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

No longer an innocent bystander: epithelial toll-like receptor signaling in the development of mucosal inflammation

Diseases of mucosal inflammation represent important causes of morbidity and mortality, and have led to intense research efforts to understand the factors that lead to their development. It is well accepted that a breakdown of the normally impermeant epithelial barrier of the intestine, the lung, and the kidney is associated with the development of inflammatory disease in these organs, yet significant controversy exists as to how this breakdown actually occurs, and how such a breakdown may lead to inflammation. In this regard, much work has focused upon the role of the epithelium as an “innocent bystander,” a target of a leukocyte-mediated inflammatory cascade that leads to its destruction in the mucosal inflammatory process. However, recent evidence from a variety of laboratories indicates that the epithelium is not merely a passive component in the steps that lead to mucosal inflammation, but is a central participant in the process. In addressing this controversy, we and others have determined that epithelial cells express Toll-like receptors (TLRs) of the innate immune system, and that activation of TLRs by endogenous and exogenous ligands may play a central role in determining the balance between a state of “mucosal homeostasis,” as is required for optimal organ function, and “mucosal injury,” leading to mucosal inflammation and barrier breakdown. In particular, activation of TLRs within intestinal epithelial cells leads to the development of cellular injury and impairment in mucosal repair in the pathogenesis of intestinal inflammation, while activation of TLRs in the lung and kidney may participate in the development of pneumonitis and nephritis respectively. Recent work in support of these concepts is extensively reviewed, while essential areas of further study that are required to determine the significance of epithelial TLR signaling during states of health and disease are outlined.

NOX enzymes and Toll-like receptor signaling

Invading microorganisms are recognized by the host innate immune system through pattern recognition receptors. Among these receptors, Toll-like receptors (TLRs) are able to sense the molecular signatures of microbial pathogens, protozoa, fungi, and virus and activate proinflammatory signaling cascades. In addition to their role in bacterial killing by phagocytes, reactive oxygen species generated by NADPH oxidase (NOX) homologues also play key roles in signaling and host defense in a variety of cell types. Recent studies have demonstrated a link between TLR activation and NOX homologues following microbial recognition highlighting their important role in the innate immune response and host defense.

Antiviral responses of human Fallopian tube epithelial cells to toll-like receptor 3 agonist poly(I:C)

OBJECTIVE

To examine the expression of toll-like receptors (TLR) by primary human Fallopian tube epithelial cells (FTEC) and to determine whether exposure to the TLR3 agonist poly(I:C) induces an antiviral response.

DESIGN

Tissue culture study.

SETTING

University medical center.

PATIENT(S)

Premenopausal women undergoing hysterectomy.

INTERVENTION(S)

Primary human FTEC were grown to confluence and high transepithelial resistance and treated with TLR agonists. Conditioned media was collected and RNA was extracted and analyzed for the expression of cytokines, chemokines, and antimicrobial genes.

MAIN OUTCOME MEASURE(S)

The RNA was analyzed by real-time polymerase chain reaction and protein levels were assessed by enzyme-linked immunosorbent assay.

RESULT(S)

The FTEC were demonstrated to express TLR1-9 but not 10. Treatment of FTEC with TLR3 agonist poly(I:C) resulted in increased expression of interleukin-8, tumor-necrosis factor alpha, human beta-defensin 2, interferon beta, and interferon stimulated genes myxovirus resistance gene 1, 2',5'-oligoadenylate synthetase, and protein kinase R. Additionally, FTEC exposed to poly(I:C) also resulted in the induction of TLR2, TLR3, and TLR7.

CONCLUSION(S)

Our results suggest that FTEC are sensitive to viral infection and/or exposure to viral double-stranded RNA and can respond by secreting proinflammatory cytokines that mediate the initiation of an inflammatory response as well as expressing genes that can directly inhibit viral replication.

Neo-ligands for innate immune receptors and the etiology of sterile inflammatory disease

Microbe recognition based on a small collection of germline-encoded receptors carries a hidden liability: the possibility that mutational changes in the proteome will lead to self-recognition. The risk of self-recognition is enhanced, because innate immune receptors display low specificity, as they are driven to accommodate heterogeneous signature molecules found in the microbial world. The proteome structure is globally constrained by the innate immune sensing apparatus to satisfy a proscription against self-reactivity. But accidents happen, and here it is proposed that mutations creating neo-ligands for innate immune receptors are the proximal cause of sterile inflammatory diseases, which in turn embody the selective pressure that constrains the proteome. Such mutations are predictably dominant and may occur in the germline and also in somatic cells (e.g. in lymphocytes), causing inflammatory effects upon clonal expansion. They may also account for the inflammatory character of selected neoplastic diseases. The neo-ligand hypothesis accounts for the heritability, ambiguous linkage characteristics, phenotypic heterogeneity, and natural history of diverse forms of sterile inflammation. It explains sterile inflammatory diseases as conditions in which aberrant immune signaling is caused by proteome encroachment upon the ligand-recognition space over which the innate immune system stands guard.

Differential constitutive and cytokine-modulated expression of human Toll-like receptors in primary neutrophils, monocytes, and macrophages

Human Toll-like receptors (TLRs) comprise a family of proteins that recognizes pathogen-associated molecular patterns (PAMPs) and initiates host innate immune responses. Neutrophils, monocytes, and macrophages are critical cellular components of the human innate immune system. Proinflammatory cytokines, such as granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), and interferon-gamma (IFN-gamma), have been shown to up-regulate microbicidal activity in these effector cells of innate immunity. Currently, the cellular and molecular mechanisms responsible for these effects are not completely understood. We hypothesized that these cytokines may up-regulate TLR expression as a mechanism to facilitate microbial recognition and augment the innate immune response. Using quantitative realtime rt-PCR technology, we examined constitutive expression of TLR2, TLR4, TLR5, and TLR9 mRNA and the effects of G-CSF, GM-CSF, M-CSF, and IFN-gamma on TLR mRNA expression in purified populations of normal human neutrophils, monocytes, and monocyte-derived macrophages. Relative constitutive expression of TLR2, TLR4, and TLR9 was similar in neutrophils and monocytes. Constitutive expression of TLR5 was less in neutrophils compared to monocytes. Constitutive expression of TLR4 was greater and that of TLR9 lower in monocyte-derived macrophages compared to monocytes. Of the cytokines examined, IFN-gamma and GM-CSF caused the greatest effects on TLR expression. IFN- gamma up-regulated TLR2 and TLR4 in neutrophils and monocytes. GM-CSF up-regulated expression of TLR2 and TLR4 in neutrophils and TLR2 in monocytes. TLR5 was down-regulated by inflammatory cytokines in monocytes. These results suggest a potential role for IFN- gamma and/or GM-CSF as therapeutic immunomodulators of the host defense to infection.

Toll-like receptors in female reproductive tract and their menstrual cycle dependent expression

Rapid innate immune defences against infection usually involve the recognition of invading pathogens by specific pattern recognition receptors recently attributed to the family of Toll-like receptors (TLR). TLRs constitute a major part of innate immune system, and have been characterised in different tissues and organs. Reports from our laboratory and others have demonstrated the existence of TLRs in the female reproductive tract, yet TLRs have not been explored completely in this system. There is little known about variation in TLR expression during the menstrual cycle and the effects that sex hormones may have on their expression and function. Here, we review recent information regarding the existence of TLRs in the female reproductive tract, their function in the maintenance of innate immune system in this tract and their potential role in pregnancy.

The role of epithelial Toll-like receptor signaling in the pathogenesis of intestinal inflammation

Emerging evidence suggests that the innate immune system, comprised of Toll-like receptors (TLRs) and their associated molecules, plays a pivotal role in the regulation of intestinal inflammation and in the response to invading pathogens. Although TLRs are thought to have predominantly beneficial effects in pathogen recognition and bacterial clearance by leukocytes, their dysregulation and unique signaling effects within intestinal epithelia in the setting of inflammation may have devastating consequences. For instance, activation of TLR4 in enterocytes leads to an inhibition of enterocyte migration and proliferation as well as the induction of enterocyte apoptosis-factors that would be expected to promote intestinal injury while inhibiting intestinal repair. TLR signaling has been shown to be abnormal in several intestinal inflammatory diseases, including Crohn's disease, ulcerative colitis, and necrotizing enterocolitis. This review serves to examine the evidence regarding the patterns of expression and signaling of TLRs in the intestinal mucosa at basal levels and during physiologic stressors to gain insights into the pathogenesis of intestinal inflammation. We conclude that the data reviewed suggest that epithelial TLR signaling-acting in concert with TLR signaling by leukocytes-participates in the development of intestinal inflammation. We further conclude that the evidence reviewed provides a rationale for the development of novel, epithelial-specific, TLR-based agents in the management of diseases of intestinal inflammation.

Calcineurin negatively regulates TLR-mediated activation pathways

In innate immunity, microbial components stimulate macrophages to produce antimicrobial substances, cytokines, other proinflammatory mediators, and IFNs via TLRs, which trigger signaling pathways activating NF-kappaB, MAPKs, and IFN response factors. We show in this study that, in contrast to its activating role in T cells, in macrophages the protein phosphatase calcineurin negatively regulates NF-kappaB, MAPKs, and IFN response factor activation by inhibiting the TLR-mediated signaling pathways. Evidence for this novel role for calcineurin was provided by the findings that these signaling pathways are activated when calcineurin is inhibited either by the inhibitors cyclosporin A or FK506 or by small interfering RNA-targeting calcineurin, and that activation of these pathways by TLR ligands is inhibited by the overexpression of a constitutively active form of calcineurin. We further found that IkappaB-alpha degradation, MAPK activation, and TNF-alpha production by FK506 were reduced in macrophages from mice deficient in MyD88, Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF), TLR2, or TLR4, whereas macrophages from TLR3-deficient or TLR9 mutant mice showed the same responses to FK506 as those of wild-type cells. Biochemical studies indicate that calcineurin interacts with MyD88, TRIF, TLR2, and TLR4, but not with TLR3 or TLR9. Collectively, these results suggest that calcineurin negatively regulates TLR-mediated activation pathways in macrophages by inhibiting the adaptor proteins MyD88 and TRIF, and a subset of TLRs.

Genetic analysis of host responses in sepsis

During much of the past century, the microbe itself stood at the heart of microbial pathogenesis. Little thought was devoted to the host per se, though it was granted that differences in susceptibility to certain infections did exist between individuals, and between different ethnic groups. During the past 20 years, extraordinary strides in our grasp of mammalian genetics have made the host side of the equation far more approachable. A restricted collection of genes now presents itself as the likely repository for genetic differences that foretell susceptibility to infectious disease. The Toll-like receptors, of which 10 are presently known to exist in humans, offer an excellent example of this genetic reductionism, in that they embody the afferent component of the innate immune system, and strongly influence the containment of an infection from its earliest stages. The Toll-like receptors were identified as the culmination of a long and relentless inquiry into the yet-unsolved clinical problem of sepsis.

Genetic variability in inflammation pathways and prostate cancer risk

Genetic susceptibility to prostate cancer has been consistently observed by a large number of studies. Recently, several pieces of evidence obtained from epidemiological and pathological studies support that chronic inflammation in prostate tissues may play a role in prostate cancer development. Multiple genes that play critical roles in inflammatory pathways have been associated with prostate cancer risk. In this article we review the key genetic findings of the associated genes. This includes 2 genes identified through family studies, ribonuclease L (RNASEL) and macrophage scavenger receptor 1 (MSR1), as well as a number of genes suggested by case-control studies, such as macrophage inhibitory cytokine-1 (MIC-1), interleukins (IL-8, IL-10), vascular endothelial growth factor (VEGF), intercellular adhesion molecule (ICAM), and Toll-like receptors (TLR-4, TLR-1-6-10 gene cluster). Overall, recent studies seem to suggest multiple genes work together to increase prostate risk, and this is consistent with the reality that inflammation is a very complex process. Thus, future studies are expected to place an emphasis on the study of gene-gene interactions. Advances in high throughput genotyping, data mining, and algorithm development are needed in order to produce interpretable results.

Cloning of canine Toll-like receptor 7 gene and its expression in dog tissues

Toll-like receptor 7 (TLR7) is activated by single strand RNA and imidazoquinoline compounds, and induces interferon production. In this study, canine TLR7 cDNA was cloned and sequenced. The full-length cDNA of canine TLR7 gene was 3419bp, encoding 1032 amino acids. The similarities of canine TLR7 with human and mouse TLR7 were 84 and 80% at the nucleotide sequence level, and 86 and 79% at amino acid sequence level, respectively. Further, the expression of TLR7 mRNA was investigated in canine normal tissues by semiquantitative RT-PCR analysis. The common expression level of TLR7 mRNA in tissues from three dogs examined was in large intestine, lung, pancreas, small intestine and skin, though the expression level in each tissue was varied among these healthy dogs. In other tissues (kidney, liver, lymph node, spleen, adrenal gland, and PBMCs), the level of TLR7 mRNA expression was different in individuals.

Time-course of Toll-like receptor 2 expression, as a predictor of recurrence in patients with bacterial infectious diseases

The clinical course of bacterial infectious diseases is often variable, especially in elderly patients. Thus, new biological markers have been sought to predict the disease outcome. Recent studies have revealed that Toll-like receptor (TLR) 2 and/or TLR4 on circulating monocytes are significantly up-regulated in bacterial infections. However, the lack of reliable quantification methods hampers extensive study on the modulation of these molecules in response to the patient's clinical condition. In this study, we developed a new quantitative flow cytometric analysis system for TLR2. We then carried out a longitudinal study on TLR2 expression levels on monocytes from patients suffering from bacterial infectious diseases during and after antibiotic treatment. The clinical outcome divided 37 patients into 'cure' (n = 24) and 'recurrence' (n = 13) groups. A significant difference between the two groups was recognized in the TLR2 levels just after antibiotic treatment (antibody-binding sites/cell, 4395 +/- 784 versus 5794 +/- 1484, P < 0.001). The risk of recurrence was associated significantly with TLR2 (P < 0.001), but not C-reactive protein (P = 0.351) levels assayed during the first remission. Furthermore, antibiotic effectiveness was associated inversely with TLR2 levels during antibiotic administration (P < 0.001). Taken together, TLR2 expression levels on monocytes provide critical information for planning treatment against bacterial infectious diseases.

Inflammation in prostate carcinogenesis

About 20% of all human cancers are caused by chronic infection or chronic inflammatory states. Recently, a new hypothesis has been proposed for prostate carcinogenesis. It proposes that exposure to environmental factors such as infectious agents and dietary carcinogens, and hormonal imbalances lead to injury of the prostate and to the development of chronic inflammation and regenerative 'risk factor' lesions, referred to as proliferative inflammatory atrophy (PIA). By developing new experimental animal models coupled with classical epidemiological studies, genetic epidemiological studies and molecular pathological approaches, we should be able to determine whether prostate cancer is driven by inflammation, and if so, to develop new strategies to prevent the disease.

MyD88-dependent changes in the pulmonary transcriptome after infection with Chlamydia pneumoniae

Chlamydia pneumoniae, an intracellular bacterium, causes pneumonia in humans and mice. Toll-like receptors and the key adaptor molecule myeloid differentiation factor-88 (MyD88) play a critical role in inducing immunity against this microorganism and are crucial for survival. To explore the influence of MyD88 on induction of immune responses in vivo on a genome-wide level, wildtype (WT) or MyD88(-/-) mice were infected with C. pneumoniae on anesthesia, and the pulmonary transcriptome was analyzed 3 days later by microarrays. We found that the infection caused pulmonary cellular infiltration in WT but not MyD88(-/-) mice. Furthermore, it induced the transcription of 360 genes and repressed 18 genes in WT mice. Of these, 221 genes were not or weakly induced in lungs of MyD88(-/-) mice. This cluster contains primarily genes encoding for chemokines and cytokines like MIP-1alpha, MIP-2, MIP-1gamma, MCP-1, TNF, and KC and other immune effector molecules like immunoresponsive gene-1 and TLR2. Arginase was highly induced after C. pneumoniae infection and was MyD88 dependent. Genes induced by interferons were abundant in a cluster of 102 genes that were only partially MyD88 dependent. Also, lcn2 (lipocalin-2) and timp1 were represented within this cluster. Interestingly, a set of 37 genes including sprr1a was induced more strongly in MyD88(-/-) mice, and most of them are involved in the regulation of cellular replication. In summary, ex vivo analysis of the pulmonary transcriptome on infection with C. pneumoniae demonstrated a major impact of MyD88 on inflammatory responses but not on interferon-type responses and identified MyD88-independent genes involved in cellular replication.

Synthesis and characterization of a dipalmitoylated lipopeptide derived from paralogous lipoproteins of Mycoplasma pneumoniae

Genomic analysis of Mycoplasma pneumoniae revealed the existence of a large number of putative lipoprotein genes compared with the numbers in other bacteria. However, the pathogenic roles of M. pneumoniae lipoproteins are still obscure. In this study, we synthesized a lipopeptide (designated M. pneumoniae paralogous lipoprotein 1 [MPPL-1]) in which an S-dipalmitoylglyceryl cysteine was coupled to a peptide with a consensus sequence of a putative paralogous lipoprotein group characteristic of M. pneumoniae. The cytokine-inducing activity of MPPL-1 in human monocytic cells was much weaker (approximately 700-fold weaker) than that of the known mycoplasmal S-dipalmitoylated lipopeptide FSL-1 or MALP-2. MPPL-1 required Toll-like receptor (TLR2) to activate NF-kappaB-dependent gene transcription in HEK293 cells, although a 1,000-fold-larger amount of MPPL-1 was needed to exert activity similar to that of FSL-1 in the cells. TLR2-mediated recognition of MPPL-1 was synergistically upregulated by TLR6 but not by TLR1 or TLR10, although the activity was still weak. In addition, MPPL-1 did not antagonize FSL-1 recognition in human monocytic cells and TLR2/TLR6-expressing HEK293 cells. Thus, these results suggest that there is preferential selective recognition of diacylated lipopeptides due to the magnitude of an affinity with TLR2 and TLR6 and the roles of increased paralogous lipoprotein genes of M. pneumoniae in evasion of TLR2 recognition.

Human Keratinocytes Express Functional Toll-Like Receptor 3, 4, 5, and 9

Keratinocytes are continuously in contact with external stimuli and have the capacity to produce several soluble mediators. Pathogen-associated molecular patterns (PAMPs) are recognized, among others, by Toll-like receptors (TLRs). The functional responses of keratinocytes to different PAMPs have not yet been fully established. Here we show that keratinocytes constitutively express TLR1, 2, 3, 4, 5, 6, 9, and 10 mRNA, but not TLR7 and 8. Stimulation of keratinocytes with TLR3, 4, 5, and 9 ligands resulted in differential immune-associated responses. Tumor necrosis factor-alpha, CXC chemokine ligand 8 (CXCL8), CCL2, and C chemokine ligand 20 (CCL20) release was enhanced in response to all PAMPs tested, in a time- and dose-dependent manner. Only TLR9 ligand CpG-oligodeoxynucleotides (ODNs) and TLR3 ligand poly-I:C could additionally induce type I IFNs. CCL27 production was selectively induced by poly-I:C and flagellin, whereas CXCL9 and CXCL10 were exclusively induced by CpG-ODNs and/or poly-I:C. Upregulation of ICAM-1, HLA-DR, HLA-ABC, FasR, and CD40 was mainly observed in response to poly-I:C, flagellin, and lipopolysaccharide. Furthermore, PAMP triggering resulted in the phosphorylation of phosphorylated-IkappaB alpha and in the nucleus translocation of NF-kappaB p65. Altogether, these findings stress an unexpectedly multifaceted role of keratinocytes in innate immunity as evident by their differential, TLR-mediated responses to PAMPs associated with different classes of pathogens.

Toll-like receptor-2 expression in normal and pathologic human placenta

Toll-like receptors (TLRs) are important components of the innate immune system and are expressed by trophoblast in normal full-term placenta. At present, not much is known about the role of TLRs during normal pregnancy and in pregnancy complicated by infection. In this study, we have used immunohistochemistry to investigate the expression of TLR2 in 58 placentas from second and third trimester with chorioamnionitis and 25 full-term placentas from uncomplicated pregnancies without chorioamnionitis. TLR2 was found to be localized to the cyto- and syncytio-trophoblast cell layer and to decidual stromal cells. The expression of TLR2 in placentas with chorioamnionitis was significantly lower than in placentas without chorioamnionitis. Furthermore, there was a significantly higher expression in placentas from liveborn children than in placentas from stillborn/aborted fetuses and also a higher expression in second- than in third-trimester placentas. These data suggest that TLR2 expression in the trophoblast could be involved in the response to infectious pathogens in the placenta.

A critical role of CpG motifs in a murine peritonitis model by their binding to highly expressed toll-like receptor-9 on liver NKT cells

BACKGROUND

Toll-like receptor (TLR)-9 plays a critical role in the recognition of the CpG motifs, which is frequently observed in bacterial DNA. To date, there have not been any reports regarding the role of bacterial DNA in the systemic circulation on the development of sepsis.

METHODS

We examined the expression of TLR-9 in the liver and spleen in a murine peritonitis model (CLP mice). We also measured the cytokine response of mononuclear cells (MNCs) from normal and CLP mice to CpG oligodeoxynucleotides (ODN) in vitro and in vivo.

RESULTS

TLR-9 expression on F4/80(+) and NK1.1(+)CD3epsilon(+) cells in the liver of CLP mice was elevated compared to sham-operated mice. With regard to cytokine production, we found that CpG ODN markedly stimulated the production of inflammatory cytokines by murine macrophages and liver MNCs. The intravenous injection of CpG ODN in mice that underwent CLP 12h earlier led to their increased cytokine production and their increased mortality. In addition, the depletion of NK/NKT cells contributed to improve their survival rate.

CONCLUSIONS

Our results suggest that, in patients with overwhelming bacterial infection, bacterial DNA may induce liver toxicity that is mediated by liver NKT cells and macrophages that express high levels of TLR-9.

Genomic organization and transcript profiling of the bovine toll-like receptor gene cluster TLR6-TLR1-TLR10

Toll-like receptors (TLRs) are a family of recognition receptors playing a crucial role in the innate immune system. Different combinations of TLRs are thought to be crucial for effective immune response, thus insight into the organization and expression of TLRs is important for understanding disease resistance. Mastitis is the most frequent and costly disease in dairy production, and the innate immune system is considered to be important in the first line defence against this disease. In the present paper we have characterized the genomic organization of TLR6-TLR1-TLR10 in a approximately 50 kb region of bovine chromosome 6, including 5'-untranslated exons not previously described. A method for gene expression analysis was developed and used for transcription profiling of the three paralogous genes in different bovine tissues. The expression analysis showed similar expression profiles for TLR1 and TLR6, which indicate a co-regulation of these two genes in cattle. TLR10 had a different expression profile, pointing toward a stronger functional diversification compared to TLR1 and TLR6. The differences in expression are in accordance with the evolutionary history of this gene cluster, where TLR10 diverged from the common ancestral gene before the duplication event that created TLR1 and TLR6.

Triad3A Regulates Ubiquitination and Proteasomal Degradation of RIP1 following Disruption of Hsp90 Binding

Toll-like receptors (TLRs) play a crucial role in innate immunity by recognizing microbial pathogens. Triad3A is an E3 ubiquitin-protein ligase that interacts with the Toll/interleukin-1 receptor domain of TLRs and promotes their proteolytic degradation. In the present study, we further investigated its activity on signaling molecules downstream of TLRs and tumor necrosis factor (TNF) receptor 1. Triad3A promoted down-regulation of two TIR domain-containing adapter proteins, TIRAP and TRIF, as well as a RIP1 but had no effect on other adapter molecules in either the TLRs or TNF-alpha signaling pathways. Multiple sequence alignment analysis suggested that RIP1 contains a TIR homologous domain, and mutation of amino acid residues in this domain identified three residues critical for its interaction with Triad3A. Moreover, Triad3A acted as a negative regulator in TNF-alpha signaling. Reduction of Triad3A expression by small interference RNAs rendered cells hyperresponsive to TNF-alpha stimulation. Conversely, overexpression of Triad3A in cells blocked TNF-alpha-induced cell activation. This negative regulation was effected independently of changes in the cellular protein level of RIP1. Further studies indicated that RIP1 formed a complex with Triad3A and heat shock protein 90 (Hsp90), which is a chaperone protein capable of maintaining the stability of its client proteins. Treatment of cells with geldanamycin to disrupt the Hsp90 complex led to proteasomal degradation of RIP1. Depletion of Triad3A by small interference RNA treatment inhibited geldanamycin-activated ubiquitination and proteolytic degradation of RIP1. These results suggest that Triad3A is an E3 ubiquitin-protein ligase to RIP1 and that Hsp90 and Triad3A cooperatively maintain the homeostasis of RIP1.

Menstrual cycle-dependent changes of Toll-like receptors in endometrium

BACKGROUND

Rapid innate immune defences against infection usually involve the recognition of invading pathogens by specific pattern recognition receptors recently attributed to the family of Toll-like receptors (TLRs). Reports from our laboratory and others have demonstrated the existence of TLRs 1-6 in the female reproductive tract. However, little has been done to identify TLRs 7-10 in the female reproductive tract, particularly in the uterus. Also little information exists regarding variation in TLRs in the female reproductive tract during the menstrual cycle.

METHOD

The distribution of TLR7-10 protein was detected by immunostaining in timed endometrial biopsies from normal women. RT-PCR was used to show the existence of TLR1-10 genes in endometrial tissue and real-time PCR analysis to investigate the relative expression of these genes during the menstrual cycle in normal human endometrium.

RESULTS

TLR7-10 proteins were detected in endometrial epithelium and stroma. TLR1-10 genes were expressed in human endometrial tissue, and the mean relative expression of TLR2-6, 9 and 10 genes was significantly higher during the secretory phase compared with other phases of the menstrual cycle.

CONCLUSIONS

TLR7-10 localization is not limited to endometrial epithelium but is also present in the stroma of the endometrial tissue. Endometrial TLR2-6, 9 and 10 genes are cyclically expressed during the menstrual cycle.

Effect of toll-like receptor (TLR) agonists on TLR and microbicide expression in uterine and vaginal tissues of the mouse

PROBLEM

Epithelial cells lining the uterine lumen are the first line of defense against pathogenic microbes. The objective of this study was to examine the expression of Toll-like receptors (TLRs), defensins and secretory leukocyte protease inhibitor (SLPI) in the mouse uterus and vagina and in primary uterine epithelial cells and to determine whether TLR agonists induce TLR and defensin expression.

METHOD OF STUDY

The mRNA expression of alpha- and beta-defensins (AD1, 2 and 5 and BD1, 2 and 4) and SLPI was examined by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) along with the secretion of macrophage chemotactic protein-1 (MCP-1), measured by enzyme-linked immunosorbent assay.

RESULTS

Expression of TLR1-9 as well as beta-defensins 1, 2 and 4 and SLPI by uterine and vaginal tissues was demonstrated by RT-PCR. beta-Defensins and SLPI expression was greater in the vagina than in the uterus. Comparison of fresh and polarized uterine epithelial cells indicated that TLR2-6 expression was unaffected by culture. Incubation of polarized epithelial cells with TLR agonists [lipopolysaccharide (LPS), Pam3Cys, Poly (I:C) or PGN] induced TLR5 and TLR9 expression but had no effect on TLR4, defensins or SLPI. Furthermore, exposure to LPS, Pam3Cys, Poly (I:C) or PGN, induced MCP-1 secretion by polarized epithelial cells in culture.

CONCLUSION

These results indicate that the uterus and vagina as well as uterine epithelial cells are responsive to bacterial and viral pathogens. Not only do epithelial cells respond to TLR agonists by releasing MCP-1, which mediates inflammatory responses, but they also influence the expression of selected TLR genes to further enhance innate immune protection.

Toll-like receptor 9 (TLR9) is present in murine liver sinusoidal endothelial cells (LSECs) and mediates the effect of CpG-oligonucleotides

BACKGROUND/AIMS

Bacterial DNA and synthetic oligonucleotides containing unmethylated motifs have become the focus of many studies due to their ability to activate cells of the innate immune system through interaction with Toll-like receptor 9 (TLR9). This study was undertaken to investigate if and how CpG-oligonucleotides (CpGs) activate liver sinusoidal endothelial cells (LSECs), known to be the main site of clearance of DNA-oligonucleotides from the circulation.

METHODS

Expression of TLR9 was analyzed by RT-PCR and immunohistochemistry. Production of IL-1beta and IL-6 was measured by ELISA.

RESULTS

Here we show for the first time that mouse LSECs express TLR9 mRNA and protein. Moreover, our findings suggest that CpGs are first taken up by LSECs by scavenger receptor(s)-mediated endocytosis, and then join TLR9 in the lysosomal compartments. Furthermore, we found that uptake of CpGs in LSECs results in the activation of transcription factor NF-kappaB and secretion of IL-1beta and IL-6.

CONCLUSIONS

The presence of functional TLR9 in LSECs emphasizes the importance of these cells in the innate defense mechanisms of the liver.

Sequence Variants in Toll-Like Receptor 10 Are Associated with Nasopharyngeal Carcinoma Risk

Nasopharyngeal carcinoma (NPC) is a common malignancy in southern China and Southeast Asia. Genetic susceptibility is a major factor in determining the individual risk of NPC in these areas. To test the association between NPC and variants in Toll-like receptor 10 (TLR10), we conducted a hospital-based case-control study in a Cantonese-speaking population in Guangdong province. Seven single nucleotide polymorphisms in TLR10, selected with a tagging algorithm, were genotyped. When assessing each unique haplotype compared with the most common haplotype, "GAGTGAA," with the expectation-maximization algorithm in Haplo.stats, the risk of developing NPC was significantly elevated among men who carried the haplotype "GCGTGGC" (P = 0.005). After adjusting for age, gender, and VCA-IgA antibody titers, this association was more significant (P = 0.0007). To further assess the overall differences of haplotype frequency profiles between cases and healthy controls, the global score test, considering all haplotypes and adjusting for age, gender, and VCA-IgA antibody titers, gave a haplo score of 27.52 with P = 0.002. The haplotype specific odds ratio was 2.66 (confidence interval, 1.34-3.82) for GCGTGGC. We concluded that in this Cantonese population-based study, haplotype GCGTGGC with frequency of 11.4% in TLR10 was found to be associated with NPC and this association was statistically significant after adjusting for age, gender, and VCA-IgA antibody titers. It is possible that this is not a causal haplotype for NPC; rather, it is in strong linkage disequilibrium with a causal single nucleotide polymorphism in close proximity.

Porcine Toll-like receptor 1, 6, and 10 genes: Complete sequencing of genomic region and expression analysis

Toll-like receptors (TLRs) recognize various microbial components and play key roles in activating the innate immune system. Hence, their function is important in swine infectious diseases. We completely determined 173,804 bp of nucleotide sequence of a genomic region including porcine TLR6 and the newly identified porcine TLR homologues TLR1 and TLR10. The porcine genomic structure of these genes was highly conserved in comparison with the corresponding region in humans. Analysis of their expression in porcine tissues showed differences in expression patterns between porcine TLR10 and TLR1 or TLR6. Moreover, phylogenetic analysis of the cytoplasmic regions of TLR genes suggested that the signal transduction pathway of TLR10 was different from those of TLR1 and TLR6. We also developed six polymorphic microsatellite markers within this genomic region; these markers will be valuable for association studies between TLR genes and resistance or susceptibility to infectious diseases in swine.

Vitamin D3 down-regulates monocyte TLR expression and triggers hyporesponsiveness to pathogen-associated molecular patterns

Toll-like receptors (TLR) represent an ancient front-line defence system that enables the host organism to sense the presence of microbial components within minutes. As inducers of inflammation, TLR act as important triggers of distinct entities such as sepsis or autoimmune disease exacerbation. We report here that vitamin D3 [1alpha,25-dihydroxycholecalciferol, 1,25(OH)(2)D3] suppresses the expression of TLR2 and TLR4 protein and mRNA in human monocytes in a time- and dose-dependent fashion. Despite 1,25(OH)(2)D3-induced up-regulation of CD14, challenge of human monocytes with either LPS or lipoteichoic acid resulted in impaired TNF-alpha and procoagulatory tissue factor (CD142) production, emphasizing the critical role of TLR in the induction of inflammation. Moreover, reduced TLR levels in 1,25(OH)(2)D3-treated phagocytes were accompanied by impaired NF-kappaB/RelA translocation to the nucleus and by reduced p38 and p42/44 (extracellular signal-regulated kinase 1/2) phosphorylation upon TLR-ligand engagement. Both TLR down-regulation and CD14 up-regulation were substantially inhibited by the vitamin D receptor (VDR) antagonist ZK 159222, indicating that the immunomodulatory effect of 1,25(OH)(2)D3 on innate immunity receptors requires VDR transcription factor activation. Our data provide strong evidence that 1,25(OH)(2)D3 primes monocytes to respond less effectively to bacterial cell wall components in a VDR-dependent mechanism, most likely due to decreased levels of TLR2 and TLR4.

Respiratory burst: role in signal transduction in alveolar macrophages

Alveolar macrophages play an important role in defense against airborne pathogens and particles. These macrophages respond through both the adaptive and acquired immune responses, and through the activation of a multitude of signaling pathways. One major macrophage defense mechanism is respiratory burst, the production of reactive oxygen species (ROS). While the ROS produced may act directly in pathogen killing, they may also be involved as secondary signaling messengers. This review focuses on the activation of four main signaling pathways following the production of reactive oxygen species. These pathways include the nuclear factor kappa beta (NFkB), activating protein-1 (AP-1), mitogen-activating protein kinase (MAPK), and phosphotidyl inositol-3 kinase (PI3K) pathways. This review also briefly examines the role of ROS in DNA damage, in particular looking at the base excision repair pathway (BER), the main pathway involved in repair of oxidative DNA damage. This review highlights many of the studies in the field of ROS, signal transduction, and DNA damage; however, work still remains to further elucidate the role of ROS in disease.

Lipopolysaccharide signaling in endothelial cells

Sepsis is the systemic immune response to severe bacterial infection. The innate immune recognition of bacterial and viral products is mediated by a family of transmembrane receptors known as Toll-like receptors (TLRs). In endothelial cells, exposure to lipopolysaccharide (LPS), a major cell wall constituent of Gram-negative bacteria, results in endothelial activation through a receptor complex consisting of TLR4, CD14 and MD2. Recruitment of the adaptor protein myeloid differentiation factor (MyD88) initiates an MyD88-dependent pathway that culminates in the early activation of nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases. In parallel, a MyD88-independent pathway results in a late-phase activation of NF-kappaB. The outcome is the production of various proinflammatory mediators and ultimately cellular injury, leading to the various vascular sequelae of sepsis. This review will focus on the signaling pathways initiated by LPS binding to the TLR4 receptor in endothelial cells and the coordinated regulation of this pathway.

The Toll-like receptors and their role in septic shock

The Toll-like receptors (TLRs) are a class of pattern recognition molecules with unique functions in the innate and the acquired immune systems. The innate immune response has evolved as the immediate host defence system in response to foreign structures and it also serves to prime the adaptive immune response. As such, the TLRs set the tone and pace of the inflammatory response that follows initial contact with a microbial pathogen over the course of the following minutes, hours and days. Sepsis, a leading cause of death in critically ill patients worldwide, is defined as 'the systemic inflammatory response syndrome that occurs during infection' [1]; that is, sepsis is the orchestration of the events controlled by the gene products triggered by signals transduced through the TLRs. Through analysis of the human genome, ten TLRs have been identified, and several of them have been characterised with respect to their associated ligands. Following engagement of the cognate ligand to the ectodomain of each TLR, the assembly of intracellular homo- or heterodimers or multimers induces cell signalling. The receptors are variably expressed on different types of cells, such as neutrophils, dendritic cells, lymphocytes, endothelial cells etc. and can be up- and downregulated, blocked or triggered by mimetic substances. By controlling or modifying TLR responses, the trajectory of the entire septic process may be modified. This review covers the events responsible for TLR activation in detail, with an emphasis on possible points of pharmacological intervention.

PPAR-γ agonists inhibit toll-like receptor-mediated activation of dendritic cells via the MAP kinase and NF-κB pathways

Dendritic cells (DCs) play an important role in initiating and maintaining primary immune responses. However, mechanisms involved in the resolution of these responses are elusive. We analyzed the effects of 15d-PGJ2 and the synthetic peroxisome proliferator-activated receptor (PPAR)-γ ligand troglitazone (TGZ) on the immunogenicity of human monocyte-derived DCs upon stimulation with toll-like receptor (TLR) ligands. Activation of PPAR-γ resulted in a reduced stimulation of DCs via the TLR ligands 2, 3, 4, and 7, characterized by down-regulation of costimulatory and adhesion molecules and reduced secretion of cytokines and chemokines involved in T-lymphocyte activation and recruitment. MCP-1 (monocyte chemotactic protein-1) production was increased due to PPAR-γ activation. Furthermore, TGZ-treated DCs showed a significantly reduced capacity to stimulate T-cell proliferation, emphasizing the inhibitory effect of PPAR-γ activation on TLR-induced DC maturation. Western blot analyses revealed that these inhibitory effects on TLR-induced DC activation were mediated via inhibition of the NF-κB and mitogen-activated protein (MAP) kinase pathways while not affecting the PI3 kinase/Akt signaling. Our data demonstrate that inhibition of the MAP kinase and NF-κB pathways is critically involved in the regulation of TLR and PPAR-γ-mediated signaling in DCs.

In response to pathogens, glial cells dynamically and differentially regulate Toll-like receptor gene expression

The mechanisms that mediate innate immune recognition of CNS infections are unknown. This study provides a comparison of Toll-like receptor (TLR) gene expression in resting and virus infected CNS cells. N2a neuroblastoma cells expressed TLR 3 but demonstrated no change in TLR gene expression in response to either LPS or virus infection. N9 microglia and differentiated primary astrocytes expressed most TLR genes. TLR 2 expression was highest in N9 microglia and TLR 7 in astrocytes. In both glial cell types, LPS stimulation upregulated pro-inflammatory cytokines, TLR 2 and TLR 3 gene expression but down-regulated other TLR genes. RNA virus infection substantially increased levels of type-I interferon (IFN) and TLR 3 transcripts and to a lesser extent TLR 9 transcripts. Microglia and astrocytes thus have the ability to discriminate between pathogens and elicit an appropriate response.

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Expression and regulation of Toll-like receptor 2 by IL-1beta and fibronectin fragments in human articular chondrocytes

OBJECTIVE

The objective of this study was to examine expression and regulation of Toll-like receptor 2 (TLR2) in human articular chondrocytes.

METHODS

Human articular chondrocytes were enzymatically isolated from normal and osteoarthritic knee cartilage. Immunohistochemistry, Western blotting, and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to assess the expression of toll-like receptors. Following stimulation of chondrocytes in vitro by IL-1beta and fibronectin proteolytic fragments, the relative levels of mRNA for TLR2 were determined by quantitative real-time PCR. MyD88 activation and nuclear factor-kappaB (NF-kappaB) translocation were evaluated by immunoprecipitation and electrophoretic mobility shift assay, respectively.

RESULTS

Human articular chondrocytes mainly expressed TLR1, 2, 5 by RT-PCR. Protein expression of TLR2 was also identified in adult human articular cartilage. TLR2 was upregulated following IL-1beta and fibronectin proteolytic fragments stimulation in primary cultures of osteoarthritic articular chondrocytes. Fibronectin proteolytic fragments-induced TLR2 upregulation involved an IL-1beta autocrine/paracrine pathway.

CONCLUSIONS

TLR2 is expressed in human articular cartilage and is upregulated by proarthritic agents including IL-1beta and fibronectin fragments. Signaling through TLR is a novel pro-inflammatory mechanism in osteoarthritis and targeting of these signaling pathways may be of value in treatment of degenerative joint disease.

Cloning of canine toll-like receptor 9 and its expression in dog tissues

Toll-like receptor 9 (TLR9) is activated by bacterial DNA and induces production of inflammatory cytokines. In this study, canine TLR9 cDNA was cloned and sequenced. Further, the expression of TLR9 mRNA was investigated in canine tissues. The full-length cDNA for the canine TLR9 gene was 3419bp encoding 1032 amino acids. The similarity of canine TLR9 with those of cat, cattle, human, mouse and pig was 90, 84.3, 83.6, 76.3 and 85.2% at the nucleotide level, and 90.5, 82.7, 81.4, 74.8 and 85.7% at the amino acid level. By reverse transcription-polymerase chain reaction (RT-PCR) analysis, canine TLR9 mRNA was detected in venous blood mononuclear cells and lymph node and weakly in spleen, whereas it was not detected in kidney, liver, pancreas, lung, small intestine, large intestine, heart, skin, muscle, stomach and bladder.

TLR agonists as vaccine adjuvants: comparison of CpG ODN and Resiquimod (R-848)

TLR ligands that mimic pathogen associated molecular patterns and activate immune cells via Toll-like receptors (TLRs) are being developed for use in humans as therapy against a variety of diseases as well as vaccine adjuvants. These include imidazoquinoline compounds such as Imiquimod and Resiquimod (R-848) that bind to TLR7 and 8, as well as CpG oligodeoxynucleotides (CpG ODN) that bind to TLR9. This study was aimed at comparing CpG ODN and R-848 for their potential use as vaccine adjuvants and to determine whether there are additive or synergistic effects when they are used together. Using HBsAg as a model antigen in mice, we show CpG ODN to be superior to R-848 for augmenting both humoral and cell mediated immune responses.

Evidence of Toll-like receptor molecules on human platelets

Platelets are primarily involved in thrombosis and haemostasis, and they have recently been shown to have a role in innate immunity and in inflammation. We have determined the markers of innate immunity that are expressed by platelets, specifically the Toll-like receptors (TLR), originating from mixes of platelet concentrates (MPC, n = 5) between day zero and day five after blood collection. The surface membrane and intracellular expression of TLR were measured, both after and without permeabilization, using flow cytometry. We observed weak expression of TLR2, TLR4 and TLR9 on the surface of CD41(+) platelets. The expression levels of TLR4 were high (59 +/- 2.2%). Moreover, there was a significant expression of TLR2 (47.5 +/- 4.8%), TLR4 (78.8 +/- 1.3%) and TLR9 (34.2 +/- 7.5%) in the cytoplasm of CD41(+) platelets. The expression of the three receptors did not change significantly during the course of the 5 day observation period. The percentage of TLR expression is significantly modulated between activated versus non-activated platelets, both after and without permeabilization (P < 0.01). Study of the expression of TLR could increase our knowledge of the level of platelet participation during an immune reaction and inflammation. In the same way as the platelet ligand/receptor pair CD40L/CD40 is, the TLR are expressed by platelets, and could serve as a link between innate and adaptive immunity.

The Toll-like receptors: analysis by forward genetic methods

Many genes, and conceivably most genes, are constitutively expressed yet have conditional functions. Their products are utilized only under special circumstances, and enforce homeostatic regulation. Mutations do not disclose the function of such genes unless the proper conditions are applied. The genes that encode the Toll-like receptors (TLRs) fall into this category. The TLRs represent the principal sensors of infection in mammals. Absent infection, mammals have little need for the TLRs; they are essential only when microbes gain access to the interior milieu of the host. The function of the TLRs in mammals was first disclosed by a spontaneous mutation in a locus called Lps, when it was shown by positional cloning to be identical to Tlr4. Random germline mutagenesis has since permitted an estimate of the total number of proteins required for TLR signaling to the level of tumor necrosis factor (TNF) synthesis and activity, and has also shown that these sensors are extremely broad in their ability to detect microbes. Ultimately, the TLRs are responsible for most infection-related phenomena, both good and bad. These include the development of fever, shock, and tissue injury, but also the activation of innate and adaptive effector mechanisms that lead to the elimination of microbes.

TLR signaling in the gut in health and disease

The human intestine has evolved in the presence of diverse enteric microflora. TLRs convert the recognition of pathogen-associated molecules in the gut into signals for anti-microbial peptide expression, barrier fortification, and proliferation of epithelial cells. Healing of injured intestinal epithelium and clearance of intramucosal bacteria require the presence of intact TLR signaling. Nucleotide oligomerization domain (Nod)1 and Nod2 are additional pattern recognition receptors that are required for defense against invasive enteric pathogens. Through spatial and functional localization of TLR and Nod molecules, the normal gut maintains a state of controlled inflammation. By contrast, patients with inflammatory bowel disease demonstrate inflammation in response to the normal flora. A subset of these patients carry polymorphisms in TLR and CARD15/NOD2 genes. A better understanding of the delicate regulation of TLR and Nod molecules in the gut may lead to improved treatment for enteric infections and idiopathic inflammatory bowel diseases.

Sequence variants in Toll-like receptor gene cluster (TLR6-TLR1-TLR10) and prostate cancer risk

BACKGROUND

Chronic inflammation plays an important role in several human cancers and may be involved in the etiology of prostate cancer. Toll-like receptors (TLRs) are important in the innate immune response to pathogens and in cross-talk between innate immunity and adaptive immunity. Our previous finding of an association of TLR4 gene sequence variants and prostate cancer risk provides evidence for a role of TLRs in prostate cancer. In this study, we investigated whether sequence variants in the TLR6-TLR1-TLR10 gene cluster, residing within a 54-kb region on 4p14, were associated with prostate cancer risk.

METHODS

We selected 32 single-nucleotide polymorphisms (SNPs) covering these three genes and genotyped these SNPs in 96 control subjects from the Cancer Prostate in Sweden (CAPS) population-based prostate cancer case-control study. Five distinct haplotype blocks were inferred at this region, and we identified 17 haplotype-tagging SNPs (htSNPs) that could uniquely describe >95% of the haplotypes. These 17 htSNPs were then genotyped in the entire CAPS study population (1383 case subjects and 780 control subjects). Odds ratios of prostate cancer for the carriers of a variant allele versus those with the wild-type allele were estimated using unconditional logistic regression.

RESULTS

The allele frequencies of 11 of the 17 SNPs were statistically significantly different between case and control subjects (P = .04-.001), with odds ratios for variant allele carriers (homozygous or heterozygous) compared with wild-type allele carriers ranging from 1.20 (95% confidence interval [CI] = 1.00 to 1.43) to 1.38 (95% CI = 1.12 to 1.70). Phylogenetic tree analyses of common haplotypes identified a clade of two evolutionarily related haplotypes that are statistically significantly associated with prostate cancer risk. These two haplotypes contain all the risk alleles of these 11 associated SNPs.

CONCLUSION

The observed multiple associated SNPs at the TLR6-TLR1-TLR10 gene cluster were dependent and suggest the presence of a founder prostate cancer risk variant on this haplotype background. The TLR6-TLR1-TLR10 gene cluster may play a role in prostate cancer risk, although further functional studies are needed to pinpoint the disease-associated variants in this gene cluster.

Apoptosis Induced by the Toll-Like Receptor Adaptor TRIF Is Dependent on Its Receptor Interacting Protein Homotypic Interaction Motif

TLRs detect specific molecular features of microorganisms and subsequently engage distinct signaling networks through the differential use of Toll/IL-1R (TIR)-domain-containing adapter proteins. In this study, we investigated the control of apoptosis by the TIR domain-containing adapter proteins MyD88, TIR-domain containing adapter protein (TIRAP), TIR-domain-containing adapter-inducing IFN-beta (TRIF), TRIF-related adapter molecule (TRAM), and sterile alpha motifs and beta-catenin/armadillo repeats (SARM). Upon overexpression, TRIF was the sole TIR-adapter to potently engage mammalian cell death signaling pathways. TRIF-induced cell death required caspase activity initiated by the Fas/Apo-1-associated DD protein-caspase-8 axis and was unaffected by inhibitors of the intrinsic apoptotic machinery. The proapoptotic potential of TRIF mapped to the C-terminal region that was found to harbor a receptor interacting protein (RIP) homotypic interaction motif (RHIM). TRIF physically interacted with the RHIM-containing proteins RIP1 and RIP3, and deletion and mutational analyses revealed that the RHIM in TRIF was essential for TRIF-induced apoptosis and contributed to TRIF-induced NF-kappa B activation. The domain that was required for induction of apoptosis could activate NF-kappa B but not IFN regulatory factor-3, yet the activation of NF-kappa B could be blocked by superrepressor I kappa B alpha without blocking apoptosis. Thus, the ability of TRIF to induce apoptosis was not dependent on its ability to activate either IFN regulatory factor-3 or NF-kappa B but was dependent on the presence of an intact RHIM. TRIF serves as an adaptor for both TLR3 and TLR4, receptors that are activated by dsRNA and LPS, respectively. These molecular motifs are encountered during viral and bacterial infection, and the apoptosis that occurs when TRIF is engaged represents an important host defense to limit the spread of infection.

Topical Immunotherapy: What's New

Further understanding of the pathogenesis of dermatologic conditions at a molecular level has led to targeted therapies. The topical immune response modifiers have contributed significantly to the treatment of cutaneous diseases. New topical remedies, particularly the Toll-like receptor agonists and calcineurin inhibitors, have added to the clinical armamentarium and have further advanced clinicians' ability to treat a wide variety of benign, premalignant, and malignant conditions. Furthermore, these agents have contributed to the understanding of the disease process. The next decade will witness even greater advances in targeted immunotherapies for dermatologic disease.

Innate immunity in the human female reproductive tract: antiviral response of uterine epithelial cells to the TLR3 agonist poly(I:C)

The objective of this study was to examine the expression of TLR by human primary uterine epithelial cells (UEC) and to determine whether exposure to the TLR agonist poly(I:C) would induce an antiviral response. The secretion of several cytokines and chemokines was examined as well as the mRNA expression of human beta-defensin-1 and -2 (HBD1 and HBD2), IFN-beta, and the IFN-beta-stimulated genes myxovirus resistance gene 1 and 2',5' oligoadenylate synthetase. The expression of TLR1-9 by UEC was demonstrated by RT-PCR, with only TLR10 not expressed. Stimulation of UEC with the TLR3 agonist poly(I:C) induced the expression of the proinflammatory cytokines TNF-alpha, IL-6, GM-CSF, and G-CSF, as well as the chemokines CXCL8/IL-8, CCL2/MCP-1, and CCL4/MIP-1beta. In addition, poly(I:C) exposure induced the mRNA expression of HBD1 and HBD2 by 6- and 4-fold, respectively. Furthermore, upon exposure to poly(I:C) UEC initiated a potent antiviral response resulting in the induction of IFN-beta mRNA expression 70-fold and myxovirus resistance gene 1 and 2',5' oligoadenylate synthetase mRNA expression (107- and 96-fold), respectively. These results suggest that epithelial cells that line the uterine cavity are sensitive to viral infection and/or exposure to viral dsRNA released from killed epithelial cells. Not only do UEC release proinflammatory cytokines and chemokines that mediate the initiation of an inflammatory response and recruitment of immune cells to the site of infection, but they also express beta-defensins, IFN-beta, and IFN-beta-stimulated genes that can have a direct inhibiting effect on viral replication.

Human TLR10 Is a Functional Receptor, Expressed by B Cells and Plasmacytoid Dendritic Cells, Which Activates Gene Transcription through MyD88

Human TLR10 is an orphan member of the TLR family. Genomic studies indicate that TLR10 is in a locus that also contains TLR1 and TLR6, two receptors known to function as coreceptors for TLR2. We have shown that TLR10 was not only able to homodimerize but also heterodimerized with TLRs 1 and 2. In addition, unlike TLR1 and TLR6, TLR10 was expressed in a highly restricted fashion as a highly N-glycosylated protein, which we detected in B cell lines, B cells from peripheral blood, and plasmacytoid dendritic cells from tonsil. We were also able to detect TLR10 in a CD1a(+) DC subset derived from CD34(+) progenitor cells which resemble Langerhans cells in the epidermis. Although we were unable to identify a specific ligand for TLR10, by using a recombinant CD4TLR10 molecule we also demonstrated that TLR10 directly associates with MyD88, the common Toll IL-1 receptor domain adapter. Additionally, we have characterized regions in the Toll IL-1 receptor domain of TLR10 that are essential in the activation of promoters from certain inflammatory cytokines. Even though TLR10 expression has not been detected in mice, we have identified a partial genomic sequence of the TLR10 gene that was present but nonfunctional and disrupted by a retroviral insertion in all mouse strains tested. However, a complete TLR10 sequence could be detected in the rat genome, indicating that a functional copy may be preserved in this species.

Characterization of Toll-like receptors in the female reproductive tract in humans

BACKGROUND

Rapid innate immune defences against infection involve the recognition of invading pathogens by specific pattern recognition receptors recently attributed to the family of Toll-like receptors (TLR). Little is known about the in vivo protein expression or distribution of TLR in the female reproductive tract in humans. It is likely that TLR distribution in the female reproductive tract reflects the immunological tolerance to the commensal organisms in lower parts of the tract (vagina, ectocervix and, partially, endocervix) and the intolerance to commensal microbial flora in the upper tract (the uterus and uterine tubes).

METHODS

Using immunohistochemistry techniques, distribution of TLR1-6 was studied in surgical sections from the vagina, ecto- and endocervix, endometrium and uterine tubes, obtained from patients undergoing abdominal hysterectomy for benign gynaecological conditions.

RESULTS

TLR1, 2, 3, 5 and 6 were present in the epithelia of different regions of female reproductive tract. However, TLR4 was only present in the endocervix, endometrium and uterine tubes and absent in vagina and ectocervix. In addition, a secretory form of TLR4 seems to be produced by the endocervical glands.

CONCLUSION

TLR4 may play an important role in modulation of immunological tolerance in the lower parts of the female reproductive tract, and in host defence against ascending infection.

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.

Deviation from major codons in the Toll-like receptor genes is associated with low Toll-like receptor expression

Microbial structures activate Toll-like receptors (TLRs) and TLR-mediated cell signalling elicits and regulates host immunity. Most TLRs are poorly expressed but the underlying expression mechanism is not clear. Examination TLR sequences revealed that most human TLR genes deviated from using major human codons. CD14 resembles TLRs in sequence but its gene preferentially uses major codons. Indeed, CD14 expression on monocytes was higher than expression of TLR1 and TLR2. The TLR9 gene is abundant in major codons and it also showed higher expression than TLR1, TLR2 and TLR7 in transfected 293T cells. Change of the 5'-end 302 base pairs of the TLR2 sequence into major human codons markedly increased TLR2 expression, which led to increased TLR2-mediated constitutive nuclear factor-kappaB activation. Change of the 5'-end 381 base pairs of the CD14 sequence into prevalent TLR codons markedly reduced CD14 expression. These results collectively show that the deviation of TLR sequences from using major codons dictates the low TLR expression and this may protect the host against excessive inflammation and tissue damages.

Surface-Expressed TLR6 Participates in the Recognition of Diacylated Lipopeptide and Peptidoglycan in Human Cells

Recognition of microbial components by TLR2 requires cooperation with other TLRs. TLR6 has been shown to be required for the recognition of diacylated lipoproteins and lipopeptides derived from mycoplasma and to activate the NF-kappaB signaling cascade in conjunction with TLR2. Human TLR2 is expressed on the cell surface in a variety of cells, including monocytes, neutrophils, and monocyte-derived, immature dendritic cells (iDCs), whereas the expression profile of TLR6 in human cells remains obscure. In this study we produced a function-blocking mAb against human TLR6 and analyzed TLR6 expression in human blood cells and cell lines and its participation in ligand recognition. TLR6 was expressed, although at a lower level than TLR2, on the cell surface in monocytes, monocyte-derived iDCs, and neutrophils, but not on B, T, or NK cells. Confocal microscopic analysis revealed that TLR6 was colocalized with TLR2 at the plasma membrane of monocytes. Importantly, TLR2/6 signaling did not require endosomal maturation, and anti-TLR6 mAb inhibited cytokine production in monocytes and iDCs stimulated with synthetic macrophage-activating lipopeptide-2 or peptidoglycan, indicating that TLR6 recognized diacylated lipopeptide and peptidoglycan at the cell surface. In addition, TLR2 mutants C30S and C36S (Cys(30) and Cys(36) in TLR2 were substituted with Ser), which were expressed intracellularly in HEK293 cells, failed to induce NF-kappaB activation upon macrophage-activating lipopeptide-2 stimulation even in the presence of TLR6. Thus, coexpression of TLR2 and TLR6 at the cell surface is crucial for recognition of diacylated lipopeptide and peptidoglycan and subsequent cellular activation in human cells.