Myeloid Differentiation Factor 88 (MyD88)-Deficiency Increases Risk of Diabetes in Mice

Background

Multiple lines of evidence suggest innate immune response pathways to be involved in the development of obesity-associated diabetes although the molecular mechanism underling the disease is unknown. Recent observations suggest that saturated fatty acids can act as a ligand for toll-like receptor (TLR) 4, which is thought to mediate obesity-associated insulin resistance. Myeloid differentiation factor 88 (MyD88) is an adapter protein for TLR/IL-1 receptor signaling, which is involved in the activation of inflammatory pathways. To evaluate molecular mechanisms linking obesity-associated diabetes down-stream of TLR4, we investigated physiological role of MyD88 in high-fat diet (HFD)-induced obesity.

Methodology/Principal Findings

In the present study, we found MyD88-deficient mice fed a HFD had increased circulating levels of insulin, leptin and cholesterol, as well as liver dysfunction (increased induction of ALT levels, increased activation of JNK and cleavage of PARP), which were linked to the onset of severe diabetes. On the other hand, TNF-α would not be involved in HFD-induced diabetes in MyD88-deficient mice, because TNF-α level was attenuated in MyD88-deficient mice fed with HFD.

Conclusions/Significance

The present finding of an unexpected role for MyD88 in preventing diabetes may provide a potential novel target/strategy for treating metabolic syndrome.     

Murine Borrelia arthritis is highly dependent on ASC and caspase-1, but independent of NLRP3

Introduction

The protein platform called the NOD-like-receptor -family member (NLRP)-3 inflammasome needs to be activated to process intracellular caspase-1. Active caspase-1 is able to cleave pro-Interleukin (IL)-1β, resulting in bioactive IL-1β. IL-1β is a potent proinflammatory cytokine, and thought to play a key role in the pathogenesis of Lyme arthritis, a common manifestation of Borrelia burgdorferi infection. The precise pathways through which B. burgdorferi recognition leads to inflammasome activation and processing of IL-1β in Lyme arthritis has not been elucidated. In the present study, we investigated the contribution of several pattern recognition receptors and inflammasome components in a novel murine model of Lyme arthritis.

Methods

Lyme arthritis was elicited by live B. burgdorferi, injected intra-articularly in knee joints of mice. To identify the relevant pathway components, the model was applied to wild-type, NLRP3-/-, ASC-/-, caspase-1-/-, NOD1-/-, NOD2-/-, and RICK-/- mice. As a control, TLR2-/-, Myd88-/- and IL-1R-/- mice were used. Peritoneal macrophages and bone marrow-derived macrophages were used for in vitro cytokine production and inflammasome activation studies. Joint inflammation was analyzed in synovial specimens and whole knee joints. Mann-Whitney U tests were used to detect statistical differences.

Results

We demonstrate that ASC/caspase-1-driven IL-1β is crucial for induction of B. burgdorferi-induced murine Lyme arthritis. In addition, we show that B. burgdorferi-induced murine Lyme arthritis is less dependent on NOD1/NOD2/RICK pathways while the TLR2-MyD88 pathway is crucial.

Conclusions

Murine Lyme arthritis is strongly dependent on IL-1 production, and B. burgdorferi induces inflammasome-mediated caspase-1 activation. Next to that, murine Lyme arthritis is ASC- and caspase-1-dependent, but NLRP3, NOD1, NOD2, and RICK independent. Also, caspase-1 activation by B. burgdorferi is dependent on TLR2 and MyD88. Based on present results indicating that IL-1 is one of the major mediators in Lyme arthritis, there is a rationale to propose that neutralizing IL-1 activity may also have beneficial effects in chronic Lyme arthritis.     

TLR2 and TLR4 Mediate Differential Responses to Limb Ischemia through MyD88-Dependent and Independent Pathways

Introduction

The danger signal HMGB1 is released from ischemic myocytes, and mediates angiogenesis in the setting of hindlimb ischemia. HMGB1 is a ligand for innate immune receptors TLR2 and TLR4. While both TLR2 and TLR4 signal through myeloid differentiation factor 88 (MyD88), TLR4 also uniquely signals through TIR-domain-containing adapter-inducing interferon-β (TRIF). We hypothesize that TLR2 and TLR4 mediate ischemic myocyte regeneration and angiogenesis in a manner that is dependent on MyD88 signaling.

Methods

Mice deficient in TLR2, TLR4, MyD88 and TRIF underwent femoral artery ligation in the right hindlimb. Laser Doppler perfusion imaging was used to assess the initial degree of ischemia and the extent of perfusion recovery. Muscle regeneration, necrosis and fat replacement at 2 weeks post-ligation were assessed histologically and vascular density was quantified by immunostaining. In vitro, endothelial tube formation was evaluated in matrigel in the setting of TLR2 and TLR4 antagonism.

Results

While control and TLR4 KO mice demonstrated prominent muscle regeneration, both TLR2 KO and TRIF KO mice exhibited marked necrosis with significant inflammatory cell infiltrate. However, MyD88 KO mice had a minimal response to the ischemic insult with little evidence of injury. This observation could not be explained by differences in perfusion recovery which was similar at two weeks in all the strains of mice. TLR2 KO mice demonstrated abnormal vessel morphology compared to other strains and impaired tube formation in vitro.

Discussion

TLR2 and TRIF signaling are necessary for muscle regeneration after ischemia while MyD88 may instead mediate muscle injury. The absence of TLR4 did not affect muscle responses to ischemia. TLR4 may mediate inflammatory responses through MyD88 that are exaggerated in the absence of TLR2. Additionally, the actions of TLR4 through TRIF may promote regenerative responses that are required for recovery from muscle ischemia.     

Pseudomonas aeruginosa LPS or Flagellin Are Sufficient to Activate TLR-Dependent Signaling in Murine Alveolar Macrophages and Airway Epithelial Cells

Background

The human lung is exposed to a large number of airborne pathogens as a result of the daily inhalation of 10,000 liters of air. Innate immunity is thus essential to defend the lungs against these pathogens. This defense is mediated in part through the recognition of specific microbial ligands by Toll-like receptors (TLR) of which there are at least 10 in humans. Pseudomonas aeruginosa is the main pathogen that infects the lungs of cystic fibrosis patients. Based on whole animal experiments, using TLR knockout mice, the control of this bacterium is believed to occur by the recognition of LPS and flagellin by TLRs 2,4 and 5, respectively.

Methodology/Principal Findings

In the present study, we investigated in vitro the role of these same TLR and ligands, in alveolar macrophage (AM) and epithelial cell (EC) activation. Cellular responses to P. aeruginosa was evaluated by measuring KC, TNF-α, IL-6 and G-CSF secretion, four different markers of the innate immune response. AM and EC from WT and TLR2, 4, 5 and MyD88 knockout mice for were stimulated with the wild-type P. aeruginosa or with a mutant devoid of flagellin production.

Conclusions/Significance

The results clearly demonstrate that only two ligand/receptor pairs are necessary for the induction of KC, TNF-α, and IL-6 synthesis by P. aeruginosa-activated cells, i.e. TLR2,4/LPS and TLR5/flagellin. Either ligand/receptor pair is sufficient to sense the bacterium and to trigger cell activation, and when both are missing lung EC and AM are unable to produce such a response as were cells from MyD88^−/− mice.     

Microglia Induce Neurotoxic IL-17+ γδ T Cells Dependent on TLR2, TLR4, and TLR9 Activation

Background

Interleukin-17 (IL-17) acts as a key regulator in central nervous system (CNS) inflammation. γδ T cells are an important innate source of IL-17. Both IL-17+ γδ T cells and microglia, the major resident immune cells of the brain, are involved in various CNS disorders such as multiple sclerosis and stroke. Also, activation of Toll-like receptor (TLR) signaling pathways contributes to CNS damage. However, the mechanisms underlying the regulation and interaction of these cellular and molecular components remain unclear.

Objective

In this study, we investigated the crosstalk between γδ T cells and microglia activated by TLRs in the context of neuronal damage. To this end, co-cultures of IL-17+ γδ T cells, neurons, and microglia were analyzed by immunocytochemistry, flow cytometry, ELISA and multiplex immunoassays.

Results

We report here that IL-17+ γδ T cells but not naïve γδ T cells induce a dose- and time-dependent decrease of neuronal viability in vitro. While direct stimulation of γδ T cells with various TLR ligands did not result in up-regulation of CD69, CD25, or in IL-17 secretion, supernatants of microglia stimulated by ligands specific for TLR2, TLR4, TLR7, or TLR9 induced activation of γδ T cells through IL-1β and IL-23, as indicated by up-regulation of CD69 and CD25 and by secretion of vast amounts of IL-17. This effect was dependent on the TLR adaptor myeloid differentiation primary response gene 88 (MyD88) expressed by both γδ T cells and microglia, but did not require the expression of TLRs by γδ T cells. Similarly to cytokine-primed IL-17+ γδ T cells, IL-17+ γδ T cells induced by supernatants derived from TLR-activated microglia also caused neurotoxicity in vitro. While these neurotoxic effects required stimulation of TLR2, TLR4, or TLR9 in microglia, neuronal injury mediated by bone marrow-derived macrophages did not require TLR signaling. Neurotoxicity mediated by IL-17+ γδ T cells required a direct cell-cell contact between T cells and neurons.

Conclusion

Taken together, these results point to a crucial role for microglia activated through TLRs in polarization of γδ T cells towards neurotoxic IL-17+ γδ T cells.     

Prognostic Value of Myeloid Differentiation Primary Response 88 and Toll-Like Receptor 4 in Breast Cancer Patients

Purpose

Breast cancer remains a major cause of death in women worldwide, and tumor metastasis is the leading cause of death in breast cancer patients after conventional treatment. Chronic inflammation is often related to the occurrence and growth of various malignancies. This study evaluated the prognosis of breast cancer patients based on contributors to the innate immune response: myeloid differentiation primary response 88 (MyD88) and Toll-like receptor 4 (TLR4).

Methods

We analyzed data from 205 breast invasive ductal carcinoma (IDC) patients who were treated at the Department of Breast Surgery, Key Laboratory of Breast Cancer in Shanghai, Fudan University Shanghai Cancer Center, from 2002 to 2006. Overall survival (OS) and disease-free survival (DFS) were compared.

Results

In total, 152 patients (74.15%) were disease-free without relapse or metastasis, whereas 53 (25.85%) patients developed recurrence or metastasis. A significant positive correlation was observed between MyD88 and TLR4 expression (p<0.001). Patients with high expression were more likely to experience death and recurrence/metastasis events (p<0.05). Patients with low MyD88 or TLR4 expression levels had better DFS and OS than patients with high expression levels (log-rank test: p<0.001). Patients with low MyD88 and TLR4 expression levels had better DFS and OS than patients with high expression levels of either (log-rank test: p<0.001). In a multivariate analysis, high MyD88 expression was an independent predictive factor for decreased DFS (adjusted HR, 3.324; 95% CI, 1.663–6.641; p = 0.001) and OS (adjusted HR, 4.500; 95% CI, 1.546–13.098; p = 0.006).

Conclusions

TLR4-MyD88 signaling pathway activation or MyD88 activation alone may be a risk factor for poor prognosis in breast cancer. Therefore, TLR4-MyD88 signaling pathway activation in tumor biology provides a novel potential target for breast cancer therapy.     

TLR–Dependent Control of Francisella tularensis Infection and Host Inflammatory Responses

Background

Francisella tularensis is the causative agent of tularemia and is classified as a Category A select agent. Recent studies have implicated TLR2 as a critical element in the host protective response to F. tularensis infection, but questions remain about whether TLR2 signaling dominates the response in all circumstances and with all species of Francisella and whether F. tularensis PAMPs are predominantly recognized by TLR2/TLR1 or TLR2/TLR6. To address these questions, we have explored the role of Toll-like receptors (TLRs) in the host response to infections with F. tularensis Live Vaccine Strain (LVS) and F. tularensis subspecies (subsp.) novicida in vivo.

Methodology/Principal Findings

C57BL/6 (B6) control mice and TLR– or MyD88-deficient mice were infected intranasally (i.n.) or intradermally (i.d.) with F. tularensis LVS or with F. tularensis subsp. novicida. B6 mice survived >21 days following infection with LVS by both routes and survival of TLR1^−/−, TLR4^−/−, and TLR6^−/− mice infected i.n. with LVS was equivalent to controls. Survival of TLR2^−/− and MyD88^−/− mice, however, was significantly reduced compared to B6 mice, regardless of the route of infection or the subspecies of F. tularensis. TLR2^−/− and MyD88^−/− mice also showed increased bacterial burdens in lungs, liver, and spleen compared to controls following i.n. infection. Primary macrophages from MyD88^−/− and TLR2^−/− mice were significantly impaired in the ability to secrete TNF and other pro-inflammatory cytokines upon ex vivo infection with LVS. TNF expression was also impaired in vivo as demonstrated by analysis of bronchoalveolar lavage fluid and by in situ immunofluorescent staining.

Conclusions/Significance

We conclude from these studies that TLR2 and MyD88, but not TLR4, play critical roles in the innate immune response to F. tularensis infection regardless of the route of infection or the subspecies. Moreover, signaling through TLR2 does not depend exclusively on TLR1 or TLR6 during F. tularensis LVS infection.     

α-Melanocyte-Stimulating Hormone Protects Retinal Vascular Endothelial Cells from Oxidative Stress and Apoptosis in a Rat Model of Diabetes

Aims

Oxidative stress and apoptosis are among the earliest lesions of diabetic retinopathy. This study sought to examine the anti-oxidative and anti-apoptotic effects of α-melanocyte-stimulating hormone (α-MSH) in early diabetic retinas and to explore the underlying mechanisms in retinal vascular endothelial cells.

Methods

Sprague-Dawley rats were injected intravenously with streptozocin to induce diabetes. The diabetic rats were injected intravitreally with α-MSH or saline. At week 5 after diabetes, the retinas were analyzed for reactive oxygen species (ROS) and gene expression. One week later, the retinas were processed for terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and transmission electron microscopy. Retinal vascular endothelial cells were stimulated by high glucose (HG) with or without α-MSH. The expression of Forkhead box O genes (Foxos) was examined through real-time PCR. The Foxo4 gene was overexpressed in endothelial cells by transient transfection prior to α-MSH or HG treatment, and oxidative stress and apoptosis were analyzed through CM-H2DCFDA and annexin-V assays, respectively.

Results

In diabetic retinas, the levels of H₂O₂ and ROS and the total anti-oxidant capacity were normalized, the apoptotic cell number was reduced, and the ultrastructural injuries were ameliorated by α-MSH. Treatment with α-MSH also corrected the aberrant changes in eNOS, iNOS, ICAM-1, and TNF-α expression levels in diabetic retinas. Furthermore, α-MSH inhibited Foxo4 up-regulation in diabetic retinas and in endothelial cells exposed to HG, whereas Foxo4 overexpression abrogated the anti-oxidative and anti-apoptotic effects of α-MSH in HG-stimulated retinal vascular endothelial cells.

Conclusions

α-MSH normalized oxidative stress, reduced apoptosis and ultrastructural injuries, and corrected gene expression levels in early diabetic retinas. The protective effects of α-MSH in retinal vascular endothelial cells may be mediated through the inhibition of Foxo4 up-regulation induced by HG. This study suggests an α-MSH-mediated potential intervention approach to early diabetic retinopathy and a novel regulatory mechanism involving Foxo4.     

Immune Modulation by Different Types of β2→1-Fructans Is Toll-Like Receptor Dependent

Introduction

β2→1-fructans are dietary fibers. Main objectives of this study were 1) to demonstrate direct signalling of β2→1-fructans on immune cells, 2) to study whether this is mediated by the pattern recognition receptors Toll-like receptors (TLRs) and nucleotide-binding oligomerisation domain-containing proteins (NODs), and 3) to relate the observed effects to the chain length differences in β2→1-fructans.

Methods

Four different β2→1-fructan formulations were characterised for their chain length profile. Human peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with β2→1-fructans, and production of IL-1Ra, IL-1β, IL-6, IL-10, IL-12p70, and TNF-α was analysed. Reporter cells for TLRs and NODs were incubated with β2→1-fructans and analysed for NF-κB/AP-1 activation.

Results

Cytokine production in human PBMCs was dose- and chain length-dependent. Strikingly, short chain enriched β2→1-fructans induced a regulatory cytokine balance compared to long chain enriched β2→1-fructans as measured by IL-10/IL-12 ratios. Activation of reporter cells showed that signalling was highly dependent on TLRs and their adapter, myeloid differentiation primary response protein 88 (MyD88). In human embryonic kidney reporter cells, TLR2 was prominently activated, while TLR4, 5, 7, 8, and NOD2 were mildly activated.

Conclusions

β2→1-fructans possess direct signalling capacity on human immune cells. By activating primarily TLR2, and to a lesser extent TLR4, 5, 7, 8, and NOD2, β2→1-fructan stimulation results in NF-κB/AP-1 activation. Chain length of β2→1-fructans is important for the induced activation pattern and IL-10/IL-12 ratios.     

Early neurodegeneration progresses independently of microglial activation by heparan sulfate in the brain of mucopolysaccharidosis IIIB mice

Background

In mucopolysaccharidosis type IIIB, a lysosomal storage disease causing early onset mental retardation in children, the production of abnormal oligosaccharidic fragments of heparan sulfate is associated with severe neuropathology and chronic brain inflammation. We addressed causative links between the biochemical, pathological and inflammatory disorders in a mouse model of this disease.

Methodology/Principal Findings

In cell culture, heparan sulfate oligosaccharides activated microglial cells by signaling through the Toll-like receptor 4 and the adaptor protein MyD88. CD11b positive microglial cells and three-fold increased expression of mRNAs coding for the chemokine MIP1α were observed at 10 days in the brain cortex of MPSIIIB mice, but not in MPSIIIB mice deleted for the expression of Toll-like receptor 4 or the adaptor protein MyD88, indicating early priming of microglial cells by heparan sulfate oligosaccharides in the MPSIIIB mouse brain. Whereas the onset of brain inflammation was delayed for several months in doubly mutant versus MPSIIIB mice, the onset of disease markers expression was unchanged, indicating similar progression of the neurodegenerative process in the absence of microglial cell priming by heparan sulfate oligosaccharides. In contrast to younger mice, inflammation in aged MPSIIIB mice was not affected by TLR4/MyD88 deficiency.

Conclusions/Significance

These results indicate priming of microglia by HS oligosaccharides through the TLR4/MyD88 pathway. Although intrinsic to the disease, this phenomenon is not a major determinant of the neurodegenerative process. Inflammation may still contribute to neurodegeneration in late stages of the disease, albeit independent of TLR4/MyD88. The results support the view that neurodegeneration is primarily cell autonomous in this pediatric disease.     

A2E Induces IL-1? Production in Retinal Pigment Epithelial Cells via the NLRP3 Inflammasome

Aims

With ageing extracellular material is deposited in Bruch’s membrane, as drusen. Lipofuscin is deposited in retinal pigment epithelial cells. Both of these changes are associated with age related macular degeneration, a disease now believed to involve chronic inflammation at the retinal-choroidal interface. We hypothesise that these molecules may act as danger signals, causing the production of inflammatory chemokines and cytokines by the retinal pigment epithelium, via activation of pattern recognition receptors.

Methods

ARPE-19 cells were stimulated in vitro with the following reported components of drusen: amyloid-ß (1-42), Carboxyethylpyrrole (CEP) modified proteins (CEP-HSA), Nε-(Carboxymethyl)lysine (CML) modified proteins and aggregated vitronectin. The cells were also stimulated with the major fluorophore of lipofuscin: N-retinylidene-N-retinylethanolamine (A2E). Inflammatory chemokine and cytokine production was assessed using Multiplex assays and ELISA. The mechanistic evaluation of the NLRP3 inflammasome pathway was assessed in a stepwise fashion.

Results

Of all the molecules tested only A2E induced inflammatory chemokine and cytokine production. 25 µM A2E induced the production of significantly increased levels of the chemokines IL-8, MCP-1, MCG and MIP-1α, the cytokines IL-1ß, IL-2, IL-6, and TNF-α, and the protein VEGF-A. The release of IL-1ß was studied further, and was determined to be due to NLRP3 inflammasome activation. The pathway of activation involved endocytosis of A2E, and the three inflammasome components NLRP3, ASC and activated caspase-1. Immunohistochemical staining of ABCA4 knockout mice, which show progressive accumulation of A2E levels with age, showed increased amounts of IL-1ß proximal to the retinal pigment epithelium.

Conclusions

A2E has the ability to stimulate inflammatory chemokine and cytokine production by RPE cells. The pattern recognition receptor NLRP3 is involved in this process. This provides further evidence for the link between A2E, inflammation, and the pathogenesis of AMD. It also supports the recent discovery of NLRP3 inflammasome activation in AMD.     

Systemic Toll-Like Receptor Stimulation Suppresses Experimental Allergic Asthma and Autoimmune Diabetes in NOD Mice

Background

Infections may be associated with exacerbation of allergic and autoimmune diseases. Paradoxically, epidemiological and experimental data have shown that some microorganisms can also prevent these pathologies. This observation is at the origin of the hygiene hypothesis according to which the decline of infections in western countries is at the origin of the increased incidence of both Th1-mediated autoimmune diseases and Th2-mediated allergic diseases over the last decades. We have tested whether Toll-like receptor (TLR) stimulation can recapitulate the protective effect of infectious agents on allergy and autoimmunity.

Methods and Findings

Here, we performed a systematic study of the disease-modifying effects of a set of natural or synthetic TLR agonists using two experimental models, ovalbumin (OVA)-induced asthma and spontaneous autoimmune diabetes, presenting the same genetic background of the non obese diabetic mouse (NOD) that is highly susceptible to both pathologies. In the same models, we also investigated the effect of probiotics. Additionally, we examined the effect of the genetic invalidation of MyD88 on the development of allergic asthma and spontaneous diabetes. We demonstrate that multiple TLR agonists prevent from both allergy and autoimmunity when administered parenterally. Probiotics which stimulate TLRs also protect from these two diseases. The physiological relevance of these findings is further suggested by the major acceleration of OVA-induced asthma in MyD88 invalidated mice. Our results strongly indicate that the TLR-mediated effects involve immunoregulatory cytokines such as interleukin (IL)-10 and transforming growth factor (TGF)-β and different subsets of regulatory T cells, notably CD4⁺CD25⁺FoxP3⁺ T cells for TLR4 agonists and NKT cells for TLR3 agonists.

Conclusions/Significance

These observations demonstrate that systemic administration of TLR ligands can suppress both allergic and autoimmune responses. They provide a plausible explanation for the hygiene hypothesis. They also open new therapeutic perspectives for the prevention of these pathologies.     

Respiratory epithelial cells require Toll-like receptor 4 for induction of Human β-defensin 2 by Lipopolysaccharide

Background

The respiratory epithelium is a major portal of entry for pathogens and employs innate defense mechanisms to prevent colonization and infection. Induced expression of human β-defensin 2 (HBD2) represents a direct response by the epithelium to potential infection. Here we provide evidence for the critical role of Toll-like receptor 4 (TLR4) in lipopolysaccharide (LPS)-induced HBD2 expression by human A549 epithelial cells.

Methods

Using RTPCR, fluorescence microscopy, ELISA and luciferase reporter gene assays we quantified interleukin-8, TLR4 and HBD2 expression in unstimulated or agonist-treated A549 and/or HEK293 cells. We also assessed the effect of over expressing wild type and/or mutant TLR4, MyD88 and/or Mal transgenes on LPS-induced HBD2 expression in these cells.

Results

We demonstrate that A549 cells express TLR4 on their surface and respond directly to Pseudomonas LPS with increased HBD2 gene and protein expression. These effects are blocked by a TLR4 neutralizing antibody or functionally inactive TLR4, MyD88 and/or Mal transgenes. We further implicate TLR4 in LPS-induced HBD2 production by demonstrating HBD2 expression in LPS non-responsive HEK293 cells transfected with a TLR4 expression plasmid.

Conclusion

This data defines an additional role for TLR4 in the host defense in the lung.     

Cigarette smoke-induced accumulation of lung dendritic cells is interleukin-1α-dependent in mice

Background

Evidence suggests that dendritic cells accumulate in the lungs of COPD patients and correlate with disease severity. We investigated the importance of IL-1R1 and its ligands IL-1α and β to dendritic cell accumulation and maturation in response to cigarette smoke exposure.

Methods

Mice were exposed to cigarette smoke using a whole body smoke exposure system. IL-1R1-, TLR4-, and IL-1α-deficient mice, as well as anti-IL-1α and anti-IL-1β blocking antibodies were used to study the importance of IL-1R1 and TLR4 to dendritic cell accumulation and activation.

Results

Acute and chronic cigarette smoke exposure led to increased frequency of lung dendritic cells. Accumulation and activation of dendritic cells was IL-1R1/IL-1α dependent, but TLR4- and IL-1β-independent. Corroborating the cellular data, expression of CCL20, a potent dendritic cells chemoattractant, was IL-1R1/IL-1α-dependent. Studies using IL-1R1 bone marrow-chimeric mice revealed the importance of IL-1R1 signaling on lung structural cells for CCL20 expression. Consistent with the importance of dendritic cells in T cell activation, we observed decreased CD4⁺ and CD8⁺ T cell activation in cigarette smoke-exposed IL-1R1-deficient mice.

Conclusion

Our findings convey the importance of IL-1R1/IL-1α to the recruitment and activation of dendritic cells in response to cigarette smoke exposure.     

Differential expression of Toll-like receptors on human alveolar macrophages and autologous peripheral monocytes

Background

Toll-like receptors (TLRs) are critical components in the regulation of pulmonary immune responses and the recognition of respiratory pathogens such as Mycobacterium Tuberculosis (M.tb). Through examination of human alveolar macrophages this study attempts to better define the expression profiles of TLR2, TLR4 and TLR9 in the human lung compartment which are as yet still poorly defined.

Methods

Sixteen healthy subjects underwent venipuncture, and eleven subjects underwent additional bronchoalveolar lavage to obtain peripheral blood mononuclear and bronchoalveolar cells, respectively. Surface and intracellular expression of TLRs was assessed by fluorescence-activated cell sorting and qRT-PCR. Cells were stimulated with TLR-specific ligands and cytokine production assessed by ELISA and cytokine bead array.

Results

Surface expression of TLR2 was significantly lower on alveolar macrophages than on blood monocytes (1.2 ± 0.4% vs. 57 ± 11.1%, relative mean fluorescence intensity [rMFI]: 0.9 ± 0.1 vs. 3.2 ± 0.1, p < 0.05). The proportion of TLR4 and TLR9-expressing cells and the rMFIs of TLR4 were comparable between alveolar macrophages and monocytes. The surface expression of TLR9 however, was higher on alveolar macrophages than on monocytes (rMFI, 218.4 ± 187.3 vs. 4.4 ± 1.4, p < 0.05) while the intracellular expression of the receptor and the proportion of TLR9 positive cells were similar in both cell types. TLR2, TLR4 and TLR9 mRNA expression was lower in bronchoalveolar cells than in monocytes.Pam3Cys, LPS, and M.tb DNA upregulated TLR2, TLR4 and TLR9 mRNA in both, bronchoalveolar cells and monocytes. Corresponding with the reduced surface and mRNA expression of TLR2, Pam3Cys induced lower production of TNF-α, IL-1β and IL-6 in bronchoalveolar cells than in monocytes. Despite comparable expression of TLR4 on both cell types, LPS induced higher levels of IL-10 in monocytes than in alveolar macrophages. M.tb DNA, the ligand for TLR9, induced similar levels of cytokines in both cell types.

Conclusion

The TLR expression profile of autologous human alveolar macrophages and monocytes is not identical, therefore perhaps contributing to compartmentalized immune responses in the lungs and systemically. These dissimilarities may have important implications for the design and efficacy evaluation of vaccines with TLR-stimulating adjuvants that target the respiratory tract.     

Changes in the Expression of the Toll-Like Receptor System in the Aging Rat Kidneys

Background

The mechanisms of kidney aging are not yet clear. Studies have shown that immunological inflammation is related to kidney aging. Toll-like receptors (TLRs) are one of the receptor types of the body''s innate immune system. The function of the TLR system and the mechanisms by which it functions in renal aging remain unclear. In the present study, we, for the first time, systematically investigated the role of the TLR system and the inflammation responses activated by TLRs during kidney aging.

Methods

We used western blot and immunohistochemistry to systematically analyze the changes in the expression and activation of the endogenous TLR ligands HSP70 and HMGB1, the TLRs (TLR1–TLR11), their downstream signaling pathway molecules MyD88 and Phospho-IRF-3, and the NF-κB signaling pathway molecules Phospho-IKKβ, Phospho-IκBα (NF-κB inhibition factor α), NF-κBp65, and Phospho-NF-κBp65 (activated NF-κB p65) in the kidneys of 3 months old (youth group), 12 months old (middle age group), and 24 months old (elderly group) rats. We used RT-qPCR to detect the mRNA expression changes of the proinflammatory cytokines CCL3, CCL4, CCL5, CD80, TNF-α, and IL-12b in the rat renal tissues of the various age groups.

Results

We found that during kidney aging, the HSP70 and HMGB1 expression levels were significantly increased, and the expression levels of TLR1, 2, 3, 4, 5, and 11 and their downstream signaling pathway molecules MyD88 and Phospho-IRF-3 were markedly elevated. Further studies have shown that in the aging kidneys, the expression levels of the NF-κB signaling pathway molecules Phospho-IKKβ, Phospho-IκBα, NF-κBp65, and Phospho-NF-κBp65 were obviously increased, and those of the proinflammatory cytokines CCL3, CCL4, CCL5, CD80, TNF-α, and IL-12b were significantly upregulated.

Conclusions

These results showed that the TLR system might play an important role during the kidney aging process maybe by activating the NF-κB signaling pathway and promoting the high expression of inflammation factors.     

Bone Marrow and Nonbone Marrow Toll Like Receptor 4 Regulate Acute Hepatic Injury Induced by Endotoxemia

Background

Toll-like receptors (TLRs) are expressed in immune cells and hepatocytes. We examined whether hepatic Toll-like receptor 4 (TLR4) is involved in the acute hepatic injury caused by the administration of lipopolysaccharide (LPS) (septic shock model).

Methods

Wild type (WT), TLR4-deficient and chimera mice underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the liver or in the immune-hematopoietic system. Mice were injected with LPS and sacrificed 4 hours later.

Results

Compared to TLR4 deficient mice, WT mice challenged with LPS displayed increased serum liver enzymes and hepatic cellular inflammatory infiltrate together with increased serum and hepatic levels of interleukin 1β (IL-1β), tumor necrosis factor α (TNFα) ,Up-regulation of hepatic mRNA encoding TLR4, IκB and c-jun expressions. TLR4 mutant mice transplanted with WT bone marrow were more protected than WT chimeric mice bearing TLR4 mutant hemopoietic cells from LPS, as seen by IL-1β and TNFα levels. We then used hepatocytes (Huh7) and macrophages from monocytic cell lines to detect TLR mRNA expression. Macrophages expressed a significantly higher level of TLR4 mRNA and TLR2 (more than 3000- and 8000-fold respectively) compared with the hepatocyte cell line. LPS administration induced TLR4 activation in a hepatocyte cell line in a dose dependent manner while TLR2 mRNA hardly changed.

Conclusions

These results suggest that TLR4 activation of hepatocytes participate in the immediate response to LPS induced hepatic injury. However, in this response, the contribution of TLR4 on bone marrow derived cells is more significant than those of the hepatocytes. The absence of the TLR4 gene plays a pivotal role in reducing hepatic LPS induced injury.     

Normalization of the levels of inflammatory molecules in Mycobacterium smegmatis-infected U937 cells by fibrate pretreatment

Background

Tuberculosis (TB) is a respiratory tract disease caused by Mycobacterium tuberculosis infection. M. tuberculosis exploits immune privilege to grow and divide in pleural macrophages. Fibrates are associated with the immune response and control lipid metabolism through glycolysis with β-oxidation of fatty acids.

Results

In this study, we investigated the effect of fibrate pretreatment on the immune response during M. smegmatis infection in U937 cells, a human leukemic monocyte lymphoma cell line. The protein expression of tumor necrosis factor α (TNF-α), an inflammatory marker, and myeloid differentiation primary response gene 88 (MyD88), a toll like receptor adaptor molecule, in the infected group increased at 1 and 6 h after M. smegmatis infection of U937 cells. Acetyl coenzyme A acetyl transferase-1 (ACAT-1), peroxisome proliferator-activated receptor-α (PPAR-α), TNF-α, and MyD88 decreased in U937 cells treated with fibrates at 12 and 24 h after treatment. More than a 24 h pretreatment with fibrate resulted in similar expression levels of ACAT-1 and PPAR-α between infected vehicle control and infected groups which were pretreated with fibrate for 24 h. However, upon exposure to M. smegmatis, the cellular expression of the TNF-α and MyD88 in the infected groups pretreated with fibrate for 24 h decreased significantly compared to that in the infected vehicle group.

Conclusion

These results suggest that fibrate pretreatment normalized the levels of inflammatory molecules in Mycobacterium smegmatis-infected U937 cells. Further studies are needed to confirm the findings on pathophysiology and immune defense mechanism of U937 by fibrates during M. tuberculosis infection.