Cloning and Characterization of Two Toll/Interleukin-1 Receptor–Like Genes TIL3 and TIL4: Evidence for a Multi-Gene Receptor Family in Humans

Gastric immune homeostasis imbalance: An important factor in the development of gastric mucosal diseases

The gastric mucosal immune system is a unique immune organ independent of systemic immunity that not only maintains nutrient absorption but also plays a role in resisting the external environment. Gastric mucosal immune disorder leads to a series of gastric mucosal diseases, including autoimmune gastritis (AIG)-related diseases, Helicobacter pylori (H. pylori)-induced diseases, and various types of gastric cancer (GC). Therefore, understanding the role of gastric mucosal immune homeostasis in gastric mucosal protection and the relationship between mucosal immunity and gastric mucosal diseases is very important. This review focuses on the protective effect of gastric mucosal immune homeostasis on the gastric mucosa, as well as multiple gastric mucosal diseases caused by gastric immune disorders. We hope to offer new prospects for the prevention and treatment of gastric mucosal diseases.

A soluble TLR5 is involved in PBLs activation and antibacterial immunity via TLR5M-MyD88-signaling pathway in tongue sole Cynoglossus semilaevis

In higher vertebrates, there is only a membranal TLR5 (TLR5M), which is crucial for host defense against microbes via MyD88 signaling pathway. In teleost, both TLR5M and soluble TLR5 (TLR5S) are identified, whereas the antibacterial mechanism of TLR5S is largely unknown. In this study, we studied the immune antibacterial mechanism of Cynoglossus semilaevis TLR5S homologue (named CsTLR5S). CsTLR5S, a 71.1 kDa protein, consists of 649 amino acid residues and shares 41.7 %-57.8 % overall sequence identities with teleost TLR5S homologues. CsTLR5S contains a single extracellular domain (ECD) composed of 12 leucine-rich repeats. CsTLR5S expression was constitutively identified and upregulated by bacterial infection in tissues. In vitro recombinant CsTLR5S (rCsTLR5S) could interact with bacteria and tongue sole rTLR5M (rCsTLR5M). Furthermore, rCsTLR5S could bind to the membranal CsTLR5M of peripheral blood leukocytes (PBLs), which led to enhancing the activity and the antibacterial role of PBLs via Myd88-NF-κB pathway. In vivo rCsTLR5S could activate the Myd88-NF-κB pathway, facilitate the release of proinflammatory cytokines, and enhance the host antibacterial response against Vibrio harveyi. Moreover, the knockdown of CsTLR5M or the Myd88 inhibitor could significantly suppress the antibacterial effect of rCsTLR5S. Collectively, our findings added important insights into the TLR5S immune antibacterial property in a TLR5M-MyD88-dependent manner.

The Challenges of Eradicating Pediatric Helicobacter pylori Infection in the Era of Probiotics

Helicobacter pylori (H. pylori), the most common infection of childhood, results in life-threatening complications during adulthood if left untreated. Most of these complications are related to H. pylori-induced chronic inflammation. The dysbiosis caused by H. pylori is not limited to the gastric microenvironment, but it affects the entire gastrointestinal tract. Eradication of H. pylori has recently become a real challenge for clinicians due to both the persistent increase in antibiotic resistance worldwide and the wide spectrum of side effects associated with the eradication regimens resulting; therefore, there is an urgent need for more effective and less noxious treatment options. Thus, probiotics might be a promising choice in both adults and children with H. pylori infection since their role in improving the eradication rate of this infection has been proved in multiple studies. The positive effects of probiotics might be explained by their abilities to produce antimicrobial compounds and antioxidants, alter local gastric pH, and subsequently decrease H. pylori colonization and adherence to gastric epithelial cells. Nevertheless, if used alone probiotics do not considerably increase the eradication rate.

Modeling Innate Antiviral Immunity in Physiological Context

An effective innate antiviral response is critical for the mitigation of severe disease and host survival following infection. In vivo, the innate antiviral response is triggered by cells that detect the invading pathogen and then communicate through autocrine and paracrine signaling to stimulate the expression of genes that inhibit viral replication, curtail cell proliferation, or modulate the immune response. In other words, the innate antiviral response is complex and dynamic. Notably, in the laboratory, culturing viruses and assaying viral life cycles frequently utilizes cells that are derived from tissues other than those that support viral replication during natural infection, while the study of viral pathogenesis often employs animal models. In recapitulating the human antiviral response, it is important to consider that variation in the expression and function of innate immune sensors and antiviral effectors exists across species, cell types, and cell differentiation states, as well as when cells are placed in different contexts. Thus, to gain novel insight into the dynamics of the host response and how specific sensors and effectors impact infection kinetics by a particular virus, the model system must be selected carefully. In this review, we briefly introduce key signaling pathways involved in the innate antiviral response and highlight how these differ between systems. We then review the application of tissue-engineered or 3D models for studying the antiviral response, and suggest how these in vitro culture systems could be further utilized to assay physiologically-relevant host responses and reveal novel insight into virus-host interactions.

Laminitis Updates: Sepsis/Systemic Inflammatory Response Syndrome-Associated Laminitis

Sepsis or systemic inflammatory response syndrome (SIRS) -associated laminitis is a sequela to primary inflammatory conditions (eg, colitis, ischemic intestinal injury, pneumonia, metritis) and results from a dysregulated systemic inflammatory response that ultimately affects the digital lamellae. Local chemokine production, leukocyte migration, and proinflammatory mediator production occur within the lamellae that can lead to catastrophic lamellar failure. Controlling the primary disease, providing supportive care and anti-inflammatory therapy, applying digital cryotherapy, and providing mechanical support are cornerstones to the prevention of sepsis/SIRS-associated laminitis. Novel therapies targeting specific signaling pathways may provide additional therapeutic options in the future.

Gastric Microenvironment-A Partnership between Innate Immunity and Gastric Microbiota Tricks Helicobacter pylori

Helicobacter pylori (H. pylori) carcinogenicity depends on three major factors: bacterial virulence constituents, environmental factors and host's genetic susceptibility. The relationship between microenvironmental factors and H. pylori virulence factors are incontestable. H. pylori infection has a major impact on both gastric and colonic microbiota. The presence of non-H. pylori bacteria within the gastric ecosystem is particularly important since they might persistently act as an antigenic stimulus or establish a partnership with H. pylori in order to augment the subsequent inflammatory responses. The gastric ecosystem, i.e., microbiota composition in children with H. pylori infection is dominated by Streptoccocus, Neisseria, Rothia and Staphylococcus. The impairment of this ecosystem enhances growth and invasion of different pathogenic bacteria, further impairing the balance between the immune system and mucosal barrier. Moreover, altered microbiota due to H. pylori infection is involved in increasing the gastric T regulatory cells response in children. Since gastric homeostasis is defined by the partnership between commensal bacteria and host's immune system, this review is focused on how pathogen recognition through toll-like receptors (TLRs-an essential class of pathogen recognition receptors-PRRs) on the surface of macrophages and dendritic cells impact the immune response in the setting of H. pylori infection. Further studies are required for delineate precise role of bacterial community features and of immune system components.

Toll-Like Receptor Signaling in the Establishment and Function of the Immune System

Toll-like receptors (TLRs) are pattern recognition receptors that play a central role in the development and function of the immune system. TLR signaling promotes the earliest emergence of hematopoietic cells during development, and thereafter influences the fate and function of both primitive and effector immune cell types. Aberrant TLR signaling is associated with hematopoietic and immune system dysfunction, and both loss- and gain-of- function variants in TLR signaling-associated genes have been linked to specific infection susceptibilities and immune defects. Herein, we will review the role of TLR signaling in immune system development and the growing number of heritable defects in TLR signaling that lead to inborn errors of immunity.

Upregulation of Toll-like receptor 4 through anti-miR-Let-7a enhances blastocyst attachment to endometrial cells in mice

Despite encouraging advances in fertility technology, the success rate of an ongoing pregnancy is relatively low and predominantly associated with implantation failure. Inflammatory responses are beneficial in the fetomaternal interface and supposedly accelerate the chances for successful implantation. The current study aims to determine the effect of Toll-like receptor 4 (TLR4) overexpression in mouse blastocysts via Let-7a downregulation using intracytoplasmic sperm injection-sperm-mediated gene transfer on embryo attachment rate. The pLenti-III-GFP-miR-Off-Let-7a vector was transmitted to oocytes derived via in vitro maturation (IVM) and in vivo oocytes by using NaOH-treated spermatozoa. Let-7a and TLR4 expression levels were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR), immunocytochemistry, and western blot analysis in both oocytes and embryos. Blastocyst adhesion on the endometrial cells was monitored by microscopic analysis. qRT-PCR results showed that Let-7a expression decreased in the IVM (GV-MII) oocytes compared to the in vivo oocyte (MII) group (p < .05). TLR4 showed a higher expression in GV-MII oocytes at both the gene and protein levels (p < .05). Following anti-miR-Let-7a transmission, the TLR4 expression level was significantly upregulated in embryos compared with the control groups (p < .05). Attachment and migration of trophoblasts cells towards endometrial cells dramatically increased compared to the control group (p < .05). Based on our results, we concluded that Let-7a might mediate embryo attachment through regulation of TLR4 expression levels.

The relationship between TLR4 rs4986790 and rs4986791 gene polymorphisms and Helicobacter pylori infection in children with gastritis

BACKGROUND

TLR4 is involved in H. pylori lipopolysaccharide recognition and its SNPs might be related to increased risk of developing premalignant conditions and gastric cancer. The objectives of the study were to evaluate the associations between both TLR4 rs4986790 and rs4986791 gene polymorphisms and H. pylori infection in children with gastritis.

METHODS

We performed a cross-sectional study on 150 children admitted in a Tertiary Centre from Romania, between March 2016 and July 2018 in order to evaluate them regarding demographic, endoscopic, histopathological and TLR4 gene polymorphisms.

RESULTS

Our final sample consisted of 50 children with H.pylori associated gastritis (group 1-Ghp group) and 97 children with gastritis without H.pylori infection (group 2). Poor socioeconomic status was a significant risk factor for H.pylori infection. We found no significant differences regarding the clinical symptoms and laboratory parameters between the two groups. Concordant results were found between the histopathological exam and rapid urease test. Variant genotypes of TLR4rs4986790 and TLR4rs4986791 gene polymorphisms acted as protective factors against H. pylori infection, without statistical significance.

CONCLUSIONS

The variant genotype of the TLR4 gene polymorphisms might be protective factors for H.pylori infection, while socioeconomic status is an risk factor for H. pylori infection. Urease test is a usefull diagnostic tool for H. pylori infection.

The Relationship between Toll-like Receptors and Helicobacter pylori-Related Gastropathies: Still a Controversial Topic

Innate immunity represents the first barrier against bacterial invasion. Toll-like receptors (TLRs) belong to the large family of pattern recognition receptors (PRRs), and their activation leads to the induction of inflammatory cytokines, chemokines, antigen-presenting molecules, and costimulatory molecules. Recent studies have focused on identifying the association between TLRs and Helicobacter pylori- (H. pylori-) related diseases. Therefore, this minireview focuses on assessing the role of these TLRs in the development of H. pylori-related gastropathies. Both TLR2 and TLR were found to be involved in H. pylori LPS recognition, with contradictory results most likely due to both the inability to obtain pure LPS in experimental studies and the heterogeneity of the bacterial LPS. In addition, TLR2 was found to be the most extensively expressed gene among all the TLRs in gastric tumors. High levels of TLR4 were also associated with a higher risk of gastric cancer. TLR5 was initially associated with the recognition of H. pylori flagellin, but it seems that this bacterium has developed mechanisms to escape this recognition representing an important factor involved in the persistence of this infection and subsequent carcinogenesis. TLR9, the only TLR with both anti- and proinflammatory roles, was involved in the recognition of H. pylori DNA. The dichotomous role of TLR9, promoting or suppressing the infection, depends on the gastric environment. Recently, TLR7 and TLR8 were shown to recognize purified H. pylori RNA, thereby inducing proinflammatory cytokines. TLR1 and TLR10 gene polymorphisms were associated with a higher risk for gastric cancer in H. pylori-infected individuals. Different gene polymorphisms of these TLRs were found to be associated with gastric cancer depending mostly on ethnicity. Further studies are required in order to develop preventive and therapeutic strategies against H. pylori infections based on the functions of TLRs.

Role of Microglia TLRs in Neurodegeneration

Toll-like receptors (TLRs) are a group of receptors widely distributed in the organism. In the central nervous system, they are expressed in neurons, astrocytes and microglia. Although their involvement in immunity is notorious, different articles have demonstrated their roles in physiological and pathological conditions, including neurodegeneration. There is increasing evidence of an involvement of TLRs, especially TLR2, 4 and 9 in neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). In this sense, their expression in microglia might modulate the activity of these cells, which in turn, lead to protective or deleterious effects over neurons and other cells. Therefore, TLRs might mediate the link between inflammation and neurodegenerative diseases. However, further studies have to be performed to elucidate the role of the other TLRs in these diseases and to further prove and confirm the pathophysiological role of all TLRs in neurodegeneration. In this article, we revise and summarize the current knowledge regarding the role of TLRs in neurodegeneration with the focus on the possible functions of these receptors in microglia.

Toll-like receptors (TLRs) signalling and expression pattern

Toll is a Drosophila gene essential for ontogenesis and antimicrobial resistance. Several homologues of Toll have been identified and cloned in vertebrates, namely Toll-like receptors (TLRs). TLRs are structurally characterized by a cytoplasmic Toll/interleukin-1R (TIR) domain and by extracellular leucine rich repeats. TLRs characterized so far activate the MyD88/IRAK signalling cascade which activates NF-κB transcription factor. Genetic, gene transfer, and dominant negative approaches have involved TLR family members (TLR2 and TLR4) in distinct bacterial components for recognition and signalling. However, very little information is available regarding other TLRs. Here we propose to classify TLRs based on their expression pattern, in ubiquitous (TLR1), restricted (TLR2, 4, 5) and specific (TLR3) TLRs. Differential expression and regulation as well as distinct, though overlapping, ligand recognition patterns may underlie the existence of a such a large, seemingly redundant, TLR family.

Differential roles of TLR2 and TLR4 in the host response to Gram-negative bacteria: lessons from a lipopolysaccharide-deficient mutant of Neisseria meningitidis

The inflammatory response to bacterial infections plays an important role in the detection and elimination of invading micro-organisms. Various components of the bacterial cell wall are capable of activating this pro-inflammatory response. In the case of Gram-negative bacteria, lipopolysaccharide (LPS) is the dominant trigger, although other bacterial factors are also capable of activating this systemic inflammatory response. Recently, Toll-like receptors (TLRs) have been implicated in host responses to bacterial pathogens. Specifically, TLR4 mediates LPS responses while TLR2 plays a broader role in the recognition of a variety of bacteria and bacterial antigens. The experiments in this study were designed to examine the role of Gram-negative cell wall components, other than LPS, and their cellular receptors in the host response to infection using an LPS-deficient mutant of Neisseria meningitidis. Although less potent than the parental strain, we found the LPS-deficient mutant to be a capable inducer of the inflammatory response in a variety of cell types. Moreover, cellular activation by this mutant required expression of CD14 and TLR2.

Abnormal expression of TLRs may play a role in lower embryo quality of women with polycystic ovary syndrome

Toll-like receptors (TLRs) localize in mammalian ovary, including granulosa cells, cumulus cells, and theca cells. Previous studies demonstrated that TLRs may be important for the cumulus-oocyte complex expansion and fertilization. There is no evidence to indicate that the deletion of TLRs will induce infertility; however, the abnormal expression of TLRs may decrease oocyte quality and fertility rate. In the present study, we investigated the effects of polycystic ovary syndrome (PCOS) on the expression of TLRs in cumulus cells by using western-blot and quantitative real-time PCR (qRT-PCR) analyses. We found that the expression of TLR4 and 9 in cumulus cells was influenced significantly by PCOS. We also observed that overweight/obesity changed the expression of TLR2 and 5 in cumulus cells of PCOS subjects. In addition, we found that the rate of available embryos of women with PCOS was slightly lower. These results indicate that the abnormal expression of TLRs in cumulus may be a reason for the lower embryo quality of women with PCOS.

ABBREVIATIONS

ART: assisted reproductive technology BMI: body mass index COC: cumulus-cell-oocyte complex PCOS: polycystic ovary syndrome q

RT-PCR

quantitative real-time PCR TLRs: Toll-like receptors.

MicroRNA-181c negatively regulates the inflammatory response in oxygen-glucose-deprived microglia by targeting Toll-like receptor 4

Cerebral hypoxia/ischemia rapidly induces inflammation in the brain, which is characterized by microglial activation and the release of inflammatory cytokines. We have previously demonstrated that miR-181c can directly regulate tumor necrosis factor (TNF)-α production post-transcriptionally. Here, we determined that hypoxia up-regulated TLR4 expression but down-regulated miR-181c expression in primary microglia. We also demonstrated that miR-181c suppresses TLR4 by directly binding its 3'-untranslated region. In addition, miR-181c inhibited NF-κB activation and the downstream production of proinflammatory mediators, such as TNF-α, IL-1β, and iNOS. Knocking down TLR4 in microglia significantly decreased TLR4 expression and inhibited NF-κB activation and the downstream production of proinflammatory mediators, whereas ectopic TLR4 expression significantly abrogated the suppressed inflammatory response induced by miR-181c. Therefore, our study identified an important role for the miR-181c-TLR4 pathway in hypoxic microglial activation and neuroinflammation. This pathway could represent a potential therapeutic target for cerebral hypoxic diseases associated with microglial activation and the inflammatory response. Cerebral hypoxia/ischemia induces microglial activation and the release of inflammatory cytokines. We found that hypoxia down-regulated miR-181c in primary microglia. In addition, miR-181c inhibited TLR4 expression through binding to its 3'UTR, thus inhibiting NF-kB activation and the production of downstream proinflammatory mediators. Therefore, the miR-181c-TLR4 pathway may be a potential therapeutic target for the treatment of cerebral hypoxic diseases.

Toll-like receptor 2 ligand, lipoteichoic acid is inhibitory against infectious laryngotracheitis virus infection in vitro and in vivo

Lipoteichoic acid (LTA) is one of the pathogen associated molecular patterns (PAMPs) that activates toll-like receptor (TLR)2-cluster of differentiation (CD)14 signalling pathway. This recognition elicits antiviral responses that have been recorded against viruses of mammals although such responses have not been characterized adequately against avian viruses. In this investigation, we characterized the LTA induced antiviral responses against infectious laryntotracheitis virus (ILTV) infection in vitro and in vivo. We found that LTA is capable of up regulating mRNA expression of innate proteins in macrophages such as MyD88, iNOS and IL-1β and reduces the ILTV plaques in vitro. Similarly, we found that LTA treatment of embryonic day 18 (ED18) eggs can lead to the antiviral response against pre-hatch ILTV infection in vivo and is associated with expansion of macrophage populations and expression of IL-1β and MyD88 in the lung. The data highlight that LTA can be a potential innate immune stimulant that can be used against ILTV infection in chickens.

Toxicological and pharmacokinetic properties of QPI-1007, a chemically modified synthetic siRNA targeting caspase 2 mRNA, following intravitreal injection

We report the toxicological and pharmacokinetic properties of the synthetic, small interfering RNA (siRNA), QPI-1007, following intravitreal administration. QPI-1007 is a chemically modified siRNA designed to act via the RNA interference (RNAi) pathway to temporarily inhibit expression of the caspase 2 protein and is being developed as a neuroprotectant for the treatment of nonarteritic anterior ischemic optic neuropathy and other optic neuropathies such as glaucoma that result in the death of retinal ganglion cells. The half-life of QPI-1007 in the vitreous and retina/choroid in the Dutch Belted rabbit was about 2 days, and there was no sign of accumulation after repeated administrations at either 2- or 4-week dosing intervals in the rabbit. QPI-1007 was well tolerated in Dutch Belted rabbits following single or repeated intravitreal administrations of up to 11 doses over 9 months. Test-article-related effects were limited to the eyes, with minimal to mild vitreal cellular infiltration being the major finding, which was reversible. In repeated-dose studies, a modest reduction in B-wave amplitude obtained by electroretinography was observed in animals treated with the highest dose level tested (3 mg, which is equivalent to a 12 mg/eye human dose) that was not considered to be clinically meaningful. Administration in the rat of either a single bolus intravenous (i.v.) injection of 100 mg/kg or daily bolus i.v. injections of 75 mg/kg/day for 28 days failed to elicit any macroscopic or microscopic changes, suggesting a low risk for systemic toxicity. QPI-1007 was negative in three genetic toxicity studies. Overall, the nonclinical studies support the further development of QPI-1007.

Toll-like receptors in central nervous system injury and disease: a focus on the spinal cord

Toll-like receptors (TLRs) are best known for recognizing pathogens and initiating an innate immune response to protect the host. However, they also detect tissue damage and induce sterile inflammation upon the binding of endogenous ligands released by stressed or injured cells. In addition to immune system-related cells, TLRs have been identified in central nervous system (CNS) neurons and glial subtypes including microglia, astrocytes and oligodendrocytes. Direct and indirect effects of TLR ligands on neurons and glial subtypes have been documented in vitro. Likewise, the effects of TLR ligands have been demonstrated in vivo using animal models of CNS trauma and disease including spinal cord injury (SCI), amyotrophic lateral sclerosis (ALS) and neuropathic pain. The indirect effects are most likely mediated via microglia or immune system cells that infiltrate the diseased or injured CNS. Despite considerable progress over the past decade, the role of TLRs in the physiological and pathological function of the spinal cord remains inadequately defined. Published reports collectively highlight TLRs as promising targets for therapeutic interventions in spinal cord pathology. The findings also underscore the complexity of TLR-mediated mechanisms and the necessity for further research in this field. The goals of the current review are to recapitulate the studies that investigated the role of TLRs in the spinal cord, to discuss potential future research directions, and to examine some of the challenges associated with pre-clinical studies pertinent to TLRs in the injured or diseased spinal cord.

Flagellin/TLR5 signaling potentiates airway serous secretion from swine tracheal submucosal glands

Airway serous secretion is essential for the maintenance of mucociliary transport in airway mucosa, which is responsible for the upregulation of mucosal immunity. Although there are many articles concerning the importance of Toll-like receptors (TLRs) in airway immune systems, the direct relationship between TLRs and airway serous secretion has not been well investigated. Here, we focused on whether TLR5 ligand flagellin, which is one of the components of Pseudomonas aeruginosa, is involved in the upregulation of airway serous secretion. Freshly isolated swine tracheal submucosal gland cells were prepared, and the standard patch-clamp technique was applied for measurements of the whole cell ionic responses of these cells. Flagellin showed potentiating effects on these oscillatory currents induced by physiologically relevant low doses of acetylcholine (ACh) in a dose-dependent manner. These potentiating effects were TLR5 dependent but TLR4 independent. Both nitric oxide (NO) synthase inhibitors and cGMP-dependent protein kinase (cGK) inhibitors abolished these flagellin-induced potentiating effects. Furthermore, TLR5 was abundantly expressed on tracheal submucosal glands. Flagellin/TLR5 signaling further accelerated the intracellular NO synthesis induced by ACh. These findings suggest that TLR5 takes part in the airway mucosal defense systems as a unique endogenous potentiator of airway serous secretions and that NO/cGMP/cGK signaling is involved in this rapid potentiation by TLR5 signaling.

Toll-like receptor triggering in cord blood mesenchymal stem cells

Recently, the antagonizing effect on the differentiation of mesenchymal stem cells (MSCs) by toll-like receptor (TLR) ligands, was described. Our study shows that on more primitive cord blood derived MSCs, the expression of TLRs and ligand-induced triggering differs from that of bone marrow derived MSCs. At the RNA level, cord blood MSCs (unrestricted somatic stem cells; USSCs) express low levels of TLR1,3,5,9 and high levels of TLR4 and TLR6. At the protein level expression of TLR5 and very low expression of TLR4 was observed. NF-κB translocation studies revealed that both TLR4 and TLR5 are functional, although signalling kinetics induced by the individual ligands differed. Stimulation of USSCs with either lipopolysaccharide (LPS) or flagellin resulted in a marked increase of interleukin (IL)-6 and/or IL-8 production although levels differed significantly between both stimuli. Interestingly, tumour necrosis factor (TNF)-α was undetectable after TLR stimulation, which appeared to be due to an inactivated TNF-α promoter in USSCs. Moreover, osteoblastic differentiation was enhanced after triggering USSCs with LPS and flagellin. In summary, TLR4 and 5 signalling in USSCs is slow and results in the up-regulation of a restricted number of pro-inflammatory cytokines and enhanced osteoblastic differentiation. Apparently, the outcome of TLR signalling depends on the cell type that expresses them.

Expression of toll-like receptor TLR-2, TLR-3, TLR-4 and TLR-9 is increased in placentas from patients with preeclampsia

BACKGROUND AND AIMS

Few studies have examined the presence of Toll-like receptors (TLRs) in term placentas from women with preeclampsia, such, have focused on TLR-4 and TLR-2 analysis. Whereas an increase in TLR-4 immunostaining has been observed in preeclampsia, it is even higher in placentas with chorioamnionitis compared with normal pregnancy. Expression of TLR-2 has not been associated with preeclampsia. The relationship of TLR-3 and TLR-9, which may recognize dsRNA or DNA, either derived either from microorganisms or from apoptotic cells and thus may be involved with this pathology, has not been studied in term placentas. We undertook this study to determine if there are changes in the expression and localization of TLR-2, TLR-4, TLR-3 and TLR-9 in preeclamptic term placentas as compared with normal placentas.

METHODS

A prospective, cross-sectional and comparative study was done in a group of ten patients with 38-40 gestation weeks, both in preeclamptic and control cases. Immunofluorescence detection of TLRs was performed in samples of placenta and analyzed by confocal microscopy.

RESULTS

It was observed that TLR-2, TLR-3, TLR-4 and TLR-9 were expressed both in normal and preeclamptic placentas, in the trophoblast, at the vascular endothelium (where TLR-2 and TLR-9 staining was pronounced), and at placental villous stroma, although increased expression was detected in preeclampsia. In addition, co-localization of TLR-2 and TLR-4 as well as of TLR-3 and TL9 was found in the trophoblast.

CONCLUSIONS

TLR-2, -3, -4 and -9 expressions are increased in preeclamptic placentas. However, more studies are required to determine the role of TLRs in pregnancy immunology and to establish its relationship with preeclampsia.

Moesin-induced signaling in response to lipopolysaccharide in macrophages

BACKGROUND AND OBJECTIVE

Many physiological and pathophysiological conditions are attributable in part to cytoskeletal regulation of cellular responses to signals. Moesin (membrane-organizing extension spike protein), an ERM (ezrin, radixin and moesin) family member, is involved in lipopolysaccharide (LPS)-mediated events in mononuclear phagocytes; however, its role in signaling is not fully understood. The aim of this study was to investigate the LPS-induced moesin signaling pathways in macrophages.

MATERIAL AND METHODS

Macrophages were stimulated with 500 ng/mL LPS in macrophage serum-free medium. For blocking experiments, cells were pre-incubated with anti-moesin antibody. Moesin total protein and phosphorylation were studied with western blotting. Moesin mRNA was assessed using quantitative real-time PCR. To explore binding of moesin to LPS, native polyacrylamide gel electrophoresis (PAGE) gel shift assay was performed. Moesin immunoprecipitation with CD14, MD-2 and Toll-like receptor 4 (TLR4) and co-immunoprecipitation of MyD88-interleukin-1 receptor-associated kinase (IRAK) and IRAK-tumor necrosis factor receptor-activated factor 6 (TRAF6) were analyzed. Phosphorylation of IRAK and activities of MAPK, nuclear factor kappaB (NF-kappaB) and IkappaBalpha were studied. Tumor necrosis factor alpha, interleukin-1beta and interferon beta were measured by ELISA.

RESULTS

Moesin was identified as part of a protein cluster that facilitates LPS recognition and results in the expression of proinflammatory cytokines. Lipopolysaccharide stimulates moesin expression and phosphorylation by binding directly to the moesin carboxyl-terminus. Moesin is temporally associated with TLR4 and MD-2 after LPS stimulation, while CD14 is continuously bound to moesin. Lipopolysaccharide-induced signaling is transferred downstream to p38, p44/42 MAPK and NF-kappaB activation. Blockage of moesin function interrupts the LPS response through an inhibition of MyD88, IRAK and TRAF6, negatively affecting subsequent activation of the MAP kinases (p38 and ERK), NF-kappaB activation and translocation to the nucleus.

CONCLUSION

These results suggest an important role for moesin in the innate immune response and TLR4-mediated pattern recognition in periodontal disease.

Approaching the asymptote: 20 years later

The pattern recognition theory proposed by the late Charles Janeway, Jr. 20 years ago provided a conceptual framework for our current understanding of the innate immune recognition and its role in the activation of adaptive immunity. Discovery of several families of pattern recognition receptors and their roles in mammalian immunity provided experimental support for the Janeway's theory. In addition to pattern recognition, there are other forms of innate immune sensing, which presumably work in specific combinations depending on the pathogen class and the type of the immune response they elicit. Here, the development of the Janeway's theory is discussed in the context of the advances made in field of innate immune recognition over the past two decades.

Toll-like receptor 4 (TLR4) and typhoid fever in Vietnam

Understanding the host genetic susceptibility to typhoid fever may provide a better understanding of pathogenesis and help in the development of new therapeutics and vaccines. Here we determine the genetic variation within the human TLR4 gene encoding the principal receptor for bacterial endotoxin recognition in typhoid fever patients. It is possible that genetic variants of TLR4 could detrimentally affect the innate immune response against S. typhi infection. Mutation detection and genotyping of TLR4 was performed on DNA from 414 Vietnamese typhoid fever patients and 372 population controls. dHPLC detected a total of 10 polymorphisms within the upstream and exonic regions of TLR4, of which 7 are novel. Two SNPs, T4025A and C4215G, were more frequent in typhoid cases than in controls however due to their low allele frequencies they showed borderline significance (T4025A: OR 1.9, 95%CI 0.9–4.3, P 0.07 and C4215G: OR 6.7, 95%CI 0.8–307, P 0.04). Six missense mutations were identified, with 5/6 positioned in the ectoplasmic domain. Four missense mutations and one promoter SNP (A-271G) were only present in typhoid cases, albeit at low allele frequencies. Here we determined the extent of genetic variation within TLR4 in a Vietnamese population and suggest that TLR4 may be involved in defense against typhoid fever in this population.

Experimental models of acute infection and Toll-like receptor driven septic shock

Mainly Gram-negative and Gram-positive bacterial infections, but also other infections such as with fungal or viral pathogens, can cause the life-threatening clinical condition of septic shock. Transgression of the host immune response from a local level limited to the pathogen's place of entry to the systemic level is recognised as a major mode of action leading to sepsis. This view has been established upon demonstration of the capacity of specific pathogen-associated molecular patterns (PAMPs) to elicit symptoms of septic shock upon systemic administration. Immune stimulatory PAMPs are agonists of soluble, cytoplasmic, as well as/or cell membrane-anchored and/or -spanning pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs). However, reflection of pathogen-host crosstalk triggering sepsis pathogenesis upon an infection by a host response to challenge with an isolated PAMP is incomplete. Therefore, an experimental model more reflective of pathogen-host interaction requires experimental host confrontation with a specific pathogen in its viable form resulting in a collective stimulation of a variety of specific PRRs. This chapter describes methods to analyse innate pathogen sensing by the host on both a cellular and systemic level.

Toll-like receptors 2 and 4 and their mutations in patients with otitis media and middle ear effusion

Objectives

Toll-like receptors (TLRs) detect microbial infections and they can directly induce innate host defense responses. TLR 2 has been shown to be primarily involved in the recognition of peptidoglycans and lipoteichoic acid of gram positive bacteria. TLR 4 recognizes lipopolysaccharides and lipoteichoic acids from both gram-negative and gram-positive bacteria. Both mutations lead a reduced capacity to elicit inflammation and they increase the risk for gram-positive and negative infections. This study was performed to investigate the expressions of TLR 2 and 4 and their mutations in patients suffering with otitis media and middle ear effusion.

Methods

Middle ear fluid samples were collected from 40 otitis media effusion (OME) patients who had ventilating tubesinserted. Bacteria in the effusion fluid were detected by standard bacterial culture. The secreted IgG, IgA and IgM were measured by Enzyme-linked immunosorbent assay. TLR 2 and 4 were assessed by performing RT-PCR. The genomic DNA from each patient was isolated from the middle ear fluid samples that were collected from 60 OME patients, and the presence of mutations was determined by performing restriction digestion and DNA sequencing analysis.

Results

Among the 40 middle ear fluid samples, bacteria were detected in 13 middle ear fluid samples. The amounts of IgM, IgA, and IgG were 151.20±60.94 ng/mL, 21.59±7.96 ng/mL and 11.55±16.98 ng/mL, respectively. TLR 2 and 4 were expressed in the middle ear fluid and the expression of TLR 2 was higher than that of TLR 4. However, there was no correlation between the expressions of TLR 2 and 4, and the concentration of immunoglobulin or the presence of bacteria (P>0.05). There ware no mutations of TLR 2 (Arg753Gln, Arg677Trp) and TLR 4 (Asp299Gly, Thr399Ile).

Conclusion

TLR 2 and 4 were expressed in all the middle ear fluid samples of OME, but the mutations of TLR 2 and 4 were not detected. TLR 2 and 4 may play a vital role in the immunological responses of patients with OME.

Molecular pathogenesis of inflammatory bowel disease: relevance for novel therapies

The immense load of microorganisms within the gastrointestinal tract is a great challenge for the mucosal immune system. Whereas the vast majority of commensal bacteria should be tolerated, pathogenic organisms have to be attacked. During inflammatory bowel disease, the balanced interaction between the mucosal flora and the intestinal immune system is disturbed. Various defective components of this complex interaction have been described, such as different susceptibility genes, impaired innate immune responses and environmental factors, suggesting that inflammatory bowel diseases are multifactorial diseases. Based on new insights into the pathogenesis of inflammatory bowel disease, various targets for future drugs have been identified and new substances are emerging. The following article will review the current understanding of inflammatory bowel disease pathogenesis in context with genetic risk factors, imbalanced innate and acquired immune responses, and altered barrier function. Clinical treatment of the diseases will be summarized and emerging therapies as well as individual management based on recent insights into pathogenesis will be discussed.

TLR4-mediated activation of dendritic cells by the heat shock protein DnaK from Francisella tularensis

Francisella tularensis is the causative agent of tularemia, a severe, debilitating disease of humans and other mammals. As this microorganism is also classified as a "category-A pathogen" and a potential biowarfare agent, there is a need for an effective vaccine. Several antigens of F. tularensis, including the heat shock protein DnaK, have been proposed for use in a potential subunit vaccine. In this study, we characterized the innate immune response of murine bone marrow-derived dendritic cells (DC) to F. tularensis DnaK. Recombinant DnaK was produced using a bacterial expression system and purified using affinity, ion-exchange, and size-exclusion chromatography. DnaK induced the activation of MAPKs and NF-kappaB in DC and the production of the proinflammatory cytokines IL-6, TNF-alpha, and IL-12 p40, as well as low levels of IL-10. DnaK induced phenotypic maturation of DC, as demonstrated by an up-regulation of costimulatory molecules CD40, CD80, and CD86. DnaK stimulated DC through TLR4 and the adapters MyD88 and Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) that mediated differential responses. DnaK induced activation of MAPKs and NF-kappaB in a MyD88- or TRIF-dependent manner. However, the presence of MyD88- and TRIF-dependent signaling pathways was essential for an optimal, DnaK-induced cytokine response in DC. In contrast, DnaK induced DC maturation in a TRIF-dependent, MyD88-independent manner. These results provide insight about the molecular interactions between an immunodominant antigen of F. tularensis and host immune cells, which is crucial for the rational design and development of a safe and efficacious vaccine against tularemia.

A review of the role of CpG oligodeoxynucleotides as toll-like receptor 9 agonists in prophylactic and therapeutic vaccine development in infectious diseases

This article reviews the biology of Toll-like receptors, the current understanding of the mechanism by which CpG oligodeoxynucleotides (ODNs) perturb immune function and the published literature describing their evaluation in the development of vaccines in humans. The role of these molecules as immune modulators in HCV treatment is also considered. There has been considerable research evaluating the role of CpG ODNs as an adjuvant and immune modulator in hepatitis B, hepatitis C and influenza. The safety and immunogenicity of the 1018 ISS compound in combination with Engerix-B was assessed in 99 healthy, adult seronegative volunteers. One month following the first immunization dose, 78.7% in the rHBsAg plus 1018 ISS group versus 11.8% in the Engerix-B group achieved protective titres. One hundred percent of rHBsAg plus 1018 ISS and 18.0% of hepatitis B vaccine-alone recipients were seroprotected 1 week following the second dose of study vaccine. After all doses of vaccine had been administered, seroprotection rates were 100% and 64%, respectively (p < 0.001). CPG 7909 was co-administered with Engerix-B in 56 healthy adults. After the second injection (week 6 time point), seroprotection was achieved in 100% of CPG 7909 recipients (0.5 mg 13/13; 1.0 mg 12/12; 0.125 mg 12/12) compared with 55% (6/11) of control participants (p = 0.0003). Twelve months post prime, all subjects who had received the full course of vaccination maintained seroprotective anti-HBs titres. The safety and immunogenicity of Engerix B plus CPG 7909 was assessed in HIV seropositive patients. All CPG 7909 recipients (n = 19) and 17/19 (89%) control subjects achieved seroprotection by 2 weeks after the third and final injection (10 weeks). Seroprotective titres remained in all CPG 7909 recipients at 48 weeks (100%) versus 12/19 (63%) for controls (p = 0.008). This cohort of HIV-infected patients was followed at 6-month intervals for up to 60 months after enrolment. The difference in seroprotection (> or =10 mIU/L) and GMT between study arms remained significant (p < 0.05) at all time points from month 24 to month 60. There is great potential for CpG ODN as vaccine adjuvants and as therapeutic immune modulators. The use of these molecules as a hepatitis B vaccine adjuvant is most promising.

The involvement of the Toll-like receptor family in ovulation

INTRODUCTION

Ovulation is similar to an inflammatory response and is associated with increased production of prostaglandins as well as local growth regulatory factors. However, the expression and function of innate immune cell-related genes in non-immune cells within the ovary has been reported recently and provides a novel and important regulatory system during ovulation.

DISCUSSION

Several members of the Toll-like receptor (TLR) surveillance system are expressed in granulosa cells and cumulus cells. These receptors can be activated by pathogens as well as endogenous ligands leading to the induction and release of potent cytokines and chemokines from cumulus cells.

CONCLUSION

These inflammatory factors exert potent effects on cumulus cell-oocyte expansion, ovulation, transport and fertilization indicating that ovulation is a more complex immune-inflammatory process than previously recognized.

Identification of cDNA encoding Toll receptor, MjToll gene from kuruma shrimp, Marsupenaeus japonicus

Toll receptors are cell-surface receptors acting as pattern recognition receptors (PRRs) that are involved in the signaling pathway for innate immunity activation and are genetically conserved from insects to mammals. Tolls from penaeid shrimp are found in white leg shrimp Litopenaeus vannamei (lToll) and black tiger shrimp Penaeus monodon (PmToll). However, the molecular ligand-recognition patterns and identification of these penaeid Toll classes remain unknown. Here, we report cDNA cloning of a new type of Toll receptor gene (MjToll) from kuruma shrimp, Marsupenaeus japonicus, and the modulation of expression by immunostimulation. The full length cDNA of MjToll gene has 3095 nucleotides coding for a putative protein of 1009 amino acids. The MjToll gene is constitutively expressed in the gill, gut, lymphoid organ, heart, hematopoietic organ, hemocyte, ventral abdominal nerve cord, eyestalk neural ganglia and brain tissues. The MjToll gene expression was significantly increased (76-fold) as compared to a control in lymphoid organ stimulated with peptidoglycan at 12h, in vitro. lToll gene showed high similarity to PmToll gene with 96.9% identity; however, MjToll gene exhibited a percentage identity of 59% with that of penaeid Toll homologues. Therefore, this suggests that the identified MjToll gene belongs to the other class of Toll receptors in shrimp.

Expression of Toll-like receptor 4 in rat liver during the course of carbon tetrachloride-induced liver injury

BACKGROUND AND AIM

It has recently been reported that Toll-like receptor 4 (TLR4) is involved in cellular responses to lipopolysaccharides (LPS) and early liver injury induced by LPS. The aim of the present study was to investigate the alterations of TLR4 gene expression in liver tissues and Kupffer cells during the course of carbon tetrachloride (CCl(4))-induced chronic liver injury and fibrosis and its role in liver injury.

METHODS

Rats were induced with liver injury and fibrosis by CCl(4) administered subcutaneously twice weekly for up to 8 weeks. The Kupffer cells were isolated by the combined collagenase-pronase perfusion method and incubated with varying doses of LPS. The mRNA expression of TLR4 in liver tissues and Kupffer cells was measured by reverse transcriptase polymerase chain reaction. The levels of tumor necrosis factor (TNF)-alpha in Kupffer cell culture supernatants were determined by enzyme-linked immunosorbent assay. The plasma levels of the endotoxin were determined by chromogenic substrate limulus amebocyte lysate assay. The association of the endotoxin receptor expression with plasma endotoxin levels was assessed.

RESULTS

CCl(4) administration elicited extensive changes in liver morphology, including steatosis, inflammation, necrosis, and fibrosis. Low levels of TLR4 mRNA were detected in normal rat liver tissues, but no expression was detected in the Kupffer cells. The expression of TLR4 mRNA in liver tissues and Kupffer cells was increased 2 weeks after CCl(4) administration, peaked at 4 and 6 weeks, and declined at 8 weeks. Basic TNF-alpha production of Kupffer cells isolated from CCl(4)-treated rats at 4 and 6 weeks was significantly higher than that of normal rats (P < 0.05). Upon LPS stimulation, production of TNF-alpha was markedly increased in Kupffer cells isolated from normal and 2-,4-, and 6-week CCl(4)-treated rats. Moreover, LPS-induced TNF-alpha production was dose-dependent. The plasma levels of the endotoxin were increased during the time of liver injury. There was a correlation between plasma endotoxin levels and TLR4 gene expression in the early and middle stage of liver injury.

CONCLUSION

The gene expression of TLR4 was upregulated during the course of CCl(4)-induced liver injury, which is associated with the degree of liver injury and Kupffer cell activation. The gut-derived endotoxin may be involved in the upregulation of TLR4 expression.

Cytosolic signaling protein Ecsit also localizes to mitochondria where it interacts with chaperone NDUFAF1 and functions in complex I assembly

Ecsit is a cytosolic adaptor protein essential for inflammatory response and embryonic development via the Toll-like and BMP (bone morphogenetic protein) signal transduction pathways, respectively. Here, we demonstrate a mitochondrial function for Ecsit (an evolutionary conserved signaling intermediate in Toll pathways) in the assembly of mitochondrial complex I (NADH:ubiquinone oxidoreductase). An N-terminal targeting signal directs Ecsit to mitochondria, where it interacts with assembly chaperone NDUFAF1 in 500- to 850-kDa complexes as demonstrated by affinity purification and vice versa RNA interference (RNAi) knockdowns. In addition, Ecsit knockdown results in severely impaired complex I assembly and disturbed mitochondrial function. These findings support a function for Ecsit in the assembly or stability of mitochondrial complex I, possibly linking assembly of oxidative phosphorylation complexes to inflammatory response and embryonic development.

Proteome modifications of the medicinal leech nervous system under bacterial challenge

Once considered as lacking intrinsic immune mechanisms, the CNS of vertebrates is now known to be capable of mounting its own innate immune response. Interestingly, while invertebrates have been very useful in the interpretation of general vertebrate innate immunity mechanisms, only scarce data are available on the immune response of nervous tissue within this group. This study provides new data on the innate immune response of medicinal leech Hirudo medicinalis CNS. We identified several spots in 2-D gels of leech CNS proteins that showed specific changes following bacterial challenge, thus demonstrating the ability of the leech nervous system to mount a response to an immune stress. Protein identifications were based on comparison of sequence data with publicly available databases and a recently established leech ESTs database. The broad nature of the identified proteins suggests a clear involvement of cytoskeletal rearrangements, endoplasmic reticulum stress, modulation of synaptic activity and calcium mobilization, all during the first 24 hours of this response. Moreover, several of these proteins are specifically expressed in glial cells, suggesting an important role for glial cells in the immune response of the leech nervous system, similar to what has been observed in vertebrates.

Evolution of an intronic microsatellite polymorphism in Toll-like receptor 2 among primates

Nonhuman primates express varying responses to Mycobacterium tuberculosis: New World monkeys appear to be resistant to tuberculosis (TB) while Old World monkeys seem to be particularly susceptible. The aim of this study was to elucidate the presence of the regulatory guanine-thymine (GT) repeat polymorphisms in intron 2 of Toll-like receptor 2 (TLR2) associated with the development of TB in humans and to determine any variations in these microsatellite polymorphisms in primates. We sequenced the region encompassing the regulatory GT repeat microsatellites in intron 2 of TLR2 in 12 different nonhuman primates using polymerase chain reaction amplification, TA cloning, and automatic sequencing. The nonhuman primates included for this study were as follows: chimpanzee (Pan troglodytes), bonobo (Pan paniscus), gorilla (Gorilla gorilla), orangutan (Pongo pygmaeus), Celebes ape (Macaca nigra), rhesus monkey (Macaca mulatta), pigtail macaque (Macaca nemestrina), patas monkey (Erythrocebus patas), spider monkey (Ateles geoffroyi), Woolly monkey (Lagothrix lagotricha), tamarin (Saguinus labiatus), and ring-tailed lemur (Lemur catta). Nucleotide sequences encompassing the regulatory GT repeat region are similar across species and are completely conserved in great apes. However, Old World monkeys lack GT repeats altogether, while New World monkeys and ring-tailed lemurs have much more complex structures around the position of the repeats. In conclusion, the genetic structures encompassing the regulatory GT repeats in intron 2 of human TLR2 are similar among nonhuman primates. The sequence is most conserved in New World monkeys and less in Old World monkeys.

[Osteoclasts activation by bacterial endotoxins during periodontal diseases]

During periodontal infections, bacterial lipopolysaccharides (LPS) from Gram negative bacteria, along with other bacterial products, drive alveolar bone destruction. Tissue destruction occurs through both direct and indirect pathways. In the indirect pathway, LPS induce the secretion of proinflammatory cytokines, which in turn provokes a cascade of reactions leading to osteoclasts activation. In the direct pathway, LPS stimulate osteoblasts, osteoclasts precursors and osteoclasts, with an inflammatory cytokines independent manner. In this paper, the mechanisms involved in these two pathways are reviewed.

Role of Toll-like receptors in health and diseases of gastrointestinal tract

The human gastrointestinal (GI) tract is colonized by non-pathogenic commensal microflora and frequently exposed to many pathogenic organisms. For the maintenance of GI homeostasis, the host must discriminate between pathogenic and non-pathogenic organisms and initiate effective and appropriate immune and inflammatory responses. Mammalian toll-like receptors (TLRs) are members of the pattern-recognition receptor (PRR) family that plays a central role in the initiation of innate cellular immune responses and the subsequent adaptive immune responses to microbial pathogens. Recent studies have shown that gastrointestinal epithelial cells express almost all TLR subtypes characterized to date and that the expression and activation of TLRs in the GI tract are tightly and coordinately regulated. This review summarizes the current understanding of the crucial dual roles of TLRs in the development of host innate and adaptive immune responses to GI infections and the maintenance of the immune tolerance to commensal bacteria through down-regulation of surface expression of TLRs in intestinal epithelial cells.

Molecular cloning and tissue expression of canine Toll-like receptor 2 (TLR2)

Toll-like receptor 2 (TLR2) is involved in an important role on inflammatory reactions against various pathogenic microorganisms. Although some investigations suggested a relation between human and murine TLR2 gene polymorphisms and infections or inflammatory reactions, canine TLR2 gene has not been investigated. In the present study, therefore, the canine full-length of cDNA of Toll-like receptor 2 gene was sequenced and the expression of canine TLR2 mRNA was investigated in various tissues. Canine TLR2 clone was 2552bp encoding 785 amino acids. The similarities of canine TLR2 with human, mouse, rat, cattle, horse and pig TLR2 were 87.6, 72.9, 73.2, 83.1, 85.1 and 80.7% at the nucleotide sequence level, and 84.6, 68.7, 68.5, 78.8, 82.9 and 79.0% at amino acid sequence level, respectively. By a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis, mRNA of canine TLR2 was detected in blood mononuclear cells (BMCs), lymph node, lung, liver, spleen, bladder, pancreas, small intestine, large intestine and skin of the dogs.

Hepatitis C virus induces toll-like receptor 4 expression, leading to enhanced production of beta interferon and interleukin-6

Hepatitis C virus (HCV) induces inflammatory signals, leading to hepatitis, hepatocellular carcinomas, and lymphomas. The mechanism of HCV involvement in the host's innate immune responses has not been well characterized. In this study, we analyzed expression and regulation of the entire panel of toll-like receptors (TLRs) in human B cells following HCV infection in vitro. Among all of the TLRs (TLRs 1 to 10) examined, only TLR4 showed an altered expression (a three- to sevenfold up-regulation) after HCV infection. Peripheral blood mononuclear cells from HCV-infected individuals also showed a higher expression level of TLR4 compared with those of healthy individuals. HCV infection significantly increased beta interferon (IFN-beta) and interleukin-6 (IL-6) secretion from B cells, particularly after lipopolysaccharide stimulation. The increased IFN-beta and IL-6 production was mediated by TLR4 induction, since the introduction of the small interfering RNA against TLR4 specifically inhibited the HCV-induced cytokine production. Among all of the viral proteins, only NS5A caused TLR4 induction in hepatocytes and B cells. NS5A specifically activated the promoter of the TLR4 gene in both hepatocytes and B cells. In conclusion, HCV infection directly induces TLR4 expression and thereby activates B cells, which may contribute to the host's innate immune responses.

Platelet Toll-like receptor expression modulates lipopolysaccharide-induced thrombocytopenia and tumor necrosis factor-alpha production in vivo

Toll-like receptors (TLRs) play a critical role in stimulating innate immunity by recognizing pathogen-associated molecular patterns (PAMPs) on invading microorganisms. Platelets also play a role in innate immunity, and we studied whether they express TLR. Results show that human and murine platelets variably expressed TLR2, TLR4, and TLR9 by flow cytometry and Western blotting. TLR4 expression was confirmed by demonstrating murine platelet binding to lipopolysaccharide (LPS). Thrombin activation of the platelets significantly enhanced the expression of TLR9, suggesting that at least some TLRs may derive from intracellular compartments. When LPS was administered to LPS-sensitive C3H/HeN and LPS-resistant C3H/HeJ mice, functional TLR4 expression in vivo was shown to be responsible for LPS-induced thrombocytopenia. However, when the C3H/HeN mice were first rendered thrombocytopenic by an antiplatelet antibody and then administered LPS, a significant reduction occurred in their ability to produce TNF-alpha. The decreased cytokine production in the thrombocytopenic mice was restored with platelet transfusion. These results suggest that platelets express various TLRs and that the functional significance of one of these, TLR4, appears to be a role in the modulation of LPS-induced thrombocytopenia and TNF-alpha production. This work implicates platelets as important mediators of innate immune responses against invading microorganisms.

Expression and function of Toll-like receptor on T cells

Toll is the founder of a group of pattern recognition receptors, which play a critical role in the innate immunity in Drosophila. At least 13 distinct Toll-like receptors (TLRs), recognising pathogen-associated molecular pattern (PAMPs), have now been identified in humans. Most investigations on TLRs have focused on cells of the innate system. We report here that naïve human T cells expressed high levels of cell surface TLR2 after activation by anti-T cell receptor (TCR) antibody and interferon-alpha. Activated cells produced elevated levels of cytokines in response to the TLR2 ligand, bacterial lipopeptide (BLP). Furthermore, CD4(+)CD45RO(+) memory T cells from peripheral blood constitutively expressed TLR2 and produced IFNgamma in response to BLP. BLP also markedly enhanced the proliferation and IFNgamma production by CD45RO(+) T cells in the presence of IL-2 or IL-15. Thus, TLR2 serves as a co-stimulatory receptor for antigen-specific T cell development and participates in the maintenance of T cell memory. This suggests that pathogens, via their PAMPs, may contribute directly to the perpetuation and activation of long term T cell memory in both antigen dependent and independent manner.

Murine TLR2 expression analysis and systemic antagonism by usage of specific monoclonal antibodies

Cellular recognition of immuno-stimulatory microbial products alarming the host immune system upon infection, as well as endogenous molecular patterns representing perturbation of regular homeostasis such as through necrosis of host cells is mediated by innate pattern recognition receptors to which toll-like receptors (TLRs) belong. A variety of agonists has been attributed to TLR2. We raised monoclonal antibodies (mAbs) toward the murine TLR2 extracellular domain (mT2ECD) in order to analyze murine TLR2 expression. Murine macrophages were stained TLR2-specifically with distinct mAbs as shown by flow cytometry, immuno precipitation, and immuno-cytochemical analysis. TLR2-specific murine macrophage activation was inhibited through pre-incubation with a mAb mT2.4 while another mTLR2-specific mAb mT2.7 did not affect cell activation through TLR2. Plasmon resonance based analysis showed inhibition of lipopeptide binding to mT2ECD if complex formation with mT2.4 preceded binding analysis. Systemic induction of IL-6, IL-12p40, and GROalpha/KC release to the serum upon lipopeptide challenge of mice was inhibited by systemic administration of mT2.4. Furthermore, 120 mg/kg of mT2.4 protected mice from lethal shock-like syndrome in an experimental low-dose model of septic shock. This result validates blockage of cell surface TLR2 for inhibition of immune cell over-activation upon microbial challenge.

Oligoclonal T cells in histiocytic necrotizing lymphadenopathy are associated with TLR9+ plasmacytoid dendritic cells

Histiocytic necrotizing lymphadenopathy (HNL), a disease of unknown cause, is characterized pathologically by the presence of plasmacytoid dendritic cells (pDCs), which are frequently mixed with oligoclonal T cells (OTCs) and myeloid cells. Toll-like receptors (TLRs 1-10) are a family of pattern recognition receptors of DCs. To investigate the interactions between pDCs and T cells, and to look for an etiology of HNL, we studied 24 HNLs for the profile of TLRs. Transcripts of TLR7, a receptor on pDCs for single-stranded RNA, were found in every case, confirming the universal presence of pDCs. Transcripts of TLR9, another receptor on pDCs for microbial unmethylated CpG-rich DNA, were correlated with OTCs, implying T-cell expansion stimulated by TLR9+ pDCs in response to a microbe. Because PCRs for bacterial 16S rDNAs were negative in the lymph nodes, a bacterial origin seems unlikely, but a virus remains a possible candidate. The pDCs lacked the maturation marker CD83, which suggested ineffective stimulation of T cells and might account for the usually benign course of HNL. Taken together, these data illustrate a novel approach, based upon TLR transcript analysis, for the integration of pathology, immunology, and clinical findings of HNL.

Intact gram-negative Helicobacter pylori, Helicobacter felis, and Helicobacter hepaticus bacteria activate innate immunity via toll-like receptor 2 but not toll-like receptor 4

Molecular and genetic studies have demonstrated that members of the Toll-like receptor (TLR) family are critical innate immune receptors. TLRs are recognition receptors for a diverse group of microbial ligands including bacteria, fungi, and viruses. This study demonstrates that distinct TLRs are responsible for the recognition of Helicobacter lipopolysaccharide (LPS) versus intact Helicobacter bacteria. We show that the cytokine-inducing activity of Helicobacter LPS was mediated by TLR4; i.e., TLR4-deficient macrophages were unresponsive to Helicobacter pylori LPS. Surprisingly, the cytokine response to whole Helicobacter bacteria (H. pylori, H. hepaticus, and H. felis) was mediated not by TLR4 but rather by TLR2. Studies of HEK293 transfectants revealed that expression of human TLR2 was sufficient to confer responsiveness to intact Helicobacter bacteria, but TLR4 transfection was not sufficient. Our studies further suggest that cag pathogenicity island genes may modulate the TLR2 agonist activity of H. pylori as cagA+ bacteria were more active on a per-cell basis compared to cagA mutant bacteria for interleukin-8 (IL-8) cytokine secretion. Consistent with the transfection studies, analysis of knockout mice demonstrated that TLR2 was required for the cytokine response to intact Helicobacter bacteria. Macrophages from both wild-type and TLR4-deficient mice produced a robust cytokine secretion response (IL-6 and MCP-1) when stimulated with intact Helicobacter bacteria. In contrast, macrophages from TLR2-deficient mice were profoundly unresponsive to intact Helicobacter stimulation, failing to secrete cytokines even at high (100:1) bacterium-to-macrophage ratios. Our studies suggest that TLR2 may be the dominant innate immune receptor for recognition of gastrointestinal Helicobacter species.

Gene expression of Toll-like receptor-2, Toll-like receptor-4, and MD2 is differentially regulated in rabbits with Escherichia coli pneumonia

Sepsis, a common sequela to Gram-negative pneumonia, results in considerable morbidity and mortality in hospitalized patients. The goal of this study was to determine whether Gram-negative pneumonia alters the expression TLR2, TLR4, and MD2 in lungs or in organs distant to the site of the primary infection. The cDNA sequence coding open reading frames for rabbit TLR2, TLR4, and MD2 were cloned and expressed in Escherichia coli, and specific polyclonal antibodies and polymerase chain reaction (PCR) probes were produced to identify changes in these receptors in rabbits with Gram-negative pneumonia. Using tissues from lungs and distant organs, we show that TLR2, TLR4, and MD2 gene expression is differentially regulated in rabbits with E. coli pneumonia. The increased expression of TLR2 and TLR4 could play an important role in the innate immune response to bacterial infection in the lungs, and improve pathogen recognition and bacterial clearance. In contrast, the increased gene expression of TLR2, TLR4, and MD2 in organs distant to the primary site of infection may contribute to the deleterious systemic inflammatory response observed in patients with sepsis.

Triacyl-lipopentapeptide adjuvants: TLR2-dependent activation of macrophages and modulation of receptor-mediated cell activation by altering acyl-moieties

Synthetic lipopeptides derived from bacterial lipoprotein are efficient immunoadjuvants. In vitro they activate antigen presenting cells (APCs) to induce the translocation of nuclear factor kappa B (NF-kappaB) and the activation of further transcription factors. This results in the expression of genes encoding cytokines such as IL-1, IL-6, TNF-alpha and in the release of reactive oxygen/nitrogen intermediates. The molecular structure of microbial products determines TLR specificity and thus their activatory potential and immunoadjuvanticity. In the present study, we investigated the lipopeptide-induced activation of leukocytes at different cellular levels by applying derivatives of a synthetic lipopentapeptide-fatty acid library. Our results show that TLR2 plays a key role for the activation of bone marrow-derived macrophages (BMDMs) by lipopentapeptide derivatives and that the fatty acid composition of the lipopeptides determines their activation potential and TLR specificity.