Innate Immune Receptors in Human Airway Smooth Muscle Cells: Activation by TLR1/2, TLR3, TLR4, TLR7 and NOD1 Agonists

Background

Pattern-recognition receptors (PRRs), including Toll-like receptors (TLRs), NOD-like receptors (NLRs) and RIG-I-like receptors (RLRs), recognize microbial components and trigger a host defense response. Respiratory tract infections are common causes of asthma exacerbations, suggesting a role for PRRs in this process. The present study aimed to examine the expression and function of PRRs on human airway smooth muscle cells (HASMCs).

Methods

Expression of TLR, NLR and RLR mRNA and proteins was determined using real-time RT-PCR, flow cytometry and immunocytochemistry. The functional responses to ligand stimulation were investigated in terms of cytokine and chemokine release, cell surface marker expression, proliferation and proteins regulating the contractile state.

Results

HASMCs expressed functional TLR2, TLR3, TLR4, TLR7 and NOD1. Stimulation with the corresponding agonists Pam₃CSK₄, poly(I:C), LPS, R-837 and iE-DAP, respectively, induced IL-6, IL-8 and GM-CSF release and up-regulation of ICAM-1 and HLA-DR, while poly(I:C) also affected the release of eotaxin and RANTES. The proliferative response was slightly increased by LPS. Stimulation, most prominently with poly(I:C), down-regulated myosin light chain kinase and cysteinyl leukotriene 1 receptor expression and up-regulated β₂-adrenoceptor expression. No effects were seen for agonist to TLR2/6, TLR5, TLR8, TLR9, NOD2 or RIG-I/MDA-5.

Conclusion

Activation of TLR2, TLR3, TLR4, TLR7 and NOD1 favors a synthetic phenotype, characterized by an increased ability to release inflammatory mediators, acquire immunomodulatory properties by recruiting and interacting with other cells, and reduce the contractile state. The PRRs might therefore be of therapeutic use in the management of asthma and infection-induced disease exacerbations.     

Combined TLR7/8 and TLR9 Ligands Potentiate the Activity of a Schistosoma japonicum DNA Vaccine

Background

Toll-like receptor (TLR) ligands have been explored as vaccine adjuvants for tumor and virus immunotherapy, but few TLR ligands affecting schistosoma vaccines have been characterized. Previously, we developed a partially protective DNA vaccine encoding the 26-kDa glutathione S-transferase of Schistosoma japonicum (pVAX1-Sj26GST).

Methodology/Principal Findings

In this study, we evaluated a TLR7/8 ligand (R848) and a TLR9 ligand (CpG oligodeoxynucleotides, or CpG) as adjuvants for pVAX1-Sj26GST and assessed their effects on the immune system and protection against S. japonicum. We show that combining CpG and R848 with pVAX1-Sj26GST immunization significantly increases splenocyte proliferation and IgG and IgG2a levels, decreases CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Treg) frequency in vivo, and enhances protection against S. japonicum. CpG and R848 inhibited Treg-mediated immunosuppression, upregulated the production of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-4, IL-10, IL-2, and IL-6, and decreased Foxp3 expression in vitro, which may contribute to prevent Treg suppression and conversion during vaccination and allow expansion of antigen-specific T cells against pathogens.

Conclusions

Our data shows that selective TLR ligands can increase the protective efficacy of DNA vaccines against schistosomiasis, potentially through combined antagonism of Treg-mediated immunosuppression and conversion.     

Biased distribution of single nucleotide polymorphisms (SNPs) in porcine Toll-like receptor 1 (TLR1), TLR2, TLR4, TLR5, and TLR6 genes

Toll-like receptors (TLRs) recognize various microbial components and induce immune responses. Polymorphisms in TLRs may influence their recognition of pathogen-derived molecules; swine TLRs are predicted to be associated with responses to infectious diseases such as pneumonia. In this study, we searched for single nucleotide polymorphisms (SNPs) in the coding sequences of porcine TLR1, TLR2, TLR4, TLR5, and TLR6 genes in 96 pigs from 11 breeds and elucidated 21, 11, 7, 13, and 11 SNPs, respectively, which caused amino acid substitutions in the respective TLRs. Distribution of these nonsynonymous SNPs was biased; many were located in the leucine-rich repeats, particularly in TLR1. These data demonstrated that the heterogeneity of TLR genes was preserved in various porcine breeds despite intensive breeding that was carried out for livestock improvement. It suggests that the heterogeneity in TLR genes is advantageous in increasing the possibility of survival in porcine populations.Electronic SupplementaryMaterial Supplementary material is available for this article at     

Effects of the TLR2 agonists MALP-2 and Pam3Cys in isolated mouse lungs

Background

Gram-positive and Gram-negative bacteria are main causes of pneumonia or acute lung injury. They are recognized by the innate immune system via toll-like receptor-2 (TLR2) or TLR4, respectively. Among all organs, the lungs have the highest expression of TLR2 receptors, but little is known about the pulmonary consequences of their activation. Here we studied the effects of the TLR2/6 agonist MALP-2, the TLR2/1 agonist Pam₃Cys and the TLR4 agonist lipopolysaccharide (LPS) on pro-inflammatory responses in isolated lungs.

Methodology/Principal Findings

Isolated perfused mouse lungs were perfused for 60 min or 180 min with MALP-2 (25 ng/mL), Pam₃Cys (160 ng/mL) or LPS (1 µg/mL). We studied mediator release by enzyme linked immunosorbent assay (ELISA), the activation of mitogen activated protein kinase (MAPK) and AKT/protein kinase B by immunoblotting, and gene induction by quantitative polymerase chain reaction. All agonists activated the MAPK ERK1/2 and p38, but neither JNK or AKT kinase. The TLR ligands upregulated the inflammation related genes Tnf, Il1β, Il6, Il10, Il12, Ifng, Cxcl2 (MIP-2α) and Ptgs2. MALP-2 was more potent than Pam₃Cys in inducing Slpi, Cxcl10 (IP10) and Parg. Remarkable was the strong induction of Tnc by MALP2, which was not seen with Pam₃Cys or LPS. The growth factor related genes Areg and Hbegf were not affected. In addition, all three TLR agonists stimulated the release of IL-6, TNF, CXCL2 and CXCL10 protein from the lungs.

Conclusions/Significance

TLR2 and TLR4 activation leads to similar reactions in the lungs regarding MAPK activation, gene induction and mediator release. Several genes studied here have not yet been appreciated as targets of TLR2-activation in the lungs before, i.e., Slpi, tenascin C, Parg and Traf1. In addition, the MALP-2 dependent induction of Tnc may indicate the existence of TLR2/6-specific pathways.     

Acquisition of Adult-Like TLR4 and TLR9 Responses during the First Year of Life

Background

Characteristics of the human neonatal immune system are thought to be responsible for heightened susceptibility to infectious pathogens and poor responses to vaccine antigens. Using cord blood as a source of immune cells, many reports indicate that the response of neonatal monocytes and dendritic cells (DC) to Toll-like receptor (TLR) agonists differs significantly from that of adult cells. Herein, we analyzed the evolution of these responses within the first year of life.

Methodology/Principal Findings

Blood samples from children (0, 3, 6, 9, 12 month old) and healthy adults were stimulated ex vivo with bacterial lipopolysaccharide (LPS, TLR4 agonist) or CpG oligonucleotides (TLR9 agonist). We determined phenotypic maturation of monocytes, myeloid (m) and plasmacytoid (p) DC and production of cytokines in the culture supernatants. We observed that surface expression of CD80 and HLA-DR reaches adult levels within the first 3 months of life for mDCs and 6–9 months of life for monocytes and pDCs. In response to LPS, production of TNF-α, IP-10 and IL-12p70 reached adult levels between 6–9 months of life. In response to CpG stimulation, production of type I IFN-dependent chemokines (IP-10 and CXCL9) gradually increased with age but was still limited in 1-year old infants as compared to adult controls. Finally, cord blood samples stimulated with CpG ODN produced large amounts of IL-6, IL-8, IL-1β and IL-10, a situation that was not observed for 3 month-old infants.

Conclusions

The first year of life represents a critical period during which adult-like levels of TLR responses are reached for most but not all cytokine responses.     

TLR3 and TLR7 modulate IgE production in antigen induced pulmonary inflammation via influencing IL-4 expression in immune organs

Background

Toll-like receptors (TLRs) as pattern recognition receptors, participate in both innate and adaptive immune responses, and seem to play an important role in the pathogenesis of asthma. This study aimed to identify key TLRs involved in antigen induced pulmonary inflammation (AIPI), a rat model for asthma, and to explore the role of TLRs in the disease development.

Methods and Findings

E3 rats were sensitized with ovalbumin (OVA)/alum intraperitoneally and intranasally challenged with OVA to induce AIPI model. TLR1-9 and cytokine mRNA expression in spleen, lung and mediastinal lymph node (mLN) tissues were screened by quantitative real-time polymerase chain reaction. TLR7 expression was found to be significantly down-regulated in spleen while TLR3 and TLR8 expression was up-regulated in mLN of AIPI rats. Furthermore, imiquimod (a ligand of TLR7) and TLR3 specific short-hairpin RNA plasmid for RNA interference were administrated, respectively, in vivo to AIPI rats to observe their effects on the disease by assessing various asthmatic parameters. The numbers of total cells, eosinophils, macrophages and lymphocytes were counted according to differential morphology in bronchoalveolar lavage fluid. Serum IgE and OVA specific IgG₁ concentration was detected by enzyme-linked immunosorbent assay. The results showed that both TLR7 ligand treatment and TLR3 RNAi in vivo decreased serum IgE level and interleukin-4 mRNA expression.

Conclusion/Significance

TLR3 in mLN and TLR7 in spleen both systemically modulate disease development in AIPI rats via altering serum IgE concentration relevant to Th2 responses. And these findings may provide an important clue for further research in the asthma pathogenesis and suggest a new remedy for asthma treatment.     

Keratinocyte TLR2 and TLR7 contribute to chronic itch through pruritic cytokines and chemokines in mice

Although neuronal Toll-like receptors (TLRs) (e.g., TLR2, TLR3, and TLR7) have been implicated in itch sensation, the roles of keratinocyte TLRs in chronic itch are elusive. Herein, we evaluated the roles of keratinocyte TLR2 and TLR7 in chronic itch under dry skin and psoriasis conditions, which was induced by either acetone-ether-water treatment or 5% imiquimod cream in mice, respectively. We found that TLR2 and TLR7 signaling were significantly upregulated in dry skin and psoriatic skin in mice. Chronic itch and epidermal hyperplasia induced by dry skin or psoriasis were comparably reduced in TLR2 and TLR7 knockout mice. In the dry skin model, the enhanced messenger RNA (mRNA) expression levels of pruritic CXCL1/2, IL-31, IL-33, ST2, IL-6, IL-17A, TNF-α, and IFN-γ were inhibited in TLR2^−/− mice, while CXCL2, IL-31, and IL-6 were inhibited in TLR7^−/− mice. In psoriasis model, the enhanced mRNA expression levels of pruritic CXCL1/2, IL-31, IL-33, ST2, IL-6, and TNF-α were inhibited in TLR2^−/− mice, while CXCL1/2, IL-31, IL-33, ST2, IL-6, IL-17A, and TNF-α were inhibited in TLR7^−/− mice. Incubation with Staphylococcus aureus (S. aureus) peptidoglycan (PGN-SA) (a TLR2 agonist), imiquimod (a TLR7 agonist), and miR142-3p (a putative TLR7 agonist) were sufficient to upregulate the expression of pruritic cytokines or chemokines in cultured keratinocyte HaCaT cells. Finally, pharmacological blockade of C-X-C Motif Chemokine Receptor 1/2 and high mobility group box protein 1 dose-dependently attenuated acute and chronic itch in mice. Together, these results indicate that keratinocyte TLR2 and TLR7 signaling pathways are distinctly involved in the pathogenesis of chronic itch.     

Mechanical ventilation modulates TLR4 and IRAK-3 in a non-infectious,ventilator-induced lung injury model

Background

Previous experimental studies have shown that injurious mechanical ventilation has a direct effect on pulmonary and systemic immune responses. How these responses are propagated or attenuated is a matter of speculation. The goal of this study was to determine the contribution of mechanical ventilation in the regulation of Toll-like receptor (TLR) signaling and interleukin-1 receptor associated kinase-3 (IRAK-3) during experimental ventilator-induced lung injury.

Methods

Prospective, randomized, controlled animal study using male, healthy adults Sprague-Dawley rats weighing 300-350 g. Animals were anesthetized and randomized to spontaneous breathing and to two different mechanical ventilation strategies for 4 hours: high tidal volume (V_T) (20 ml/kg) and low V_T (6 ml/kg). Histological evaluation, TLR2, TLR4, IRAK3 gene expression, IRAK-3 protein levels, inhibitory kappa B alpha (IκBα), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL6) gene expression in the lungs and TNF-α and IL-6 protein serum concentrations were analyzed.

Results

High V_T mechanical ventilation for 4 hours was associated with a significant increase of TLR4 but not TLR2, a significant decrease of IRAK3 lung gene expression and protein levels, a significant decrease of IκBα, and a higher lung expression and serum concentrations of pro-inflammatory cytokines.

Conclusions

The current study supports an interaction between TLR4 and IRAK-3 signaling pathway for the over-expression and release of pro-inflammatory cytokines during ventilator-induced lung injury. Our study also suggests that injurious mechanical ventilation may elicit an immune response that is similar to that observed during infections.     

Study of TLR3, TLR4, and TLR9 in prostate carcinomas and their association with biochemical recurrence

Background  

Toll-like receptors (TLRs) have garnered an extraordinary amount of interest in cancer research due to their role in tumor progression. By activating the production of several biological factors, TLRs induce type I interferons and other cytokines, which drive an inflammatory response and activate the adaptive immune system. The aim of this study was to investigate the expression and clinical relevance of TLR3, 4, and 9 in prostate cancer.     

17beta-estradiol suppresses TLR3-induced cytokine and chemokine production in endometrial epithelial cells

Background  

The human endometrium is an important site for contact between the host and pathogens ascending the reproductive tract, and thus plays an important role in female reproductive tract immunity. Previous work in our laboratory has suggested that Toll-like receptors (TLRs) are involved in endometrial epithelial recognition of pathogens and that ligation of endometrial TLRs results in the production of cytokines and chemokines important for both immune and reproductive functions of the endometrium. We have also demonstrated cyclic regulation of TLR3 mRNA and protein expression in human endometrium, suggesting that steroid hormones might play a role in the expression and function of TLR3. In this study, the effects of 17beta-estradiol (E2) and progesterone (P) on TLR3 expression and function in endometrial cell lines were investigated.     

TLR9 Activation Dampens the Early Inflammatory Response to Paracoccidioides brasiliensis,Impacting Host Survival

Background

Paracoccidioides brasiliensis causes paracoccidioidomycosis, one of the most prevalent systemic mycosis in Latin America. Thus, understanding the characteristics of the protective immune response to P. brasiliensis is of interest, as it may reveal targets for disease control. The initiation of the immune response relies on the activation of pattern recognition receptors, among which are TLRs. Both TLR2 and TLR4 have been implicated in the recognition of P. brasiliensis and regulation of the immune response. However, the role of TLR9 during the infection by this fungus remains unclear.

Methodology/Principal findings

We used in vitro and in vivo models of infection by P. brasiliensis, comparing wild type and TLR9 deficient (^−/−) mice, to assess the contribution of TLR9 on cytokine induction, phagocytosis and outcome of infection. We show that TLR9 recognizes either the yeast form or DNA from P. brasiliensis by stimulating the expression/production of pro-inflammatory cytokines by bone marrow derived macrophages, also increasing their phagocytic ability. We further show that TLR9 plays a protective role early after intravenous infection with P. brasiliensis, as infected TLR9^−/− mice died at higher rate during the first 48 hours post infection than wild type mice. Moreover, TLR9^−/− mice presented tissue damage and increased expression of several cytokines, such as TNF-α and IL-6. The increased pattern of cytokine expression was also observed during intraperitoneal infection of TLR9^−/− mice, with enhanced recruitment of neutrophils. The phenotype of TLR9^−/− hosts observed during the early stages of P. brasiliensis infection was reverted upon a transient, 48 hours post-infection, neutrophil depletion.

Conclusions/Significance

Our results suggest that TLR9 activation plays an early protective role against P. brasiliensis, by avoiding a deregulated type of inflammatory response associated to neutrophils that may lead to tissue damage. Thus modulation of TLR9 may be of interest to potentiate the host response against this pathogen.     

Cigarette smoke increases TLR4 and TLR9 expression and induces cytokine production from CD8+ T cells in chronic obstructive pulmonary disease

Background

Cigarette smoke is a major risk factor for chronic obstructive pulmonary disease (COPD), an inflammatory lung disorder. COPD is characterized by an increase in CD8⁺ T cells within the central and peripheral airways. We hypothesized that the CD8⁺ T cells in COPD patients have increased Toll-like receptor (TLR) expression compared to control subjects due to the exposure of cigarette smoke in the airways.

Methods

Endobronchial biopsies and peripheral blood were obtained from COPD patients and control subjects. TLR4 and TLR9 expression was assessed by immunostaining of lung tissue and flow cytometry of the peripheral blood. CD8⁺ T cells isolated from peripheral blood were treated with or without cigarette smoke condensate (CSC) as well as TLR4 and TLR9 inhibitors. PCR and western blotting were used to determine TLR4 and TLR9 expression, while cytokine secretion from these cells was detected using electrochemiluminescence technology.

Results

No difference was observed in the overall expression of TLR4 and TLR9 in the lung tissue and peripheral blood of COPD patients compared to control subjects. However, COPD patients had increased TLR4 and TLR9 expression on lung CD8⁺ T cells. Exposure of CD8⁺ T cells to CSC resulted in an increase of TLR4 and TLR9 protein expression. CSC exposure also caused the activation of CD8⁺ T cells, resulting in the production of IL-1β, IL-6, IL-10, IL-12p70, TNFα and IFNγ. Furthermore, inhibition of TLR4 or TLR9 significantly attenuated the production of TNFα and IL-10.

Conclusions

Our results demonstrate increased expression of TLR4 and TLR9 on lung CD8⁺ T cells in COPD. CD8⁺ T cells exposed to CSC increased TLR4 and TLR9 levels and increased cytokine production. These results provide a new perspective on the role of CD8⁺ T cells in COPD.     

Association of TLR5 Gene Polymorphisms in Ulcerative Colitis Patients of North India and Their Role in Cytokine Homeostasis

Background and Aim

In health, TLR signaling protects the intestinal epithelial barrier and in disease, aberrant TLR signaling stimulates diverse inflammatory responses. Association of TLR polymorphisms is ethnicity dependent but how they impact the complex pathogenesis of IBD is not clearly defined. So we propose to study the status of polymorphisms in TLR family of genes and their effect on cytokines level in UC patients.

Methods

The genotypes of the six loci TLR1-R80T, TLR2-R753Q, TLR3-S258G, TLR5-R392X, TLR5-N592S and TLR6-S249P were determined in 350 controls and 328 UC patients by PCR-RFLP and sequencing. Cytokine levels were measured by ELISA in blood plasma samples. Data were analyzed statistically by SPSS software.

Results

TLR5 variants R392X and N592S showed significant association (p = 0.007, 0.021) with UC patients but TLR 1, 2, 3, 6 variants did not show any association. Unlike other studies carried out in different ethnic groups, TLR 6 (S249P) SNP was universally present in our population irrespective of disease. Genotype-phenotype correlation analysis revealed that the patients having combination of multiple SNPs both in TLR5 and TLR4 gene suffered from severe disease condition and diagnosed at an early age. The level of TNFα (p = 0.004), IL-6 (p = 0.0001) and IFNγ (p = 0.006) significantly increased in patients as compared to controls having wild genotypes for the studied SNPs. However, there was decreased level of TNFα (p = 0.014), IL-6 (p = 0.028) and IFNγ (p = 0.001) in patients carrying TLR5-R392X variant as compared to wild type patients. Patients carrying two simultaneous SNPs D299G in TLR4 gene and N592S in TLR5 gene showed significant decrease in the levels of TNFα (p = 0.011) and IFNγ (p = 0.016).

Conclusion

Polymorphisms in TLR 5 genes were significantly associated with the UC in North Indian population. The cytokine level was significantly modulated in patients with different genotypes of TLR4 and TLR5 SNPs.     

TLR4 and TLR2 expression in biopsy specimens from antral and corporal stomach zones in Helicobacter pylori infections

Background:

It is not yet known which types of Toll-like receptors (TLRs) are most effective in Helicobacter pylori (H. pylori) recognition. It is also not known which gastric zones have the most prominent roles in TLR-mediated bacterial recognition. The aim of this work was to analyze the expression of TLR2 and TLR4 in biopsy specimens from H. pylori-infected patients.

Methods:

Thirty-eight patients with gastrointestinal disorders were divided into four groups in this study. The groups were: (A) H. pylori infection and peptic ulcer (n=15), (B) peptic ulcer only (n=5), (C) H. pylori infection only (n=10) and (D) control, with neither H. pylori infection nor peptic ulcer (n=8). Biopsy specimens from sites of redness or atrophic mucosa from gastric antrum and body in patients with gastritis were collected. RNAs from the antrum and body specimens were isolated. TLR2 and TLR4 mRNA expression was assessed by RT-PCR and quantified as densitometric ratios of TLR2 and TLR4/β-actin mRNA.

Results:

In the antral zones of H. pylori-infected patients (Groups A and C) TLR2 and TLR4 expression was significantly greater than in uninfected patients (Groups B and D) regardless of peptic ulcers (p < 0.05). In the gastric body samples TLR2 expression was significantly greater in Group C (H. pylori infection only) than in Group B (peptic ulcer only) and TLR4 expression was significantly greater in group A (H. pylori infection and peptic ulcer) than in Group B (peptic ulcer only) (p < 0.05). No significant differences in expression of TLR4 and TLR2 were observed between samples from the antrum and body in same groups.

Conclusions:

We conclude that H. pylori infection leads to significant increase in TLR2 and TLR4 molecules expression in antral region related to the control group. Considering the stimulatory effect of H. pylori on TLRs expression in the gastric tissue, we assume that colonization of H. pylori infection might occurs more in the gastric antral region than in the gastric body.Key Words: Helicobacter pylori, Toll-like receptors, TLR4; TLR2, Peptic ulcer     

The Role of TLR2, TLR4 and CD14 Genetic Polymorphisms in Gastric Carcinogenesis: A Case-Control Study and Meta-Analysis

Background

In addition to Helicobacter pylori infection, host genetic factors contribute to gastric cancer (GC). Recognition of H. pylori is known to involve Toll-like receptors (TLR), which subsequently leads to activation of NF-κB. Thus, the overall aim of this study was to estimate for the first time the pooled effect size of polymorphisms in TLR2, TLR4 and CD14 on GC development through a meta-analysis.

Methods

A case-control study comprising 284 ethnic Chinese individuals (70 non-cardia GC cases and 214 functional dyspepsia controls) was conducted for the genotyping of TLR2 -196 to -174del, CD14 -260 C/T and TLR4 rs11536889 using PCR, RT-PCR and mass spectrometry. Case-control studies of TLR2, TLR4 and CD14 polymorphisms and GC were searched up to June 2012. Pooled odds ratios and 95% confidence intervals were obtained by means of the random effects model.

Results

In our ethnic Chinese case-control study, the TLR4 rs11536889 C allele increased the risk of GC (OR: 1.89, 95%CI: 1.23–2.92) while the CD14 -260 T allele was protective (OR: 0.62, 95%CI: 0.42–0.91). TLR2 -196 to -174 increased the risk of GC only in H. pylori-infected individuals (OR: 3.10, 95%CI: 1.27–7.60). In the meta-analysis, TLR4 Asp299Gly showed borderline results in the general analysis (pooled OR: 1.58, 95%CI: 0.98–2.60), nevertheless, stratified analysis by ethnicity showed that the mutant allele was a definitive risk factor for GC in Western populations (pooled OR: 1.87, 95%CI: 1.31–2.65). There was a potential association between the TLR2 -196 to -174 deletion allele and GC in Japanese (pooled OR: 1.18, 95%CI: 0.96–1.45). TLR4 Thr399Ile did not provide significant results.

Conclusions

TLR4 rs11536889 and CD14 -260 C/T are associated with non-cardia GC in Chinese. Based on our meta-analysis, the TLR signalling pathway is involved in gastric carcinogenesis, TLR4 Asp299Gly and TLR2 -196 to -174del showing associations with GC in an ethnic-specific manner.