Immunohistochemical localization of Toll-like receptors 2 and 4 in gingival tissue from patients with periodontitis

Effect of different forms of tobacco on the oral microbiome in healthy adults: a systematic review

Objective

The study aimed to evaluate the impact of tobacco use on the composition and functions of the oral microbiome in healthy adult humans.

Methods

We conducted a systematic search on PubMed, Web of Science, and Cinhal databases for literature published until 15 December 2023, to identify studies that have evaluated the oral microbiome with culture-independent next-generation techniques comparing the oral microbiome of tobacco users and non-users. The search followed the PECO format. The outcomes included changes in microbial diversity and abundance of microbial taxa. The quality assessment was performed using the Newcastle-Ottawa Scale (NOS) (PROSPERO ID CRD42022340151).

Results

Out of 2,435 articles screened, 36 articles satisfied the eligibility criteria and were selected for full-text review. Despite differences in design, quality, and population characteristics, most studies reported an increase in bacterial diversity and richness in tobacco users. The most notable bacterial taxa enriched in users were Fusobacteria and Actinobacteria at the phylum level and Streptococcus, Prevotella, and Veillonella at the genus level. At the functional level, more similarities could be noted; amino acid metabolism and xenobiotic biodegradation pathways were increased in tobacco users compared to non-users. Most of the studies were of good quality on the NOS scale.

Conclusion

Tobacco smoking influences oral microbial community harmony, and it shows a definitive shift towards a proinflammatory milieu. Heterogeneities were detected due to sampling and other methodological differences, emphasizing the need for greater quality research using standardized methods and reporting.

Systematic Review Registration

CRD42022340151.

The Receptor AT1 Appears to Be Important for the Maintenance of Bone Mass and AT2 Receptor Function in Periodontal Bone Loss Appears to Be Regulated by AT1 Receptor

A large number of experimental studies has demonstrated that angiotensin II (Ang II) is involved in key events of the inflammatory process. This study aimed to evaluate the role of Ang II type 1 (AT1) and Ang II type 2 (AT2) receptors on periodontitis. Methods: Experimental periodontitis was induced by placing a 5.0 nylon thread ligature around the second upper left molar of AT1 mice, no-ligature or ligature (AT1-NL and AT1-L), AT2 (AT2-NL or AT2-L) and wild type (WT-NL or L). Alveolar bone loss was scanned using Micro-CT. Cytokines, peptides and enzymes were analyzed from gingival tissues by Elisa and RT-PCR. Results: The blockade of AT1 receptor resulted in bone loss, even in healthy animals. Ang II receptor blockades did not prevent linear bone loss. Ang II and Ang 1-7 levels were significantly increased in the AT2-L (p < 0.01) group compared to AT2-NL and AT1-L. The genic expression of the Mas receptor was significantly increased in WT-L and AT2-L compared to (WT-NL and AT2-NL, respectively) and in AT1-L. Conclusions: Our data suggest that the receptor AT1 appears to be important for the maintenance of bone mass. AT2 receptor molecular function in periodontitis appears to be regulated by AT1.

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.

Oral lichen planus: a microbiologist point of view

Oral lichen planus (OLP) is a chronic disease of uncertain etiology, although it is generally considered as an immune-mediated disease that affects the mucous membranes and even the skin and nails. Over the years, this disease was attributed to a variety of causes, including different types of microorganisms. This review analyzes the present state of the art of the disease, from a microbiological point of view, while considering whether or not the possibility of a microbial origin for the disease can be supported. From the evidence presented here, OLP should be considered an immunological disease, as it was initially proposed, as opposed to an illness of microbiological origin. The different microorganisms so far described as putative disease-causing agents do not fulfill Koch’s postulates; they are, actually, not the cause, but a result of the disease that provides the right circumstances for microbial colonization. This means that, at this stage, and unless new data becomes available, no microorganism can be envisaged as the causative agent of lichen planus.

Expression of osteoclastogenic and anti-osteoclastogenic cytokines differs in mouse gingiva injected with lipopolysaccharide, peptidoglycan, or both

OBJECTIVE

Bacterial substances in subgingival biofilm evoke alveolar bone resorption. We previously reported that gingival injection of bacterial lipopolysaccharide (LPS) and peptidoglycan (PGN) induced alveolar bone resorption in mice. However, the mechanism by which LPS and PGN induce osteoclast formation has not been investigated. The aim of this study is to clarify the role of osteoclastogenic and anti-osteoclastogenic cytokines in the alveolar bone resorption induced by LPS and PGN.

MATERIALS

LPS from Escherichia coli, PGN from Staphylococcus aureus, or both were injected into the gingiva of mice every 48 h for a total of 13 times. Alveolar bone resorption was assessed histochemically by tartrate-resistant acid phosphatase staining. Expression of the receptor activator of nuclear factor-κB ligand (RANKL), tumor necrosis factor (TNF)-α, interleukin (IL)-17, and IL-10 were analyzed by immunostaining. To analyze the role of these cytokines, RANKL-pretreated mouse bone marrow macrophages were stimulated with LPS, PGN, or LPS + PGN with or without anti-TNF-α antibody, IL-17, or IL-10.

RESULTS

Alveolar bone resorption was induced by both LPS and PGN and exacerbated by LPS + PGN. LPS induced higher RANKL expression than PGN. Expression of TNF-α and IL-10 was correlated with bone resorption. PGN injections induced the strongest expression of IL-17, followed by LPS + PGN and LPS. In an in vitro osteoclastogenesis assay, anti-TNF-α antibody and IL-10 inhibited osteoclast formation, but IL-17 promoted it.

CONCLUSION

LPS, PGN, or LPS + PGN injections induce distinctive expression of TNF-α, IL-10, and IL-17, suggesting that the composition of these bacterial ligands in dental plaque is critical for alveolar bone resorption.

Association of TLR-2 Gene Polymorphisms with the Risk of Periodontitis: A Meta-Analysis

Background

Periodontitis is a kind of chronic infectious disease, affecting the health of billions of people. In recent years, a number of studies have shown that multiple immune gene polymorphisms are associated with the susceptibility to periodontitis, among which TLR-2 plays a critical role in periodontitis. But most of the studies reported TLR-2 gene polymorphism and susceptibility to periodontitis are not consistent. Therefore, we included all eligible studies in our study for further meta-analysis.

Methods

We used electronic databases, including CNKI, PubMed, EMBASE, and Web of Science databases, and relevant research published through June, 2020. Selecting studies involved case-control trials. For all eligibility studies, odds ratios (ORs) and 95% confidence intervals (95% CI) are provided or can be calculated from the study data. The size of the combined effect was calculated using STATA 15.0.

Results

Our meta-analysis included 14 articles representing 18 case-control studies with a total of 3873 cases and 3438 control subjects. Significant association was found between periodontitis and TLR-2 rs1898830 polymorphism under the allelic model (A allele vs. G allele: p = 0.014, OR = 1.208, 95% CI: 1.039-1.406), recessive model (GG vs. GA+AA: p = 0.028, OR = 0.755, 95% CI: 0.588-0.970), and codominant model (GG VS. AA: p = 0.014, OR = 0.681, 95% CI: 0.501-0.925). In subgroup analysis, TLR-2 rs5743708 polymorphism was associated with periodontitis risk in Asians under an allelic model (G allele vs. A allele: p = 0.017, OR = 12.064, 95% CI: 1.570-92.688), dominant model (GA+AA vs.GG: p = 0.016, OR = 0.08, 95% CI: 0.010-0.620), and codominant model (GA VS. GG: p = 0.016, OR = 1.026, 95% CI: 0.821-1.282).

Conclusion

The TLR-2 rs1898830, rs5743708 polymorphism may be associated with susceptibility to periodontitis. In the future, genome-wide approaches and large-scale, multiethnic case-control trials are still needed.

Chronic Exposure of Gingival Fibroblasts to TLR2 or TLR4 Agonist Inhibits Osteoclastogenesis but Does Not Affect Osteogenesis

Chronic exposure to periodontopathogenic bacteria such as Porphyromonas gingivalis and the products of these bacteria that interact with the cells of the tooth surrounding tissues can ultimately result in periodontitis. This is a disease that is characterized by inflammation-related alveolar bone degradation by the bone-resorbing cells, the osteoclasts. Interactions of bacterial products with Toll-like receptors (TLRs), in particular TLR2 and TLR4, play a significant role in this chronic inflammatory reaction, which possibly affects osteoclastic activity and osteogenic capacity. Little is known about how chronic exposure to specific TLR activators affects these two antagonistic activities. Here, we studied the effect of TLR activation on gingival fibroblasts (GF), cells that are anatomically close to infiltrating bacterial products in the mouth. These were co-cultured with naive osteoclast precursor cells (i.e., monocytes), as part of the peripheral blood mononuclear cells (PBMCs). Activation of GF co-cultures (GF + PBMCs) with TLR2 or TLR4 agonists resulted in a weak reduction of the osteoclastogenic potential of these cultures, predominantly due to TLR2. Interestingly, chronic exposure, especially to TLR2 agonist, resulted in increased release of TNF-α at early time points. This effect, was reversed at later time points, thus suggesting an adaptation to chronic exposure. Monocyte cultures primed with M-CSF + RANKL, led to the formation of bone-resorbing osteoclasts, irrespective of being activated with TLR agonists. Late activation of these co-cultures with TLR2 and with TLR4 agonists led to a slight decrease in bone resorption. Activation of GF with TLR2 and TLR4 agonists did not affect the osteogenic capacity of the GF cells. In conclusion, chronic exposure leads to diverse reactions; inhibitory with naive osteoclast precursors, not effecting already formed (pre-)osteoclasts. We suggest that early encounter of naive monocytes with TLR agonists may result in differentiation toward the macrophage lineage, desirable for clearing bacterial products. Once (pre-)osteoclasts are formed, these cells may be relatively insensitive for direct TLR stimulation. Possibly, TLR activation of periodontal cells indirectly stimulates osteoclasts, by secreting osteoclastogenesis stimulating inflammatory cytokines.

Response of Human Mesenchymal Stromal Cells from Periodontal Tissue to LPS Depends on the Purity but Not on the LPS Source

Human periodontal ligament stromal cells (hPDLSCs) and gingival mesenchymal stromal cells (hGMSCs) are resident mesenchymal stromal cells (MSCs) of the periodontal tissue. The lipopolysaccharide (LPS) from Porphyromonas gingivalis is structurally distinct from that of other Gram-negative bacteria, and earlier studies linked this structural difference to a distinct virulence activity and the ability to activate toll-like receptor 2 (TLR-2), besides TLR-4 as commonly occurring upon LPS challenge. Later studies, in contrast, argue that TLR-2 activation by P. gingivalis LPS is due to lipoprotein contamination. In the present study, we aimed to define the influence of structure versus purity of P. gingivalis LPS on the immune response of hPDLSCs and hGMSCs. Cells were stimulated with commercially available "standard" P. gingivalis LPS, "ultrapure" P. gingivalis LPS, or "ultrapure" Escherichia coli LPS, and the expression of interleukin- (IL-) 8, IL-6, monocyte chemoattractant protein- (MCP-) 1, TLR-2, and TLR-4 was evaluated. The contribution of TLR-4 to the LPS-induced response was assessed using the specific TLR-4 inhibitor TAK-242. "Standard" P. gingivalis LPS induced significantly higher IL-8, IL-6, and MCP-1 production compared to the "ultrapure" LPS preparations, with no significant difference detectable for "ultrapure" LPS from P. gingivalis and E. coli. By using TAK-242, the response of hPDLSCs and hGMSCs to "ultrapure" LPS preparations was effectively inhibited to the levels comparable to those of nonstimulated controls. In contrast, high levels of response to "standard" LPS were observed, even in the presence of TAK-242. Our data show that the response of MSCs from periodontal tissue to LPS depends more on the purity of the LPS preparation than on the LPS source. Even a small amount of contaminating lipoproteins can drastically enhance the hPDLSCs' and hGMSCs; responsiveness to P. gingivalis LPS, which might also contribute to the progression of periodontal disease.

Myd88 plays a major role in the keratinocyte response to infection with Porphyromonas gingivalis

AIM

To explore the role of keratinocyte myeloid differentiation primary response 88 (MyD88) expression in the adhesion of Porphyromonas gingivalis to the cells and its subsequent invasion and intracellular survival.

MATERIALS AND METHODS

Primary mouse keratinocytes from wild-type (WT) or Myd88^-/- mice were infected with P gingivalis alone or co-infected with Fusobacterium nucleatum. Bacterial adhesion and invasion were measured using fluorescent microscopy and flow cytometry, and intracellular survival in keratinocytes was quantified by an antibiotic protection assay. Keratinocyte expression of antimicrobial peptides was measured by real-time PCR.

RESULTS

In the absence of MyD88, P gingivalis adherence, invasion, and intracellular survival were enhanced compared with WT keratinocytes. The presence of F nucleatum during infection increased the adhesion of P gingivalis to WT keratinocytes but reduced the adhesion to Myd88^-/- keratinocytes. Fusobacterium nucleatum improved mildly the invasion and survival of P gingivalis in both cell types. Baseline expression of beta-defensin 2, 3, 4 and RegIII-γ was elevated in Myd88^-/- keratinocytes compared to WT cells; however, following infection beta-defensin expression was strongly induced in WT cells but decreased dramatically in the MyD88 deficient cells.

CONCLUSION

In the absence of MyD88 expression, P gingivalis adhesion to keratinocytes is improved, and invasion and intracellular survival are increased. Furthermore, keratinocyte infection by P gingivalis induces antimicrobial peptide expression in a MyD88-dependent manner. Thus, MyD88 plays a key role in the interaction between P gingivalis and keratinocytes.

Differential profiles of soluble and cellular toll like receptor (TLR)-2 and 4 in chronic periodontitis

Chronic periodontitis is a common inflammatory disease initiated by a complex microbial biofilm and mediated by the host response causing destruction of the supporting tissues of the teeth. Host recognition of pathogens is mediated by toll-like receptors (TLRs) that bind conserved molecular patterns shared by large groups of microorganisms. The oral epithelial cells respond to most periodontopathic bacteria via TLR-2 and TLR-4. In addition to the membrane-associated receptors, soluble forms of TLR-2 (sTLR-2) and TLR-4 (sTLR-4) have been identified and are thought to play a regulatory role by binding microbial ligands. sTLR-2 has been shown to arise from ectodomain shedding of the extracellular domain of the membrane receptor and sTLR-4 is thought to be an alternate spliced form. Many studies have previously reported the presence of elevated numbers of viable exfoliated epithelial cells in the saliva of patients with chronic periodontitis. The objective of this study was to investigate the potential value of salivary sTLR-2 and sTLR-4 together with the paired epithelial cell-associated TLR-2/4 mRNA as diagnostic markers for chronic periodontitis. Unstimulated whole saliva was collected after obtaining informed consent from 40 individuals with either periodontitis or gingivitis. The sTLR-2 and sTLR4 in saliva was measured by enzyme-linked immunosorbent assay. The TLR-2 and TLR-4 transcript in the epithelial cells in saliva was measured by real time polymerase chain reaction. While levels of sTLR-2 exhibited an inverse correlation, sTLR-4 positively correlated with clinical parameters in the gingivitis cohort. Interestingly, both correlations were lost in the periodontitis cohort indicating a dysregulated host response. On the other hand, while the sTLR-2 and the paired epithelial cell associated TLR-2 mRNA exhibited a direct correlation (r2 = 0.62), that of sTLR4 and TLR-4 mRNA exhibited an inverse correlation (r2 = 0.53) in the periodontitis cohort. Collectively, assessments of salivary sTLR2 and sTLR4 together with the respective transcripts in the epithelial cells could provide clinically relevant markers of disease progression from gingivitis to periodontitis.

Impaired innate immune signaling due to combined Toll-like receptor 2 and 4 deficiency affects both periodontitis and atherosclerosis in response to polybacterial infection

Plasma membrane-associated Toll-like receptor (TLR2 and TLR4) signaling contributes to oral microbe infection-induced periodontitis and atherosclerosis. We recently reported that either TLR2 or TLR4 receptor deficiency alters recognition of a consortium of oral pathogens, modifying host responses in periodontitis and atherosclerosis. We evaluated the effects of combined TLR2-/-TLR4-/- double knockout mice on innate immune signaling and induction of periodontitis and atherosclerosis after polybacterial infection with Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia and Fusobacterium nucleatum in a mouse model. Multispecies infections established gingival colonization in all TLR2-/-TLR4-/- mice and induced production of bacterial-specific IgG antibodies. In combined TLR2-/-TLR4-/- deficiency there was, however, reduced alveolar bone resorption and mild gingival inflammation with minimal migration of junctional epithelium and infiltration of inflammatory cells. This indicates a central role for TLR2 and TLR4 in periodontitis. Atherosclerotic plaque progression was markedly reduced in infected TLR2-/-TLR4-/- mice or in heterozygotes indicating a profound effect on plaque growth. However, bacterial genomic DNA was detected in multiple organs in TLR2-/-TLR4-/- mice indicating an intravascular dissemination from gingival tissue to heart, aorta, kidney and lungs. TRL2 and TLR4 were dispensable for systemic spread after polybacterial infections but TLR2 and 4 deficiency markedly reduces atherosclerosis induced by oral bacteria.

Genes Critical for Developing Periodontitis: Lessons from Mouse Models

Since the etiology of periodontitis in humans is not fully understood, genetic mouse models may pinpoint indispensable genes for optimal immunological protection of the periodontium against tissue destruction. This review describes the current knowledge of genes that are involved for a proper maintenance of a healthy periodontium in mice. Null mutations of genes required for leukocyte cell–cell recognition and extravasation (e.g., Icam-1, P-selectin, Beta2-integrin/Cd18), for pathogen recognition and killing (e.g., Tlr2, Tlr4, Lamp-2), immune modulatory molecules (e.g., Cxcr2, Ccr4, IL-10, Opg, IL1RA, Tnf-α receptor, IL-17 receptor, Socs3, Foxo1), and proteolytic enzymes (e.g., Mmp8, Plasmin) cause periodontitis, most likely due to an inefficient clearance of bacteria and bacterial products. Several mechanisms resulting in periodontitis can be recognized: (1) inefficient bacterial control by the polymorphonuclear neutrophils (defective migration, killing), (2) inadequate antigen presentation by dendritic cells, or (3) exaggerated production of pro-inflammatory cytokines. In all these cases, the local immune reaction is skewed toward a Th1/Th17 (and insufficient activation of the Th2/Treg) with subsequent osteoclast activation. Finally, genotypes are described that protect the mice from periodontitis: the SCID mouse, and mice lacking Tlr2/Tlr4, the Ccr1/Ccr5, the Tnf-α receptor p55, and Cathepsin K by attenuating the inflammatory reaction and the osteoclastogenic response.

Immunohistochemical localization of TLR2 and CD14 in gingival tissue of healthy individuals and patients with chronic periodontitis

We used immunohistochemistry to quantify and compare the expression of Toll-like receptor 2 (TLR2) and cluster of differentiation 14 (CD14) in gingival tissues of both healthy individuals and patients with chronic periodontitis. We also correlated the expression of TLR2 and CD14 with the histological grades of chronic periodontitis. We examined 30 gingival specimens from chronic periodontitis patients and 10 from healthy individuals. Tissues from both groups were immunostained with antibodies against TLR2 and CD14. TLR2 and CD14 were expressed by endothelial cells, fibroblasts, lymphocytes and plasma cells. The immunohistochemical expression of TLR2 and CD14 was significantly greater in inflammatory cells of the chronic periodontitis group than in healthy individuals. Expression of these molecules was greater in the inflammatory cells of connective tissue adjacent to pocket epithelium in both groups. The expression of TLR2 and CD14 was greatest in the periodontitis group that was classified as severe grade, followed by moderate and mild grades, which suggests a role of TLR2 and CD14 in the pathogenesis of chronic periodontitis. The positive correlation of TLR2 and CD14 expression levels with the severity grades of chronic periodontitis suggests that they are correlated also with disease severity; therefore, they may be useful for predicting disease progression. Our findings are consistent with the possibility that CD14 acts as a co-receptor for TLR2.

HIV Infection and Compromised Mucosal Immunity: Oral Manifestations and Systemic Inflammation

Mucosal surfaces account for the vast majority of HIV transmission. In adults, HIV transmission occurs mainly by vaginal and rectal routes but rarely via oral route. By contrast, pediatric HIV infections could be as the result of oral route by breastfeeding. As such mucosal surfaces play a crucial role in HIV acquisition, and spread of the virus depends on its ability to cross a mucosal barrier. HIV selectively infects, depletes, and/or dysregulates multiple arms of the human immune system particularly at the mucosal sites and causes substantial irreversible damage to the mucosal barriers. This leads to microbial products translocation and subsequently hyper-immune activation. Although introduction of antiretroviral therapy (ART) has led to significant reduction in morbidity and mortality of HIV-infected patients, viral replication persists. As a result, antigen presence and immune activation are linked to “inflammaging” that attributes to a pro-inflammatory environment and the accelerated aging process in HIV patients. HIV infection is also associated with the prevalence of oral mucosal infections and dysregulation of oral microbiota, both of which may compromise the oral mucosal immunity of HIV-infected individuals. In addition, impaired oral immunity in HIV infection may predispose the patients to periodontal diseases that are associated with systemic inflammation and increased risk of cardiovascular diseases. The purpose of this review is to examine existing evidence regarding the role of innate and cellular components of the oral cavity in HIV infection and how HIV infection may drive systemic hyper-immune activation in these patients. We will also discuss current knowledge on HIV oral transmission, HIV immunosenescence in relation to the oral mucosal alterations during the course of HIV infection and periodontal disease. Finally, we discuss oral manifestations associated with HIV infection and how HIV infection and ART influence the oral microbiome. Therefore, unraveling how HIV compromises the integrity of the oral mucosal tissues and innate immune components of the oral cavity and its association with induction of chronic inflammation are critical for the development of effective preventive interventions and therapeutic strategies.

HIV Infection and Compromised Mucosal Immunity: Oral Manifestations and Systemic Inflammation

Mucosal surfaces account for the vast majority of HIV transmission. In adults, HIV transmission occurs mainly by vaginal and rectal routes but rarely via oral route. By contrast, pediatric HIV infections could be as the result of oral route by breastfeeding. As such mucosal surfaces play a crucial role in HIV acquisition, and spread of the virus depends on its ability to cross a mucosal barrier. HIV selectively infects, depletes, and/or dysregulates multiple arms of the human immune system particularly at the mucosal sites and causes substantial irreversible damage to the mucosal barriers. This leads to microbial products translocation and subsequently hyper-immune activation. Although introduction of antiretroviral therapy (ART) has led to significant reduction in morbidity and mortality of HIV-infected patients, viral replication persists. As a result, antigen presence and immune activation are linked to "inflammaging" that attributes to a pro-inflammatory environment and the accelerated aging process in HIV patients. HIV infection is also associated with the prevalence of oral mucosal infections and dysregulation of oral microbiota, both of which may compromise the oral mucosal immunity of HIV-infected individuals. In addition, impaired oral immunity in HIV infection may predispose the patients to periodontal diseases that are associated with systemic inflammation and increased risk of cardiovascular diseases. The purpose of this review is to examine existing evidence regarding the role of innate and cellular components of the oral cavity in HIV infection and how HIV infection may drive systemic hyper-immune activation in these patients. We will also discuss current knowledge on HIV oral transmission, HIV immunosenescence in relation to the oral mucosal alterations during the course of HIV infection and periodontal disease. Finally, we discuss oral manifestations associated with HIV infection and how HIV infection and ART influence the oral microbiome. Therefore, unraveling how HIV compromises the integrity of the oral mucosal tissues and innate immune components of the oral cavity and its association with induction of chronic inflammation are critical for the development of effective preventive interventions and therapeutic strategies.

The paradox of painless periodontal disease

Periodontal diseases, primarily gingivitis and periodontitis, are characterised by progressive inflammation and tissue destruction. However, they are unusual in that they are not also accompanied by the pain commonly seen in other inflammatory conditions. This suggests that interactions between periodontal bacteria and host cells create a unique environment in which the pro-algesic effects of inflammatory mediators and factors released during tissue damage are directly or indirectly inhibited. In this review, we summarise the evidence that periodontal disease is characterised by an accumulation of classically pro-algesic factors from bacteria and host cells. We then discuss several mechanisms by which inflammatory sensitisation of nociceptive fibres could be prevented through inactivation or inhibition of these factors. Further studies are necessary to fully understand the molecular processes underlying the endogenous localised hypoalgesia in human periodontal disease. This knowledge might provide a rational basis to develop future therapeutic interventions, such as host modulation therapies, against a wide variety of other human pain conditions.

Immature, but Not Mature, Dendritic Cells Are More Often Present in Aggressive Periodontitis Than Chronic Periodontitis: An Immunohistochemical Study

BACKGROUND

Dendritic cells (DCs) form a key link between innate and adaptive immune responses. The aim of this study is to analyze presence and distribution of immature (im) and mature (m) DCs in gingival tissue samples obtained from patients diagnosed with aggressive periodontitis (AgP), chronic periodontitis (CP), and clinically healthy periodontium (control group).

METHODS

Gingival tissue samples obtained from patients with: 1) AgP (aged <35 years); 2) CP (aged ≥35 years); and 3) control group (aged >18 years) (n = 10 per group) were collected. Two-way analysis of variance and posterior Fisher least significant difference test were used to observe differences between the means of cells positively marked for imDC (S100, CD1a, and CD207) and mDC (CD208) immunomarkers.

RESULTS

imDCs were more numerous in AgP than CP and control groups, being statistically significant only for S100+ cells. Conversely, mDCs were visualized in higher numbers in CP than AgP and control groups (both P <0.05). Considering frequency of immunostained cells, the number of S100+ cells was greater than CD207+ and CD1a+ cells, followed by a lesser number of CD208+ cells, in all groups.

CONCLUSIONS

Considering that the ability of DCs to regulate immunity is dependent on DC maturation, results suggest that predominance of imDCs appears to be involved in AgP pathogenesis, probably due to lack of ability to induce immune cell activation. Further studies are necessary to elucidate the role of DC maturation in regulating immune responses in periodontal disease.

A Modified Glycosaminoglycan, GM-0111, Inhibits Molecular Signaling Involved in Periodontitis

Background

Periodontitis is characterized by microbial infection, inflammation, tissue breakdown, and accelerated loss of alveolar bone matrix. Treatment targeting these multiple stages of the disease provides ways to treat or prevent periodontitis. Certain glycosaminoglycans (GAGs) block multiple inflammatory mediators as well as suppress bacterial growth, suggesting that these GAGs may be exploited as a therapeutic for periodontitis.

Methods

We investigated the effects of a synthetic GAG, GM-0111, on various molecular events associated with periodontitis: growth of Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) pathogenic bacteria associated with periodontitis; activation of pro-inflammatory signaling through TLR2 and TLR4 in mouse macrophage RAW 264.7 cells and heterologously expressed HEK 293 cells; osteoclast formation and bone matrix resorption in cultured mouse pre-osteoclasts.

Results

(1) GM-0111 suppressed the growth of P. gingivalis and A. actinomycetemcomitans even at 1% (w/v) solution. The antibacterial effects of GM-0111 were stronger than hyaluronic acid (HA) or xylitol in P. gingivalis at all concentrations and comparable to xylitol in A. actinomycetemcomitans at ≥2% (w/v) solution. We also observed that GM-0111 suppressed biofilm formation of P. gingivalis and these effects were much stronger than HA. (2) GM-0111 inhibited TLR-mediated pro-inflammatory cellular signaling both in macrophage and HEK 293 cells with higher selectivity for TLR2 than TLR4 (IC₅₀ of 1–10 ng/mL vs. > 100 μg/mL, respectively). (3) GM-0111 blocked RANKL-induced osteoclast formation (as low as 300 ng/mL) and bone matrix resorption. While GM-0111 showed high affinity binding to RANKL, it did not interfere with RANKL/RANK/NF-κB signaling, suggesting that GM-0111 inhibits osteoclast formation by a RANKL-RANK-independent mechanism.

Conclusions

We report that GM-0111 inhibits multiple molecular events involved in periodontitis, spanning from the early pro-inflammatory TLR signaling, to pathways activated at the later stage component of bone loss.

Evaluation of TLR2 and 4 in Chronic Periodontitis

INTRODUCTION

Periodontal disease is the major cause of adult tooth loss and is commonly characterized by a chronic inflammation caused by infection due to oral bacteria. Members of Toll-Like Receptor (TLR) family recognize conserved microbial structures, such as bacterial lipopolysaccharides and activate signalling pathways that result in immune responses against microbial infections.

AIM

The aim of the present study was to assess the mRNA expression of Toll-Like Receptor 2 and 4 in tissues with or without chronic periodontitis.

MATERIALS AND METHODS

Gingival tissue samples were collected from controls (30 subjects with healthy periodontal tissues) and experimental group (30 subjects with chronic periodontitis). Total RNA was extracted and RT-PCR was done for evaluation of TLR-2 and TLR-4. Mann Whitney U-test, Pearson Chi-square Test was used for statistics.

RESULTS

The results showed that there is a significant (p-value= 0.004) association between TLR-4 and the experimental group comprising of chronic periodontitis patients in comparison to the insignificant (p-value= 0.085) TLR-2 expression.

CONCLUSION

This study concludes that TLR-2 and TLR-4 expressed in the gingival tissues recognize different bacterial cell wall components thus helping us to associate its potential in diagnosing periodontal disease. Hence, in the future, these scientific findings can pave the way in using TLR as a diagnostic biomarker for periodontal disease.

Variability of the dendritic cell response triggered by different serotypes of Aggregatibacter actinomycetemcomitans or Porphyromonas gingivalis is toll-like receptor 2 (TLR2) or TLR4 dependent

BACKGROUND

Different serotypes of Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis have been shown to induce differential dendritic cell (DC) responses. This study investigates whether cytokine and CC-chemokine receptor (CCR) production by DCs stimulated with different serotypes of A. actinomycetemcomitans or P. gingivalis is Toll-like receptor 2 (TLR2) and/or TLR4 dependent.

METHODS

DCs were obtained from healthy individuals and primed at a multiplicity of infection (MOI) of 10(2) with different A. actinomycetemcomitans or P. gingivalis serotypes in the presence or absence of anti-TLR2 or anti-TLR4 blocking antibodies. TLR2 and TLR4 expression, CCR5 and CCR6 expression, and interleukin (IL)-1β, IL-10, IL-12, and IL-23 expression and secretion were quantified by flow cytometry, real-time reverse-transcription polymerase chain reaction, and enzyme-linked immunosorbent assay.

RESULTS

When DCs were stimulated with serotype b of A. actinomycetemcomitans or serotype K1 of P. gingivalis, higher levels of TLR2 or TLR4, respectively, were detected compared to DCs stimulated with the other serotypes. Similarly, higher levels of cytokines and CCRs were detected in serotype b- or serotype K1-primed DCs compared to the others, and these increased levels positively correlated with levels of TLR2 or TLR4. When TLR2 signaling was blocked using a specific anti-TLR2 monoclonal antibody, serotype b-induced cytokine and CCR expression was inhibited; when TLR4 signaling was blocked, serotype K1-induced response was inhibited.

CONCLUSIONS

These results demonstrate that the variability of secretion of cytokines and expression of CCRs detected in DCs stimulated with different serotypes of A. actinomycetemcomitans or P. gingivalis is TLR2 or TLR4 dependent, respectively.

Autonomous immunity in mucosal epithelial cells: fortifying the barrier against infection

Mucosal epithelial cells express an autonomous innate immune response that controls the overgrowth of invaded bacteria, mitigates the harmful effects of the bacteria carried within, and does not rely on other external arms of the immune response. Epithelial cell autonomous innate immunity "respects" the social biology of invading bacteria to achieve symbiosis, and is the primary protective mechanism against pathogens.

Increase in receptor activator of nuclear factor κB ligand/osteoprotegerin ratio in peri-implant gingiva exposed to Porphyromonas gingivalis lipopolysaccharide

Background/purpose

The prevalence of peri-implant diseases, including peri-implant mucositis and peri-implantitis, is increasing. The aim of this study was to elucidate the pathological mechanisms of inflammation and alveolar bone resorption in peri-implant tissues. To do this, we fabricated inflamed gingiva around mini-implants in the palatine processes of rats using lipopolysaccharide derived from Porphyromonas gingivalis (P.g-LPS).

Materials and methods

Pure titanium mini-implants were implanted into the palatine processes of rats, and then intermittent injections of P.g-LPS were made into the gingival tissues surrounding the mini-implants. The expression patterns of tumor necrosis factor-α, interleukin-1β, chemokine (C-C motif) ligand 2, receptor activator of nuclear factor κB ligand (RANKL), and osteoprotegerin (OPG) in the tissues were examined using real-time reverse transcriptase polymerase chain reaction or enzyme-linked immunosorbent assays. Immunohistochemical analysis was also performed to compare the T and B cells expressing RANKL.

Results

P.g-LPS increased the expressions of tumor necrosis factor-α, interleukin-1β, chemokine (C-C motif) ligand 2, and RANKL in the gingival tissues surrounding the mini-implants. In contrast, the expression of OPG in the P.g-LPS samples was decreased. Consequently, the RANKL/OPG ratio was significantly increased. Moreover, cells stained positively for both anti-CD3 and anti-RANKL antibodies were only found in the samples treated with P.g-LPS.

Conclusion

These data revealed that P.g-LPS injections increased the RANKL/OPG ratio in the gingival tissues surrounding mini-implants in the rat model. In addition, the CD3-positive cells in the gingival tissues injected with P.g-LPS expressed RANKL. This suggests that the activated T cells capable of infiltrating gingival tissues affected by P.g-LPS may be one of the sources of RANKL and may also be involved in the disease progression from peri-implant mucositis to peri-implantitis.

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.

PLAP-1/Asporin Regulates TLR2- and TLR4-induced Inflammatory Responses

Periodontal ligament-associated protein 1 (PLAP-1)/asporin is an extracellular matrix protein preferentially expressed in periodontal ligaments. PLAP-1/asporin inhibits the cytodifferentiation and mineralization of periodontal ligament cells and has important roles in the maintenance of periodontal tissue homeostasis. However, the involvement of PLAP-1/asporin in inflammatory responses during periodontitis is poorly understood. This study hypothesized that PLAP-1/asporin might affect the pathogenesis of periodontitis by regulating periodontopathic bacteria-induced inflammatory responses. Proinflammatory cytokine expression induced by Toll-like receptor 2 (TLR2) and TLR4 was significantly downregulated when PLAP-1/asporin was overexpressed in periodontal ligament cells. Similarly, recombinant PLAP-1/asporin inhibited TLR2- and TLR4-induced proinflammatory cytokine expression in macrophages. We also confirmed that NF-κB activity induced by TLR2 and TLR4 signaling was suppressed by the addition of recombinant PLAP-1/asporin. Furthermore, IκB kinase α degradation induced by TLR4 was reduced by PLAP-1/asporin. Immunoprecipitation assays demonstrated the binding abilities of PLAP-1/asporin to both TLR2 and TLR4. Taken together, PLAP-1/asporin negatively regulates TLR2- and TLR4-induced inflammatory responses through direct molecular interactions. These findings indicate that PLAP-1/asporin has a defensive role in periodontitis lesions by suppressing pathophysiologic TLR signaling and that the modulating effects of PLAP-1/asporin might be useful for periodontal treatments.

Microbial composition of atherosclerotic plaques

OBJECTIVE

The association of infections such as periodontitis with atherosclerotic diseases is well documented. In spite of the high diversity of the human oral microbiota, and its close contact with the circulatory system, few oral species were detected in atherosclerotic plaques. Thus, we attempted to evaluate the microbial diversity of atherosclerotic plaques from patients with different periodontal conditions, submitted to endarterectomy by a broad-range microbial method.

MATERIALS AND METHODS

Patients indicated for aorta endarterectomy due to myocardial infarction were recruited for periodontal clinical examination. The microbial diversity of atherosclerotic plaques (n = 35) was evaluated by sequence analysis of bacterial 16S rRNA libraries.

RESULTS

Bacterial DNA was detected in 12 endarterectomy specimens (34.3%). Twenty-three bacterial species/phylotypes were identified. Proteobacteria and Firmicutes comprised 78.3% and 21.7% of the identified taxa, respectively. Fifteen (60.9%) phylotypes were reported as yet uncultivable or as yet uncharacterized species. Two uncultured phylotypes were previously detected in the human mouth. The periodontopathogen Aggregatibacter actinomycetemcomitans was detected in seven samples (20%), followed by Pseudomonas species. There was no association between periodontal parameters and detection of A. actinomycetemcomitans or other phylotypes in atherosclerotic plaques.

CONCLUSION

Our results suggest a role of the oral microbiota in the development of inflammation in atherogenesis, particularly of A. actinomycetemcomitans.

High acid phosphatase level in the gingival tissues of periodontitis subjects

Aim:

Periodontitis is one of the major problems slowly progressing and could affect 70% of the global population. The prevalence of periodontitis differs from mild to moderate forms of race and geographic region. The aim of this study is to determine the acid phosphatase (ACP) activity in the gingival tissues of periodontitis subjects. In this study, the activity of ACP in the gingival tissue of subjects with periodontitis was examined.

Materials and Methods:

A total of 30 subjects were selected for the study and are divided into group I (n = 15, healthy subjects in control) and in group II (n = 15, periodontitis subjects). The gingival tissue from group I and group II subjects were collected after the surgery and the ACP enzyme level was analyzed using ultraviolet spectrophotometer. Assessment of periodontitis was done based on periodontal probing depth (PPD) and clinical attachment level (CAL). The statistical analysis applied was independent sample t-test, P < 0.05 was considered as significant.

Results:

The results of group II periodontitis subjects showed statistically significant increased gingival tissues ACP level when compared with the control group I subject. The mean levels of CAL and PPD were significantly >4 mm in periodontitis subjects when compared to control.

Conclusions:

The elevated level of ACP in the gingival tissue and Gram-negative microorganisms found in sub-gingival plaque was greater in periodontitis. Based on these results, gingival tissue ACP level can be considered as an independent risk factor for evaluating the microbial status and periodontal tissue damage.

Host Responses in the Link Between Periodontitis and Rheumatoid Arthritis

Periodontitis and rheumatoid arthritis (RA) are common chronic inflammatory conditions and share many clinical and pathologic features. There is evidence to suggest that similar profiles of cytokine genotypes and their coding proteins are involved in the pathogenesis of periodontitis and RA. In particular, constitutive overproduction of pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), has been implicated to play a pathologic role in the two inflammatory diseases. Results from studies with animal and human subjects have suggested an improvement of periodontal inflammatory condition after treatment with TNF-α inhibitors. Likewise, IL-6 receptor inhibition therapy has been suggested to have an effect on control of periodontal inflammation in patients with RA. In the present review, we provide an overview of studies showing the pathological role of cytokines in the linkage between periodontitis and RA, and further summarize the current studies assessing the effect of cytokine targeted therapy on periodontal condition.

Toll gates: An emerging therapeutic target

Innate immune system forms the first line of defense against microbial infections, as it exerts an immediate response. Innate immunity works through Toll-like receptors (TLRs) which functions as primary sensors of pathogens. TLR activates multiple signaling cascades leading to the induction of genes responsible for the release of inflammatory cytokines and type I interferon. Thus, they induce antimicrobial responses and also have an instructive role in adaptive immunity. However, TLR-mediated inflammation is said to be responsible for many of the destructive host responses in inflammatory diseases like periodontitis. Hence, therapeutics targeting TLRs are being used to treat disease such as HIV, Hepatitis B, asthma etc. Recently, synthetic TLR agonists are tried as novel vaccine adjuvant in treating periodontal diseases. This paper reviews the scope of TLR-based therapeutics in treating periodontitis.

Aging and contribution of MyD88 and TRIF to expression of TLR pathway-associated genes following stimulation with Porphyromonas gingivalis

BACKGROUND AND OBJECTIVE

Periodontal disease is a highly complex chronic inflammatory disease of the oral cavity. Multiple factors influence periodontal disease, including socio-economic status, genetics and age; however, inflammation elicited by the presence of specific bacteria in the subgingival space is thought to drive the majority of soft- and hard-tissue destruction. Porphyromonas gingivalis is closely associated with periodontal disease. Toll-like receptors (TLRs) and their intracellular signaling pathways play roles in the host response to P. gingivalis. The focus of the current study was to use microarray analysis to define the contributions of the TLR adaptor molecules myeloid differentiation factor 88 (MyD88) and Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-beta (TRIF), and aging, on the expression of TLR pathway-associated mRNAs in response to P. gingivalis.

MATERIAL AND METHODS

Bone marrow-derived macrophages (BMØ) from wild-type (Wt), MyD88 knockout (MyD88-KO) and Trif(Lps2) [i.e. containing a point mutation in the lipopolysaccharide 2 (Lps2) gene rendering the Toll/interleukin (IL)-1 receptor domain-containing adaptor inducing interferon-beta (TRIF) protein nonfunctional] mice, at 2-and 12-mo of age, were cultured with P. gingivalis. Expression of genes in BMØ cultured with P. gingivalis was determined in comparison with expression of genes in BMØ cultured in medium only.

RESULTS

Using, as criteria, a twofold increase or decrease in mRNA expression, differential expression of 32 genes was observed when Wt BMØ from 2-mo-old mice were cultured with P. gingivalis compared with the medium-only control. When compared with 2-mo-old Wt mice, 21 and 12 genes were differentially expressed (p < 0.05) as a result of the mutations in MyD88 or TRIF, respectively. The expression of five genes was significantly (p < 0.05) reduced in Wt BMØ from 12-mo-old mice compared with those from 2-mo-old mice following culture with P. gingivalis. Age also influenced the expression of genes in MyD88-KO and Trif(Lps2) mice challenged with P. gingivalis.

CONCLUSIONS

Our results indicate that P. gingivalis induces differential expression of TLR pathway-associated genes, and both MyD88 and TRIF play roles in the expression of these genes. Age also played a role in the expression of TLR-associated genes following stimulation of BMØ with P. gingivalis.

Differential expression of Toll-like receptor 4 in healthy and diseased human gingiva

BACKGROUND AND OBJECTIVE

Lipopolysaccharide (LPS)-mediated signaling in host cells involves Toll-like receptor 4 (TLR4) accessory molecules, including LPS-binding protein (LBP), cluster of differentiation 14 (CD14) and lymphocyte antigen 96 (MD-2). However, expression of these innate defense molecules in various compartments of the human periodontium is unclear. The aim of this study was to investigate the expression profile of TLR4 in human gingiva.

MATERIAL AND METHODS

Human gingival biopsies were collected from healthy gingival or chronic periodontitis tissue. Primary gingival keratinocytes and fibroblasts were cultured. Immunohistochemical analysis for TLR4 was performed. Transcripts of TLR4, MD-2, CD14 and LBP, and their protein products, were examined using RT-PCR, immunoprecipitation and immunoblotting. The interactions between these molecules in keratinocytes and fibroblasts were investigated by co-immunoprecipitation.

RESULTS

TLR4 immunoreactivity was found in healthy gingival epithelium and periodontitis tissue, and appeared to be lower in junctional epithelium ( p ≤ 0.01). Fibroblasts and inflammatory cells stained more strongly for TLR4 in diseased periodontal tissues (p < 0.001). Three TLR4 splicing variants, two MD-2 splicing variants and one CD14 mRNA were expressed by gingival keratinocytes and fibroblasts. Expression of TLR4, CD14 and MD-2 proteins was detected in keratinocytes and fibroblasts in vitro. TLR4 protein from gingival keratinocytes and fibroblasts could be co-immunoprecipitated with CD14 or MD-2, suggesting an association between the related molecules in vivo. LBP transcript was detected in gingival biopsies, but not in primary cultures of gingival keratinocytes or fibroblasts.

CONCLUSION

TLR4, CD14 and MD-2, but not LBP, are expressed in human gingival keratinocytes and fibroblasts. The TLR4 expression level in the junctional epithelium appeared to be lowest within the periodontal epithelial barrier.

Analysis of Expression and Localization of TLR-2 by Immunofluorescent Technique in Healthy and Inflammed Oral Tissues

INTRODUCTION

Toll-like receptors (TLRs) are an important component of immune system. Among them, TLR-2 plays a dominant role in the oral tissues in initiating inflammation in chronic periodontitis. Not many studies have been done on quantitative expression of TLR-2 by using immunofluorescent techniques (IFT) in oral tissues. In this study, the expression and localisation of TLR-2 were detected in gingival tissues of chronic periodontitis patients and healthy individuals.

MATERIAL AND METHODS

Immuno Fluorescent Technique (IFT) was used for the expression and localization of TLR-2 in gingival tissue samples from 25 chronic periodontitis patients and from 25 healthy controls. Haematoxylin and Eosin staining was also done for all the samples to determine the histological characteristics of the gingival tissue samples.

RESULT

Both healthy and periodontitis gingival tissues expressed TLR-2. We found that the expression level of TLR-2 was higher in all the periodontitis patients than in healthy individuals. We also found out that the expression of TLR-2 was higher in the epithelial cells than in the connective tissue cells.

CONCLUSION

These data suggest a definite involvement of TLR-2 in initiating an inflammatory response in periodontal tissues. More studies are required to define the mechanisms and expression levels of TLR-2 in oral health and diseases.

The role of TLR4 896 A>G and 1196 C>T in susceptibility to infections: a review and meta-analysis of genetic association studies

Background

Toll-like receptor 4 plays a role in pathogen recognition, and common polymorphisms may alter host susceptibility to infectious diseases.

Purpose

To review the association of two common polymorphisms (TLR4 896A>G and TLR4 1196C>T) with infectious diseases.

Data Sources

We searched PubMed and EMBASE up to March 2013 for pertinent literature in English, and complemented search with references lists of eligible studies.

Study Selection

We included all studies that: reported an infectious outcome; had a case-control design and reported the TLR4 896A>G and/or TLR4 1196C>T genotype frequencies; 59 studies fulfilled these criteria and were analyzed.

Data Extraction

Two authors independently extracted study data.

Data Synthesis

The generalized odds ratio metric (OR_G) was used to quantify the impact of TLR4 variants on disease susceptibility. A meta-analysis was undertaken for outcomes reported in >1 study. Eleven of 37 distinct outcomes were significant. TLR4 896 A>G increased risk for all parasitic infections (OR_G 1.59; 95%CI 1.05-2.42), malaria (1.31; 95%CI 1.04-1.66), brucellosis (2.66; 95%CI 1.66-4.27), cutaneous leishmaniasis (7.22; 95%CI 1.91-27.29), neurocysticercosis (4.39; 95%CI 2.53-7.61), Streptococcus pyogenes tonsillar disease (2.93; 95%CI 1.24-6.93) , typhoid fever (2.51; 95%CI 1.18-5.34) and adult urinary tract infections (1.98; 95%CI 1.04-3.98), but was protective for leprosy (0.36; 95%CI 0.22-0.60). TLR4 1196 C>T effects were similar to TLR4 896 A>G for brucellosis, cutaneous leishmaniasis, leprosy, typhoid fever and S. pyogenes tonsillar disease, and was protective for bacterial vaginosis in pregnancy (0.55; 95%CI 0.31-0.98) and Haemophilus influenzae tonsillar disease (0.42; 95%CI 0.17-1.00). The majority of significant associations were among predominantly Asian populations and significant associations were rare among European populations.

Conclusions

Depending on the type of infection and population, TLR4 polymorphisms are associated with increased, decreased or no difference in infectious disease. This may be due to differential functional expression of TLR4, the co-segregation of TLR4 variants or a favorable inflammatory response.

Comparison of relative TLR-2 and TLR-4 expression level of disease and healthy gingival tissue of smoking and non-smoking patients and periodontally healthy control patients

BACKGROUND

Toll-like receptors are a family of sensor proteins that induce the inflammatory diseases in context of microbial infection. The role of these proteins in periodontal disease and their interaction with smoking status are yet to be investigated. The aim of the present study was to evaluate the effect of smoking on gene expression of toll like receptor 2 (TLR-2) and toll-like receptor 4 (TLR-4) in patients with periodontitis.

METHODS

RNAs were extracted from gingival biopsies of healthy sites (no bleeding on probing and pocket depth ≤3 mm) as well as diseased sites (with bleeding on probing and pocket depth ≥5 mm) of 20 smoker and 17 non-smoker subjects with chronic periodontitis. Gingival biopsies from eight periodontally healthy, never-smoker subjects served as control. Real-time PCR was carried out to evaluate the relative quantities of TLR-2 and TLR-4 mRNA concentrations.

RESULTS

Regardless of smoking status, the relative expression levels of TLR-2 and TLR-4 were significantly greater (about 3 fold) at diseased sites compared to healthy sites of patients with periodontitis and healthy controls (p < 0.05). In sites with periodontitis, smoking caused an increase of about 6.5 fold in mRNA levels of TLR-4 in gingival tissue (p < 0.05).

CONCLUSIONS

Although periodontitis might significantly increase TLR-2 and TLR-4 gene expression in gingival tissues, smoking habit in periodontitis subjects could selectively potentiate TLR-4 gene expression.

MyD88 is essential for alveolar bone loss induced by Aggregatibacter actinomycetemcomitans lipopolysaccharide in mice

Aggregatibacter actinomycetemcomitans is a Gram-negative bacteria highly associated with localized aggressive periodontitis. The recognition of microbial factors, such as lipopolysaccharide from A. actinomycetemcomitans ((Aa)LPS), in the oral environment is made mainly by surface receptors known as Toll-like receptors (TLR). TLR4 is the major LPS receptor. This interaction leads to the production of inflammatory cytokines by myeloid differentiation primary-response protein 88 (MyD88) -dependent and -independent pathways, which may involve the adaptor Toll/interleukin-1 receptor-domain-containing adaptor inducing interferon-β (TRIF). The aim of this study was to assess the involvement of MyD88 in alveolar bone loss induced by (Aa)LPS in mice. C57BL6/J wild-type (WT) mice, MyD88, TRIF or TRIF/MyD88 knockout mice received 10 injections of Aa LPS strain FDC Y4 (5 μg in 3 μl), in the palatal gingival tissue of the right first molar, every 48 h. Phosphate-buffered saline was injected in the opposite side and used as control. Animals were sacrificed 24 h after the 10th injection and the maxillae were removed for macroscopic and biochemical analyses. The injections of Aa LPS induced significant alveolar bone loss in WT mice. In the absence of MyD88 or TRIF/MyD88 no bone loss induced by (Aa)LPS was observed. In contrast, responses in TRIF(-/-) mice were similar to those in WT mice. Diminished bone loss in the absence of MyD88 was associated with fewer TRAP-positive cells and increased expression of osteoblast markers, RUNX2 and osteopontin. There was also reduced tumor necrosis factor-α production in MyD88(-/-) mice. There was less osteoclast differentiation of hematopoietic bone marrow cells from MyD88(-/-) mice after (Aa)LPS stimulation. Hence, the signaling through MyD88 is pivotal for (Aa)LPS-induced osteoclast formation and alveolar bone loss.

The role of Toll-like receptor 2 and 4 in gingival tissues of chronic periodontitis subjects with type 2 diabetes

BACKGROUND AND OBJECTIVE

Diabetes is one important risk factor of chronic periodontitis. However, the roles of toll-like receptor (TLR) 2 and TLR4, which are implicated in the inflammatory process in both chronic periodontitis and diabetes, have not been studied. This study aimed to determine whether TLR2 and TLR4 might be involved in the relationship between chronic periodontitis and diabetes by examining TLR2 and TLR4 expression in gingival tissues from subjects with chronic periodontitis without diabetes (CP) and with diabetes (CP+DM) and from periodontally healthy subjects without diabetes (PH) and with diabetes (PH+DM).

MATERIAL AND METHODS

Gingival tissues were collected from 23 CP subjects, 21 CP+DM subjects, 22 PH subjects and 20 PH+DM subjects. The expression of TLR2 and TLR4 in gingival tissues was determined using an immunohistochemical method. In gingival epithelium, staining patterns and intensity levels of TLR2 and TLR4 expression were studied. In connective tissues, the percentages of TLR2- and TLR4-positive cells were calculated. The intensity levels and the percentages of positive cells were statistically analyzed.

RESULTS

Chronic periodontitis or diabetes showed no significant effect on TLR2 expression in the oral epithelium. However, diabetes increased the expression of TLR2 in sulcular epithelium and changed the pattern of TLR2 expression in gingival epithelium. Chronic periodontitis decreased the expression of TLR4 in gingival epithelium. In connective tissue under sulcular epithelium, CP+DM subjects showed statistically significant higher percentages of TLR2- and TLR4-positive cells compared with PH and PH+DM subjects.

CONCLUSION

Our results suggest that hyperglycemia and chronic periodontitis had effects on TLR2 and TLR4 expression in gingival tissue. The differences in TLR2 and TLR4 expression could contribute to a greater inflammatory response, leading to periodontal disease initiation and progression.

Differential expression of mitogen activating protein kinases in periodontitis

AIM

Following toll-like receptor (TLR) engagement, lipopolysaccharide (LPS) can stimulate the expression of pro-inflammatory cytokines thus activating the innate immune response. The production of inflammatory cytokines results, in part, from the activation of kinase-induced signalling cascades and transcriptional factors. Of the four distinct classes of mitogen-activated protein kinases (MAPK) described in mammals, p38, c-Jun N-terminal activated kinases (JNK1-3) and extracellular activated kinases (ERK1,2) are the best studied. Previous data have established that p38 MAPK signalling is required for inflammation and bone loss in periodontal disease pre-clinical animal models.

MATERIALS & METHODS

In this study, we obtained healthy and diseased periodontal tissues along with clinical parameters and microbiological parameters. Excised fixed tissues were immunostained with total and phospho-specific antibodies against p38, JNK and ERK kinases.

RESULTS

Intensity scoring from immunostained tissues was correlated with clinical periodontal parameters. Rank correlations with clinical indices were statistically significantly positive (p-value < 0.05) for total p38 (correlations ranging 0.49-0.68), phospho-p38 (range 0.44-0.56), and total ERK (range 0.52-0.59) levels, and correlations with JNK levels also supported association (range 0.42-0.59). Phospho-JNK and phospho-ERK showed no significant positive correlation with clinical parameters of disease.

CONCLUSION

These data strongly implicate p38 MAPK as a major MAPK involved in human periodontal inflammation and severity.

High glucose induces inflammatory cytokine through protein kinase C-induced toll-like receptor 2 pathway in gingival fibroblasts

Toll-like receptors (TLRs) play a key role in innate immune response and inflammation, especially in periodontitis. Meanwhile, hyperglycemia can induce inflammation in diabetes complications. However, the activity of TLRs in periodontitis complicated with hyperglycemia is still unclear. In the present study, high glucose (25 mmol/l) significantly induced TLR2 expression in gingival fibroblasts (p<0.05). Also, high glucose increased nuclear factor kappa B (NF-κB) p65 nuclear activity, tumor necrosis factor-α (TNF-α) and interleukin-lβ (IL-1β) levels. Protein kinase C (PKC)-α and δ knockdown with siRNA significantly decreased TLR2 and NF-κB p65 expression (p<0.05), whereas inhibition of PKC-β had no effect on TLR2 and NF-κB p65 under high glucose (p<0.05). Additional studies revealed that TLR2 knockdown significantly abrogated high-glucose-induced NF-κB expression and inflammatory cytokine secretion. Collectively, these data suggest that high glucose stimulates TNF-α and IL-1β secretion via inducing TLR2 through PKC-α and PKC-δ in human gingival fibroblasts.

TLR4 and TLR9 are induced in oral lichen planus

BACKGROUND

The role of Toll-like receptors (TLRs) has been elucidated in many human infectious, autoimmune and neoplastic diseases. Previously, TLR2 and TLR4 expression in oral lichen planus (OLP) was described. The aim of our study was to examine expression patterns of TLR4 and TLR9 in normal oral mucosa and OLP and describe the effect of topical tacrolimus treatment on the expression of TLR4 and TLR9 in OLP.

METHODS

Toll-like receptor 4 and TLR9 expression was analysed by immunohistochemistry in five samples of normal oral mucosa and 50 samples of OLP (31 representing clinically white and 19 clinically erythematous/erosive lesions). We evaluated also the effect of topical tacrolimus on TLR4 and TLR9 expression in a patient with OLP.

RESULTS

Toll-like receptor 4 and TLR9 expression was increased in OLP epithelium compared with normal epithelium (P < 0.001); no significant difference between the two clinical types of OLP was observed. TLR9 expression was strongest in the superficial layer of the epithelium (P < 0.001), while the expression of TLR4 was strongest in the basal layer (P < 0.001). Treatment of OLP lesions with topical tacrolimus resulted in clinical improvement but had no effect on TLR expression levels.

CONCLUSIONS

Toll-like receptor 4 and TLR9 are induced in OLP; our finding confirms the results of a previous study. TLR4 and TLR9 may play a part in the pathogenesis of OLP. Further studies are needed to dissect the definitive role of TLRs in OLP pathogenesis and progression and to determine the effect of tacrolimus on the function of TLRs.

Mechanical stress-activated immune response genes via Sirtuin 1 expression in human periodontal ligament cells

Recently, Sirtuin 1 (SIRT1) has been implicated in the molecular control of ageing and immune response. Although the remodelling of periodontal ligament (PDL) in response to mechanical stress (MS) is mediated by several host factors, including cytokines and chemokines, the transmission of mechanical stimuli into specific cellular activity is still not understood fully. This study aimed to investigate the effects of MS, particularly cyclic strain, on immune response genes, as well as SIRT1 and its signal transduction pathways, in human PDL cells. MS up-regulated the expression of SIRT1 and immune response genes encoding cytokines [tumour necrosis factor (TNF)-α, interleukin (IL)-1β], chemokines [IL-8, monocyte cheoattractant protein (CCL)-20], defensins [human β-defensin (hBD)-2, hBD-3] and Toll-like receptors (TLR-2 and TLR-4) in a force- and time-dependent manner. The SIRT1 inducers resveratrol and isonicotinamide attenuated MS-induced cytokine and chemokine expression, but enhanced the expression of defensins and TLRs. Blockade of SIRT1 activity by the SIRT1 inhibitors sirtinol and nicotinamide and down-regulation of SIRT1 expression by SIRT1 siRNA reduced the stimulatory effects of MS on defensins and TLRs, but increased its effects on cytokines and chemokines. MS induced activation of protein kinase B (Akt), protein kinase C (PKC), nuclear factor (NF)-κB and p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Treatment with the anti-oxidants N-acetylcysteine and glutathione inhibited MS-induced reactive oxygen species production and expression of cytokines, chemokines, defensins and TLRs. These results suggest that MS activates human PDL cells to express immune/defence genes encoding cytokines, chemokines, defensins and TLRs via a SIRT1 pathway.

Involvement of Toll-like receptor 2 in apoptosis of Aggregatibacter actinomycetemcomitans-infected THP-1 cells

BACKGROUND/PURPOSE

Aggregatibacter (Actinobacillus) actinomycetemcomitans is a gram-negative bacterium that has been associated with aggressive periodontitis. A actinomycetemcomitans infection induces apoptosis in the human monocytic cell line THP-1, and p38 mitogen-activated protein kinase (p38) activity and tumor necrosis factor-α (TNF-α) production are enhanced by A actinomycetemcomitans infection. However, mechanisms governing the recognition of A actinomycetemcomitans by monocytes during apoptosis have not been elucidated. A actinomycetemcomitans cell wall components stimulate Toll-like receptor (TLR)2 and/or TLR4. The authors examined whether TLR2 and/or TLR4 were involved in the apoptosis of A actinomycetemcomitans-infected THP-1 cells.

METHODS

A actinomycetemcomitans-infected THP-1 cells were transferred to six-well culture plates and incubated for 0 to 6 hours. In some experiments, THP-1 cells were incubated with anti-TLR2, anti-TLR4, or isotype control antibody (10 μg/mL) for 30 minutes prior to A actinomycetemcomitans infection. Expression of messenger RNA (mRNA) was examined by reverse transcription-polymerase chain reaction. Intracellular bacteria recovered from A actinomycetemcomitans-infected cells and apoptotic cells were detected by APOPercentage dye (Biocolor Ltd, Northern Ireland, UK) staining. Cellular p38 activity and TNF-α production were assessed with enzyme-linked immunosorbent assay.

RESULTS

The expression of TLR2 mRNA was increased by A actinomycetemcomitans infection. Phagocytosis and apoptosis in A actinomycetemcomitans-infected THP-1 cells were inhibited by the addition of anti-TLR2 antibody. Also, anti-TLR2 antibody suppressed the activation of p38 and production of TNF-α in A actinomycetemcomitans-infected THP-1 cells.

CONCLUSION

These results suggest that A actinomycetemcomitans induces increased expression of TLR2, leading to phagocytosis and apoptosis of THP-1 cells via p38 activation and TNF-α production.

TLR4 polymorphisms and disease susceptibility

Toll-like receptors (TLRs) play a central role in the regulation of the host immune system. Each TLR recognizes specific pathogen-associated molecular patterns (PAMPs). TLR4 is one of the well characterized pathogen recognition receptors (PRRs) that recognizes the lipopolysaccharide (LPS) of Gram-negative bacteria, some conserved structures from fungal to mycobacterial pathogens and some endogenous ligands. A complex signaling cascade initiates after the ligand binds to the TLR4 ectodomain, leading to the activation of multiple inflammatory genes. Genetic variations greatly influence immune responses towards pathogenic challenges and disease outcome. In this review, we summarize various reports regarding TLR4 polymorphisms and disease susceptibility.