Human variability in innate immunity

Understanding the peroxisome proliferator-activated receptor gamma (PPAR-γ) role in periodontitis and diabetes mellitus: A molecular perspective

Periodontitis and Type 2 Diabetes Mellitus (T2DM) are chronic conditions with dysregulated immune responses. Periodontitis involves immune dysfunction and dysbiotic biofilms, leading to tissue destruction. T2DM is marked by insulin resistance and systemic inflammation, driving metabolic and tissue damage. Both conditions share activation of key pathways, including Nuclear Factor Kappa B (NF-κB), Activator Protein-1 (AP-1), and Signal Transducer and Activator of Transcription (STAT) proteins, reinforcing an inflammatory feedback loop. This review highlights the role of Peroxisome Proliferator-Activated Receptor Gamma (PPAR-γ), a transcription factor central to lipid and glucose metabolism, adipogenesis, and immune regulation. PPAR-γ activation has been shown to suppress inflammatory mediators such as Tumor Necrosis Factor Alpha (TNF-α) and Interleukin 6 (IL-6) through the inhibition of NF-κB, AP-1, and STAT pathways, thereby potentially disrupting the inflammatory-metabolic cycle that drives both diseases. PPAR-γ agonists, including thiazolidinediones (TZDs) and endogenous ligands such as 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), show promise in reducing inflammation and improving insulin sensitivity, but they are limited by adverse effects. Therapies, including Selective Peroxisome Proliferator-Activated Receptor Modulators (SPPARMs), have been developed to offer a more targeted approach, allowing for selective modulation of PPAR-γ activity to retain its anti-inflammatory benefits while minimizing their side effects. By integrating insights into PPAR-γ's molecular mechanisms, this review underscores its therapeutic potential in mitigating inflammation and enhancing metabolic control.

Nucleotide-binding oligomerization domain-like receptor family caspase recruitment domain containing protein 5 affects the progression of periodontitis by regulating the function of periodontal membrane cells

Background/purpose

Nucleotide-binding oligomerization domain-like receptor family caspase recruitment domain containing protein 5 (NLRC5) plays a regulatory role in innate and adaptive immunity. However, its role in periodontitis remains unclear. This study investigated the effects of NLRC5 on periodontitis and the underlying mechanism.

Materials and methods

Experimental periodontitis models of wild-type and Nlrc5 knockout mice were established to detect alveolar bone loss. The inflammatory environment was established with Porphyromonas. gingivalis lipopolysaccharide (P. gingivalis LPS). The expression of NLRC5 in periodontal ligament stem cells (PDLSCs) were detected with P. gingivalis LPS stimulated. After knocking-down or overexpressing the NLRC5 expression level, the inflammatory cytokine level and osteogenic ability of PDLSCs were detected.

Results

The Nlrc5 knockout mice exhibited greater alveolar bone loss in periodontitis. In the presence of P. gingivalis LPS, the expression of NLRC5 decreased. Downregulating NLRC5 increased the expression of interleukin (IL)-1β, IL-6 and tumor necrosis factor-α (TNF-α). Upregulated NLRC5 inhibited nuclear factor kappa-B (NF-κB) signaling and inhibited the expression of those proinflammatory factors. NLRC5 had a positive regulatory effect on the osteogenic differentiation of PDLSCs. When NLRC5 was knocked down, the ALP activity and the number of mineralized nodules in PDLSCs decreased. Conversely, overexpression of NLRC5 enhanced the osteogenic differentiation ability of PDLSCs. Overexpression of NLRC5 increased the osteogenic differentiation of PDLSCs in inflammatory environments.

Conclusion

NLRC5 affects the progression of periodontitis by regulating the function of PDLSCs. NLRC5 reduced the expression of inflammatory factors by inhibiting NF-κB, and had a positive regulatory effect on the osteogenic differentiation of PDLSCs.

Identification of disulfidptosis- and ferroptosis-related transcripts in periodontitis by bioinformatics analysis and experimental validation

Background

Disulfidptosis and ferroptosis are forms of programmed cell death that may be associated with the pathogenesis of periodontitis. Our study developed periodontitis-associated biomarkers combining disulfidptosis and ferroptosis, which provides a new perspective on the pathogenesis of periodontitis.

Methods

Firstly, we obtained the periodontitis dataset from public databases and found disulfidptosis- and ferroptosis-related differentially expressed transcripts based on the disulfidptosis and ferroptosis transcript sets. After that, transcripts that are tissue biomarkers for periodontitis were found using three machine learning methods. We also generated transcript subclusters from two periodontitis microarray datasets: GSE16134 and GSE23586. Furthermore, three transcripts with the best classification efficiency were further screened. Their expression and classification efficacy were validated using qRT-PCR. Finally, periodontal clinical indicators of 32 clinical patients were collected, and the correlation between three transcripts above and periodontal clinical indicators was analyzed.

Results

We identified six transcripts that are tissue biomarkers for periodontitis, the top three transcripts with the best classification, and delineated two expression patterns in periodontitis.

Conclusions

Our study found that disulfidptosis and ferroptosis were associated with immune responses and may involve periodontitis genesis.

Smart stimuli-responsive hydrogels for drug delivery in periodontitis treatment

Periodontitis is a chronic inflammatory disease initiated by pathogenic biofilms and host immunity that damages tooth-supporting tissues, including the gingiva, periodontal ligament and alveolar bone. The physiological functions of the oral cavity, such as saliva secretion and chewing, greatly reduce the residence of therapeutic drugs in the area of a periodontal lesion. In addition, complex and diverse pathogenic mechanisms make effectively treating periodontitis difficult. Therefore, designing advanced local drug delivery systems and rational therapeutic strategies are the basis for successful periodontitis treatment. Hydrogels have attracted considerable interest in the field of periodontitis treatment due to their biocompatibility, biodegradability and convenient administration to the periodontal pocket. In recent years, the focus of hydrogel research has shifted to smart stimuli-responsive hydrogels, which can undergo flexible sol-gel transitions in situ and control drug release in response to stimulation by temperature, light, pH, ROS, glucose, or enzymes. In this review, we systematically introduce the development and rational design of emerging smart stimuli-responsive hydrogels for periodontitis treatment. We also discuss the state-of-the-art therapeutic strategies of smart hydrogels based on the pathogenesis of periodontitis. Additionally, the challenges and future research directions of smart hydrogels for periodontitis treatment are discussed from the perspective of developing efficient hydrogel delivery systems and potential clinical applications.

mTOR Signaling in the Regulation of CD4+ T Cell Subsets in Periodontal Diseases

Periodontal disease results from the inflammatory infiltration by the microbial community which is marked through tooth mobility and alveolar bone resorption. The inflammation in periodontal disease is mediated by CD4⁺ T cells through cytokine secretion and osteoclastogenetic activity. Historically, the inflammatory model in periodontal disease is described through disruption of the balance between two subsets of T helper cells which are T-helper type 1 (Th1) and T-helper type 2 (Th2). However, more and more studies have found that apart from subsets of helper T cells, regulatory T-cells and Th17 cells are also involved in the pathogenesis of periodontal diseases. Growing evidence proves that helper T cells differentiation, activation, and subset determination are under the strong impact of mTOR signaling. mTOR signaling could promote Th1 and Th17 cell differentiation and inhibit Treg commitment through different mTOR complexes, therefore we anticipate a regulation effect of mTOR signaling on periodontal diseases by regulating CD4⁺ T cell subsets. This review aims to integrate the topical researches about the role of different types of Th cells in the pathogenesis of periodontal diseases, as well as the regulation of mTOR signaling in the specification and selection of Th cell commitment.

Human Umbilical Cord Mesenchymal Stem Cells: Current Literature and Role in Periodontal Regeneration

Periodontal disease can cause irreversible damage to tooth-supporting tissues such as the root cementum, periodontal ligament, and alveolar bone, eventually leading to tooth loss. While standard periodontal treatments are usually helpful in reducing disease progression, they cannot repair or replace lost periodontal tissue. Periodontal regeneration has been demonstrated to be beneficial in treating intraosseous and furcation defects to varied degrees. Cell-based treatment for periodontal regeneration will become more efficient and predictable as tissue engineering and progenitor cell biology advance, surpassing the limitations of present therapeutic techniques. Stem cells are undifferentiated cells with the ability to self-renew and differentiate into several cell types when stimulated. Mesenchymal stem cells (MSCs) have been tested for periodontal regeneration in vitro and in humans, with promising results. Human umbilical cord mesenchymal stem cells (UC-MSCs) possess a great regenerative and therapeutic potential. Their added benefits comprise ease of collection, endless source of stem cells, less immunorejection, and affordability. Further, their collection does not include the concerns associated with human embryonic stem cells. The purpose of this review is to address the most recent findings about periodontal regenerative mechanisms, different stem cells accessible for periodontal regeneration, and UC-MSCs and their involvement in periodontal regeneration.

Photothermal therapy with regulated Nrf2/NF-κB signaling pathway for treating bacteria-induced periodontitis

Periodontitis is an inflammatory disease initiated by bacterial infection, developed by excessive immune response, and aggravated by high level of reactive oxygen species (ROS). Hence, herein, a versatile metal-organic framework (MOF)-based nanoplatform is prepared using mesoporous Prussian blue (MPB) nanoparticles to load BA, denoted as MPB-BA. The established MPB-BA nanoplatform serves as a shelter and reservoir for vulnerable immunomodulatory drug BA, which possesses antioxidant, anti-inflammatory and anti-bacterial effects. Thus, MPB-BA can exert its antioxidant, anti-inflammatory functions through scavenging intracellular ROS to switch macrophages from M1 to M2 phenotype so as to relieve inflammation. The underlying molecular mechanism lies in the upregulation of phosphorylated nuclear factor erythroid 2-related factor 2 (Nrf2) to scavenge ROS and subsequently inhibit the nuclear factor kappa-B (NF-κB) signal pathway. Moreover, MPB-BA also exhibited efficient photothermal antibacterial activity against periodontal pathogens under near-infrared (NIR) light irradiation. In vivo RNA sequencing results revealed the high involvement of both antioxidant and anti-inflammatory pathways after MPB-BA application. Meanwhile, micro-CT and immunohistochemical staining of p-Nrf2 and p-P65 further confirmed the superior therapeutic effects of MPB-BA than minocycline hydrochloride. This work may provide an insight into the treatment of periodontitis by regulating Nrf2/NF-κB signaling pathway through photothermal bioplatform-assisted immunotherapy.

Mesenchymal Stem Cell-Derived Exosome Therapy of Microbial Diseases: From Bench to Bed

Microbial diseases are a global health threat, leading to tremendous casualties and economic losses. The strategy to treat microbial diseases falls into two broad categories: pathogen-directed therapy (PDT) and host-directed therapy (HDT). As the typical PDT, antibiotics or antiviral drugs directly attack bacteria or viruses through discerning specific molecules. However, drug abuse could result in antimicrobial resistance and increase infectious disease morbidity. Recently, the exosome therapy, as a HDT, has attracted extensive attentions for its potential in limiting infectious complications and targeted drug delivery. Mesenchymal stem cell-derived exosomes (MSC-Exos) are the most broadly investigated. In this review, we mainly focus on the development and recent advances of the application of MSC-Exos on microbial diseases. The review starts with the difficulties and current strategies in antimicrobial treatments, followed by a comprehensive overview of exosomes in aspect of isolation, identification, contents, and applications. Then, the underlying mechanisms of the MSC-Exo therapy in microbial diseases are discussed in depth, mainly including immunomodulation, repression of excessive inflammation, and promotion of tissue regeneration. In addition, we highlight the latest progress in the clinical translation of the MSC-Exo therapy, by summarizing related clinical trials, routes of administration, and exosome modifications. This review will provide fundamental insights and future perspectives on MSC-Exo therapy in microbial diseases from bench to bedside.

Burden of chronic diseases associated with periodontal diseases: a retrospective cohort study using UK primary care data

OBJECTIVES

To identify the association between periodontal diseases (gingivitis and periodontitis) and chronic diseases including cardiovascular disease, cardiometabolic disease, autoimmune disease and mental ill health.

DESIGN

Retrospective cohort.

SETTING

IQVIA Medical Research Data-UK between 1 January 1995 and 1 January 2019.

PARTICIPANTS

64 379 adult patients with a general practitioner recorded diagnosis of periodontal disease (exposed patients) were matched to 251 161 unexposed patients by age, sex, deprivation and registration date.

MAIN OUTCOME MEASURES

Logistic regression models accounting for covariates of clinical importance were undertaken to estimate the adjusted OR (aOR) of having chronic diseases at baseline in the exposed compared with the unexposed group. Incidence rates for each outcome of interest were then provided followed by the calculation of adjusted HRs using cox regression modelling to describe the risk of outcome development in each group.

RESULTS

The average age at cohort entry was 45 years and the median follow-up was 3.4 years. At study entry, the exposed cohort had an increased likelihood of having a diagnosis of cardiovascular disease (aOR 1.43; 95% CI 1.38 to 1.48), cardiometabolic disease (aOR 1.16; 95% CI 1.13 to 1.19), autoimmune disease (aOR 1.33; 95% CI 1.28 to 1.37) and mental ill health (aOR 1.79; 95% CI 1.75 to 1.83) compared with the unexposed group. During the follow-up of individuals without pre-existing outcomes of interest, the exposed group had an increased risk of developing cardiovascular disease (HR 1.18; 95% CI 1.13 to 1.23), cardiometabolic disease (HR 1.07; 95% CI 1.03 to 1.10), autoimmune disease (HR 1.33; 95% CI 1.26 to 1.40) and mental ill health (HR 1.37; 95% CI 1.33 to 1.42) compared with the unexposed group.

CONCLUSIONS

In this cohort, periodontal diseases appeared to be associated with an increased risk of developing cardiovascular, cardiometabolic, autoimmune diseases and mental ill health. Periodontal diseases are very common; therefore, an increased risk of other chronic diseases represent a substantial public health burden.

Impact of tooth loss due to periodontal disease on the prognosis of rehabilitation

When periodontal disease is diagnosed, it is difficult to predict the clinical response of treatment of a tooth over time because the result of treatment is affected by several factors and will depend on the maintenance and support of periodontal treatment. Rehabilitation with removable dental prostheses, fixed prostheses, and dental implants makes it possible to restore the function and esthetics of patients with tooth loss due to periodontal disease. The predictive factors of tooth loss in periodontitis patients should be assessed by dentists to inform their clinical decision-making during dental treatment planning. This will provide detailed individualized information and level of risk of patients considered suitable for dental rehabilitation. Therefore, the aim of this article was to review the subject of "Impact of tooth loss due to periodontal disease on the prognosis of rehabilitation" and the effect of fixed, removable, and implant-supported prostheses in periodontal patients.

Magnetic resonance imaging as a diagnostic tool for periodontal disease: A prospective study with correlation to standard clinical findings-Is there added value?

AIM

To evaluate the correlation between standard clinical findings, radiographic (OPT) and magnetic resonance imaging (MRI) as well as to assess whether MRI is capable of providing additional information related to the severity and extent of periodontal disease.

METHODS

42 patients with generalized periodontitis received pre-interventional MRI scans. These were compared to MR images of a periodontal healthy control group (n = 34). The extent of the osseous oedema, detected by MRI, was set in correlation with clinical periodontitis-associated findings.

RESULTS

A highly significant correlation between bone oedema and clinical testings such as probing depth (p < 0.0001) and bleeding on probing (p < 0.0001) was revealed. The oedema exceeded the extent of demineralized bone. Patients with a positive BOP test showed a 2.51-fold increase in risk of already having a bone oedema around the respective tooth even if probing depth was ≤3 mm (logistic binary regression analysis, OR 2.51; 95% CI: 1.54-4.11; p < 0.0001).

CONCLUSION

MRI findings correlated with standard clinical findings, and MRI was able to depict intraosseous changes before any osseous defect had occurred.

Galectin-3, Possible Role in Pathogenesis of Periodontal Diseases and Potential Therapeutic Target

Periodontal diseases are chronic inflammatory diseases that occur due to the imbalance between microbial communities in the oral cavity and the immune response of the host that lead to destruction of tooth supporting structures and finally to alveolar bone loss. Galectin-3 is a β-galactoside-binding lectin with important roles in numerous biological processes. By direct binding to microbes and modulation of their clearence, Galectin-3 can affect the composition of microbial community in the oral cavity. Galectin-3 also modulates the function of many immune cells in the gingiva and gingival sulcus and thus can affect immune homeostasis. Few clinical studies demonstrated increased expression of Galectin-3 in different forms of periodontal diseases. Therefore, the objective of this mini review is to discuss the possible effects of Galectin-3 on the process of immune homeostasis and the balance between oral microbial community and host response and to provide insights into the potential therapeutic targeting of Gal-3 in periodontal disease.

Local application of curcumin-loaded nanoparticles as an adjunct to scaling and root planing in periodontitis: Randomized, placebo-controlled, double-blind split-mouth clinical trial

OBJECTIVE

Assess a single local application of curcumin-loaded nanoparticles as an adjunct to scaling and root planing (SRP) in nonsurgical periodontal treatment (NPT).

MATERIALS AND METHODS

Twenty healthy subjects with periodontitis received SRP+PLGA/PLA nanoparticles loaded with 50 μg of curcumin (N-Curc) or SRP+empty nanoparticles. Probing pocket depth (PPD), clinical attachment level (CAL), and bleeding on probing (BOP) were monitored at baseline, 30, 90, and 180 days. IL-1α, IL-6, TNFα, and IL-10 in the gingival crevicular fluid (GCF) were assessed by ELISA, and counts of 40 bacterial species were determined by DNA hybridization at baseline, 3, 7, and 15 days post-therapy.

RESULTS

PPD, CAL, and BOP were similarly and significantly improved in both experimental groups. There was no difference in GCF cytokine levels between experimental groups, although IL-6 was decreased at 3 days only in the N-Curc group. NPT reduced counts of red complex bacterial species in both groups. Veillonella Parvula counts increased significantly only in N-Curc group at 7 days, whereas Aggregatibacter actinomycetemcomitans counts increased significantly only in the control group from day 3 to day 15.

CONCLUSION

We conclude that a single local administration of nanoencapsulated curcumin in periodontally diseased sites had no additive benefits to NPT.

CLINICAL RELEVANCE

Our results showed that a single local application of curcumin-loaded nanoparticles associated with nonsurgical periodontal therapy did not improve clinical outcomes. Hence, our findings do not support the use of curcumin as an adjunct to nonsurgical periodontal therapy.

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.

Clinical association between chronic periodontitis and the leukocyte extravasation inhibitors developmental endothelial locus-1 and pentraxin-3

This clinical study aimed to determine whether periodontal disease is associated with expression of developmental endothelial locus-1 (Del-1) and pentraxin-3 (PTX-3), endogenous inhibitors of leukocyte extravasation in humans. Expression of DEL1, PTX3, interleukin-17A (IL17A), and lymphocyte function-associated antigen-1 (LFA1) was determined, using RT-PCR and melting curve analysis, in biopsies of gingival tissues from 95 patients: 42 with moderate periodontitis; 40 with severe periodontitis; and 13 healthy controls. Relative expression of DEL1 and PTX3 was statistically significantly weaker in patients with periodontitis than in the control subjects. On the contrary, both IL17A and LFA1 showed statistically significant stronger expression in patients with periodontitis than in healthy controls. Correlation analysis, performed using Spearman's test, showed that expression of DEL1 was statistically significantly linked to periodontitis (ρ = -0.103) and to age (ρ = -0.134), but not to the gender of the patient, and that expression of PTX3 was significantly correlated with periodontitis (ρ = -0.354). Expression of neutrophil extravasation inhibitors DEL1 and PTX3 show significant, but weak, association with the clinical manifestation of chronic periodontitis.

Periodontal diseases

Periodontal diseases comprise a wide range of inflammatory conditions that affect the supporting structures of the teeth (the gingiva, bone and periodontal ligament), which could lead to tooth loss and contribute to systemic inflammation. Chronic periodontitis predominantly affects adults, but aggressive periodontitis may occasionally occur in children. Periodontal disease initiation and propagation is through a dysbiosis of the commensal oral microbiota (dental plaque), which then interacts with the immune defences of the host, leading to inflammation and disease. This pathophysiological situation persists through bouts of activity and quiescence, until the affected tooth is extracted or the microbial biofilm is therapeutically removed and the inflammation subsides. The severity of the periodontal disease depends on environmental and host risk factors, both modifiable (for example, smoking) and non-modifiable (for example, genetic susceptibility). Prevention is achieved with daily self-performed oral hygiene and professional removal of the microbial biofilm on a quarterly or bi-annual basis. New treatment modalities that are actively explored include antimicrobial therapy, host modulation therapy, laser therapy and tissue engineering for tissue repair and regeneration.

Gingival crevicular fluid levels of monocyte chemoattractant protein-1 in patients with aggressive periodontitis

OBJECTIVES

The purpose of this study was to investigate the gingival crevicular fluid (GCF) levels of monocyte chemoattractant protein (MCP)-1 in aggressive periodontitis (AgP) and whether GCF MCP-1 levels differ among localized (L) AgP and generalized (G) AgP.

MATERIAL AND METHODS

A total of 160 subjects including 80 AgP and 80 age- and gender-matched periodontally healthy (H) controls were recruited in this cross-sectional study (NCT02927704). GCF samples were collected from 160 patients including 50 LAgP, 30 GAgP, and 80 H. Volume of GCF was measured by Periotron 8000^® , and enzyme-linked immunosorbent assay was used to assess MCP-1 levels.

RESULTS

Compared to H controls, all clinical parameters and total amounts (pg 30 s^-1 ) of MCP-1 were significantly higher in subjects with LAgP and GAgP (P < 0.05). Although concentrations of GCF MCP-1 did not differ between LAgP and GAgP (P > 0.05), total amounts of MCP-1 were higher in GAgP than LAgP (P < 0.05).

CONCLUSION

It can be concluded that the total amount of MCP-1 level in GCF may be a potential determinant in AgP subjects. Increased MCP-1 levels in line with the degree of periodontal destruction in GAgP patients reveal that MCP-1 can be used to understand the disease pathogenesis of LAgP and GAgP.

The Effect of Nonsurgical Periodontal Therapy on HNP1-3 Level in Gingival Crevicular Fluid of Chronic Periodontitis Patients

The rich bacterial flora of oral cavity is controlled by innate immune response, including antibacterial peptides and among them human neutrophil peptides 1–3 (HNP1-3). The knowledge of the involvement of HNPs in innate and acquired immunity of the periodontium is fragmentary. The aim of the study was to assess alterations in HNP1-3 levels in the gingival crevicular fluid (GCF) of chronic periodontitis patients before and after nonsurgical periodontal therapy. Nineteen patients with chronic periodontitis were qualified to the study. After periodontal examination, one site with pocket depth (PD) ≥4 mm was selected. All the patients received periodontal treatment involving scaling and root planing with additional systemic antibiotic therapy (Amoxicillin 375 mg three times daily and Metronidazole 250 mg three times daily for 7 days). Prior to therapy, 3 and 6 months after it, clinical periodontal parameters were measured and GCF was collected from previously chosen site. The level of HNP1-3 in GCF was determined by means of a commercially available enzyme-linked immunoassay kit. The periodontal therapy caused a statistically significant (p < 0.001) decrease in all the assessed clinical parameters at the sites of sample collection except for bleeding on probing. The level of HNP1-3 per measure point showed a statistically significant increase (baseline—3 months: p = 0.05, baseline—6 months: p = 0.007). Within the limits of the study, it can be stated that nonsurgical periodontal therapy with additional systemic administration of Amoxicillin and Metronidazole increases the level of HNP1-3 in GCF.

Secretable Small RNAs via Outer Membrane Vesicles in Periodontal Pathogens

MicroRNAs (miRNAs) have been shown to be major regulators of eukaryotic gene expression. However, bacterial RNAs comparable in size to eukaryotic miRNAs (18-22 nucleotides) have received little attention. Recently, a novel class of small RNAs similar in size to miRNAs (miRNA-size, small RNAs or msRNAs) have also been found in several bacteria. Like miRNAs, msRNAs are approximately 15 to 25 nucleotides in length, and their precursors are predicted to form a hairpin loop secondary structure. Here, we identified msRNAs in the periodontal pathogens Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Treponema denticola. We examined these msRNAs using a deep sequencing method and characterized dozens of msRNAs through bioinformatic analysis. Highly expressed msRNAs were selected for further validation. The findings suggest that this class of small RNAs is well conserved across the domains of life. Indeed, msRNAs secreted via bacterial outer membrane vesicles (OMVs) were detected. The ability of bacterial OMVs to deliver RNAs into eukaryotic cells was also observed. These msRNAs in OMVs allowed us to identify their potential human immune-related target genes. Furthermore, we found that exogenous msRNAs could suppress expression of certain cytokines in Jurkat T cells. We propose msRNAs may function as novel bacterial signaling molecules that mediate bacteria-to-human interactions. Furthermore, this study may provide fresh insight into bacterial pathogenic mechanisms of periodontal diseases.

Host response mechanisms in periodontal diseases

Periodontal diseases usually refer to common inflammatory disorders known as gingivitis and periodontitis, which are caused by a pathogenic microbiota in the subgingival biofilm, including Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia and Treponema denticola that trigger innate, inflammatory, and adaptive immune responses. These processes result in the destruction of the tissues surrounding and supporting the teeth, and eventually in tissue, bone and finally, tooth loss. The innate immune response constitutes a homeostatic system, which is the first line of defense, and is able to recognize invading microorganisms as non-self, triggering immune responses to eliminate them. In addition to the innate immunity, adaptive immunity cells and characteristic cytokines have been described as important players in the periodontal disease pathogenesis scenario, with a special attention to CD4⁺ T-cells (T-helper cells). Interestingly, the T cell-mediated adaptive immunity development is highly dependent on innate immunity-associated antigen presenting cells, which after antigen capture undergo into a maturation process and migrate towards the lymph nodes, where they produce distinct patterns of cytokines that will contribute to the subsequent polarization and activation of specific T CD4+ lymphocytes. Skeletal homeostasis depends on a dynamic balance between the activities of the bone-forming osteoblasts (OBLs) and bone-resorbing osteoclasts (OCLs). This balance is tightly controlled by various regulatory systems, such as the endocrine system, and is influenced by the immune system, an osteoimmunological regulation depending on lymphocyte- and macrophage-derived cytokines. All these cytokines and inflammatory mediators are capable of acting alone or in concert, to stimulate periodontal breakdown and collagen destruction via tissue-derived matrix metalloproteinases, a characterization of the progression of periodontitis as a stage that presents a significantly host immune and inflammatory response to the microbial challenge that determine of susceptibility to develop the destructive/progressive periodontitis under the influence of multiple behavioral, environmental and genetic factors.

Genotype-specific regulation of oral innate immunity by T2R38 taste receptor

The bitter taste receptor T2R38 has been shown to regulate mucosal innate immune responses in the upper airway epithelium. Furthermore, SNPs in T2R38 influence the sensitivity to 6-n-propylthiouracil (PROP) and are associated with caries risk/protection. However, no study has been reported on the role of T2R38 in the innate immune responses to oral bacteria. We hypothesize that T2R38 regulates oral innate immunity and that this regulation is genotype-specific. Primary gingival epithelial cells carrying three common genotypes, PAV/PAV (PROP super-taster), AVI/PAV (intermediate) and AVI/AVI (non-taster) were stimulated with cariogenic bacteria Streptococcus mutans, periodontal pathogen Porphyromonas gingivalis or non-pathogen Fusobacterium nucleatum. QRT-PCR analyzed T2R38 mRNA, and T2R38-specific siRNA and ELISA were utilized to evaluate induction of hBD-2 (antimicrobial peptide), IL-1α and IL-8 in various donor-lines. Experiments were set up in duplicate and repeated three times. T2R38 mRNA induction in response to S. mutans was highest in PAV/PAV (4.3-fold above the unstimulated controls; p<0.05), while lowest in AVI/AVI (1.2-fold). In PAV/PAV, hBD-2 secretion in response to S. mutans was decreased by 77% when T2R38 was silenced. IL-1α secretion was higher in PAV/PAV compared to AVI/PAV or AVI/AVI with S. mutans stimulation, but it was reduced by half when T2R38 was silenced (p<0.05). In response to P. gingivalis, AVI/AVI showed 4.4-fold increase (p<0.05) in T2R38 expression, whereas the levels in PAV/PAV and AVI/PAV remained close to that of the controls. Secretion levels of IL-1α and IL-8 decreased in AVI/AVI in response to P. gingivalis when T2R38 was silenced (p<0.05), while the changes were not significant in PAV/PAV. Our data suggest that the regulation of gingival innate immunity by T2R38 is genotype-dependent and that the ability to induce a high level of hBD-2 by PAV/PAV carriers may be a reason for protection against caries in this group.

Natural resolution of inflammation

Inflammation is a protective response essential for maintaining human health and for fighting disease. As an active innate immune reaction to challenge, inflammation gives rise to clinical cardinal signs: rubor, calor, dolor, tumor and functio laesa. Termination of acute inflammation was previously recognized as a passive process; a natural decay of pro-inflammatory signals. We now understand that the natural resolution of inflammation involves well-integrated, active, biochemical programs that return tissues to homeostasis. This review focuses on recent advances in the understanding of the role of endogenous lipid mediators that modulate cellular fate and inflammation. Biosynthesis of eicosanoids and other lipids in exudates coincides with changes in the types of inflammatory cells. Resolution of inflammation is initiated by an active class switch in lipid mediators, such as classic prostaglandins and leukotrienes, to the production of proresolution mediators. Endogenous pro-resolving lipid mediators, including arachidonic acid-derived lipoxins, aspirin-triggered lipoxins, ω3-eicosapentaenoic acid-derived resolvins of the E-series, docosahexaenoic acid-derived resolvins of the D-series, protectins and maresins, are biosynthesized during the resolution phase of acute inflammation. Depending on the type of injury and the type of tissue, the initial cells that respond are polymorphonuclear leukocytes, monocytes/macrophages, epithelial cells or endothelial cells. The selective interaction of specific lipid mediators with G protein-coupled receptors expressed on innate immune cells (e.g. G protein-coupled receptor 32, lipoxin A4 receptor/formyl peptide receptor2, chemokine-like receptor 1, leukotriene B4 receptor type 1 and cabannoid receptor 2) induces cessation of leukocyte infiltration; vascular permeability/edema returns to normal with polymorphonuclear neutrophil death (mostly via apoptosis), the nonphlogistic infiltration of monocyte/macrophages and the removal (by macrophages) of apoptotic polymorphonuclear neutrophils, foreign agents (bacteria) and necrotic debris from the site. While an acute inflammatory response that is resolved in a timely manner prevents tissue injury, inadequate resolution and failure to return tissue to homeostasis results in neutrophil-mediated destruction and chronic inflammation. A better understanding of the complex mechanisms of lipid agonist mediators, cell targets and actions allows us to exploit and develop novel therapeutic strategies to treat human inflammatory diseases, including periodontal diseases.

The inflammophilic character of the periodontitis-associated microbiota

In periodontitis, dysbiotic microbial communities exhibit synergistic interactions for enhanced protection from host defenses, nutrient acquisition, and persistence in an inflammatory environment. This review discusses evidence that periodontitis-associated communities are 'inflammo-philic' (=loving or attracted to inflammation) in that they have evolved to not only endure inflammation but also to take advantage of it. In this regard, inflammation can drive the selection and enrichment of these pathogenic communities by providing a source of nutrients in the form of tissue breakdown products (e.g. degraded collagen peptides and heme-containing compounds). In contrast, those species that cannot benefit from the altered ecological conditions of the inflammatory environment, or for which host inflammation is detrimental, are likely to be outcompeted. Consistent with the concept that inflammation fosters the growth of dysbiotic microbial communities, the bacterial biomass of human periodontitis-associated biofilms was shown to increase with increasing periodontal inflammation. Conversely, anti-inflammatory treatments in animal models of periodontitis were shown to diminish the periodontal bacterial load, in addition to protecting from bone loss. The selective flourishing of inflammophilic bacteria can perpetuate inflammatory tissue destruction by setting off a 'vicious cycle' for disease progression, in which dysbiosis and inflammation reinforce each other. Therefore, the control of inflammation appears to be central to the treatment of periodontitis, as it is likely to control both dysbiosis and disease progression.

Are proteinase 3 and cathepsin C enzymes related to pathogenesis of periodontitis?

Aim. Cathepsin C is the activator of the polymorphonuclear leukocyte-derived proteinase 3, which contributes to inflammatory processes. The aim of the present study was to investigate gingival crevicular fluid (GCF) proteinase 3 and cathepsin C levels in periodontal diseases. Design. Eighteen patients with chronic periodontitis (CP), 20 patients with generalized aggressive periodontitis (G-AgP), 20 patients with gingivitis, and 18 healthy subjects were included in the study. Periodontal parameters including probing depth, clinical attachment level, papilla bleeding index, and plaque index were assessed in all study subjects. GCF proteinase 3 and cathepsin C levels were analyzed by ELISA. Results. GCF proteinase 3 total amount was significantly higher in diseased groups compared to control group, after adjusting age (P < 0.05). No differences were found in GCF cathepsin C levels among the study groups (P > 0.05). Periodontal parameters of sampling sites were positively correlated with GCF proteinase 3 total amounts (P < 0.01) but not with cathepsin C total amounts (P > 0.05). Conclusions. Elevated levels of GCF proteinase 3 in CP, G-AgP, and gingivitis might suggest that proteinase 3 plays a role during inflammatory periodontal events in host response. However, cathepsin C in GCF does not seem to have an effect on the pathogenesis of periodontal diseases.

Moving into a new era of periodontal genetic studies: relevance of large case-control samples using severe phenotypes for genome-wide association studies

Studies to elucidate the role of genetics as a risk factor for periodontal disease have gone through various phases. In the majority of cases, the initial 'hypothesis-dependent' candidate-gene polymorphism studies did not report valid genetic risk loci. Following a large-scale replication study, these initially positive results are believed to be caused by type 1 errors. However, susceptibility genes, such as CDKN2BAS (Cyclin Dependend KiNase 2B AntiSense RNA; alias ANRIL [ANtisense Rna In the Ink locus]), glycosyltransferase 6 domain containing 1 (GLT6D1) and cyclooxygenase 2 (COX2), have been reported as conclusive risk loci of periodontitis. The search for genetic risk factors accelerated with the advent of 'hypothesis-free' genome-wide association studies (GWAS). However, despite many different GWAS being performed for almost all human diseases, only three GWAS on periodontitis have been published - one reported genome-wide association of GLT6D1 with aggressive periodontitis (a severe phenotype of periodontitis), whereas the remaining two, which were performed on patients with chronic periodontitis, were not able to find significant associations. This review discusses the problems faced and the lessons learned from the search for genetic risk variants of periodontitis. Current and future strategies for identifying genetic variance in periodontitis, and the importance of planning a well-designed genetic study with large and sufficiently powered case-control samples of severe phenotypes, are also discussed.

Aging and its Impact on Innate Immunity and Inflammation: Implications for Periodontitis

The elderly exhibit increased susceptibility to a number of inflammatory or degenerative pathologies. Aging is similarly thought to be associated with increased prevalence and severity of periodontitis, although the underlying causes are poorly understood. Among the plausible mechanisms whereby aging could contribute to increased susceptibility to periodontitis are age-dependent alterations in the innate immune and inflammatory status of the host. This hypothesis is supported by studies in humans and animal models outlined in this Review. Indeed, innate immune cells isolated from elderly subjects exhibit age-related cell-intrinsic defects that could predispose the elderly to deregulated immune and inflammatory responses. Moreover, the investigation of age-related alterations in the tissue environment where recruited inflammatory cells ultimately function could provide complementary, if not better, insights into the impact of aging on periodontitis. Integrative approaches combining in vitro and in vivo mechanistic models are underway and can potentially contribute to targeted molecular therapies that can reverse or mitigate the effects of aging on periodontitis and other inflammatory diseases.

Gene polymorphism of β-defensin-1 is associated with susceptibility to periodontitis in Japanese

Periodontitis is a multifactorial disease associated with genetic and environmental factors. Single-nucleotide polymorphisms (SNPs) are associated with susceptibility to common diseases such as diabetes and periodontitis. Although the oral cavity is exposed to various organisms, the conditions are well controlled by innate and acquired immune systems. Antimicrobial peptides (AMPs) play an important role in the innate immune system; however, the association of AMP-SNPs with periodontitis has not been fully elucidated. This study investigated the relationship between AMP-SNPs and periodontitis in Japanese. One hundred and five Japanese subjects were recruited, which included patients with aggressive, severe, moderate and mild periodontitis, and age-matched healthy controls. Genomic DNA was isolated from peripheral blood and genotypes of SNPs of β-defensin-1 and lactoferrin genes (DEFB1: rs1799946, rs1800972 and rs11362; and LTF: rs1126478) were investigated using the PCR-Invader assay. Protein level of AMPs in gingival crevicular fluid (GCF) was quantified by ELISA. Case-control studies revealed that the -44 CC genotype of DEFB1 (rs1800972) was associated with periodontitis (OR 2.51), particularly with severe chronic periodontitis (OR 4.15) and with combined severe and moderate chronic periodontitis (OR 4.04). No statistical differences were found in other genotypes. The β-defensin-1 concentrations in GCF were significantly lower in subjects with the -44 CC genotype of DEFB1 than in those without this genotype. No significant differences between GCF concentrations of AMPs and other genotypes were detected. The -44 CC genotype of the β-defensin-1 gene (DEFB1 rs1800972) may be associated with susceptibility to chronic periodontitis in Japanese.

Cotinine inhibits the pro-inflammatory response initiated by multiple cell surface Toll-like receptors in monocytic THP cells

Background

The primary, stable metabolite of nicotine [(S)-3-(1-methyl-2-pyrrolidinyl) pyridine] in humans is cotinine [(S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone]. We have previously shown that cotinine exposure induces convergence and amplification of the GSK3β-dependent PI3 kinase and cholinergic anti-inflammatory systems. The consequence is reduced pro-inflammatory cytokine secretion by human monocytes responding to bacteria or LPS, a TLR4 agonist.

Findings

Here we show that cotinine-induced inflammatory suppression may not be restricted to individual Toll-like receptors (TLRs). Indeed, in monocytic cells, cotinine suppresses the cytokine production that is normally resultant upon agonist-specific engagement of all of the major surface exposed TLRs (TLR 2/1; 2/6; 4 and 5), although the degree of suppression varies by TLR.

Conclusions

These results provide further mechanistic insight into the increased susceptibility to multiple bacterial infections known to occur in smokers. They also establish THP-1 cells as a potentially suitable model with which to study the influence of tobacco components and metabolites on TLR-initiated inflammatory events.

Antimicrobial peptides and nitric oxide production by neutrophils from periodontitis subjects

Neutrophils play an important role in periodontitis by producing nitric oxide (NO) and antimicrobial peptides, molecules with microbicidal activity via oxygen-dependent and -independent mechanisms, respectively. It is unknown whether variation in the production of antimicrobial peptides such as LL-37, human neutrophil peptides (HNP) 1-3, and NO by neutrophils influences the pathogenesis of periodontal diseases. We compared the production of these peptides and NO by lipopolysaccharide (LPS)-stimulated neutrophils isolated from healthy subjects and from patients with periodontitis. Peripheral blood neutrophils were cultured with or without Aggregatibacter actinomycetemcomitans-LPS (Aa-LPS), Porphyromonas gingivalis-LPS (Pg-LPS) and Escherichia coli-LPS (Ec-LPS). qRT-PCR was used to determine quantities of HNP 1-3 and LL-37 mRNA in neutrophils. Amounts of HNP 1-3 and LL-37 proteins in the cell culture supernatants were also determined by ELISA. In addition, NO levels in neutrophil culture supernatants were quantitated by the Griess reaction. Neutrophils from periodontitis patients cultured with Aa-LPS, Pg-LPS and Ec-LPS expressed higher HNP 1-3 mRNA than neutrophils from healthy subjects. LL-37 mRNA expression was higher in neutrophils from patients stimulated with Aa-LPS. Neutrophils from periodontitis patients produced significantly higher LL-37 protein levels than neutrophils from healthy subjects when stimulated with Pg-LPS and Ec-LPS, but no difference was observed in HNP 1-3 production. Neutrophils from periodontitis patients cultured or not with Pg-LPS and Ec-LPS produced significantly lower NO levels than neutrophils from healthy subjects. The significant differences in the production of LL-37 and NO between neutrophils from healthy and periodontitis subjects indicate that production of these molecules might influence individual susceptibility to important periodontal pathogens.

Quantification of subgingival bacterial pathogens at different stages of periodontal diseases

Anaerobic gram-negative oral bacteria such as Treponema denticola, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia, Campylobacter rectus, and Fusobacterium nucleatum are closely associated with periodontal diseases. We measured the relative population (bacterial levels) of these oral pathogens in subgingival tissues of patients at different stages of Korean chronic periodontal diseases. We divided the individuals into those with chronic gingivitis (G), moderate periodontitis (P1), severe periodontitis (P2), and normal individuals (N) (n = 20 for each group) and subgingival tissue samples were collected. We used real-time PCR with TaqMan probes to evaluate the change of periodontal pathogens among different stages of periodontitis. Bacterial levels of A. actinomycetemcomitans and C. rectus are significantly increased in individuals with chronic gingivitis and moderate periodontitis, but unchanged in severe periodontitis patients. These results suggest that analyzing certain bacterial levels among total oral pathogens may facilitate understanding of the role of periodontal bacteria in the early stages of periodontitis.

How has neutrophil research improved our understanding of periodontal pathogenesis?

BACKGROUND

Neutrophils are the predominant cells responsible for host defence against bacterial infection. Loss of neutrophil defence, due either to deficient number or function, strongly predisposes to bacterial infections such as periodontitis. Yet, the neutrophil oxidative and proteolytic arsenal has also been implicated in perpetrating periodontal tissue damage in periodontitis.

AIM

In this review, we focus on recent developments that shed light on these two aspects of neutrophil function in periodontitis.

METHODS

Primary search: using PubMed search for "neutophil", "periodontal", and "periodontitis". Secondary search: using references from the articles found in the first stage.

RESULTS

Early histological studies showed that infiltrating neutrophils form a wall of cells abutting the junctional epithelium in periodontal inflammatory lesions. The chronic standoff between these neutrophils and the bacterial community suggests that bacterial evasion of neutrophil clearance is a major characteristic of periodontitis. Indeed, not all functional neutrophil deficiencies increase the risk of periodontitis, an observation that points the way towards identification of particular anti-bacterial pathways essential for protection against periodontal pathogens. The net result in the majority of periodontitis patients who exhibit normal neutrophil number and function, is that neutrophils accumulate in the periodontal tissue where they are available to participate in tissue destruction. Diminished neutrophil clearance further contributes to the persistence of activated neutrophils in the periodontal tissue.

CONCLUSIONS

Data on the role of neutrophils in the pathogenesis of periodontitis are mixed. Neutrophils are a critical arm of the defence against periodontitis, but bacterial evasion of the neutrophil microbicidal machinery coupled with delayed neutrophil apoptosis may transform the neutrophil from defender to perpetrator. At this stage of knowledge, attempts to induce host modulation through neutrophil suppression or activation are premature.

Antimicrobial peptides and periodontal disease

AIMS

The goal of this review is to identify the antimicrobial proteins in the oral fluids, saliva and gingival crevicular fluid and identify functional families and candidates for antibacterial treatment.

RESULTS

Periodontal biofilms initiate a cascade of inflammatory and immune processes that lead to the destruction of gingival tissues and ultimately alveolar bone loss and tooth loss. Treatment of periodontal disease with conventional antibiotics does not appear to be effective in the absence of mechanical debridement. An alternative treatment may be found in antimicrobial peptides and proteins, which can be bactericidal and anti-inflammatory and block the inflammatory effects of bacterial toxins. The peptides have co-evolved with oral bacteria, which have not developed significant peptide resistance. Over 45 antibacterial proteins are found in human saliva and gingival crevicular fluid. The proteins and peptides belong to several different functional families and offer broad protection from invading microbes. Several antimicrobial peptides and proteins (AMPs) serve as templates for the development of therapeutic peptides and peptide mimetics, although to date none have demonstrated efficacy in human trials.

CONCLUSIONS

Existing and newly identified AMPs may be developed for therapeutic use in periodontal disease or can serve as templates for peptide and peptide mimetics with improved therapeutic indices.

Variants of the human PPARG locus and the susceptibility to chronic periodontitis

Apart from its regulatory function in lipid and glucose metabolism, peroxisome proliferator-activated receptor (PPAR)γ has impact on the regulation of inflammation and bone metabolism. The aim of the study was to investigate the association of five polymorphisms (rs10865710, rs2067819, rs3892175, rs1801282, rs3856806) within the PPARG gene with chronic periodontitis. The study population comprised 402 periodontitis patients and 793 healthy individuals. Genotyping of the PPARG gene polymorphisms was performed by PCR and melting curve analysis. Comparison of frequency distribution of genotypes between individuals with periodontal disease and healthy controls for the polymorphism rs3856806 showed a P-value of 0.04 but failed to reach significance after correction for multiple testing ( P < 0.01). Two single nucleotide polymorphisms (SNPs) (rs10865710 and rs3892175) were found to be in strong linkage disequilibrium to rs2067819 (D’ > 0.90). A 3-site analysis (rs2067819-rs1801282-rs3856860) revealed five haplotypes with a frequency of ≥1% among cases and controls. Following adjustment for age, gender and smoking, none of the haplotypes was significantly different between periodontitis and healthy controls after Bonferroni correction. This study could not show a significant association between PPARG gene variants and chronic periodontitis.

Association of periodontitis with rheumatoid arthritis and atherosclerosis: Novel paradigms in etiopathogeneses and management?

There is increasing documentation of a link between inflammatory periodontal disease affecting the supporting structure of teeth, rheumatoid arthritis, and coronary artery disease. Periodontitis is initiated predominantly by Gram-negative bacteria and progresses as a consequence of the host inflammatory response to periodontal pathogens. Lipopolysaccharide, a cell wall constituent stimulates the production of inflammatory cytokines via the activation of signaling pathways perpetuating inflammatory pathogenesis in a cyclical manner in susceptible individuals; with an element of autoimmune stimulation, not dissimilar to the sequential events seen in RA. Periodontitis, also implicated as a risk factor for cardiovascular disease, promotes mechanisms for atherosclerosis by enhancing an imbalance in systemic inflammatory mediators; more direct mechanisms attributed to microbial products are also implicated in both RA and atherogenesis. Severe periodontal disease characterized by clinical and radiographic parameters has been associated with ischemic stroke risk, significant levels of C-reactive protein and serum amyloid A, amongst others common to both periodontitis and atherosclerosis. Existing data supports the hypothesis that persistent localized infection in periodontitis may influence systemic levels of inflammatory markers and pose a risk for RA and atherosclerosis. A common nucleus of activity in their pathogeneses provides novel paradigms of therapeutic targeting for reciprocal benefit.

Defensins as anti-inflammatory compounds and mucosal adjuvants

Human neutrophil peptide alpha-defensins and human beta-defensins are small, well-characterized peptides with broad antimicrobial activities. In mixtures with microbial antigens, defensins attenuate proinflammatory cytokine responses by dendritic cells in culture, attenuate proinflammatory cytokine responses in the nasal fluids of exposed mice and enhance antibody responses in the serum of vaccinated mice. Although the exact mechanisms are unknown, defensins first start by binding to microbial antigens and adhesins, often attenuating toxic or inflammatory-inducing capacities. Binding is not generic; it appears to be both defensin-specific and antigen-specific with high affinities. Binding of defensins to antigens may, in turn, alter the interaction of antigens with epithelial cells and antigen-presenting cells attenuating the production of proinflammatory cytokines. The binding of defensins to antigens may also facilitate the delivery of bound antigen to antigen-presenting cells in some cases via specific receptors. These interactions enhance the immunogenicity of the bound antigen in an adjuvant-like fashion. Future research will determine the extent to which defensins can suppress early events in inflammation and enhance systemic antibody responses, a very recent and exciting concept that could be exploited to develop therapeutics to prevent or treat a variety of oral mucosal infections, particularly where inflammation plays a role in the pathogenesis of disease and its long-term sequelae.