Augmentation of Actinobacillus actinomycetemcomitans invasion of human oral epithelial cells and up-regulation of interleukin-8 production by saliva CD14

Soluble LPS receptor CD14 is increased in saliva of patients with geographic tongue

OBJECTIVES

The soluble bacterial pattern recognition receptor, sCD14 augments inflammatory responses in oral cavity. The aim of the study was to investigate whether patients with geographic tongue (GT) with and without fissured tongue (FT) have impaired inflammatory regulation, manifesting as increased levels of sCD14 in the saliva.

MATERIAL AND METHODS

An enzyme-linked immunosorbent assay was used to measure the amount of sCD14 in whole and parotid saliva of patients diagnosed with GT (GT whole, n = 21; GT parotid, n = 23) and control subjects (GT whole, n = 25; GT parotid, n = 18). The levels of sCD14 were also evaluated according to our previous clinical assessment of GT based on the number of lesions detected on the tongue, as 'mild' (a single lesion), 'moderate' (2-5 lesions), or 'severe' (≥6 lesions). Diagnosis of FT was established when multiple grooves or fissures were observed on the dorsal and lateral surfaces of the tongue.

RESULTS

GT patients had significantly higher sCD14 levels in whole (p<.05) and parotid saliva (p<.001), compared with controls. GT patients with FT had significantly increased sCD14 levels only in parotid saliva. A gradual increase in sCD14 levels in parotid and unstimulated saliva was seen in GT patients with multiple tongue lesions compared with single lesions.

CONCLUSIONS

GT patients had increased sCD14 in both parotid and unstimulated saliva. sCD14 seems to increase local inflammatory responses, which suggests its involvement in the pathophysiology of GT.

Macrophage migration inhibitory factor regulates specific innate immune sensor responses in gingival epithelial cells

BACKGROUND

The gingival epithelium protects periodontal tissues and the alveolar bone by maintaining a steady state of regulated inflammatory surveillance, also known as healthy homeostasis. Accordingly, the repertoire of receptors present within the gingival epithelium showcases its ability to recognize microbial colonization and contribute to bacterial sensing. Macrophage migration inhibitory factor (MIF) is one of many cytokines that are expressed in this protective state and is involved in neutrophil regulation. However, its role in the maintenance of healthy gingival tissue has not been described.

METHODS

Gingival tissues from wild-type (WT) and Mif knock-out (KO) mice were stained for neutrophils and three key neutrophil chemoattractants: MIF, Gro-α/CXCL1, and Gro-β/CXCL2 in the junctional epithelium (JE). In addition, gene silencing studies were performed using gingival epithelial cells (GECs) to examine the role of MIF on transcription of key bacterial recognition receptors Toll-like receptors (TLR)-1, -2, -4, -6, -9 and interleukin-1 receptors (IL-1R1 and IL-1R2) in response to oral bacterial stimulation.

RESULTS

WT murine gingival tissues demonstrated high expression of MIF in the JE. In Mif KO mice, despite the significant reduction of Gro-α/CXCL1 and Gro-β/CXCL2, there was a slight increase in neutrophils. Gene silencing experiments showed that MIF down-regulated the mRNA expression of TLR4, IL-1R1, and IL-1R2 in GEC, in addition to decreasing secreted IL-8/CXCL8 in response to bacteria.

CONCLUSIONS

MIF regulates the expression of TLR4, IL-1Rs, and IL-8/CXCL8, components that are all involved in maintaining oral health. Our data demonstrate that MIF is a significant contributor to the maintenance of healthy oral homeostasis.

sCD14 Level in Saliva of Children and Adolescents with and without Dental Caries, a Hurdle Model

Objective: Soluble CD14 (sCD14) plays an important role in the innate immune response of the oral cavity. The investigation of this biomarker for detection of carious lesions is an even more actual procedure due to its non-invasiveness and the ease of withdrawal. The purpose of the present observational case-control study was to evaluate whether the quantification of sCD14 in children and adolescent’s saliva can discriminate healthy subjects from those suffering from tooth decay. Materials and Methods: 164 subjects (6 to 17 years) were selected and divided into 2 groups: those with at least 1 decayed tooth were assigned to group Decayed (n = 82) and those free from dental caries to group Healthy (n = 82). The amount of salivary soluble CD14 was quantified. Results: Mean salivary soluble CD14 was 28.3 ± 10.8 μg/mL in the Healthy group and 22 ± 9.6 μg/mL in the Decayed group. A hurdle model was applied to the data to estimate both the probability of having carious lesions and their number in relation to sCD14 levels. sCD14 was strongly associated (p < 0.01) with an inverse relation to both the probability of having caries and their number (falling rate of 5% per unit CD14 μg/mL). Conclusions: This data confirms the relationship between sCD14 and the presence of dental caries. However, there is no clear cut off level between healthy and unhealthy subjects, so it is currently not possible to use sCD14 as a biomarker to determine the risk of decays.

Understanding the microbial components of periodontal diseases and periodontal treatment-induced microbiological shifts

In the mid-1960s the microbial aetiology of periodontal diseases was introduced based on classical experimental gingivitis studies . Since then, numerous studies have addressed the fundamental role that oral microbiota plays in the initiation and progression of periodontal diseases. Recent advances in laboratory identification techniques have contributed to a better understanding of the complexity of the oral microbiome in both health and disease. Modern culture-independent methods such as human oral microbial identification microarray and next-generation sequencing have been used to identify a wide variety of microbial taxa residing in the gingival sulcus and the periodontal pocket. The first theory of the 'non-specific plaque' hypothesis gave rise to the 'ecological plaque' hypothesis and more recently to the 'polymicrobial synergy and dysbiosis hypothesis'. Periodontitis is now considered to be a multimicrobial inflammatory disease in which the various bacterial species within the dental biofilm are in a dysbiotic state and this imbalance favours the establishment of chronic inflammatory conditions and ultimately the destruction of tooth-supporting tissues. Apart from the known putative periodontal pathogens, the whole biofilm community is now considered to play a role in the establishment of inflammation and the initiation and progression of periodontitis in a susceptible host. Treatment is unlikely to eliminate putative pathogens but, when it is thoroughly performed it has the potential to establish a healthy ecosystem by altering the microbial community in numbers and composition and also contribute to the maturation of the host immune response.

Saliva initiates the formation of pro-inflammatory macrophages in vitro

OBJECTIVES

Saliva can support oral wound healing, a process that requires a temporary inflammatory reaction. We have reported previously that saliva provokes a strong inflammatory response in oral fibroblasts. Bone marrow cells also give rise to macrophages, a heterogeneous subset of cell population involved in wound healing. Lipopolysaccharide (LPS) and interleukin 4 (IL-4) induce activation of pro-(M1), and anti-(M2) inflammatory macrophages, respectively. Yet, the impact of saliva on programming bone marrow cells into either M1 or M2 macrophages remains unclear .

DESIGN

Herein, we examined whether sterile saliva affects the in vitro process of macrophage polarization based on murine bone marrow cultures and RAW264.7 mouse macrophages.

RESULTS

We report that sterile saliva, similar to lipopolysaccharides, provoked a robust activation of the M1 phenotype which is characterized by a strong increase of the respective genes IL-12 and IL-6, based on a real-time gene expression analysis, and for IL-6 with immunoassay. Arginase-1 and Ym1, both genes characteristic for the M2 phenotype, were not considerably modulated by saliva. Inhibition of TLR4 signaling with TAK-242, blocking NFκB signaling with Bay 11-7085, but also autoclaving saliva greatly reduced the development of the M1 phenotype.

CONCLUSION

These data suggest that saliva activates the TLR4 dependent polarization into pro-inflammatory M1 macrophages in vitro.

Protein biomarkers of periodontitis in saliva

Periodontitis is a chronic inflammatory condition of the tissues that surround and support the teeth and is initiated by inappropriate and excessive immune responses to bacteria in subgingival dental plaque leading to loss of the integrity of the periodontium, compromised tooth function, and eventually tooth loss. Periodontitis is an economically important disease as it is time-consuming and expensive to treat. Periodontitis has a worldwide prevalence of 5-15% and the prevalence of severe disease in western populations has increased in recent decades. Furthermore, periodontitis is more common in smokers, in obesity, in people with diabetes, and in heart disease patients although the pathogenic processes underpinning these links are, as yet, poorly understood. Diagnosis and monitoring of periodontitis rely on traditional clinical examinations which are inadequate to predict patient susceptibility, disease activity, and response to treatment. Studies of the immunopathogenesis of periodontitis and analysis of mediators in saliva have allowed the identification of many potentially useful biomarkers. Convenient measurement of these biomarkers using chairside analytical devices could form the basis for diagnostic tests which will aid the clinician and the patient in periodontitis management; this review will summarise this field and will identify the experimental, technical, and clinical issues that remain to be addressed before such tests can be implemented.

Gene expression based evidence of innate immune response activation in the epithelium with oral lichen planus

OBJECTIVE

Oral lichen planus (OLP) is a disease of the oral mucosa of unknown cause producing lesions with an intense band-like inflammatory infiltrate of T cells to the subepithelium and keratinocyte cell death. We performed gene expression analysis of the oral epithelium of lesions in subjects with OLP and its sister disease, oral lichenoid reaction (OLR), in order to better understand the role of the keratinocytes in these diseases.

DESIGN

Fourteen patients with OLP or OLR were included in the study, along with a control group of 23 subjects with a variety of oral diseases and a normal group of 17 subjects with no clinically visible mucosal abnormalities. Various proteins have been associated with OLP, based on detection of secreted proteins or changes in RNA levels in tissue samples consisting of epithelium, stroma, and immune cells. The mRNA level of twelve of these genes expressed in the epithelium was tested in the three groups.

RESULTS

Four genes showed increased expression in the epithelium of OLP patients: CD14, CXCL1, IL8, and TLR1, and at least two of these proteins, TLR1 and CXCL1, were expressed at substantial levels in oral keratinocytes.

CONCLUSIONS

Because of the large accumulation of T cells in lesions of OLP it has long been thought to be an adaptive immunity malfunction. We provide evidence that there is increased expression of innate immune genes in the epithelium with this illness, suggesting a role for this process in the disease and a possible target for treatment.

Estimation of sCD14 levels in saliva obtained from patients with various periodontal conditions

AIM

To assess the concentration of soluble CD14 receptor in saliva of people with periodontal disease and healthy patients and its relationship with periodontal status.

SUBJECTS AND METHODS

Unstimulated whole saliva samples from patients with chronic periodontitis (n = 34), aggressive periodontitis (n = 19) and healthy controls (n = 17) were obtained for the study. The periodontal status of each subject was assessed by criteria based on probing depth, clinical attachment loss and the extent of periodontal breakdown. The levels of sCD14 were measured in saliva samples with an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Although no significant difference (P > 0.05) was found for salivary sCD14 levels between periodontitis groups, they were significantly greater (P < 0.05) than those detected for healthy controls. Furthermore, Spearman's correlation analysis showed statistically significant correlations (P < 0.01) between data from salivary sCD14 levels and clinical measurements.

CONCLUSION

The findings of the present study reemphasize the importance of whole saliva as sampling method in terms of immunological purposes in periodontal disease and suggest that the elevated sCD14 concentration may be one of the host-response components associated with the clinical manifestations of periodontal disease.

Absence of soluble CD14 in saliva of young patients with dental caries

It is generally accepted that salivary components are important for dental health, but to date no clear correlation has been found between one or more of these components and the outcome of dental caries. The identification of salivary factors preventing, favoring or signaling dental caries might help to control the disease. In the present study, western blotting analysis of whole saliva from 20 healthy caries-free children showed the presence of the soluble form of CD14, a bacterial pattern-recognition receptor for many bacterial components that is involved in the innate immune response. The identity of the protein was confirmed through N-terminal sequencing by Edman degradation, and by partial sequencing with mass spectrometry of tryptic peptides. Conversely, CD14 was completely absent in the saliva of 20 age-matched patients affected by two to eight carious lesions, but appeared in their saliva a few weeks after dental restoration. These results suggest that the absence of salivary soluble CD14 could represent an useful index of caries activity, and might be used to detect early carious lesions not visible by oral inspection.

Human parotid saliva contains soluble toll-like receptor (TLR) 2 and modulates TLR2-mediated interleukin-8 production by monocytic cells

Toll-like receptor (TLR) family members are pattern-recognition receptors and very important molecules in innate immunity. Although TLRs are originally type I transmembrane receptors, soluble forms of TLRs are detected in human plasma and milk. This study showed that soluble TLR2 (sTLR2) is detected in human parotid saliva. Western blotting with anti-TLR2 antibodies (Abs) showed that three polypeptides are detected as sTLR2 with molecular weights of 55, 40 and 27kDa, respectively. Parotid saliva neutralized the binding of anti-TLR2 polyclonal Ab to cell-surface TLR2 on THP-1, a human monocytic cell line. Immunohistochemical analysis revealed that TLR2 is expressed in serous and interlobular ductal cells of human salivary gland. Human salivary gland cell lines, AZA3 and HSY, constitutively expressed TLR2. Parotid saliva augmented IL-8 production of THP-1 cells stimulated with a synthetic TLR2 ligand, Pam(3)Cys-Ser-(Lys)(4) (Pam(3)CSK(4)). Depletion of sCD14 from parotid saliva by immunoprecipitation eliminated the augmentation of IL-8 production, indicating that the augmentable effects depended on sCD14 in parotid saliva. On the other hand, preincubation of Pam(3)CSK(4) with parotid saliva abrogated the augmentation of IL-8 production, indicating that sTLR2 in saliva bound to Pam(3)CSK(4) and neutralized its function. These results suggest that parotid saliva modulates the TLR2-mediated immune responses with binary mechanisms via sTLR2 and sCD14 in the oral cavity.

Cleaved inflammatory lactoferrin peptides in parotid saliva of periodontitis patients

Lactoferrin (Lf) is a member of the transferrin family of iron-binding anti-bacterial proteins, present in most exocrine secretions, such as saliva, and plays an important role in mucosal defense. In this study, we identified small Lf peptides with Con A low-affinity in the parotid saliva of chronic periodontitis patients by Con A two-dimensional immunoelectrophoresis, Con A affinity chromatography and Western blotting using anti-human Lf polyclonal Ab. N-terminal amino acid sequencing of the four Con A low-affinity Lf peptides confirmed them to be fragments of intact Lf. The detection ratio of the proteinase 3 (PR3)-like activity was elevated in the parotid saliva of periodontitis patients and was associated with the severity of clinical symptoms. PR3 protein was also detected in the parotid saliva of periodontitis patients, and PR3, but not human leukocyte elastase and cathepsin G, degraded intact Lf. Con A low-affinity saliva Lf peptides showed no anti-bacterial activity against Escherichia coli, and had a reduced iron-chelating capacity. Con A low-affinity saliva Lf peptides, PR3-treated Lf preparation and two of four synthetic polypeptides induced the production of interleukin IL-6, monocyte chemoattractant protein-1 and IL-8, and the activation of NF-kappaB in human oral epithelial HSC-2 cells. Furthermore, concentrations of the Lf peptides in the parotid saliva of periodontitis patients were increased with a correlation to the severity of clinical symptoms. These results suggest that Lf in the parotid saliva of periodontitis patients was degraded into small peptides by the PR3-like activity with the capability to induce inflammatory mediators.

The vital status of human buccal epithelial cells and the bacteria associated with them

OBJECTIVE

We have shown that buccal epithelial cells (BEC) from humans can contain a polymicrobial intracellular flora. Members of that flora can induce proinflammatory responses. However, our subjects all had healthy oral mucosa. This might reflect tolerance of bacterial invasion by live BEC. Alternatively, inflammation might not occur if invaded cells were mostly dead, and thus unable to mount a response. This study addressed that issue, by determining the vital status of BEC and the bacteria associated with them.

DESIGN

Initial experiments indicated that BEC were anomalously permeable to the DNA stain propidium iodide. We used that property to develop a protocol that combined the DNA stains SYTO 9 and propidium iodide (indicators of bacterial viability) with the esterase substrate calcein blue AM (an indicator of BEC viability), and Annexin V Alexa Fluor 647 conjugate (an apoptosis marker). That protocol was applied to BEC collected from 36 human subjects.

RESULTS

On average, 70% of BEC displayed calcein blue staining, with no binding of Annexin V, 25% showed signs of apoptosis, and 5% did not stain with calcein blue. The mean percent of BEC with live cell-associated bacteria was 29%. Collectively, 25% of total BEC displayed calcein blue staining and live (SYTO 9 stained) bacteria. Only 1% of total BEC were negative for calcein blue and associated with live bacteria.

CONCLUSIONS

Our findings suggest that live BEC are tolerant of bacterial invasion. This may be due to complex interactions between members of the polymicrobial flora and their host BEC.

Critical pathways in microbial virulence

The virulence of a microbe represents a combination of complex factors including the agent's transmissibility and the severity of the disease associated with infection and is also significantly influenced by the susceptibility of the colonized host. Virulence factors may be defined as those products of the organism which are required to complete the various stages of the life cycle leading to pathology in the host. In this review, we examine some of the approaches which have been adopted in other fields of infectious disease in order to categorically identify virulence factors using a classical genetics approach with relevant models or human subjects. The absence of an accurate experimental model for periodontal disease means that our understanding of the microbial virulence determinants and pathways in this disease remains hypothetical and based largely on observations in vitro. However, factors which enable the organism to persist in spite of the elevated immune and inflammatory pressure at sites of disease are liable to be critical. Periodontal bacterial genomics is liable to make a significant impact on the field through an increased appreciation of the role of gene acquisition and gene loss in the evolution of periodontal bacteria and of the consequences of strain variation in gene content on virulence potential.

Distinct transcriptional profiles characterize oral epithelium-microbiota interactions

Transcriptional profiling, bioinformatics, statistical and ontology tools were used to uncover and dissect genes and pathways of human gingival epithelial cells that are modulated upon interaction with the periodontal pathogens Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Consistent with their biological and clinical differences, the common core transcriptional response of epithelial cells to both organisms was very limited, and organism-specific responses predominated. A large number of differentially regulated genes linked to the P53 apoptotic network were found with both organisms, which was consistent with the pro-apoptotic phenotype observed with A. actinomycetemcomitans and anti-apoptotic phenotype of P. gingivalis. Furthermore, with A. actinomycetemcomitans, the induction of apoptosis did not appear to be Fas- or TNF(alpha)-mediated. Linkage of specific bacterial components to host pathways and networks provided additional insight into the pathogenic process. Comparison of the transcriptional responses of epithelial cells challenged with parental P. gingivalis or with a mutant of P. gingivalis deficient in production of major fimbriae, which are required for optimal invasion, showed major expression differences that reverberated throughout the host cell transcriptome. In contrast, gene ORF859 in A. actinomycetemcomitans, which may play a role in intracellular homeostasis, had a more subtle effect on the transcriptome. These studies help unravel the complex and dynamic interactions between host epithelial cells and endogenous bacteria that can cause opportunistic infections.

Concurrence between the gene expression pattern of Actinobacillus actinomycetemcomitans in localized aggressive periodontitis and in human epithelial cells

Actinobacillus actinomycetemcomitans is a facultatively intracellular pathogen and the aetiological agent of localized aggressive periodontitis. Screening of the genome of A. actinomycetemcomitans for in vivo-induced antigen determinants previously demonstrated that the proteome of this organism differs in laboratory culture compared with conditions found during active infection. The aim of the present study was to determine whether the bacterial gene expression pattern inferred with in vivo-induced antigen technology (IVIAT) in human infections was consistent with the gene expression pattern occurring upon epithelial cell association. To this end, a real-time PCR method was developed and used to quantify absolute and relative bacterial gene expression of A. actinomycetemcomitans grown extra- and intracellularly in two human epithelial cell lines (HeLa and IHGK). The amount of template used in the assay was normalized using the total count of viable bacteria (c.f.u.) as a reference point and performed in duplicate in at least two independent experiments. Controls for this experiment included 16S rRNA and gapdh. Transcription of all eight ORFs tested increased significantly (P < 0.05) in HeLa and IHGK cells compared with bacteria grown extracellularly. The concurrence of gene expression patterns found in the two models suggests that these epithelial cells are valid in vitro models of infection for the genes tested. IVIAT is an experimental platform that can be used as a validation tool to assess the reliability of animal and other models of infection and is applicable to most pathogens.

Differential regulation of cytokine genes in gingival epithelial cells challenged by Fusobacterium nucleatum and Porphyromonas gingivalis

IL-8 mRNA in human gingival epithelial cells (HGECs) is up-regulated by Fusobacterium nucleatum, and up-/down-regulated by Porphyromonas gingivalis in a complex interaction in the early stages (< or = 4 h) after infection. The mechanisms involved in this regulation in response to F. nucleatum and/or P. gingivalis infection, and identification of co-regulated cytokine genes, are the focus of this investigation. Heat, formalin or protease treatment of F. nucleatum cells attenuated the IL-8 mRNA up-regulation. NF-kappaB, mitogen-activated protein kinase (MAPK) p38 and MAPK kinase/extracellular signal-regulated kinase (MEK/ERK) pathways were involved in IL-8 mRNA induction by F. nucleatum. Pretreatment of P. gingivalis with heat, formalin or protease enhanced IL-8 mRNA induction. NF-kappaB, MARK p38, and MEK/ERK pathways were also involved in this induction. In contrast, down-regulation of IL-8 mRNA by P. gingivalis involved MEK/ERK, but not NF-kappaB or MAPK p38 pathways. cDNA arrays analysis revealed that mRNA down-regulation by P. gingivalis is a specific reaction that only a number of genes, e.g. IL-1beta, IL-8, macrophage inflammatory protein-2alpha, and migration inhibitory factor-related protein-14, are affected based on examination of 278 cytokine/receptor genes. These data indicate that F. nucleatum and P. gingivalis trigger specific and differential gene regulation pathways in HGECs.