet and no Pep14 immunization with or without Pep14 challenge. An immunoblot profile failed to detect serum reactivity to Pep14 in any of the study groups. Stimulation by either Pep14 or Pep19 strongly promoted the induction of CD4⁺CD25⁺forkhead box P3 (FoxP3)⁺ human regulatory T cells (Tregs) in vitro. However, the expression of mouse splenic CD4⁺CD25⁺FoxP3⁺ Tregs was lower in the Pep14-immunized mice than in the Pep14-challenged or Pep19-immunized mice. Levels of serum interferon gamma (IFN-γ) and transforming growth factor beta were higher and levels of interleukin (IL) 10 were lower in the Pep14-immunized mice than in the other groups. Induction of CD25⁻ IL-17⁺ T helper 17 (Th17) cells was attenuated in the Pep14-immunized mice.

Conclusions

Nasal immunization with Pep14 may be a mechanism for attenuating atherogenesis by promoting the secretion of IFN-γ and/or suppressing Th17-mediated immunity.

Role of OmpA2 surface regions of Porphyromonas gingivalis in host-pathogen interactions with oral epithelial cells

Outer membrane protein A (OmpA) is a key outer membrane protein found in Gram‐negative bacteria that contributes to several crucial processes in bacterial virulence. In Porphyromonas gingivalis, OmpA is predicted as a heterotrimer of OmpA1 and OmpA2 subunits encoded by adjacent genes. Here we describe the role of OmpA and its individual subunits in the interaction of P. gingivalis with oral cells. Using knockout mutagenesis, we show that OmpA2 plays a significant role in biofilm formation and interaction with human epithelial cells. We used protein structure prediction software to identify extracellular loops of OmpA2, and determined these are involved in interactions with epithelial cells as evidenced by inhibition of adherence and invasion of P. gingivalis by synthetic extracellular loop peptides and the ability of the peptides to mediate interaction of latex beads with human cells. In particular, we observe that OmpA2‐loop 4 plays an important role in the interaction with host cells. These data demonstrate for the first time the important role of P. gingivalis OmpA2 extracellular loops in interaction with epithelial cells, which may help design novel peptide‐based antimicrobial therapies for periodontal disease.

Porphyromonas gingivalis: An Overview of Periodontopathic Pathogen below the Gum Line

Periodontal disease represents a group of oral inflammatory infections initiated by oral pathogens which exist as a complex biofilms on the tooth surface and cause destruction to tooth supporting tissues. The severity of this disease ranges from mild and reversible inflammation of the gingiva (gingivitis) to chronic destruction of connective tissues, the formation of periodontal pocket and ultimately result in loss of teeth. While human subgingival plaque harbors more than 500 bacterial species, considerable research has shown that Porphyromonas gingivalis, a Gram-negative anaerobic bacterium, is the major etiologic agent which contributes to chronic periodontitis. This black-pigmented bacterium produces a myriad of virulence factors that cause destruction to periodontal tissues either directly or indirectly by modulating the host inflammatory response. Here, this review provides an overview of P. gingivalis and how its virulence factors contribute to the pathogenesis with other microbiome consortium in oral cavity.

Alzheimer's disease vaccine development: A new strategy focusing on immune modulation

Despite significant advances in the development of Alzheimer's disease (AD) vaccines effective in animal models, these prototypes have been clinically unsuccessful; apparently the result of using immunogens modified to prevent inflammation. Hence, a new paradigm is needed that uses entire AD-associated immunogens, a notion supported by recent successful passive immunotherapy results, with adjuvants that induce Th2-only while inhibiting without abrogating Th1 immunity. Here, we discuss the obstacles to AD vaccine development and Th2-adjuvants that by acting on dendritic and T cells, would elicit regardless of the antigen a safe and effective antibody response, while preventing damaging neuroinflammation and ameliorating immunosenescence.

Evaluation of a novel immunochromatographic device for rapid and accurate clinical detection of Porphyromonas gingivalis in subgingival plaque

An important goal for the improved diagnosis and management of infectious and inflammatory diseases, such as periodontitis, is the development of rapid and accurate technologies for the decentralized detection of bacterial pathogens. The aim of this prospective multicenter study was to evaluate the clinical use of a novel immunochromatographic device with monoclonal antibodies for the rapid point-of-care detection and semi-quantification of Porphyromonas gingivalis in subgingival plaque. Sixty-three patients with chronic periodontitis and 28 periodontally healthy volunteers were subjected to clinical and microbiological examinations. Subgingival plaque samples were analyzed for the presence of P. gingivalis using a novel immunochromatography based device DK13-PG-001, designed to detect the 40k-outer membrane protein of P. gingivalis, and compared with a PCR-Invader method. In the periodontitis group, a significant strong positive correlation in detection results was found between the test device score and the PCR-Invader method (Spearman rank correlation, r=0.737, p<0.0001). The sensitivity, specificity, and positive and negative predictive values of the test device were 96.2%, 91.8%, 90.4% and 96.7%, respectively. The detection threshold of the test device was determined to be approximately 10(4) (per two paper points). There were significant differences in the bacterial counts by the PCR-Invader method among groups with different ranges of device scores. With a cut-off value of ≥0.25 in device score, none of periodontally healthy volunteers were tested positive for the subgingival presence of P. gingivalis, whereas 76% (n=48) of periodontitis subjects were tested positive. There was a significant positive correlation between device scores for P. gingivalis and periodontal parameters including probing pocket depth and clinical attachment level (r=0.317 and 0.281, respectively, p<0.01). The results suggested that the DK13-PG-001 device kit can be effectively used for rapid, chair-side detection and semi-quantification of P. gingivalis in subgingival plaque.

TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN-CTR) UMIN000011943.

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.

Intranasal immunization with fusion protein MrpH·FimH and MPL adjuvant confers protection against urinary tract infections caused by uropathogenic Escherichia coli and Proteus mirabilis

Urinary tract infections (UTIs) caused by Uropathogenic Escherichia coli (UPEC) and Proteus mirabilis are among the most common infections in the world. Currently there are no vaccines available to confer protection against UTI in humans. In this study, the immune responses and protection of FimH of UPEC with MrpH antigen of P. mirabilis in different vaccine formulations with and without MPL adjuvant were assessed. Mice intranasally immunized with the novel fusion protein MrpH·FimH induced a significant increase in IgG and IgA in serum, nasal wash, vaginal wash, and urine samples. Mice immunized with fusion MrpH·FimH also showed a significant boost in cellular immunity. Addition of MPL as the adjuvant enhanced FimH and MrpH specific humoral and cellular responses in both systemic and mucosal samples. Vaccination with MrpH·FimH alone or in combination with MPL showed the highest efficiency in clearing bladder and kidney infections in mice challenged with UPEC and P. mirabilis. These findings may indicate that the protection observed correlates with the systemic, mucosal and cellular immune responses induced by vaccination with these preparations. Our data suggest MrpH·FimH fusion protein with or without MPL as adjuvant could be potential vaccine candidates for elimination of UPEC and P. mirabilis. These data altogether are promising and these formulations are good candidates for elimination of UPEC and P. mirabilis.

New Th2 adjuvants for preventive and active immunotherapy of neurodegenerative proteinopathies

Active immunotherapy of neurodegenerative proteinopathies, such as Alzheimer's disease, requires a Th2 antibody immune response with exclusion of damaging inflammatory Th1 immunity. Because these diseases affect the elderly whom, owing to immunosenescence, are frequently immune compromised, a successful therapy would require immune agonists capable of eliciting Th2 immunity solely while ameliorating the immune decline linked to aging; an objective hampered by the scarcity of Th2 immune agonists. The fact that some helminth-derived glycans and modified triterpene glycosides elicit Th2 immunity only, even when administered with antigens carrying T cell epitopes, presents new ways to improve the active immune therapy of proteinopathies. Of additional benefit is that these triterpene glycosides could amend some of the detrimental effects of the immunosenescence.

Mucosal vaccination shapes the expression of salivary antibodies and establishment of CD8+ T-cells

BACKGROUND

Mucosal vaccination for preventing periodontitis shows promising results. However, various administration routes and adjuvants may have a substantial role in the efficacy of the vaccination. The aim of the study is to compare different modes of mucosal vaccination with whole-cell Porphyromonas gingivalis and to test the role of various adjuvants as potential modifiers of this process.

METHODS

Mucosal vaccine was administered through oral or nasal routes to BALB/C mice. The tested adjuvants included Escherichia coli cholera toxin, E. coli labile toxin (LT), and unmethylated CpG dinucleotide (CpG). Control mice were vaccinated subcutaneously. Saliva and serum were collected; anti-P. gingivalis salivary immunoglobulin A (IgA) and serum IgG were quantified. A quantitative enzyme-linked immunosorbent assay to measure anti-P. gingivalis IgA levels was established. In addition, cells were extracted from head and neck lymph nodes, and the relative CD8(+) cells were quantified using flow cytometry.

RESULTS

All mucosal vaccination modes induced anti-P. gingivalis salivary IgA but not anti-P. gingivalis serum IgG. Subcutaneous vaccination induced both salivary IgA and serum IgG against P. gingivalis. Mucosal vaccination also induced greater establishment of CD8(+) cells compared to the subcutaneous vaccination. Oral mucosal vaccinations with LT or CpG were the most efficient for salivary IgA expression and CD8 cell establishment in lymph nodes.

CONCLUSIONS

Oral and nasal mucosal vaccination induced a local host response with little systemic effect. The use of CpG or LT as adjuvants with the oral mucosal vaccination was the most efficient vaccination mode in the present mouse model.