Toll-like receptors 7, 8, and 9: linking innate immunity to autoimmunity

Nanostructured DNA for the delivery of therapeutic agents

DNA and RNA, the nucleic acids found in every living organism, are quite crucial, because not only do they store the genetic information, but also they are used as signals through interaction with various molecules within the body. The nature of nucleic acids, especially DNA, to form double-helix makes it possible to design nucleic acid-based nanostructures with various shapes. Because the shapes as well as the physicochemical properties determine their interaction with proteins or cells, nanostructured DNAs will have different features in the interaction compared with single- or double-stranded DNA. Some of these unique features of nanostructured DNA make ways for efficient delivery of therapeutic agents to specific targets. In this review, we begin with the factors affecting the properties of nanostructured DNA, followed by summarizing the methods for the development of nanostructured DNA. Further, we discuss the characteristics of nanostructured DNA and their applications for the delivery of bioactive compounds.

BANK1 interacts with TRAF6 and MyD88 in innate immune signaling in B cells

Evidence supports a possible role of BANK1 in innate immune signaling in B cells. In the present study, we investigated the interaction of BANK1 with two key mediators in interferon and inflammatory cytokine production, TRAF6 and MyD88. We revealed by coimmunoprecipitation (CoIP) analyses the binding of BANK1 with TRAF6 and MyD88, which were mediated by the BANK1 Toll/interleukin-1 receptor (TIR) domain. In addition, the natural BANK1–40C variant showed increased binding to MyD88. Next, we demonstrated in mouse splenic B cells that BANK1 colocalized with Toll-like receptor (TLR) 7 and TLR9 and that after stimulation with TLR7 and TLR9 agonists, the number of double-positive BANK1–TLR7, –TLR9, –TRAF6, and –MyD88 cells increased. Furthermore, we identified five TRAF6-binding motifs (BMs) in BANK1 and confirmed by point mutations and decoy peptide experiments that the C-terminal domain of BANK1-full-length (-FL) and the N-terminal domain of BANK1–Delta2 (-D2) are necessary for this binding. Functionally, we determined that the absence of the TIR domain in BANK1–D2 is important for its lysine (K)63-linked polyubiquitination and its ability to produce interleukin (IL)-8. Overall, our study describes a specific function of BANK1 in MyD88–TRAF6 innate immune signaling in B cells, clarifies functional differences between the two BANK1 isoforms and explains for the first time a functional link between autoimmune phenotypes including SLE and the naturally occurring BANK1–40C variant.

DDX3 directly facilitates IKKα activation and regulates downstream signalling pathways

DDX3 is a DEAD-box RNA helicase that we and others have previously implicated in antiviral immune signalling pathways leading to type I interferon (IFN) induction. We previously demonstrated that it directly interacts with the kinase IKKε (IκB kinase ε), enhances it activation, and then facilitates phosphorylation of the transcription factor IRF3 by IKKε. However, the TLR7/9 (Toll-like receptor 7/9)-mediated pathway, one of the most physiologically relevant IFN induction pathways, proceeds independently of IKKε or the related kinase TBK1 (TANK-binding kinase 1). This pathway induces type I IFN production via the kinases NIK (NF-κB-inducing kinase) and IKKα and is activated when plasmacytoid dendritic cells sense viral nucleic acids. In the present study, we demonstrate that DDX3 also directly interacts with IKKα and enhances its autophosphorylation and -activation. Modulation of DDX3 expression consequently affected NIK/IKKα-mediated IRF7 phosphorylation and induction of type I interferons. In addition, alternative NF-κB (nuclear factor-κB) activation, another pathway regulated by NIK and IKKα, was also down-regulated in DDX3 knockdown cells. This substantially broadens the effects of DDX3 in innate immune signalling to pathways beyond TBK1/IKKε and IFN induction. Dysregulation of these pathways is involved in disease states, and thus, our research might implicate DDX3 as a potential target for their therapeutic manipulation.

Association of TLR8 and TLR9 polymorphisms with tuberculosis in a Chinese Han population: a case-control study

Background

Toll-like receptor (TLR) single nucleotide polymorphisms (SNPs) have been associated with regulation of TLR expression and development of active tuberculosis (TB). The objectives of this study were to determine whether TLR8 and TLR9 SNPs were associated with the development of latent TB infection (LTBI) and the subsequent pulmonary TB (PTB) in a Chinese Han population.

Methods

Two independent samples were enrolled. The first sample contained 584 TB cases and 608 controls; the second sample included 204 healthy controls, 201 LTBI subjects and 209 bacteria-confirmed active PTB patients. Three SNPs (rs3764880, rs187084 and rs5743836) were genotyped. The associations between the SNPs and risk of LTBI or PTB were investigated using unconditional logistic regression analysis.

Results

The A-allele of TLR8 rs3764880 SNP was protective against the development of TB in males (A vs G, OR = 0.58, 95%CI = 0.37–0.91). The AA genotype of rs3764880 SNP was found to increase the risk of PTB among females with an OR of 4.81 (1.11–20.85). The G allele of TLR9 SNP rs187084 was found to increase the risk of PTB (G vs A, P = 0.01, OR = 1.48, 95% CI = 1.10–2.00), the significance was also observed under dominant genetic models. The GA-genotype of TLR9 rs187084 SNP was found to increase the risk of PTB with an OR of 1.68 (1.07–2.65), but was found to decrease the risk of MTB infection with an OR = 0.64 (0.41–0.98). TLR9_rs5743836 SNP was excluded from the data analyses, because the minimum allele frequency was< 1%.

Conclusions

Our findings in two independent samples indicated that SNPs in TLR8 and TLR9 were associated with the development of TB, and highlight that SNPs may have different effects on disease pathogenesis and progression.

Intestinal macrophages in mucosal immunity and their role in systemic lupus erythematosus disease

Monocytes play an important role in inducing host systemic immunity against invading pathogens and inflammatory responses. After activation, monocytes migrate to tissue sites, where they initiate both innate and adaptive immune responses, and become macrophages. Although mucosal macrophages produce inflammatory cytokines in response to pathogens, the perturbations in innate immune signaling pathway have been implicated in autoimmune diseases such as systemic lupus erythematosus (SLE). In this review, we focus on the role of human macrophages in intestinal innate immune responses, homeostasis, and SLE disease. We further discuss sex differences in the intestinal macrophages and their role in the physiology and pathogenesis of SLE.

Small-Molecule TLR8 Antagonists via Structure-Based Rational Design

Rational design of drug-like small-molecule ligands based on structural information of proteins remains a significant challenge in chemical biology. In particular, designs targeting protein-protein interfaces have met little success given the dynamic nature of the protein surfaces. Herein, we utilized the structure of a small-molecule ligand in complex with Toll-like receptor 8 (TLR8) as a model system due to TLR8's clinical relevance. Overactivation of TLR8 has been suggested to play a prominent role in the pathogenesis of various autoimmune diseases; however, there are still few small-molecule antagonists available, and our rational designs led to the discovery of six exceptionally potent compounds with ∼picomolar IC₅₀ values. Two X-ray crystallographic structures validated the contacts within the binding pocket. A variety of biological evaluations in cultured cell lines, human peripheral blood mononuclear cells, and splenocytes from human TLR8-transgenic mice further demonstrated these TLR8 inhibitors' high efficacy, suggesting strong therapeutic potential against autoimmune disorders.

Potential Chronotherapeutic Optimization of Antimalarials in Systemic Lupus Erythematosus: Is Toll-Like Receptor 9 Expression Dependent on the Circadian Cycle in Humans?

Toll-like receptor 9 (TLR9) belongs to the group of endosomal receptors of the innate immune system with the ability to recognize hypomethylated CpG sequences from DNA. There is scarce information about TLR9 expression and its association with the circadian cycle (CC). Different patterns of TLR9 expression are regulated by the CC in mice, with an elevated expression at Zeitgeber time 19 (1:00 a.m.); nevertheless, we still need to corroborate this in humans. In systemic lupus erythematosus (SLE), the inhibitory effect of chloroquine (CQ) on TLR9 is limited. TLR9 activation has been associated with the presence of some autoantibodies: anti-Sm/RNP, anti-histone, anti-Ro, anti-La, and anti-double-stranded DNA. Treatment with CQ for SLE has been proven to be useful, in part by interfering with HLA-antigen coupling and with TLR9 ligand recognition. Studies have shown that TLR9 inhibitors such as antimalarial drugs are able to mask TLR9-binding sites on nucleic acids. The data presented here provide the basic information that could be useful for other clinical researchers to design studies that will have an impact in achieving a chronotherapeutic effect by defining the ideal time for CQ administration in SLE patients, consequently reducing the pathological effects that follow the activation of TLR9.

Smaller CpG-Conjugated Gold Nanoconstructs Achieve Higher Targeting Specificity of Immune Activation

This study describes a side-by-side comparison of the in vitro immunostimulatory activity of cytosine-phosphate-guanine (CpG)-conjugated gold nanoparticles. Three different gold nanoparticle cores (13 nm spheres, 50 nm spheres, and 40 nm stars) with the same CpG surface density were investigated for toll-like receptor 9 activation. For this parameter set, 13 nm spheres displayed significantly higher specificity for targeting immune receptors and larger nanoparticles (50 nm spheres and 40 nm stars) showed higher cellular uptake and higher immune activation because of off-target effects. Changes in nanoparticle size and presentation of activating ligands affect construct-induced immune responses at different levels, and care must be taken when considering practical and global design rules for CpG delivery.

Systemic Lupus Erythematosus: Definitions, Contexts, Conflicts, Enigmas

Systemic lupus erythematosus (SLE) is an inadequately defined syndrome. Etiology and pathogenesis remain largely unknown. SLE is on the other hand a seminal syndrome that has challenged immunologists, biologists, genetics, and clinicians to solve its nature. The syndrome is characterized by multiple, etiologically unlinked manifestations. Unexpectedly, they seem to occur in different stochastically linked clusters, although single gene defects may promote a smaller spectrum of symptoms/criteria typical for SLE. There is no known inner coherence of parameters (criteria) making up the disease. These parameters are, nevertheless, implemented in The American College of Rheumatology (ACR) and The Systemic Lupus Collaborating Clinics (SLICC) criteria to classify SLE. Still, SLE is an abstraction since the ACR or SLICC criteria allow us to define hundreds of different clinical SLE phenotypes. This is a major point of the present discussion and uses "The anti-dsDNA antibody" as an example related to the problematic search for biomarkers for SLE. The following discussion will show how problematic this is: the disease is defined through non-coherent classification criteria, its complexity is recognized and accepted, its pathogenesis is plural and poorly understood. Therapy is focused on dominant symptoms or organ manifestations, and not on the syndrome itself. From basic scientific evidences, we can add substantial amount of data that are not sufficiently considered in clinical medicine, which may change the paradigms linked to what "The Anti-DNA antibody" is-and is not-in context of the imperfectly defined syndrome SLE.

Dietary N-Glycans from Bovine Lactoferrin and TLR Modulation

SCOPE

Bovine lactoferrin (bLF) is an ingredient of food supplements and infant formulas given its antimicrobial and antiviral properties. We modified bLF enzymatically to alter its N-glycosylation and to isolate the glycan chains. The aims of this study include (1) to evaluate whether such derivates induce responses via pattern recognition receptors namely Toll-like receptors (TLRs) and (2) to relate those responses to their different glycosylation profiles.

METHODS AND RESULTS

The unmodified and modified bLF fractions are incubated with reporter cell lines expressing pattern recognition receptors. Afterwards, we screen for TLRs and analyze for nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) activation. Activation of reporter cell lines show that signaling is highly dependent on TLRs. The activation pattern of bLF is reduced with the desialylated form and increased with the demannosylated form. In reporter cells for TLR, bLF activate TLR-4 and inhibit TLR-3. The isolated glycans from bLF inhibit TLR-8. TLR-2, TLR-5, TLR-7, and TLR-9 are not significantly altered.

CONCLUSION

The profile of glycosylation is key for the biological activity of bLF. By understanding how this affects the human defense responses, the bLF glycan profile can be modified to enhance its immunomodulatory effects when used as a dietary ingredient.

Toll-Like Receptor 3 Signal in Dendritic Cells Benefits Cancer Immunotherapy

Pattern recognition receptors (PRRs) play a crucial role in the innate immune system and contribute to host defense against microbial infection. PRR-mediated antimicrobial signals provide robust type-I IFN/cytokine production and trigger inflammation, thereby affecting tumor progression and autoimmune diseases. Accumulating evidence demonstrates that among the PRRs, only the signaling pathway of endosomal toll-like receptor 3 (TLR3) induces no systemic inflammation and mediates cross-priming of antigen-specific CD8⁺ T cells by dendritic cells. Treatment with a newly developed TLR3-specific ligand, ARNAX, along with tumor-associated antigens (TAAs), induces tumor-specific cytotoxic T lymphocytes, modulates the tumor microenvironment to establish Th1-type antitumor immunity, and leads to tumor regression without inflammation in mouse tumor models. Combination therapy using ARNAX/TAA and PD-1/PD-L1 blockade potently enhances antitumor response and overcomes anti-PD-1/PD-L1 resistance. In this review, we will discuss the TLR3-mediated signaling in antitumor immunity and its application to cancer immunotherapy.

Inhibition of IRAK1 Ubiquitination Determines Glucocorticoid Sensitivity for TLR9-Induced Inflammation in Macrophages

Inflammatory responses are controlled by signaling mediators that are regulated by various posttranslational modifications. Recently, transcription-independent functions for glucocorticoids (GC) in restraining inflammation have emerged, but the underlying mechanisms are unknown. In this study, we report that GC receptor (GR)-mediated actions of GC acutely suppress TLR9-induced inflammation via inhibition of IL-1R-associated kinase 1 (IRAK1) ubiquitination. β-TrCP-IRAK1 interaction is required for K48-linked ubiquitination of IRAK1 at Lys¹³⁴ and subsequent membrane-to-cytoplasm trafficking of IRAK1 interacting partners TNFR-associated factor 6 and TAK1 that facilitates NF-κB and MAPK activation. Upon costimulation of macrophages with GC and TLR9-engaging ligand, GR physically interacts with IRAK1 and interferes with protein-protein interactions between β-TrCP and IRAK1. Ablation of GR in macrophages prevents GC-dependent suppression of β-TrCP-IRAK1 interactions. This GC-mediated suppression of IRAK1 activation is unique to TLR9, as GC treatment impairs TLR9 but not TLR4 ligand-induced K48-linked IRAK1 ubiquitination and trafficking of IRAK1 interacting partners. Furthermore, mutations in IRAK1 at Lys¹³⁴ prevent TLR9 ligand-induced activation of inflammatory signaling mediators and synthesis of proinflammatory cytokines to an extent comparable to GC-mediated inhibition. Collectively, these findings identify a transcription-independent, rapid, and nongenomic GC suppression of TLR9 ligand-mediated IRAK1 ubiquitination as a novel mechanism for restraining acute inflammatory reactions.

The Toll for Trafficking: Toll-Like Receptor 7 Delivery to the Endosome

Toll-like receptor (TLR)-7 is an endosomal innate immune sensor capable of detecting single-stranded ribonucleic acid. TLR7-mediated induction of type I interferon and other inflammatory cytokine production is important in antiviral immune responses. Furthermore, altered TLR7 expression levels are implicated in various autoimmune disorders, indicating a key role for this receptor in modulating inflammation. This review is focused on the regulation of TLR7 expression and localization compared to that of the other endosomal TLRs: TLR3, 8, and 9. Endosomal TLR localization is a tightly controlled and intricate process with some shared components among various TLRs. However, TLR-specific mechanisms must also be in place in order to regulate the induction of pathogen- and cell-specific responses. It is known that TLR7 is shuttled from the endoplasmic reticulum to the endosome via vesicles from the Golgi. Several chaperone proteins are required for this process, most notably uncoordinated 93 homolog B1 (Caenorhabditis elegans), recently identified to also be involved in the localization of the other endosomal TLRs. Acidification of the endosome and proteolytic cleavage of TLR7 are essential for TLR7 signaling in response to ligand binding. Cleavage of TLR7 has been demonstrated to be accomplished by furin peptidases in addition to cathepsins and asparagine endopeptidases. Moreover, triggering receptor expressed on myeloid cells like 4, a protein associated with antigen presentation and apoptosis in immune cells, has been implicated in the amplification of TLR7 signaling. Understanding these and other molecular mechanisms controlling TLR7 expression and trafficking will give insight into the specific control of TLR7 activity compared to the other endosomal TLRs.

Use of Toll-Like Receptor Agonists to Induce Ectopic Lymphoid Structures in Myasthenia Gravis Mouse Models

Myasthenia gravis (MG) is an autoimmune disease mediated by autoantibodies against the acetylcholine receptor (AChR) at the neuromuscular junction. MG symptoms are characterized by muscle weaknesses. The thymus of MG patients is very often abnormal and possesses all the characteristics of tertiary lymphoid organs such as neoangiogenesis processes, overexpression of inflammatory cytokines and chemokines, and infiltration of B lymphocytes leading to ectopic germinal center (GC) development. We previously demonstrated that injections of mice with polyinosinic–polycytidylic acid [Poly(I:C)], a synthetic double-stranded RNA mimicking viral infection, induce thymic changes and trigger MG symptoms. Upon Poly(I:C) injections, we observed increased thymic expressions of α-AChR, interferon-β and chemokines such as CXCL13 and CCL21 leading to B-cell recruitment. However, these changes were only transient. In order to develop an experimental MG model associated with thymic GCs, we used Poly(I:C) in the classical experimental autoimmune MG model induced by immunizations with purified AChR emulsified in complete Freund’s adjuvant. We observed that Poly(I:C) strongly favored the development of MG as almost all mice displayed MG symptoms. Nevertheless, we did not observe any ectopic GC development. We next challenged mice with Poly(I:C) together with other toll-like receptor (TLR) agonists known to be involved in GC development and that are overexpressed in MG thymuses. Imiquimod and CpG oligodeoxynucleotides that activate TLR7 and TLR9, respectively, did not induce thymic changes. In contrast, lipopolysaccharide that activates TLR4 potentiated Poly(I:C) effects and induced a significant expression of CXCL13 mRNA in the thymus associated with a higher recruitment of B cells that induced over time thymic B-lymphoid structures. Altogether, these data suggest that tertiary lymphoid genesis in MG thymus could result from a combined activation of TLR signaling pathways.

The Role of Toll-Like Receptors in Autoimmune Diseases through Failure of the Self-Recognition Mechanism

Toll-like receptors (TLRs), part of the innate immune system that recognises molecular signatures, are important in the recognition of pathogenic components. However, when specific cellular contexts develop in which TLRs are inappropriately activated by self-components, this may lead to sterile inflammation and result in the occurrence of autoimmunity. This review analyses the available data regarding TLR biochemistry, the specific mechanisms which are brought about by TLR activation, and the importance of these mechanisms in the light of any existing and potential therapies in the field of autoimmunity.

Heterogeneity of Toll-like receptor 9 signaling in B cell malignancies and its potential therapeutic application

Toll-like receptor 9 (TLR9) is expressed in a variety of B-cell malignancies and works as a bridge between innate and adaptive immunity. CpG oligodeoxynucleotides (CpG ODNs), TLR9 agonists, are able to induce anticancer immune responses and exert direct effects against cancer cells, serving as cancer therapeutic agents. Therefore, TLR9 might be a potential therapeutic target for drug development. However, several new evidences have revealed that direct effects of TLR9 agonists on B-cell malignancies is controversial. For example, CpG ODNs can induce apoptosis in certain type of chronic lymphocytic leukemia and lymphoma cells, while induce proliferation in multiple myeloma and other types of lymphoma cells. In this review, we summarize current understanding of the heterogeneity in responses of normal and malignant B cells to TLR9 agonists, due to differences in TLR9 expression levels, genetic alterations (such as MyD88 mutation), and signaling pathway activation. Especially, the downstream molecules of NF-κB signaling pathway play an important role in the heterogeneous response. In order to provide possibilities for therapeutic manipulation of TLR9 agonists in the treatment of these disorders, the preclinical and clinical advances in using CpG ODNs alone and in combination therapies are also summarized in this review.

Rationale for stimulator of interferon genes-targeted cancer immunotherapy

The efficacy of checkpoint inhibitor therapy illustrates that cancer immunotherapy, which aims to foster the host immune response against cancer to achieve durable anticancer responses, can be successfully implemented in a routine clinical practice. However, a substantial proportion of patients does not benefit from this treatment, underscoring the need to identify alternative strategies to defeat cancer. Despite the demonstration in the 1990's that the detection of danger signals, including the nucleic acids DNA and RNA, by dendritic cells (DCs) in a cancer setting is essential for eliciting host defence, the molecular sensors responsible for recognising these danger signals and eliciting anticancer immune responses remain incompletely characterised, possibly explaining the disappointing results obtained so far upon the clinical implementation of DC-based cancer vaccines. In 2008, STING (stimulator of interferon genes), was identified as a protein that is indispensable for the recognition of cytosolic DNA. The central role of STING in controlling anticancer immune responses was exemplified by observations that spontaneous and radiation-induced adaptive anticancer immunity was reduced in the absence of STING, illustrating the potential of STING-targeting for cancer immunotherapy. Here, we will discuss the relevance of manipulating the STING signalling pathway for cancer treatment and integrating STING-targeting based strategies into combinatorial therapies to obtain long-lasting anticancer immune responses.

1-ethyl-3-(6-methylphenanthridine-8-il) urea modulates TLR3/9 activation and induces selective pro-inflammatory cytokine expression in vitro

We have previously demonstrated the nucleic acid binding capacity of phenanthridine derivatives (PHTs). Because nucleic acids are potent inducers of innate immune response through Toll-like receptors (TLRs), and because PTHs bear a structural resemblance to commonly used synthetic ligands for TLR7/8, we hypothesized that PHTs could modulate/activate immune response. We found that compound M199 induces secretion of IL-6, IL-8 and TNFα in human PBMCs and inhibits TLR3/9 activation in different cellular systems (PBMCs, HEK293 and THP-1 cell lines).

Role of intestinal microbiota and metabolites on gut homeostasis and human diseases

Background

A vast diversity of microbes colonizes in the human gastrointestinal tract, referred to intestinal microbiota. Microbiota and products thereof are indispensable for shaping the development and function of host innate immune system, thereby exerting multifaceted impacts in gut health.

Methods

This paper reviews the effects on immunity of gut microbe-derived nucleic acids, and gut microbial metabolites, as well as the involvement of commensals in the gut homeostasis. We focus on the recent findings with an intention to illuminate the mechanisms by which the microbiota and products thereof are interacting with host immunity, as well as to scrutinize imbalanced gut microbiota (dysbiosis) which lead to autoimmune disorders including inflammatory bowel disease (IBD), Type 1 diabetes (T1D) and systemic immune syndromes such as rheumatoid arthritis (RA).

Results

In addition to their well-recognized benefits in the gut such as occupation of ecological niches and competition with pathogens, commensal bacteria have been shown to strengthen the gut barrier and to exert immunomodulatory actions within the gut and beyond. It has been realized that impaired intestinal microbiota not only contribute to gut diseases but also are inextricably linked to metabolic disorders and even brain dysfunction.

Conclusions

A better understanding of the mutual interactions of the microbiota and host immune system, would shed light on our endeavors of disease prevention and broaden the path to our discovery of immune intervention targets for disease treatment.

Toll-like receptor-mediated immune responses in intestinal macrophages; implications for mucosal immunity and autoimmune diseases

Monocytes are precursors of macrophages and key players during inflammation and pathogen challenge in the periphery, whereas intestinal resident macrophages act as innate effector cells to engulf and clear bacteria, secrete cytokines, and maintain intestinal immunity and homeostasis. However, perturbation of toll-like receptor signaling pathway in intestinal macrophages has been associated with tolerance breakdown in autoimmune diseases. In the present review, we have summarized and discussed the role of toll-like receptor signals in human intestinal macrophages, and the role of human intestinal macrophages in keeping human intestinal immunity, homeostasis, and autoimmune diseases.

Effect of glucocorticoid on cytokines TLR9 and TLR7 in peripheral blood for patients with uveitis

The effect of glucocorticoid on cytokines Toll-like receptor (TLR)9 and TLR7 in peripheral blood of patients with uveitis was explored. Forty-six patients with uveitis admitted to our hospital from April 2014 to April 2015 were selected as the research observational group. Thirty-five able-bodied individuals in the same period were selected as the control group. To treat uveitis, the observational group was injected with glucocorticoid (1–2 mg/kg/day) daily, while the control group did not receive any treatment. The quantity of expression of peripheral blood cytokines TLR9 and TLR7 were detected by the methods of fluorescence quantitative PCR, enzyme-linked immunosorbent assay and western blotting. The content of peripheral blood TLR9 and TLR7 (0.21±0.01, 0.19±0.01) decreased significantly (P<0.05) in observational group after glucocorticoid treatment. Compared with data of control group (0.21±0.01, 0.19±0.01), TLR9 and TLR7 content in peripheral blood after glucocorticoid treatment on the patients with uveitis from observation group (0.19±0.01, 0.17±0.01) did not show any significant difference, for correlation between TLR9 and TLR7 in observation group before and after treatment. It was observed that the cytokine content of TLR9 was associated with TLR7 positively (r=0.653, P=0.012). In conclusion, glucocorticoid can improve uveitis by reducing the content of cytokines TLR9 and TLR7 in peripheral blood.

IL-27 Is Essential for Suppression of Experimental Allergic Asthma by the TLR7/8 Agonist R848 (Resiquimod)

Different models of experimental allergic asthma have shown that the TLR7/8 agonist resiquimod (R848) is a potential inhibitor of type 2 helper cell-driven inflammatory responses. However, the mechanisms mediating its therapeutic effects are not fully understood. Using a model of experimental allergic asthma, we show that induction of IL-27 by R848 is critical for the observed ameliorative effects. R848 significantly inhibited all hallmarks of experimental allergic asthma, including airway hyperreactivity, eosinophilic airway inflammation, mucus hypersecretion, and Ag-specific Ig production. Whereas R848 significantly reduced IL-5, IL-13, and IL-17, it induced IFN-γ and IL-27. Neutralization of IL-27 completely reversed the therapeutic effect of R848 in the experimental asthma model, demonstrating dependence of R848-mediated suppression on IL-27. In vitro, R848 induced production of IL-27 by murine alveolar macrophages and dendritic cells and enhanced expression of programmed death-ligand 1, whose expression on monocytes and dendritic cells has been shown to regulate peripheral tolerance in both murine and human studies. Moreover, in vitro IL-27 enhanced secretion of IFN-γ whereas it inhibited IL-5 and IL-13, demonstrating its direct effect on attenuating Th2 responses. Taken together, our study proves that R848-mediated suppression of experimental asthma is dependent on IL-27. These data provide evidence of a central role of IL-27 for the control of Th2-mediated allergic diseases.

An inhibitory alternative splice isoform of Toll-like receptor 3 is induced by type I interferons in human astrocyte cell lines

Toll-like receptor 3 (TLR3) recognizes viral double-stranded RNA. It stimulates pro-inflammatory cytokine and interferon production. Here we reported the expression of a novel isoform of TLR3 in human astrocyte cell lines whose message is generated by alternative splicing. The isoform represents the N-terminus of the protein. It lacks many of the leucine-rich repeat domains, the transmembrane domain, and the intracellular Toll/interleukin-1 receptor domain of TLR3. Type I interferons (interferon-α and interferon-β) induced the expression of this isoform. Exogenous overexpression of this isoform inhibited interferon regulatory factor 3, signal transducers and activators of transcription 1, and Inhibitor of kappa B α signaling following stimulation. This isoform of TLR3 also inhibited the production of chemokine interferon-γ-inducible protein 10. Our study clearly demonstrated that the expression of this isoform of TLR3 was a negative regulator of signaling pathways and that it was inducible by type I interferons. We also found that this isoform could modulate inflammation in the brain. [BMB Reports 2015; 48(12): 696-701]

Nucleic acid-sensing TLRs and autoimmunity: novel insights from structural and cell biology

Invasion of pathogenic microorganisms or tissue damage activates innate immune signaling receptors that sample subcellular locations for foreign molecular structures, altered host molecules, or signs of compartment breaches. Upon engagement of innate immune receptors an acute but transient inflammatory response is initiated, aimed at the clearance of pathogens and cellular debris. Among the molecules that are sensed are nucleic acids, which activate several members of the transmembrane Toll-like receptor (TLR) family. Inappropriate recognition of nucleic acids by TLRs can cause inflammatory pathologies and autoimmunity. Here, we review the mechanisms involved in triggering nucleic acid-sensing TLRs and indicate checkpoints that restrict their activation to endolysosomal compartments. These mechanisms are crucial to sample the content of endosomes for nucleic acids in the context of infection or tissue damage, yet prevent accidental activation by host nucleic acids under physiological conditions. Decoding the molecular mechanisms that regulate nucleic acid recognition by TLRs is central to understand pathologies linked to unrestricted nucleic acid sensing and to develop novel therapeutic strategies.

Vaccination with trifunctional nanoparticles that address CD8+ dendritic cells inhibits growth of established melanoma

AIM

We wanted to assess the potency of a trifunctional nanoparticle (NP) that targeted and activated CD8⁺ dendritic cells (DC) and delivered an antigen to induce antitumor responses.

MATERIALS & METHODS

The DC targeting and activating properties of ferrous NPs conjugated with immunostimulatory CpG-oligonucleotides, anti-DEC205 antibody and ovalbumin (OVA) as a model antigen to induce antigen-specific T-cell responses and antitumor responses were analyzed.

RESULTS

OVA-loaded NP conjugated with immunostimulatory CpG-oligonucleotides and anti-DEC205 antibody efficiently targeted and activated CD8⁺ DC in vivo, and induced strong OVA-specific T-cell activation. Vaccination of B16/OVA tumor-burdened mice with this NP formulation resulted in tumor growth arrest.

CONCLUSION

CD8⁺ DC-targeting trifunctional nanocarriers bear significant potential for antitumor immunotherapy.

The effect of imiquimod on taste bud calcium transients and transmitter secretion

BACKGROUND AND PURPOSE

Imiquimod is an immunomodulator approved for the treatment of basal cell carcinoma and has adverse side effects, including taste disturbances. Paracrine transmission, representing cell-cell communication within taste buds, has the potential to shape the final signals that taste buds transmit to the brain. Here, we tested the underlying assumption that imiquimod modifies taste transmitter secretion in taste buds of mice.

EXPERIMENTAL APPROACH

Taste buds were isolated from C57BL/6J mice. The effects of imiquimod on transmitter release in taste buds were measured using calcium imaging with cellular biosensors, and examining the net effect of imiquimod on taste-evoked ATP secretion from mouse taste buds.

KEY RESULTS

Up to 72% of presynaptic (Type III) taste cells responded to 100 μM imiquimod with an increase in intracellular Ca²⁺ concentrations. These Ca²⁺ responses were inhibited by thapsigargin, an inhibitor of the sarco/endoplasmic reticulum Ca²⁺ -ATPase, and by U73122, a PLC inhibitor, suggesting that the Ca²⁺ mobilization elicited by imiquimod was dependent on release from internal Ca²⁺ stores. Moreover, combining studies of Ca²⁺ imaging with cellular biosensors showed that imiquimod evoked secretion of 5-HT, which then provided negative feedback onto receptor (Type II) cells to reduce taste-evoked ATP secretion.

CONCLUSION AND IMPLICATIONS

Our results provide evidence that there is a subset of taste cells equipped with a range of intracellular mechanisms that respond to imiquimod. The findings are also consistent with a role of imiquimod as an immune response modifier, which shapes peripheral taste responses via 5-HT signalling.

Murine and Human Lupus Nephritis: Pathogenic Mechanisms and Theoretical Strategies for Therapy

Lupus nephritis is one of the most serious manifestations of systemic lupus erythematosus, and represents one of the criteria implemented to classify systemic lupus erythematosus. Although studied for decades, no consensus has been reached related to the basic cellular, molecular, and immunologic mechanism(s) responsible for lupus nephritis. No causal treatments have been developed; therapy is approached mainly with nonspecific immunosuppressive medications. More detailed insight into disease mechanisms therefore is indispensable to develop new therapeutic strategies. In this review, contemporary knowledge on the pathogenic mechanisms of lupus nephritis is discussed based on recent data in murine and human lupus nephritis. Specific focus is given to the effect of anti-double-stranded DNA/antinucleosome antibodies in the kidneys and whether they bind exposed chromatin fragments in glomeruli or whether they bind inherent glomerular structures by cross-recognition. Overall, the data presented here favor the exposed chromatin model because we did not find any indication to substantiate the anti-double-stranded DNA antibody cross-reacting model. At the end of this review we present data on why chromatin fragments are expressed in the glomeruli of patients with lupus nephritis, and discuss how this knowledge can be used to direct the development of future therapies.

The Role of Anti-DNA Antibodies in the Development of Lupus Nephritis: A Complementary, or Alternative, Viewpoint?

Kidney disease, or lupus nephritis, is the organ involvement that is most closely associated with specific autoantibodies in patients with SLE. The concept of anti-DNA antibodies being instrumental in the pathogenesis of lupus nephritis emerged ~50 years ago, and has been a topic of debate ever since. This article focuses on the description of the renal sub-cellular targets of nephritogenic autoantibodies and offers a counter-point opinion to the article by Pedersen et al. In addition, we provide an overview of some of the mechanisms by which anti-DNA antibodies bind to their renal targets and the pathogenic relevance to clinical nephritis.

Low Circulating Levels of Mitochondrial and High Levels of Nuclear DNA Predict Mortality in Chronic Heart Failure

BACKGROUND

Mitochondrial DNA (mtDNA) and possibly nuclear DNA (nDNA) are released as danger-associated molecular patterns during cardiac stress, and may activate several innate immune receptors. The purpose of this study was to investigate the regulation of these danger-associated molecular patterns during human heart failure (HF).

METHODS AND RESULTS

Plasma levels of mtDNA and nDNA from HF patients (n = 84) were analyzed by reverse transcriptase-polymerase chain reaction and compared with controls (n = 72). Increased levels of mtDNA were found in New York Heart Association (NYHA) I-II and NYHA III-IV. There was evidence of increased nDNA in NYHA III-IV compared with controls and NYHA I-II. Kaplan-Meier analysis revealed higher mortality in patients with high nDNA levels, whereas high levels of mtDNA were associated with survival.

CONCLUSIONS

Plasma levels of mtDNA and nDNA are elevated in human HF associated with increased and decreased mortality, respectively. This study may suggest a rationale for exploring interventions within inflammatory signaling pathways activated by nucleic acids as novel targets in treatment of HF.

Low expression of Toll-like receptors in peripheral blood mononuclear cells of pediatric patients with acute lymphoblastic leukemia

Cancer is the second most common cause of death among children aged 1-14 years. Leukemia accounts for one-third of all childhood cancers, 78% of which is acute lymphoblastic leukemia (ALL). The development of cancer has been associated with malignant cells that express low levels of immunogenic molecules, which facilitates their escape from the antineoplastic immune response. It is thought that it may be possible to rescue the antineoplastic immune response through the activation of recognition receptors, such as Toll-like receptors (TLRs), which activate the innate immune system. TLRs are type I membrane glycoproteins expressed mainly in immune system cells such as monocytes, neutrophils, macrophages, dendritic cells, T, B and natural killer cells. The aim of the present study was to evaluate the expression of TLR1, TLR3, TLR4, TLR7 and TLR9 in peripheral blood mononuclear cells (PBMCs) in patients with ALL and prior to any treatment. PBMCs were obtained from 50 pediatric patients diagnosed with ALL and from 20 children attending the ophthalmology and orthopedics services. The mean fluorescence intensity was obtained by analysis of immunofluorescence. We found lower expression levels of TLR1, TLR3, TLR4, TLR7 and TLR9 in PBMCs from patients with ALL compared with those from control patients. We also observed that the PBMCs from patients with Pre-B and B ALL had lower TLR4 expression than controls and patients with Pro-B, Pre-B, B and T ALL had lower TLR7 expression than controls. The present study is the first to demonstrate reduced expression of TLRs in PBMCs from pediatric patients with ALL. This finding is of great relevance and may partly explain the reduction in the antineoplastic immune response in patients with ALL.

Discovery of 6-Amino-2-{[(1S)-1-methylbutyl]oxy}-9-[5-(1-piperidinyl)pentyl]-7,9-dihydro-8H-purin-8-one (GSK2245035), a Highly Potent and Selective Intranasal Toll-Like Receptor 7 Agonist for the Treatment of Asthma

Induction of IFNα in the upper airways via activation of TLR7 represents a novel immunomodulatory approach to the treatment of allergic asthma. Exploration of 8-oxoadenine derivatives bearing saturated oxygen or nitrogen heterocycles in the N-9 substituent has revealed a remarkable selective enhancement in IFNα inducing potency in the nitrogen series. Further potency enhancement was achieved with the novel (S)-pentyloxy substitution at C-2 leading to the selection of GSK2245035 (32) as an intranasal development candidate. In human cell cultures, compound 32 resulted in suppression of Th2 cytokine responses to allergens, while in vivo intranasal administration at very low doses led to local upregulation of TLR7-mediated cytokines (IP-10). Target engagement was confirmed in humans following single intranasal doses of 32 of ≥20 ng, and reproducible pharmacological response was demonstrated following repeat intranasal dosing at weekly intervals.

Proinflammatory Stimulation of Toll-Like Receptor 9 with High Dose CpG ODN 1826 Impairs Endothelial Regeneration and Promotes Atherosclerosis in Mice

Background

Toll-like receptors (TLR) of the innate immune system have been closely linked with the development of atherosclerotic lesions. TLR9 is activated by unmethylated CpG motifs within ssDNA, but also by CpG motifs in nucleic acids released during vascular apoptosis and necrosis. The role of TLR9 in vascular disease remains controversial and we sought to investigate the effects of a proinflammatory TLR9 stimulation in mice.

Methods and Findings

TLR9-stimulation with high dose CpG ODN at concentrations between 6.25nM to 30nM induced a significant proinflammatory cytokine response in mice. This was associated with impaired reendothelialization upon acute denudation of the carotid and increased numbers of circulating endothelial microparticles, as a marker for amplified endothelial damage. Chronic TLR9 agonism in apolipoprotein E-deficient (ApoE^-/-) mice fed a cholesterol-rich diet increased aortic production of reactive oxygen species, the number of circulating endothelial microparticles, circulating sca-1/flk-1 positive cells, and most importantly augmented atherosclerotic plaque formation when compared to vehicle treated animals. Importantly, high concentrations of CpG ODN are required for these proatherogenic effects.

Conclusions

Systemic stimulation of TLR9 with high dose CpG ODN impaired reendothelialization upon acute vascular injury and increased atherosclerotic plaque development in ApoE^-/- mice. Further studies are necessary to fully decipher the contradictory finding of TLR9 agonism in vascular biology.

Toll-Like Receptors in the Pathogenesis of Autoimmune Diseases

Human Toll-like receptors (TLRs) are a family of transmembrane receptors, which play a key role in both innate and adaptive immune responses. Beside of recognizing specific molecular patterns that associated with different types of pathogens, TLRs may also detect a number of self-proteins and endogenous nucleic acids. Activating TLRs lead to the heightened expression of various inflammatory genes, which have a protective role against infection. Data rising predominantly from human patients and animal models of autoimmune disease indicate that, inappropriate triggering of TLR pathways by exogenous or endogenous ligands may cause the initiation and/or perpetuation of autoimmune reactions and tissue damage. Given their important role in infectious and non-infectious disease process, TLRs and its signaling pathways emerge as appealing targets for therapeutics. In this review, we demonstrate how TLRs pathways could be involved in autoimmune disorders and their therapeutic application.

Early clinical evaluation of the intranasal TLR7 agonist GSK2245035: Use of translational biomarkers to guide dosing and confirm target engagement

Modulation of the airways' immune milieu is a key therapeutic goal for remission from respiratory allergies. To explore this hypothesis, GSK2245035, a selective Toll-like receptor 7 (TLR7) agonist with preferential Type-1 interferon (IFN)-stimulating properties, was developed for intranasal application. Doses for clinical assessment were extrapolated from translational biomarker studies in primates. Randomized, double-blind, placebo-controlled trials in healthy volunteers and patients with allergic rhinitis demonstrated that intranasal GSK2245035 doses <100 ng were tolerated and did not cause nasal inflammation. Higher doses were not tested due to considerable cytokine release syndrome-related symptoms observed at 100 ng. Clear target engagement, reflected by local and peripheral increase of IFN-gamma-inducible protein-10, was observed at 20 ng, indicating IFN-stimulated immune changes at tolerated doses. Repeat intranasal administration at weekly intervals did not tolerize or amplify the pharmacological response. Intranasal GSK2245035 has an acceptable safety profile at doses that induce local TLR7-mediated immune responses.

NLRP3 and ASC suppress lupus-like autoimmunity by driving the immunosuppressive effects of TGF-β receptor signalling

OBJECTIVES

The NLRP3/ASC inflammasome drives host defence and autoinflammatory disorders by activating caspase-1 to trigger the secretion of mature interleukin (IL)-1β/IL-18, but its potential role in autoimmunity is speculative.

METHODS

We generated and phenotyped Nlrp3-deficient, Asc-deficient, Il-1r-deficient and Il-18-deficient C57BL/6-lpr/lpr mice, the latter being a mild model of spontaneous lupus-like autoimmunity.

RESULTS

While lack of IL-1R or IL-18 did not affect the C57BL/6-lpr/lpr phenotype, lack of NLRP3 or ASC triggered massive lymphoproliferation, lung T cell infiltrates and severe proliferative lupus nephritis within 6 months, which were all absent in age-matched C57BL/6-lpr/lpr controls. Lack of NLRP3 or ASC increased dendritic cell and macrophage activation, the expression of numerous proinflammatory mediators, lymphocyte necrosis and the expansion of most T cell and B cell subsets. In contrast, plasma cells and autoantibody production were hardly affected. This unexpected immunosuppressive effect of NLRP3 and ASC may relate to their known role in SMAD2/3 phosphorylation during tumour growth factor (TGF)-β receptor signalling, for example, Nlrp3-deficiency and Asc-deficiency significantly suppressed the expression of numerous TGF-β target genes in C57BL/6-lpr/lpr mice and partially recapitulated the known autoimmune phenotype of Tgf-β1-deficient mice.

CONCLUSIONS

These data identify a novel non-canonical immunoregulatory function of NLRP3 and ASC in autoimmunity.

Type I IFN Contributes to the Phenotype of Unc93b1D34A/D34A Mice by Regulating TLR7 Expression in B Cells and Dendritic Cells

TLR7 recognizes pathogen-derived and self-derived RNA, and thus a regulatory system for control of the TLR7 response is required to avoid excessive activation. Unc93 homolog B1 (Unc93B1) is a regulator of TLR7 that controls the TLR7 response by transporting TLR7 from the endoplasmic reticulum to endolysosomes. We have previously shown that a D34A mutation in Unc93B1 induces hyperactivation of TLR7, and that Unc93b1(D34A/D34A) mice (D34A mice) have systemic inflammation spontaneously. In this study, we examined the roles of inflammatory cytokines such as IFN-γ, IL-17A, and type I IFNs to understand the mechanism underlying the phenotype in D34A mice. mRNAs for IFN-γ and IL-I7A in CD4(+) T cells increased, but inflammatory phenotype manifesting as thrombocytopenia and splenomegaly was still observed in Ifng(-/-) or Il17a(-/-) D34A mice. In contrast to T cell-derived cytokines, Ifnar1(-/-) D34A mice showed an ameliorated phenotype with lower expression of TLR7 in B cells and conventional dendritic cells (cDCs). The amount of TLR7 decreased in B cells from Ifnar1(-/-) D34A mice, but the percentage of TLR7(+) cells decreased among CD8α(-) cDCs. In conclusion, type I IFNs maintain expression of TLR7 in B cells and cDCs in different ways; total amount of TLR7 is kept in B cells and TLR7(+) population is retained among cDCs. Our results suggested that these TLR7-expressing cells are activated initially and influence TLR7-dependent systemic inflammation.

U1-RNP and Toll-like receptors in the pathogenesis of mixed connective tissue diseasePart II. Endosomal TLRs and their biological significance in the pathogenesis of mixed connective tissue disease

Mixed connective tissue disease (MCTD) is a chronic autoimmune immunopathological disease of unknown etiology, which is characterized by the presence of various clinical symptoms and the presence of autoantibodies against U1-RNP particles. The U1-RNP component engages immune cells and their receptors in a complex network of interactions that ultimately lead to autoimmunity, inflammation, and tissue injury. The anti-U1-RNP autoantibodies form an immune complex with self-RNA, present in MCTD serum, which can act as endosomal Toll-like receptor (TLR) ligands. Inhibition of TLRs by nucleic acids is a promising area of research for the development of novel therapeutic strategies against pathogenic infection, tumorigenesis and autoimmunity. In this review we summarize current knowledge of endogenous TLRs and discuss their biological significance in the pathogenesis of MCTD. In part I we described the structure, biological function and significance of the U1-RNP complex in MCTD.

Endogenous Toll-Like Receptor 9 Regulates AKI by Promoting Regulatory T Cell Recruitment

Toll-like receptor 9 (TLR9) enhances proinflammatory responses, but whether it can act in a regulatory capacity remains to be established. In experimental murine AKI induced by cisplatin, Tlr9(-/-) mice developed enhanced renal injury and exhibited fewer intrarenal regulatory T cells (Tregs) compared with genetically intact mice. A series of reconstitution and depletion studies defined a role for TLR9 in maintaining Treg-mediated homeostasis in cisplatin-induced AKI. When Rag1(-/-) mice were reconstituted with nonregulatory CD25(-) splenocytes from wild-type (WT) or Tlr9(-/-) mice, AKI was similarly enhanced. However, when Rag1(-/-) mice were reconstituted with CD4(+)CD25(+) regulatory cells, WT CD4(+)CD25(+) cells were more renoprotective and localized to the kidney more efficiently than Tlr9(-/-) CD4(+)CD25(+) cells. In Treg-depleted Foxp3(DTR) mice, reconstitution with naive WT CD4(+)CD25(+) cells resulted in less severe AKI than did reconstitution with Tlr9(-/-) Tregs. Tlr9(-/-) mice were not deficient in CD4(+)CD25(+) cells, and WT and TLR9-deficient Tregs had similar suppressive function ex vivo. However, expression of adhesion molecules important in Treg trafficking was reduced on peripheral CD4(+)CD25(+) cells from Tlr9(-/-) mice. In conclusion, we identified a pathway by which TLR9 promotes renal Treg accumulation in AKI.

Treatment with 8-OH-modified adenine (TLR7 ligand)-allergen conjugates decreases T helper type 2-oriented murine airway inflammation

A strategy to improve allergen-specific immunotherapy is to employ new adjuvants stably linked to allergens. The study is addressed to evaluate the in vivo and in vitro effects of allergens [natural Dermatophagoides pteronyssinus 2 (nDer p 2) and ovalbumin (OVA)] chemically bound to an 8-OH-modified adenine. Humoral and cellular responses were analysed in allergen-sensitized and challenged mice by using conjugates (Conj) in a therapeutic setting. The in vitro activity of the conjugates on cytokine production induced by bone marrow dendritic cells and the co-culture system was also investigated. The nDer p 2-Conj treatment in nDer p 2-primed and challenged BALB/c mice reduced the numbers of eosinophils in bronchoalveolar lavage fluid and lung, airway allergen-driven interleukin-13 (IL-13) production in lung mononuclear cells and IgE, in comparison with nDer p 2-treated mice. The increase of IgG2a paralleled that of interferon-γ (IFN-γ) and IL-10 in allergen-stimulated spleen cells. Similar effects were elicited by treatment with OVA-Conj in an OVA-driven BALB/c model. The nDer p 2-Conj or OVA-Conj redirected memory T helper type 2 cells towards the production of IL-10 and IFN-γ also in C57BL/6 mice and when subcutaneously administered. Interleukin-10, IL-12 and IL-27 were produced in vitro by Conj-stimulated bone marrow dendritic cells, whereas IL-10 and IFN-γ were up-regulated in co-cultures of CD11c⁺ and CD4⁺ T cells from Conj-treated mice stimulated with allergen. Cytofluorometric analysis indicated that the Conj expanded IFN-γ- and IL-10- producing memory T cells. The Conj effects on IL-10^−/− and IL-12^−/− mice confirmed the role of IL-10 and IFN-γ in inducing a protective and balanced redirection the T helper type 2-mediated airway inflammation.

The anti-DNA antibody: origin and impact, dogmas and controversies

The inclusion of 'the anti-DNA antibody' by the ACR and the Systemic Lupus International Collaborating Clinics (SLICC) as a criterion for systemic lupus erythematosus does not convey the diverse origins of these antibodies, whether their production is transient or persistent (which is heavily influenced by the nature of the inducing antigens), the specificities exerted by these antibodies or their clinical impact-or lack thereof. A substantial amount of data not considered in clinical medicine could be added from basic immunology evidence, which could change the paradigms linked to what 'the anti-DNA antibody' is, in a pathogenic, classification or diagnostic context.