Identification of hTLR10: a novel human Toll-like receptor preferentially expressed in immune cells

Toll-like receptors and damage-associated molecular patterns: novel links between inflammation and hypertension

Low-grade systemic inflammation is a common manifestation of hypertension; however, the exact mechanisms that initiate this pathophysiological response, thereby contributing to further increases in blood pressure, are not well understood. Aberrant vascular inflammation and reactivity via activation of the innate immune system may be the first step in the pathogenesis of hypertension. One of the functions of the innate immune system is to recognize and respond to danger. Danger signals can arise from not only pathogenic stimuli but also endogenous molecules released following cell injury and/or death [damage-associated molecular patterns (DAMPs)]. In the short-term, activation of the innate immune system is beneficial in the vasculature by providing cytoprotective mechanisms and facilitating tissue repair following injury or infection. However, sustained or excessive immune system activation, such as in autoimmune diseases, may be deleterious and can lead to maladaptive, irreversible changes to vascular structure and function. An initial source of DAMPs that enter the circulation to activate the innate immune system could arise from modest elevations in peripheral vascular resistance. These stimuli could subsequently lead to ischemic- or pressure-induced events aggravating further cell injury and/or death, providing more DAMPs for innate immune system activation. This review will address and critically evaluate the current literature on the role of the innate immune system in hypertension pathogenesis. The role of Toll-like receptor activation on somatic cells of the vasculature in response to the release of DAMPs and the consequences of this activation on inflammation, vasoreactivity, and vascular remodeling will be specifically discussed.

Gene expression and protein localization of TLR-1, -2, -4 and -6 in amniochorion membranes of pregnancies complicated by histologic chorioamnionitis

OBJECTIVES

To determine whether histologic chorioamnionitis is associated with changes in gene expression of TLR-1, -2, -4 and -6, and to describe the localization of these receptors in fetal membranes.

STUDY DESIGN

A total of 135 amniochorion membranes with or without histologic chorioamnionitis from preterm or term deliveries were included. Fragments of membranes were submitted to total RNA extraction. RNA was reverse transcribed and the quantification of TLRs expression measured by real time PCR.

RESULTS

All amniochorion membranes expressed TLR-1 and TLR-4, whereas 99.1% of membranes expressed TLR-2 and 77.4% expressed TLR-6. TLR-1 and TLR-2 expressions were significantly higher in membranes with histologic chorioamnionitis as compared to membranes without chorioamnionitis in preterm pregnancies (p=0.003 and p<0.001, respectively). Among the membranes of term pregnancies there were no differences in the expressions of such receptors regardless of inflammatory status. Regarding TLR-4 and TLR-6 expression, there was no difference among membranes with or without histologic chorioamnionitis, regardless gestational age at delivery. TLR-1, TLR-2, TLR-4 and TLR-6 expressions were observed in amniotic epithelial, chorionic and decidual cells.

CONCLUSION

Amniochorion membranes express TLR-1, TLR-2, TLR-4 and TLR-6 and increased expression of TLR-1 and TLR-2 is related to the presence of histologic chorioamnionitis in preterm pregnancies. This study provides further evidence that amniochorion membranes act as a mechanical barrier to microorganisms and as components of the innate immune system.

Toll-like receptors' pathway disturbances are associated with increased susceptibility to infections in humans

Toll-like receptors (TLRs) sense microbial products and play an important role in innate immunity. Currently, 11 members of TLRs have been identified in humans, with important function in host defense in early steps of the inflammatory response. TLRs are present in the plasma membrane (TLR1, TLR2, TLR4, TLR5, TLR6) and endosome (TLR3, TLR7, TLR8, TLR9) of leukocytes. TLRs and IL-1R are a family of receptors related to the innate immune response that contain an intracellular domain known as the Toll-IL-1R (TIR) domain that recruits the TIR-containing cytosolic adapters MyD88, TRIF, TIRAP and TRAM. The classical pathway results in the activation of both nuclear factor κB and MAPKs via the IRAK complex, with two active kinases (IRAK-1 and IRAK-4) and two non-catalytic subunits (IRAK-2 and IRAK-3/M). The classical pro-inflammatory TLR signaling pathway leads to the synthesis of inflammatory cytokines and chemokines, such as IL-1β, IL-6, IL-8, IL-12 and TNF-α. In humans, genetic defects have been identified that impair signaling of the TLR pathway and this may result in recurrent pyogenic infections, as well as virus and fungi infections. In this review, we discuss the main mechanisms of microbial recognition and the defects involving TLRs.

Sperm protection in the male reproductive tract by Toll-like receptors

Sperm function can be affected by infection. Our understanding of innate immune system molecular mechanisms has been expanded, by the discovery of 'Toll-like receptors' (TLRs). It seems that these receptors could play a critical role in the protection of spermatozoa. This study seeks to examine the presence and distribution of TLRs in different parts of the human male reproductive tract and spermatozoa. So, TLR gene expression was examined by RT-PCR. Quantitative real-time PCR (Q-PCR) analysis used to compare the expression of TLRs in all sections of the male reproductive tract and TLRs 2, 3 and 4 in testicular sperm extraction (TESE) samples, which contained spermatozoa (TESE+) and those that did not (TESE-). Results showed that all TLR genes were expressed in different parts of the human male reproductive tract and spermatozoa. Moreover, Q-PCR indicated that the relative expression of TLRs did not significantly change in different parts of the male reproductive tract but this technique has shown only relative TLR2 expression in TESE- is lower than TESE+ samples. It could be concluded that TLRs may provide a broad spectrum of protection from infection in the male reproductive tract. Furthermore, TLRs may influence on the developmental process during spermatogenesis.

Toll-like receptors in prostate infection and cancer between bench and bedside

Toll-Like receptors (TLRs) are a family of evolutionary conserved transmembrane proteins that recognize highly conserved molecules in pathogens. TLR-expressing cells represent the first line of defence sensing pathogen invasion, triggering innate immune responses and subsequently priming antigen-specific adaptive immunity. In vitro and in vivo studies on experimental cancer models have shown both anti- and pro-tumoural activity of different TLRs in prostate cancer, indicating these receptors as potential targets for cancer therapy. In this review, we highlight the intriguing duplicity of TLR stimulation by pathogens: their protective role in cases of acute infections, and conversely their negative role in favouring hyperplasia and/or cancer onset, in cases of chronic infections. This review focuses on the role of TLRs in the pathophysiology of prostate infection and cancer by exploring the biological bases of the strict relation between TLRs and prostate cancer. In particular, we highlight the debated question of how reliable mutations or deregulated expression of TLRs are as novel diagnostic or prognostic tools for prostate cancer. So far, the anticancer activity of numerous TLR ligands has been evaluated in clinical trials only in organs other than the prostate. Here we review recent clinical trials based on the most promising TLR agonists in oncology, envisaging a potential application also in prostate cancer therapy.

A missense polymorphism (rs11466653, Met326Thr) of toll-like receptor 10 (TLR10) is associated with tumor size of papillary thyroid carcinoma in the Korean population

Toll-like receptors (TLRs) are important components of innate immune response. The aim of this study was to investigate whether TLR gene cluster (TLR10-TLR1-TLR6) polymorphisms are associated with the etiology of papillary thyroid carcinoma (PTC) and its clinicopathologic characteristics. We recruited 94 PTC patients and 325 control subjects. Genotypes for each SNP were determined by direct sequencing. SNPStats and SPSS 18.0 were used to evaluate odds ratios (ORs), 95 % confidence intervals (CIs), and P values. Multiple logistic regression analyzes of genetic data were performed. The missense SNP rs11466653 was associated with small tumor size (<1 cm) in PTC. The frequency of the rs11466653 T allele was higher in PTC patients with tumors <1 cm in size than in the control group (95.8 vs. 87.2 %; P = 0.021, OR = 0.30, 95 % CI = 0.11-0.83). The T allele of rs11466653 (T/C, Met326Thr) in TLR10 may be a risk factor for the development of tumors in PTC in the Korean population.

Human blood mDC subsets exhibit distinct TLR repertoire and responsiveness

Human blood DCs encompass pDCs and two subsets of mDCs: CD1c(+) mDCs and CD141(+) mDCs. The rare CD141(+) DC population is thought to be the equivalent of mouse CD8α(+) cDCs that play a significant role in antigen cross-presentation. Here, we analyzed by Q-PCR TLR1-10 expression in blood DC subsets. Whereas CD1c(+) DCs express all TLR except TLR9, CD141(+) DCs present a more restricted pattern with high expression of TLR3 and -10, expression of TLR1,-2, -6, and -8, and lack of TLR4, -5, -7, and -9. The in vitro analysis of isolated mDC subset reponsiveness to an extensive panel of TLR ligands confirmed these results, with CD141(+) DCs responding only to TLR1/2, -3, and -7/8. The cytokine/chemokine production profile of isolated CD141(+) DCs was also more restricted, as they produced mainly proinflammatory cytokines but no IL-12 and to a lower level, in comparison with CD1c(+) DCs, except for CXCL10, CCL5, and IFN-β. In contrast, with the use of a whole blood assay, we found that CD141(+) DCs produce IL-12 in response to TLR1/2, -3, and more surprisingly, -9. Finally, both mDC subsets are potent inducers of Th1 response, particularly after TLR3 triggering. Taken together, these data confirmed functional differences between blood mDC subsets. The major response of CD141(+) mDCs to TLR3 ligand and their cytokine production pattern suggest a role for these cells in antiviral immunity.

Lack of association of three common polymorphisms in toll-like receptors (TLRs), TLR2+597T>C, +1350C>T and Arg753Gln with cancer risk: a meta-analysis

BACKGROUND

Single nucleotide polymorphisms (SNPs) occurring in Toll-like receptors (TLRs) may contribute to cancer risk. Many polymorphisms of TLR2 have been studied for associations, but the findings are conflicting.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a meta-analysis of 14 studies to confirm the association between TLR2+597T>C (rs3804099), +1350C>T (rs3804100) and Arg753Gln (rs5743708) polymorphisms and cancer risk. Odds ratio (OR) and 95% confidence intervals (95% CI) were used to assess the strength of associations. There was no significant association between TLR2+597T>C and cancer risk in the codominant models (CC vs. TT: OR = 1.01, 95%CI = 0.86-1.17, Pheterogeneity = 0.148; CT vs. TT: OR = 0.92, 95%CI = 0.69-1.23, Pheterogeneity < 0.001), the recessive model (CC vs. CT+TT: OR = 0.86, 95%CI = 0.67-1.10, Pheterogeneity = 0.007) , the dominant model (CC+CT vs. TT: OR = 0.93, 95%CI = 0.76-1.15, Pheterogeneity = 0.001) and the allele model (C vs. T: OR = 0.93, 95%CI = 0.81-1.08, Pheterogeneity = 0.019). Similarly, no significant associations between TLR2+1350C>T, Arg753Gln polymorphisms and cancer risk were found. However, in the sub-group analysis of ethnicities, the trend of pooled ORs in Asians was opposite to Caucasians.

CONCLUSIONS

The present meta-analysis suggests that TLR2+597T>C (rs3804099), +1350C>T (rs3804100) and Arg753Gln (rs5743708) polymorphisms are not associated with cancer risk.

Cutting-edge report: TLR10 plays a role in mediating bacterial peptidoglycan-induced trophoblast apoptosis

PROBLEM

There is a strong correlation between intrauterine bacterial infection and preterm labor. While inflammation is a common mechanism, certain pathogens may trigger placental apoptosis. TLR2 activation by gram-positive bacterial peptidoglycan (PDG) induces first-trimester trophoblast apoptosis and decreased IL-6 secretion. This is dependent upon the presence of TLR1 and the absence of TLR6 and both TLR2 coreceptors. As TLR10 is also a TLR2 coreceptor, the objective of this study was to determine its expression and function in the trophoblast.

METHOD OF STUDY

First-and third-trimester human placental tissue and isolated trophoblast were evaluated for TLR10 expression. A first-trimester human trophoblast cell line stably transfected with a TLR10 dominant negative (TLR10-DN) or vector control was treated with or without PDG and analyzed for apoptosis and IL-6.

RESULTS

TLR10 was expressed by trophoblasts during the first and third trimesters of pregnancy. PDG-induced trophoblast caspase-3 activity was inhibited by the presence of the TLR10-DN. The presence of the TLR10-DN had no effect on PDG reduction in trophoblast IL-6 secretion.

CONCLUSION

This study demonstrates that trophoblast TLR10 plays a role in promoting apoptosis triggered by gram-positive bacterial components and suggests that TLR10 may regulate the balance between trophoblast survival and cell death.

Distinct signaling pathways regulate TLR2 co-stimulatory function in human T cells

Toll-like receptor 2 (TLR2) serves as a co-stimulatory receptor for human T cells by enhancing T cell receptor (TCR)-induced cytokine production and proliferation. However, it is unknown where signals from the TCR and TLR2 converge to enhance T cell activation. To address this gap, we examined changes in TCR-induced signaling following concurrent TLR2 activation in human T cells. Both proximal TCR-mediated signaling and early NFκB activation were not enhanced by TCR and TLR2 co-activation, potentially due to the association of TLR2 with TLR10. Instead, TLR2 co-induction did augment Akt and Erk1/Erk2 activation in human T cells. These findings demonstrate that TLR2 activates distinct signaling pathways in human T cells and suggest that alterations in expression of TLR2 co-receptors may contribute to aberrant T cell responses.

The role of UNC93B1 protein in surface localization of TLR3 receptor and in cell priming to nucleic acid agonists

Translocation of nucleic acid-sensing (NAS) Toll-like receptors (TLRs) to endosomes is essential for response to microbial nucleic acids as well as for prevention of the autoimmune response. The accessory protein UNC93B1 is indispensable for activation of NAS TLRs because it regulates their response through trafficking to endosomes. We observed that poly(I:C) up-regulates transcription of UNC93B1 and promotes trafficking of TLR3 to the plasma membrane in human epithelial cell line. Up-regulation of UNC93B1 is triggered through TLR3 activation by poly(I:C). Further studies revealed that expression of UNC93B1 promotes trafficking of differentially glycosylated TLR3, but not other NAS TLRs, to the plasma membrane. UNC93B1 promoter region contains binding sites for poly(I:C)- and type I interferon-inducible regulatory elements. UNC93B1 also increases the protein lifetime of TLR3 and TLR9 and augments signaling of all NAS TLRs. Furthermore, we discovered that poly(I:C) pretreatment primes B-cells to the activation by ssDNA via up-regulation of UNC93B1. Our findings identified TLR3 as the important regulator of UNC93B1 that in turn governs the responsiveness of all NAS TLRs.

Toll-like receptor gene polymorphisms confer susceptibility to graft-versus-host disease in allogenic hematopoietic stem cell transplantation

Graft-versus-host disease (GvHD) is a major complication in hematopoietic stem cell transplantation (HSCT). The immune response against gut microbes is thought to be an important factor in the beginning of GvHD. Toll-like receptors (TLR) recognize molecular structures of microbes and viruses and play central part in the innate immunity. We studied whether genetic variation in the TLR1, TLR2, TLR4, TLR5, TLR6 and TLR10 genes confers susceptibility to GvHD in 305 human leucocyte antigen-identical sibling donor HSCT's performed in a single Finnish centre. The results showed that the genetic markers rs4833079 (P = 0.035) in TLR1, rs4837656 (P = 0.032) and rs17582214 (P = 0.029) in TLR4, rs10737416 (P = 0.048) in TLR5, rs6531656 (P = 0.035) in TLR6, and rs337629 (P = 0.005) in TLR10 were associated with the occurrence of acute GvHD. Interestingly, two markers in the TLR5 gene, rs2800230 (P = 0.010) and rs2800237 (P = 0.017), were associated with chronic GvHD. These results indicate that many genes of the TLR system are involved in the overall genetic risk for GvHD and emphasize the role of innate immunity in GvHD.

Herpesviral infection and Toll-like receptor 2

In the last decade, substantial progress has been made in understanding the molecular mechanisms involved in the initial host responses to viral infections. Herpesviral infections can provoke an inflammatory cytokine response, however, the innate pathogen-sensing mechanisms that transduce the signal for this response are poorly understood. In recent years, it has become increasingly evident that the Toll-like receptors (TLRs), which are germline-encoded pattern recognition receptors (PRRs), function as potent sensors for infection. TLRs can induce the activation of the innate immunity by recruiting specific intracellular adaptor proteins to initiate signaling pathways, which then culminating in activation of the nuclear factor kappa B (NF-κB) and interferon-regulatory factors (IRFs) that control the transcription of genes encoding type I interferon (IFN I) and other inflammatory cytokines. Furthermore, activation of innate immunity is critical for mounting adaptive immune responses. In parallel, common mechanisms used by viruses to counteract TLR-mediated responses or to actively subvert these pathways that block recognition and signaling through TLRs for their own benefit are emerging. Recent findings have demonstrated that TLR2 plays a crucial role in initiating the inflammatory process, and surprisingly that the response TLR2 triggers might be overzealous in its attempt to counter the attack by the virus. In this review, we summarize and discuss the recent advances about the specific role of TLR2 in triggering inflammatory responses in herpesvirus infection and the consequences of the alarms raised in the host that they are assigned to protect.

Activation of rabbit TLR9 by different CpG-ODN optimized for mouse and human TLR9

Synthetic CpG-oligodeoxynucleotides (CpG-ODN) are potent adjuvants that accelerate and boost antigen-specific immune responses. Toll-like receptor 9 (TLR9) is the cellular receptor for these CpG-ODN. Previous studies have shown species-specific activation of mouse TLR9 (mTLR9) and human TLR9 (hTLR9) by their optimized CpG-ODN. The interaction between rabbit TLR9 (rabTLR9) and CpG-ODN, however, has not been previously investigated. Here, we cloned and characterized rabTLR9 and comparatively investigated the activation of the rabbit, mouse, and human TLR9 by CpG-ODN. The complete open reading frame of rabTLR9 encodes 1028 amino acid residues, which share 70.6% and 75.5% of the identities of mTLR9 and hTLR9, respectively. Rabbit TLR9 is preferentially expressed in immune cells rich tissues, and is localized in intracellular vesicles. While mTLR9 and hTLR9 displayed species-specific recognition of their optimized CpG-ODN, rabbit TLR9 was activated by these CpG-ODN without any preference. This result suggests that rabTLR9 has a broader ligand-recognition profile than mouse and human TLR9.

Phosphatidylinositol 3-kinase interacts with the glucocorticoid receptor upon TLR2 activation

Airway inflammation is a common condition where glucocorticoids (GC) are a well-established therapy. It has been demonstrated that GC stimulate components of innate immunity. Specifically, GC up-regulate TLR2 expression and activation upon inflammatory stimuli; however, little is known about the signalling involved in this process. To determine the mechanism by which dexamethasone modulates TLR2-induced cytokine production this signalling pathway was monitored in a lung epithelial cell line exposed to the TLR2 synthetic agonist, Pam(3) -Cys-Ser-Lys(4) . These experiments demonstrate that phosphatidylinositol 3-kinase (PI3K) is critical for the TLR2 downstream effects of GC. Cells expressing a PI3K mutant (p85-dominant negative, DN; p85 Δ478-511) and exposed to Pam(3) -Cys-Ser-Lys(4) in the presence or absence of dexamethasone, showed enhanced tumour necrosis factor (TNF)α expression while AP-1 and NF-κB transcriptional activity were repressed. We provide experimental evidence that PI3K physically interacts with the glucocorticoid receptor (GR) through two putative PI3K recruitment consensus YxxM binding motifs in the GR, suggesting that some functions regulated by this receptor might occur through kinase interaction. Mutations of two tyrosine residues in the GR, 598 and 663, to phenylalanine significantly reduced interaction with PI3K and the GC effects on TLR2-induced TNF-α expression. However, these mutations did not alter GR transcriptional activity nor affect cellular localization of the expressed mutant GR in COS-1 cells. Therefore, the PI3K-GR interaction may contribute to the effects of GC on the TLR2 pro-inflammatory signalling cascade, thus defining a novel signalling mechanism with a profound impact on innate immune responses.

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.

Primary IgA nephropathy: new insights into pathogenesis

Since its first description more than 40 years ago, IgA nephropathy has become the most common pattern of primary glomerulonephritis identified in all areas of the world where renal biopsy is routinely performed. This review discusses advances in our understanding of the pathogenesis of IgA nephropathy, principally focusing on work published in the past 5 years. It has been recognized for some time that one of the most consistent features of IgA nephropathy is an alteration in the complement of serum IgA1 O-glycoforms, with an overrepresentation of poorly galactosylated IgA1 O-glycoforms both in the serum and mesangial deposits of patients with IgA nephropathy. New data suggest that poorly galactosylated IgA1 O-glycoforms might act either as autoantigens driving the formation of glycan-specific antibodies, or antigens for cross-reactive antimicrobial antibodies. Formation of these circulating and mesangial IgA-containing immune complexes appears pivotal to the pathogenesis of IgA nephropathy and there is strong in vitro data to support their role in activation of mesangial cells, induction of podocyte injury, and activation of proximal tubular epithelial cells. Genetic factors are likely to influence many facets of pathogenesis both in primary and familial IgA nephropathy, however, to date work in this area has failed to identify consistent candidate genes.

IL-27 enhances LPS-induced proinflammatory cytokine production via upregulation of TLR4 expression and signaling in human monocytes

IL-27, which is produced by activated APCs, bridges innate and adaptive immunity by regulating the development of Th cells. Recent evidence supports a role for IL-27 in the activation of monocytic cells in terms of inflammatory responses. Indeed, proinflammatory and anti-inflammatory activities are attributed to IL-27, and IL-27 production itself is modulated by inflammatory agents such as LPS. IL-27 primes LPS responses in monocytes; however, the molecular mechanism behind this phenomenon is not understood. In this study, we demonstrate that IL-27 priming results in enhanced LPS-induced IL-6, TNF-α, MIP-1α, and MIP-1β expression in human primary monocytes. To elucidate the molecular mechanisms responsible for IL-27 priming, we measured levels of CD14 and TLR4 required for LPS binding. We determined that IL-27 upregulates TLR4 in a STAT3- and NF-κB-dependent manner. Immunofluorescence microscopy revealed enhanced membrane expression of TLR4 and more distinct colocalization of CD14 and TLR4 upon IL-27 priming. Furthermore, IL-27 priming enhanced LPS-induced activation of NF-κB family members. To our knowledge, this study is the first to show a role for IL-27 in regulating TLR4 expression and function. This work is significant as it reveals new mechanisms by which IL-27 can enhance proinflammatory responses that can occur during bacterial infections.

Toll-like receptors: new players in myocardial ischemia/reperfusion injury

Innate immune and inflammatory responses have been implicated in myocardial ischemia/reperfusion (I/R) injury. However, the mechanisms by which innate immunity and inflammatory response are involved in myocardial I/R have not been elucidated completely. Recent studies highlight the role of Toll-like receptors (TLRs) in the induction of innate immune and inflammatory responses. Growing evidence has demonstrated that TLRs play a critical role in myocardial I/R injury. Specifically, deficiency of TLR4 protects the myocardium from ischemic injury, whereas modulation of TLR2 induces cardioprotection against ischemic insult. Importantly, cardioprotection induced by modulation of TLRs involves activation of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway, suggesting that there is a crosstalk between TLRs and PI3K/Akt signaling pathways. In addition, TLRs also associate with other coreceptors, such as macrophage scavenger receptors in the recognition of their ligands. TLRs are also involved in the induction of angiogenesis, modulation of stem cell function, and expression of microRNA, which are currently important topic areas in myocardial I/R. Understanding how TLRs contribute to myocardial I/R injury could provide basic scientific knowledge for the development of new therapeutic approaches for the treatment and management of patients with heart attack.

Toll-like receptor 4 stimulation initiates an inflammatory response that decreases cardiomyocyte contractility

Toll-like receptors (TLRs) have been identified as primary innate immune receptors for the recognition of pathogen-associated molecular patterns by immune cells, initiating a primary response toward invading pathogens and recruitment of the adaptive immune response. TLRs, especially Toll-like receptor 4 (TLR4), can also be stimulated by host-derived molecules and are expressed in the cardiovascular system, thus acting as a possible key link between cardiovascular diseases and the immune system. TLR4 is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia. We used wild-type (WT) mice, TLR4-deficient (TLR4-knockout [ko]) mice, and chimeras that underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the heart (TLR4-ko/WT) and the immunohematopoietic system (WT/TLR4-ko). Following lipopolysaccharide (LPS) challenge (septic shock model) or coronary artery ligation, myocardial ischemia (MI) model, we found WT/TLR4-ko mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of interleukin-1β and tumor necrosis factor-α, and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. The cardiac function of TLR4-ko or WT/TLR4-ko mice was less affected by LPS and demonstrated reduced suppression by MI compared with WT. These results suggest that TLR4 expressed in the cardiomyocytes plays a key role in this acute phenomenon.

Association of Toll-like receptor 10 and susceptibility to Crohn's disease independent of NOD2

Impaired innate inflammatory response has a key role in the Crohn's disease (CD) pathogenesis. The aim of this study was to investigate the possible role of the TLR10-TLR1-TLR6 gene cluster in CD susceptibility. A total of 508 CD patients (284, cohort 1 and 224, cohort 2) and 576 controls were included. TLR10-TLR1-TLR6 cluster single-nucleotide polymorphisms genotyping, NOD2 mutations and TLR10 mRNA quantification were performed using TaqMan assays. Nucleotide-binding oligomerization domain containing 2 (NOD2) and Toll-like receptor (TLR) loci interaction was analyzed by logistic regression and multifactor-dimensionality reduction (MDR). Entropy-based analysis was used to interpret combination effects. One TLR10 haplotype (TLR10(GGGG)) was found associated with CD susceptibility in both cohorts, individuals with two copies had approximately twofold more risk of CD susceptibility than individuals having no copies (odds ratio=1.89, P-value=0.0002). No differences in the mRNA levels were observed among the genotypes. The strongest model for predicting CD risk according to the MDR analysis was a two-locus model including NOD2 mutations and TLR10(GGGG) haplotype (P(c)<0.0001). The interaction gain attributed to the combination of both genes was negative (IG=-2.36%), indicating redundancy or independent effects. Our results support association of the TLR10 gene with CD susceptibility. The effect of TLR10 would be independent of NOD2, suggesting different signaling pathways for both genes.

Identifying innate immune pathways of the chicken may lead to new antiviral therapies

Zoonotic viruses, such as highly pathogenic avian influenza (HPAI), present a significant threat to both the poultry industry and public health. The present method of controlling avian influenza (AI) relies on good farming practice with limited use of vaccination in some countries. However, new ways to control disease outbreaks might be possible with additional knowledge of the natural host response to virus. Moreover, manipulation of the innate immune system in mammals improves the outcomes following viral infection. A similar approach might be applied to the chicken, nevertheless, a greater knowledge of the chicken innate immune system is required. This review outlines important mammalian antiviral mechanisms that have been modulated to strengthen viral immunity and highlights the potential application of these strategies in the chicken, especially in regards, to AI.

Functional interaction of heat shock protein 90 and Beclin 1 modulates Toll-like receptor-mediated autophagy

Autophagy is one of the downstream effector mechanisms for elimination of intracellular microbes following activation of the Toll-like receptors (TLRs). Although the detailed molecular mechanism for this cellular process is still unclear, Beclin 1, a key molecule for autophagy, has been suggested to play a role. Heat shock protein 90 (Hsp90) is a molecular chaperone that regulates the stability of signaling proteins. Herein, we show that Hsp90 forms a complex with Beclin 1 through an evolutionarily conserved domain to maintain the stability of Beclin 1. In monocytic cells, geldanamycin (GA), an Hsp90 inhibitor, effectively promoted proteasomal degradation of Beclin 1 in a concentration-dependent (EC(50) 100 nM) and time-dependent (t(50) 2 h) manner. In contrast, KNK437/Hsp inhibitor I had no effect. Hsp90 specifically interacted with Beclin 1 but not with other adapter proteins in the TLR signalsome. Treatment of cells with GA inhibited TLR3- and TLR4-mediated autophagy. In addition, S. typhimurium infection-induced autophagy was blocked by GA treatment. This further suggested a role of the Hsp90/Beclin 1 in controlling autophagy in response to microbial infections. Taken together, our data revealed that by maintaining the homeostasis of Beclin 1, Hsp90 plays a novel role in TLR-mediated autophagy.

Association between toll-like receptor 10 (TLR10) gene polymorphisms and childhood IgA nephropathy

Toll-like receptors (TLRs) play an important role in the induction and regulation of the innate immune system and adaptive immune responses. TLR10 gene polymorphisms have been reported to be associated with a range of immune-related diseases. In this study, we investigated the association of TLR10 gene polymorphisms with immunoglobulin A nephropathy (IgAN) in Korean children. To examine the association, we genotyped one promoter single nucleotide polymorphisms (SNP) [rs10004195 (-113T/A)] and three missense SNPs [rs11096957 (Asn241His), rs11096955 (Ile369Leu), and rs4129009 (Ile775Val)] using direct sequencing in 199 IgAN patients and 289 control subjects. Our case-control analysis showed that rs10004195 was associated with IgAN (codominant model, p = 0.016 in TT vs. TA; p = 0.044 in TT vs. AA; dominant model, p = 0.0068). In addition, when comparing the proteinuria level of IgAN patients according to the genotypes of each SNP, we found that in dominant model of rs1004195, the level of proteinuria of patients with TA or AA genotypes (median, 4.01 mg/m(2)/h) was higher than that of patients with TT genotype (2.00 mg/m²/h, p = 0.033). In conclusion, these results suggest that TLR10 gene may be associated with susceptibility to IgAN in Korean children.

LPS Sensitizes TRPV1 via Activation of TLR4 in Trigeminal Sensory Neurons

Recent studies have demonstrated that the lipopolysaccharide (LPS) receptor (TLR4) is expressed in TRPV1 containing trigeminal sensory neurons. In this study, we evaluated whether LPS activates trigeminal neurons, and sensitizes TRPV1 responses via TLR4. To test this novel hypothesis, we first demonstrated that LPS binds to receptors in trigeminal neurons using competitive binding. Second, we demonstrated that LPS evoked aconcentration-dependent increase in intracellular calcium accumulation (Ca2+)i and inward currents. Third, LPS significantly sensitized TRPV1 to capsaicin measured by (Ca2+)i, release of calcitonin gene-related peptide, and inward currents. Importantly, a selective TLR4 antagonist blocked these effects. Analysis of these data, collectively, demonstrates that LPS is capable of directly activating trigeminal neurons, and sensitizing TRPV1 via a TLR4-mediated mechanism. These findings are consistent with the hypothesis that trigeminal neurons are capable of detecting pathogenic bacterial components leading to sensitization of TRPV1, possibly contributing to the inflammatory pain often observed in bacterial infections.

Toll-like receptor signaling pathways and the evidence linking toll-like receptor signaling to cardiac ischemia/reperfusion injury

Toll-like receptors (TLRs) play a key role in innate immune defenses. After activation by foreign pathogens or host-derived molecules, TLRs signal via overlapping or distinct signaling cascades and eventually induce numerous genes involved in a variety of cellular responses. A growing body of evidence suggests that TLR signaling also plays an important role in cardiac ischemia/reperfusion injury. We review our current understanding of the TLR signaling pathways and their roles in the pathophysiology of cardiac ischemia/reperfusion injury, as well as discuss several mechanisms for TLR activation and regulation.

Expression of Toll-like receptors by neonatal leukocytes

The immune system of neonates is poorly developed; this increases the susceptibility of neonates to infection. For neonates to counter infection effectively, they first need to recognize the presence of pathogens. Toll-like receptors (TLR) are a family of pattern recognition receptors that alert the host to the presence of invading pathogens. To determine whether differences in TLR expression by leukocytes compensate for immunologic immaturity in neonates, TLR expression by monocytes and T lymphocytes from adults and neonates was compared. Expression of TLR1, TLR2, TLR3, TLR4, TLR8 and TLR9 by monocytes and T lymphocytes was detected with antibodies by flow cytometry. TLR1, TLR2, TLR3, TLR4, TLR8 and TLR9 expression by monocytes was detected in adults and neonates. TLR2, TLR3, TLR4, TLR8 and TLR9 expression by T lymphocytes was detected in adults and neonates. Monocytes and T lymphocytes from neonates are capable, like adults, of recognizing the presence of pathogens through TLR.

Polysaccharides from the root of Angelica sinensis promotes hematopoiesis and thrombopoiesis through the PI3K/AKT pathway

Background

Dozens of Traditional Chinese Medicine (TCM) formulas have been used for promotion of "blood production" for centuries, and we are interested in developing novel thrombopoietic medicines from these TCMs. Our previous studies have demonstrated the hematopoietic effects of DangGui BuXue Tong (DBT), a formula composed of Radix Angelicae Sinensis and Radix Astragali in animal and cellular models. As a step further to identify and characterize the active chemical components of DBT, we tested the hematopoietic and particularly, thrombopoietic effects of polysaccharide-enriched fractions from the root of Radix Angelicae Sinensis (APS) in this study.

Methods

A myelosuppression mouse model was treated with APS (10 mg/kg/day). Peripheral blood cells from APS, thrombopoietin and vehicle-treated samples were then counted at different time-points. Using the colony-forming unit (CFU) assays, we determined the effects of APS on the proliferation and differentiation of hematopoietic stem/progenitor cells and megakaryocytic lineages. Using a megakaryocytic cell line M-07e as model, we analyzed the cellular apoptosis progression with and without APS treatment by Annexin V, Mitochondrial Membrane Potential and Caspase 3 assays. Last, the anti-apoptotic effect of APS on cells treated with Ly294002, a Phosphatidylinositol 3-Kinse inhibitor (PI3K) was also tested.

Results

In animal models, APS significantly enhanced not only the recovery of platelets, other blood cells and their progenitor cells, but also the formation of Colony Forming Unit (CFU). In M-07e cells, we observed the anti-apoptotic effect of APS. Treatment by Ly294002 alone increased the percentage of cells undergoing apoptosis. However, addition of APS to Ly294002-treated cells significantly reduced the percentage of cells undergoing apoptosis.

Conclusions

APS promotes hematopoiesis and thrombopoiesis in the mouse model. This effect likely resulted from the anti-apoptosis activity of APS and is likely to involve the PI3K/AKT pathway.

Toll-like receptors: a novel target for therapeutic intervention in intestinal and hepatic ischemia-reperfusion injury?

IMPORTANCE OF THE FIELD

Toll-like receptors (TLRs) are transmembrane proteins that act mainly as sensors of microbes, orchestrating an organism's defense against infections, while they sense also host tissue injury by recognizing products of dying cells. Ischemia-reperfusion injury (IRI) represents one of these tissue damage states in which TLR-mediated mechanisms might be implicated.

AREAS COVERED IN THIS REVIEW

The most recent data on TLR signaling and the latest knowledge regarding the involvement of TLRs in the pathogenesis and progression of intestinal and hepatic IRI are presented. The potential effectiveness of TLR-modulating therapy in intestinal and liver IRI is also analyzed.

WHAT THE READER WILL GAIN

A comprehensive summary of the data suggesting TLR involvement in intestinal and hepatic IRI. Knowledge required for developing TLR modulation strategies against intestinal and hepatic IRI.

TAKE HOME MESSAGE

TLRS play a significant role in both intestinal and hepatic IRI pathophysiology. Better understanding of TLR involvement in such processes may enable the invention of novel TLR-based therapies for IRI in the intestine and liver.

Reactive oxygen species enhance TLR10 expression in the human monocytic cell line THP-1

We investigated TLR10 expression in human monocytes, THP-1 cells, cultured in hypoxia (3% O₂). Levels of both TLR10 mRNA and protein in THP-1 cells cultured in hypoxia were significantly higher than those cultured in normoxia (20% O₂). We examined intracellular reactive oxygen species (ROS) content in hypoxic cells, and TLR10 expression in cells treated with hydrogen peroxide (H₂O₂), to determine whether the increase in TLR10 expression observed with hypoxia was due to an increase in intracellular ROS levels. We found that the level of intracellular ROS in cells subject to hypoxia was significantly higher than in normoxia. Experiments with ROS synthesis inhibitors revealed that hypoxia induced ROS production is mainly due to NADPH oxidase activity. TLR10 mRNA expression was increased by treatment with H₂O₂ at concentrations ranging from 50 to 250 μM. We screened the TLR10 promoter and found putative binding sites for transcription factors (TFs), such as NF-κB, NF-AT and AP-1. Next, we examined TF activities using a luciferase reporter assay. Activities of NF-κB, NF-AT and AP-1 in the cells treated with H₂O₂ were significantly higher than in untreated cells. The experiment with TF inhibitors revealed that ROS-induced upregulation of TLR10 expression is mainly due to NF-κB activation. Overall, our results suggest that hypoxia or ROS increase TLR10 expression in human monocytes and the transcriptional activities of NF-κB are involved in this process. Therefore, it is suggested that ROS produced by various exogenous stimuli may play a crucial role in the regulation of expression and function of TLR10 as second messengers.

The investigation of toll-like receptor 3, 9 and 10 gene polymorphisms in Turkish rheumatoid arthritis patients

Toll-like receptors (TLRs) play an important role in the induction and regulation of the innate immune system or adaptive immune responses. Genetic variations within human TLRs have been reported to be associated with a range of immune-related diseases. This study was conducted to investigate the frequencies of TLR3 rs3775290, TLR9 rs187084, and TLR10 rs4129009 polymorphisms and to detect between polymorphisms and autoantibody positive as RF, collagen type II, anti-RNP, and anti-CCP in patient group. We performed a case-control study of 100 rheumatoid arthritis (RA) cases and 100 healthy controls matched on age, sex, and residence. All polymorphisms in TLRs were determined by polymerase chain reaction-based restriction fragment length polymorphism. Serum autoantibody level was measured using quantitative ELISA. SNPs were genotyped in all samples. Our results showed that TT genotype for SNP 1237 T/C increased the RA risk significantly (p < 0.05). No statistically significant differences were found in the TLR3 and TLR10 genotypes or allele distribution between RA patients and control individuals. No associations were noted with autoantibody production and TLR3, TLR9, and TLR10 polymorphisms genotypes (p > 0.05). Our study suggests that a single nucleotide polymorphism (rs187084) in TLR9 gene may be a susceptibility factor for RA in Turkish population. Further studies are required to explore the role of TLRs gene polymorphisms in the risk of RA, especially in ethnically different populations to confirm our results.

Pattern recognition via the toll-like receptor system in the human female genital tract

The mucosal surface of the female genital tract is a complex biosystem, which provides a barrier against the outside world and participates in both innate and acquired immune defense systems. This mucosal compartment has adapted to a dynamic, non-sterile environment challenged by a variety of antigenic/inflammatory stimuli associated with sexual intercourse and endogenous vaginal microbiota. Rapid innate immune defenses against microbial infection usually involve the recognition of invading pathogens by specific pattern-recognition receptors recently attributed to the family of Toll-like receptors (TLRs). TLRs recognize conserved pathogen-associated molecular patterns (PAMPs) synthesized by microorganisms including bacteria, fungi, parasites, and viruses as well as endogenous ligands associated with cell damage. Members of the TLR family, which includes 10 human TLRs identified to date, recognize distinct PAMPs produced by various bacterial, fungal, and viral pathogens. The available literature regarding the innate immune system of the female genital tract during human reproductive processes was reviewed in order to identify studies specifically related to the expression and function of TLRs under normal as well as pathological conditions. Increased understanding of these molecules may provide insight into site-specific immunoregulatory mechanisms in the female reproductive tract.

Human TLRs 10 and 1 share common mechanisms of innate immune sensing but not signaling

TLRs are central receptors of the innate immune system that drive host inflammation and adaptive immune responses in response to invading microbes. Among human TLRs, TLR10 is the only family member without a defined agonist or function. Phylogenetic analysis reveals that TLR10 is most related to TLR1 and TLR6, both of which mediate immune responses to a variety of microbial and fungal components in cooperation with TLR2. The generation and analysis of chimeric receptors containing the extracellular recognition domain of TLR10 and the intracellular signaling domain of TLR1, revealed that TLR10 senses triacylated lipopeptides and a wide variety of other microbial-derived agonists shared by TLR1, but not TLR6. TLR10 requires TLR2 for innate immune recognition, and these receptors colocalize in the phagosome and physically interact in an agonist-dependent fashion. Computational modeling and mutational analysis of TLR10 showed preservation of the essential TLR2 dimer interface and lipopeptide-binding channel found in TLR1. Coimmunoprecipitation experiments indicate that, similar to TLR2/1, TLR2/10 complexes recruit the proximal adaptor MyD88 to the activated receptor complex. However, TLR10, alone or in cooperation with TLR2, fails to activate typical TLR-induced signaling, including NF-kappaB-, IL-8-, or IFN-beta-driven reporters. We conclude that human TLR10 cooperates with TLR2 in the sensing of microbes and fungi but possesses a signaling function distinct from that of other TLR2 subfamily members.

TLRs antiviral effect on hepatitis B virus in HepG2 cells

AIMS

A hepatoma cell line, HepG2, was used as a model system to detect Toll-like receptor (TLR) expression in hepatocytes and examine the antiviral effect on hepatitis B virus (HBV).

METHODS AND RESULTS

Toll-like receptor expression was detected in HepG2 cells by RT-PCR. The TLRs, which were strongly expressed in HepG2 cells, were stimulated with specific ligands. Interferon (IFN) response was evaluated poststimulation with Western blotting for signal transduction and activators of transcription-1. Furthermore, HepG2 cells were transiently transfected with wild-type HBV 1.3-fold over-length plasmid and treated with specific ligands at indicated times. Replication of HBV DNA, transcription of HBV RNA intermediate and expression of HBV antigens were respectively detected by Southern blotting, real time PCR, ELISA and Western blotting. Activation of different TLRs induced antiviral effects on HBV to varying degrees.

CONCLUSIONS

The TLRs, which were strongly expressed in HepG2 cells, could be stimulated with specific ligands. Activation of TLRs induced apparent production of antiviral cytokines such as IFN-alpha/beta and inhibited HBV lifecycle in the hepatocyte cell model.

SIGNIFICANCE AND IMPACT OF THE STUDY

Expression of TLRs in hepatocytes may be related to local immunity of liver and participate in the outcome of viral hepatitis.

TLR2 ligands attenuate cardiac dysfunction in polymicrobial sepsis via a phosphoinositide 3-kinase-dependent mechanism

Myocardial dysfunction is a major consequence of septic shock and contributes to the high mortality of sepsis. In the present study, we examined the effect of Toll-like receptor 2 (TLR2) ligands, peptidoglycan (PGN), and Pam3CSK4 (Pam3) on cardiac function in cecal ligation and puncture (CLP)-induced sepsis in mice. We also investigated whether the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway is involved in the effect of TLR2 ligands on cardiac function in CLP mice. PGN was administered to C57B6/L mice 1 h before the induction of CLP. Sham surgically operated mice served as a control. Cardiac function indexes (rate of change in left ventricular pressure, stroke work, cardiac output, and ejection fraction) were examined by a microconductance pressure catheter. Cardiac function was significantly decreased 6 h after CLP-induced sepsis compared with sham-operated control. In contrast, PGN administration attenuated CLP-induced cardiac dysfunction. Importantly, the therapeutic treatment with Pam3 1 h after CLP also significantly attenuated cardiac dysfunction in CLP mice. However, the beneficial effect of TLR2 ligands on cardiac dysfunction in CLP-mice was abolished in TLR2-deficient mice. PGN administration significantly increased the levels of phospho-Akt and phospho-GSK-3beta in the myocardium compared with the levels in untreated CLP mice. PI3K inhibition abolished the PGN-induced attenuation of cardiac dysfunction in CLP mice. In conclusion, these data demonstrate that the administration of TLR2 ligands, PGN, or Pam3 attenuates cardiac dysfunction in septic mice via a TLR2/PI3K-dependent mechanism. More significantly, Pam3 therapeutic treatment will have a potential clinical relevance.

TLR4 signaling induced by lipopolysaccharide or paclitaxel regulates tumor survival and chemoresistance in ovarian cancer

Toll-like receptors (TLRs) expressed on immune cells trigger inflammatory responses. TLRs are also expressed on ovarian cancer (OvCa) cells, but the consequences of signaling by the TLR4/MyD88 pathway in these cells are unclear. Here, TLR4 and MyD88 expression in OvCa tissues (n=20) and cell lines (OVCAR3, SKOV3, AD10, A2780 and CP70) was evaluated by reverse transcriptase-PCR, western blots and immunohistochemistry. Cell growth, apoptosis, nuclear factor-kappaB (NF-kappaB) translocation, IRAK4 and TRIF expression and cJun phosphorylation were measured following tumor cell exposure to the TLR4 ligands, lipopolysaccharide (LPS) or paclitaxel (PTX). Culture supernatants were tested for cytokine levels. TLR4 was expressed in all tumors, tumor cell lines and normal epithelium. MyD88 was detectable in tumor tissues and in 3/5 OvCa lines but not in normal cells. In MyD88(+) SCOV3 cells, LPS or PTX binding to TLR4 induced IRAK4 activation and cJun phosphorylation, activated the NF-kappaB pathway and promoted interleukin (IL)-8, IL-6, vascular endothelial growth factor and monocyte chemotactic protein-1 production and resistance to drug-induced apoptosis. Silencing of TLR4 in SCOV3 cells with small interference RNA resulted in phosphorylated-cJun (p-cJun) downregulation and a loss of PTX resistance. In PTX-sensitive, MyD88(neg) A2780 cells, TLR4 stimulation upregulated TRIF, and TLR4 silencing eliminated this effect. Thus, TLR4/MyD88 signaling supports OvCa progression and chemoresistance, promoting immune escape.

A five-amino-acid motif in the undefined region of the TLR8 ectodomain is required for species-specific ligand recognition

Toll-like receptors play important roles in regulating immunity against microbial infections. Toll-like receptor 8 (TLR8) belongs to a subfamily comprising TLR7, TLR8 and TLR9. Human TLR8 mediates anti-viral immunity by recognizing ssRNA viruses, and triggers potent anti-viral and antitumor immune responses upon ligation by synthetic small molecular weight ligands. Interestingly, distinct from human TLR8, mouse TLR8 was not responsive to ligand stimulation in the absence of polyT-oligodeoxynucleotides (polyT-ODN). The molecular basis for this distinct ligand recognition is still unclear. In the present study, we compared the activation of TLR8 from different species including mouse, rat, human, bovine, porcine, horse, sheep, and cat by ligand ligations. Only the TLR8s from the rodent species (i.e., mouse and rat TLR8s) failed to respond to ligand stimulation in the absence of polyT-ODN. Multiple sequence alignment analysis suggested that these two rodent TLR8s lack a five-amino-acid motif that is conserved in the non-rodent species with varied sequence. This small motif is located in an undefined region of the hTLR8 ectodomain, immediately following LRR-14. Deletion mutation analysis suggested that this motif is essential for the species-specific ligand recognition of hTLR8, whereas it is not required for self-dimerization and intracellular localization of this receptor.

The heterogeneous allelic repertoire of human toll-like receptor (TLR) genes

Toll-Like Receptors (TLR) are critical elements of the innate arm of the vertebrate immune system. They constitute a multigenic family of receptors which collectively bind a diverse array of – exogeneous as well as endogeneous – ligands. An exponential burst of knowledge has defined their biological role in fight against infections and generation/modulation of auto-immune disorders. Hence, they could at least be conceptually recognized – despite being structurally unrelated – as innate counterparts to Major Histocompatibility Complex (MHC) molecules – equally recognizing antigenic ligands (albeit structurally more homogeneous i.e., peptides), again derived from self and/or non-self sources – preeminent this time in adaptive immunity. Our great disparities in face of infections and/or susceptibility to auto-immune diseases have provoked an intense search for genetic explanations, in part satisfied by the extraordinary MHC allelic repertoire. An equally in-depth and systematic analysis of TLR diversity is lacking despite numerous independent reports of a growing number of SNPs within these loci. The work described here aims at providing a preliminary picture of the allelic repertoire – and not purely SNPs – of all 10 human TLR coding sequences (with exception of TLR3) within a single cohort of up to 100 individuals. It appears from our work that TLR are unequally polymorphic: TLR2 (DNA alleles: 7/protein alleles: 3), 4 (4/3), 7 (6/3), 8 (9/2) and 9 (8/3) being comparatively least diverse whereas TLR1 (11/10), 5 (14/12), 6 (10/8) and 10 (15/10) show a substantial number of alleles. In addition to allelic assignment of a large number of SNPs, 10 new polymorphic positions were hereby identified. Hence this work depicts a first overview of the diversity of almost all human TLR genes, a prelude for large-scale population genetics as well as genetic association studies.

The TRIF-dependent signaling pathway is not required for acute cerebral ischemia/reperfusion injury in mice

TIR domain-containing adaptor protein (TRIF) is an adaptor protein in Toll-like receptor (TLR) signaling pathways. Activation of TRIF leads to the activation of interferon regulatory factor 3 (IRF3) and nuclear factor kappa B (NF-kappaB). While studies have shown that TLRs are implicated in cerebral ischemia/reperfusion (I/R) injury and in neuroprotection against ischemia afforded by preconditioning, little is known about TRIF's role in the pathological process following cerebral I/R. The present study investigated the role that TRIF may play in acute cerebral I/R injury. In a mouse model of cerebral I/R induced by transient middle cerebral artery occlusion, we examined the activation of NF-kappaB and IRF3 signaling in ischemic cerebral tissue using ELISA and Western blots. Neurological function and cerebral infarct size were also evaluated 24h after cerebral I/R. NF-kappaB activity and phosphorylation of the inhibitor of kappa B (IkappaBalpha) increased in ischemic brains, but IRF3, inhibitor of kappaB kinase complex-epsilon (IKKepsilon), and TANK-binding kinase1 (TBK1) were not activated after cerebral I/R in wild-type (WT) mice. Interestingly, TRIF deficit did not inhibit NF-kappaB activity or p-IkappaBalpha induced by cerebral I/R. Moreover, although cerebral I/R induced neurological and functional impairments and brain infarction in WT mice, the deficits were not improved and brain infarct size was not reduced in TRIF knockout mice compared to WT mice. Our results demonstrate that the TRIF-dependent signaling pathway is not required for the activation of NF-kappaB signaling and brain injury after acute cerebral I/R.

Polymorphism distribution and structural conservation in RNA-sensing Toll-like receptors 3, 7, and 8 in pigs

BACKGROUND

Viral genomic RNA-both single-stranded (ss) and double-stranded (ds)-is recognized by RNA-sensing Toll-like receptors (TLRs), notably TLR3 (dsRNA), TLR7 (ssRNA), and TLR8 (ssRNA). However, our knowledge of the roles of porcine TLR3, 7, and 8 in antiviral immunity is inadequate.

METHODS

From information on exon-intron boundaries obtained through comparisons of the genomic and cDNA sequences, polymorphisms in the coding sequences of each gene were detected in 84 male pigs of 11 breeds.

RESULTS

Genomic structures are conserved between pigs and humans. The RNA-sensing TLR genes had fewer polymorphisms causing amino acid alterations than did the cell-surface TLR genes, but the alterations were distributed with a similar bias toward ectodomains.

CONCLUSIONS

The low level of diversity of substitutive polymorphisms in RNA-sensing TLRs than cell-surface ones implies that polymorphisms severely affecting function have been eliminated by selection pressure during longstanding pig breeding.

GENERAL SIGNIFICANCE

Recognition of virus-derived RNA is critical in host defense against infection. These results should provide a useful clue to analysis of the association between polymorphisms in RNA-sensing TLRs and disease resistance.

High expression of Toll-like receptor 4 on CD14+ monocytes in acute infectious diseases

Toll-like receptor 4 (TLR4) recognizes lipopolysaccharide (LPS) and other exogenous and endogenous molecules, and is thought to contribute to defense mechanisms against infections. Our objective was to elucidate the clinical significance of TLR4 in acute infectious diseases by analyzing its sequential expression on CD14+ monocytes. Peripheral blood samples were obtained from 36 patients with acute infectious diseases on admission and after treatment within certain intervals. The TLR4 expression on CD14+ monocytes was analyzed using flow cytometry and was presented as a mean fluorescence intensity (MFI). TLR4 expression during the acute phase of infection was highly enhanced compared to that of normal subjects (MFI: 22.1 vs 8.5). TLR4 expression was promptly reduced to normal levels in parallel with the disease improvement. In patients who died despite treatment, the enhancement of TLR4 expression during the acute phase was less prominent compared to those who survived (MFI: 14.6 vs 23.5) and its sequential change was also subtle. These results indicate that monocytes respond to acute infections by the induction of TLR4 expression and that a poor response may be associated with a poor prognosis.

Nuclear factor kappaB (NF-kappaB) activation primes cells to a pro-inflammatory polarized response to a Toll-like receptor 7 (TLR7) agonist

TLR7 (Toll-like receptor 7) mediates anti-viral immunity by recognizing ssRNA (single-stranded RNA) viruses. Small-molecular-mass TLR7 agonists have been approved, or are being evaluated, for treatment of cancers or infectious diseases. Although TLR7 is predominantly expressed in a restricted set of immune cell types, including pDCs (plasmacytoid dendritic cells), it is also expressed in non-native expressing cells (e.g. hepatocytes) under certain circumstances. To elucidate the molecular basis of TLR7 induction by pro-inflammatory stimulation and the subsequent cellular responses in these non-native TLR7-expressing cell types, we first cloned and characterized the 5'-promoter region of TLR7. The proximal region of this promoter drives the transcription of the TLR7 gene. Pro-inflammatory stimuli activated TLR 7 transcription via a NF-kappaB (nuclear factor kappaB)-binding motif in this region, and this activation could be blocked by mutation of the NF-kappaB binding site or addition of NF-kappaB inhibitors. Further studies showed that pretreatment of the Hep3B hepatocytes with TNF-alpha (tumour necrosis factor-alpha) or IL-1 (interleukin-1) rendered them responsive to TLR7 activation by a TLR7 agonist. However, distinct from TLR7 activation in pDCs, which respond to stimulation with Th1 polarized cytokine production, TLR7 induction by pro-inflammatory signals in hepatocytes reconstitutes the NF-kappaB-dependent cascade but not the IRF7 (interferon regulatory factor 7)-dependent cascade, resulting in a pro-inflammatory polarized response rather than a Th1 polarized response. These results indicate that inflammatory stimulation is capable of priming cells to respond to TLR7 agonist with an immune response that differs from that in native TLR7-expressing cells.

Characterization of possible correlates of protective response against Brucella ovis infection in rams immunized with the B. melitensis Rev 1 vaccine

Vaccination with the live attenuated Brucella melitensis Rev 1 vaccine is used to control ovine brucellosis caused by Brucella ovis in sheep. The objective of this study was to identify possible correlates of protective response to B. ovis infection through the characterization by microarray hybridization and real-time RT-PCR of inflammatory and immune response genes differentially expressed in rams previously immunized with B. melitensis Rev 1 and experimentally challenged with B. ovis. Gene expression profiles were compared before and after challenge with B. ovis between rams protected and those vaccinated but found infected after challenge. The TLR10, Bak and ANXI genes were expressed at higher levels in vaccinated and protected rams. These genes provide possible correlates of protective response to B. ovis infection in rams immunized with the B. melitensis Rev 1 vaccine.

Microbial antigens mediate HLA-B27 diseases via TLRs

HLA-B27 positive individuals are predisposed to reactive arthritis developing 1-3 weeks after urogenital and gastrointestinal infections. Also ankylosing spondylitis (AS) associates strongly to HLA-B27, but no specific infection, Klebsiella pneumoniae excluded, has been linked to it. Before the discovery of its HLA-B27 association there were many reports suggesting a link between chronic prostatitis in men or pelvic inflammatory disease in women and AS. They have since been forgotten although HLA-B27 did not help to understand, why this disease has an axial and ascending nature. It is proposed that the urogenital organs form a source of damage (or danger)-associated molecular patterns (DAMPs), either exogenous pathogen-associated molecular patterns (PAMPs) from microbes or endogenous alarmins, such as uric acid, released from necrotic cells or urate deposits. DAMPs are slowly seeded from low-down upwards via the pelvic and spinal lymphatic pathways. They reach Toll-like receptors (TLRs) in their target mesenchymal stem cells, which are stimulated to ectopic enchondral bone formation leading to syndesmophytes and bamboo spine. At the same time inflammatory cytokines induce secondary osteoporosis of the spine. This new paradigm places microbes, HLA-B27 and TLRs in the pathogenic centre stage, but without pinpointing any (one) specific pathogen; instead, shared microbial patterns are indicated.

Activation of dendritic cells by toll-like receptors and C-type lectins

As sentinels of the immune system, dendritic cells (DC) scan their environment for the presence of pathogens. DC sense pathogens either directly or indirectly via endogenous factors such as cytokines and chemokines, which are produced by other cell types in response to infection. Although indirect signals in form of endogenous factors alert DC, direct activation of DC by pathogen-associated molecular patterns (PAMP) is crucial for the induction of primary T cell responses. Direct recognition of PAMP is mediated by pattern recognition receptors (PRR) such as Toll-like receptors (TLR) and C-type lectin receptors (CLR). The molecular patterns that are recognized by these receptors are indispensable for the life cycle of the pathogens, and their structure or cellular localization is different from that of the host. TLR detect cell-wall components of bacteria, fungi, and protozoa at the cell surface or bacterial and viral nucleic acid structures in a specialized endosomal compartment, while CLR that are involved in pattern recognition bind to carbohydrate structures associated with pathogens.

Toll-like receptors and cytokines as surrogate biomarkers for evaluating vaginal immune response following microbicide administration

Topical microbicides are intended for frequent use by women in reproductive age. Hence, it is essential to evaluate their impact on mucosal immune function in the vagina. In the present study, we evaluated nisin, a naturally occurring antimicrobial peptide (AMP), for its efficacy as an intravaginal microbicide. Its effect on the vaginal immune function was determined by localizing Toll-like receptors (TLRs-3, 9) and cytokines (IL-4, 6 , 10 and TNF-α) in the rabbit cervicovaginal epithelium following intravaginal administration of high dose of nisin gel for 14 consecutive days. The results revealed no alteration in the expression of TLRs and cytokines at both protein and mRNA levels. However, in SDS gel-treated group, the levels were significantly upregulated with the induction of NF-κB signalling cascade. Thus, TLRs and cytokines appear as sensitive indicators for screening immunotoxic potential of candidate microbicides.

FimH adhesin of type 1 fimbriae is a potent inducer of innate antimicrobial responses which requires TLR4 and type 1 interferon signalling

Components of bacteria have been shown to induce innate antiviral immunity via Toll-like receptors (TLRs). We have recently shown that FimH, the adhesin portion of type 1 fimbria, can induce the innate immune system via TLR4. Here we report that FimH induces potent in vitro and in vivo innate antimicrobial responses. FimH induced an innate antiviral state in murine macrophage and primary MEFs which was correlated with IFN-beta production. Moreover, FimH induced the innate antiviral responses in cells from wild type, but not from MyD88(-/-), Trif(-/-), IFN-alpha/betaR(-/-) or IRF3(-/-) mice. Vaginal delivery of FimH, but not LPS, completely protected wild type, but not MyD88(-/-), IFN-alpha/betaR(-/-), IRF3(-/-) or TLR4(-/-) mice from subsequent genital HSV-2 challenge. The FimH-induced innate antiviral immunity correlated with the production of IFN-beta, but not IFN-alpha or IFN-gamma. To examine whether FimH plays a role in innate immune induction in the context of a natural infection, the innate immune responses to wild type uropathogenic E. coli (UPEC) and a FimH null mutant were examined in the urinary tract of C57Bl/6 (B6) mice and TLR4-deficient mice. While UPEC expressing FimH induced a robust polymorphonuclear response in B6, but not TLR4(-/-) mice, mutant bacteria lacking FimH did not. In addition, the presence of TLR4 was essential for innate control of and protection against UPEC. Our results demonstrate that FimH is a potent inducer of innate antimicrobial responses and signals differently, from that of LPS, via TLR4 at mucosal surfaces. Our studies suggest that FimH can potentially be used as an innate microbicide against mucosal pathogens.