Chlorogenic acid alleviates crayfish allergy by altering the structure of crayfish tropomyosin and upregulating TLR8

Studies have shown that high hydrostatic pressure (HHP) processing and chlorogenic acid (CA) treatment can effectively reduce food allergenicity. We hypothesize that these novel processing techniques can help tackle crayfish allergy and examined the impact and mechanism of HHP (300 MPa, 15 min) and CA (CA:tropomyosin = 1:4000, 15 min) on the allergenicity of crayfish tropomyosin. Our results revealed that CA, rather than HHP, effectively reduced tropomyosin's allergenicity, as evident in the alleviation of allergic symptoms in a food allergy mouse model. Spectroscopy and molecular docking analyses demonstrated that CA could reduce the allergenicity of tropomyosin by covalent or non-covalent binding, altering its secondary structure (2.1 % decrease in α-helix; 1.9 % increase in β-fold) and masking tropomyosin's linear epitopes. Moreover, CA-treated tropomyosin potentially induced milder allergic reactions by up-regulating TLR8. While our results supported the efficacy of CA in alleviating crayfish allergy, further exploration is needed to determine clinical effectiveness.

Transcriptomics-based identification of TYROBP and TLR8 as novel macrophage-related biomarkers for the diagnosis of acute rejection after kidney transplantation

Macrophages play an important role in the development and progression of acute rejection after kidney transplantation. The study aims to investigate the biological role and significance of macrophage-associated genes (MAG) in acute rejection after kidney transplantation. We utilized transcriptome sequencing results from public databases related to acute rejection of kidney transplantation for comprehensive analysis and validation in animal experiments. We found that a large number of immune-related signaling pathways are activated in acute rejection. PPI protein interaction networks and machine learning were used to establish a Hub gene consisting of TYROBP and TLR8 for the diagnosis of acute rejection. The single-gene GSEA enrichment analysis and immune cell correlation analysis revealed a close correlation between the expression of Hub genes and immune-related biological pathways as well as the expression of multiple immune cells. In addition, the study of TF, miRNAs, and drugs provided a theoretical basis for regulating and treating the Hub genes in acute rejection. Finally, the animal experiments demonstrated once again that acute rejection can aggravate kidney tissue damage, apoptosis level, and increase the release of inflammatory factors. We established and validated a macrophage-associated diagnostic model for acute rejection after kidney transplantation, which can accurately diagnose the biological alterations in acute rejection after kidney transplantation.

A computational approach to design a multiepitope vaccine against H5N1 virus

Since 1997, highly pathogenic avian influenza viruses, such as H5N1, have been recognized as a possible pandemic hazard to men and the poultry business. The rapid rate of mutation of H5N1 viruses makes the whole process of designing vaccines extremely challenging. Here, we used an in silico approach to design a multi-epitope vaccine against H5N1 influenza A virus using hemagglutinin (HA) and neuraminidase (NA) antigens. B-cell epitopes, Cytotoxic T lymphocyte (CTL) and Helper T lymphocyte (HTL) were predicted via IEDB, NetMHC-4 and NetMHCII-2.3 respectively. Two adjuvants consisting of Human β-defensin-3 (HβD-3) along with pan HLA DR-binding epitope (PADRE) have been chosen to induce more immune response. Linkers including KK, AAY, HEYGAEALERAG, GPGPGPG and double EAAAK were utilized to link epitopes and adjuvants. This construct encodes a protein having 350 amino acids and 38.46 kDa molecular weight. Antigenicity of ~ 1, the allergenicity of non-allergen, toxicity of negative and solubility of appropriate were confirmed through Vaxigen, AllerTOP, ToxDL and DeepSoluE, respectively. The 3D structure of H5N1 was refined and validated with a Z-Score of - 0.87 and an overall Ramachandran of 99.7%. Docking analysis showed H5N1 could interact with TLR7 (docking score of - 374.08 and by 4 hydrogen bonds) and TLR8 (docking score of - 414.39 and by 3 hydrogen bonds). Molecular dynamics simulations results showed RMSD and RMSF of 0.25 nm and 0.2 for H5N1-TLR7 as well as RMSD and RMSF of 0.45 nm and 0.4 for H5N1-TLR8 complexes, respectively. Molecular Mechanics Poisson-Boltzmann Surface Area (MM/PBSA) confirmed stability and continuity of interaction between H5N1-TLR7 with the total binding energy of - 29.97 kJ/mol and H5N1-TLR8 with the total binding energy of - 23.9 kJ/mol. Investigating immune response simulation predicted evidence of the ability to stimulate T and B cells of the immunity system that shows the merits of this H5N1 vaccine proposed candidate for clinical trials.

UNC93B1 variants underlie TLR7-dependent autoimmunity

UNC93B1 is critical for trafficking and function of nucleic acid-sensing Toll-like receptors (TLRs) TLR3, TLR7, TLR8, and TLR9, which are essential for antiviral immunity. Overactive TLR7 signaling induced by recognition of self-nucleic acids has been implicated in systemic lupus erythematosus (SLE). Here, we report UNC93B1 variants (E92G and R336L) in four patients with early-onset SLE. Patient cells or mouse macrophages carrying the UNC93B1 variants produced high amounts of TNF-α and IL-6 and upon stimulation with TLR7/TLR8 agonist, but not with TLR3 or TLR9 agonists. E92G causes UNC93B1 protein instability and reduced interaction with TLR7, leading to selective TLR7 hyperactivation with constitutive type I IFN signaling. Thus, UNC93B1 regulates TLR subtype-specific mechanisms of ligand recognition. Our findings establish a pivotal role for UNC93B1 in TLR7-dependent autoimmunity and highlight the therapeutic potential of targeting TLR7 in SLE.

Combining antibiotic with anti-TLR2/TLR13 therapy prevents brain pathology in pneumococcal meningitis

Despite effective antibiotic therapy, brain-destructive inflammation often cannot be avoided in pneumococcal meningitis. The causative signals are mediated predominantly through TLR-recruited myeloid differentiation primary response adaptor 88 (MyD88), as indicated by a dramatic pneumococcal meningitis phenotype of Myd88-/- mice. Because lipoproteins and single-stranded RNA are crucial for recognition of Gram-positive bacteria such as Streptococcus pneumoniae by the host immune system, we comparatively analyzed the disease courses of Myd88-/- and Tlr2-/- Tlr13-/- mice. Their phenotypic resemblance indicated TLR2 and -13 as master sensors of S. pneumoniae in the cerebrospinal fluid. A neutralizing anti-TLR2 antibody (T2.5) and chloroquine (CQ) - the latter applied here as an inhibitor of murine TLR13 and its human ortholog TLR8 - abrogated activation of murine and human primary immune cells exposed to antibiotic-treated S. pneumoniae. The inhibitory effect of the T2.5/CQ cocktail was stronger than that of dexamethasone, the current standard adjunctive drug for pneumococcal meningitis. Accordingly, TLR2/TLR13 blockade concomitant with ceftriaxone application significantly improved the clinical course of pneumococcal meningitis compared with treatment with ceftriaxone alone or in combination with dexamethasone. Our study indicates the importance of murine TLR13 and human TLR8, besides TLR2, in pneumococcal meningitis pathology, and suggests their blockade as a promising antibiotic therapy adjunct.

Antibody preparation and age-dependent distribution of TLR8 in Bactrian camel spleens

BACKGROUND

Toll-like receptor 8 (TLR8) can recognize specific pathogen-associated molecular patterns and exert multiple immunological functions through activation of signaling cascades. However, the precise distribution and age-related alterations of TLR8 in the spleens of Bactrian camels have not yet been investigated. This study aimed to prepare a rabbit anti-Bactrian camel TLR8 polyclonal antibody and elucidate the distribution of TLR8 in the spleens of Bactrian camels at different age groups. The methodology involved the construction of the pET-28a-TLR8 recombinant plasmid, followed by the expression of TLR8 recombinant protein via prokaryotic expression. Subsequently, rabbits were immunized with the purified protein to prepare the TLR8 polyclonal antibody. Finally, twelve Alashan Bactrian camels were categorized into four groups: young (1-2 years), pubertal (3-5 years), middle-aged (6-16 years) and old (17-20 years). These camels received intravenous sodium pentobarbital (20 mg/kg) anesthesia and were exsanguinated to collect spleen samples. Immunohistochemical techniques were employed to observe and analyze the distribution patterns and age-related changes of TLR8 in the spleen.

RESULTS

The results showed that the TLR8 recombinant protein was expressed in the form of inclusion body with a molecular weight of 52 kDa, and the optimal induction condition involved 0.3 mmol/L IPTG induction for 8 h. The prepared antibody yielded a titer of 1:32 000, and the antibody demonstrated specific binding to TLR8 recombinant protein. TLR8 positive cells exhibited a consistent distribution pattern in the spleen across different age groups of Bactrian camels, primarily scattered within the periarterial lymphatic sheath of the white pulp, marginal zone, and red pulp. The predominant cell type expressing TLR8 was macrophages, with expression also observed in neutrophils and dendritic cells. Statistical analysis revealed that there were significant differences in the distribution density of TLR8 positive cells among different spleen regions at the same age, with the red pulp, marginal zone, and white pulp showing a descending order (P<0.05). Age-related changes indicated that the distribution density in the marginal zone and red pulp exhibited a similar trend of initially increasing and subsequently decreasing from young to old camels. As camels age, there was a significant decrease in the distribution density across all spleen regions (P<0.05).

CONCLUSIONS

The results confirmed that this study successfully prepared a rabbit anti-Bactrian camel TLR8 polyclonal antibody with good specificity. TLR8 positive cells were predominantly located in the red pulp and marginal zone of the spleen, signifying their pivotal role in the innate immune response of the spleen. Aging was found to significantly reduce the density of TLR8 positive cells, while leaving their scattered distribution characteristics unaffected. These findings provide valuable support for further investigations into the immunomorphology and immunosenescence of the spleen in Bactrian camels.

Intracellular Toll-Like Receptors Modulate Adaptive Immune Responses in Head and Neck Cancer

The percentage of head and neck cancer (HNC) positive for human papillomavirus (HPV) is unknown in most parts of India. How toll-like receptors (TLRs) affect the adaptive immune response in HNC is also mainly unknown. We here assessed the expressions of HPV DNA, p16, inflammation, and TLRs in oral squamous cell carcinoma (OC) and oropharyngeal squamous cell carcinoma (OPC). Patients with OC (n = 31) and OPC (n = 41), diagnosed during 2017-2018 at the Malabar Cancer Centre (tertiary cancer center), Kerala, India, were included in the study. Immunohistochemistry was performed on tumor specimens against p16, TLR3, TLR7, TLR8, TLR9, CD4, and CD8. Quantitate polymerase chain reaction for 14 high-risk HPVs (HPV16/18/31/33/35/39/45/51/52/56/58/59/66/68) was performed. Seven out of 31 OC (22.6%) were p16+ but only 3.2% (1/31) of OC were positive for HPV DNA. While 24.4% (10/41) of OPC were p16+, HPV DNA was found in only one P16+ OPC and in no P16- OPC. TLR3, TLR7, TLR8, and TLR9 were expressed both in OC and in OPC. The expression of TLR7 was significantly higher in OPC compared with OC. TLR8 expression was correlated with and TLR7 tended to be correlated with the inflammatory score in OPC (r = 0.56, p < 0.05 and r = 0.52, p = 0.08, respectively). In conclusion, the role of HPV in OC and OPC is minor, and p16 constitutes a poor biomarker for HPV positivity in Kerala, India. Intracellular TLRs are correlated with the degree of inflammation in OPC but not in OC and may potentially constitute a medical target in the therapy of HNC in the future.

Hypoxia is correlated with the tumor immune microenvironment: Potential application of immunotherapy in bladder cancer

OBJECTIVE

Hypoxia, which can considerably affect the tumor microenvironment, hinders the use of immunotherapy in bladder cancer (BLCA). Therefore, we aimed to identify reliable hypoxia-related biomarkers to guide clinical immunotherapy in BLCA.

METHODS

Using data downloaded from TCGA-BLCA cohort, we determined BLCA subtypes which divide 408 samples into different subtypes. Tumor immune infiltration levels of two clusters were quantified using ssGSEA, MCPcounter, EPIC, ESTIMATE, and TIMER algorithms. Next, we constructed a hypoxia score based on the expression of hypoxia-related genes. The IMvigor210 cohort and SubMap analysis were used to predict immunotherapeutic responses in patients with different hypoxia scores. Hub genes were screened using cytoscape, immunohistochemistry (IHC), and multispectral immunofluorescence were used to detect the spatial distribution of immune markers.

RESULTS

Patients with BLCA were categorized into cluster1 (n = 227) and Cluster2 (n = 181). Immune infiltration and expression of immune markers were higher in Cluster1. Immune infiltration was also more obvious in the high-hypoxia score group which related to a better predicted response to immunotherapy. IHC, and multispectral immunofluorescence confirmed the importance of TLR8 in immune infiltration and immune phenotype.

CONCLUSIONS

BLCA subtype can evaluate the infiltration of immune cells in the tumor microenvironment of different patients. Hypoxia score in this study could effectively predict immunotherapeutic responses in patients with BLCA. TLR8 may be a potential target for clinical immunotherapy.

Dichotomous roles of RIPK3 in regulating the IFN response and NLRP3 inflammasome in human monocytes

Regulation of the profile and magnitude of toll-like receptor (TLR) responses is important for effective host defense against infections while minimizing inflammatory toxicity. The chemokine CXCL4 regulates the TLR8 response to amplify inflammatory gene and inflammasome activation while attenuating the interferon (IFN) response in primary monocytes. In this study, we describe an unexpected role for the kinase RIPK3 in suppressing the CXCL4 + TLR8-induced IFN response and providing signal 2 to activate the NLRP3 inflammasome and interleukin (IL)-1 production in primary human monocytes. RIPK3 also amplifies induction of inflammatory genes such as TNF, IL6, and IL1B while suppressing IL12B. Mechanistically, RIPK3 inhibits STAT1 activation and activates PI3K-Akt-dependent and XBP1- and NRF2-mediated stress responses to regulate downstream genes in a dichotomous manner. These findings identify new functions for RIPK3 in modulating TLR responses and provide potential mechanisms by which RIPK3 plays roles in inflammatory diseases and suggest targeting RIPK3 and XBP1- and NRF2-mediated stress responses as therapeutic strategies to suppress inflammation while preserving the IFN response for host defense.

Identification of new potent agonists for toll-like receptor 8 by virtual screening methods, molecular dynamics simulation, and MM-GBSA

Toll-like receptor 8 (TLR8), as an endosomal transmembrane receptor, plays a crucial role in the innate immune response to neoplasia and viruses. Previous studies have shown that TLR8 agonists e.g. Motolimod can be used to treat patients with last-stage cancer. In this study, in order to find new suitable ligands for TLR8, 16 PBD codes related to TLR8 complexes were collected to design the pharmacophore models using the Pharmit server. Then the PubChem, and ZINC databases were screened by them. Subsequently, the ADME-Tox features of the compounds were detected using FAF-Drugs4 and the selected compounds were docked to TLR8 (PDB: 3w3j). Molecular dynamics simulation was used to compare compounds with the best docking scores, with Motolimod in complex with TLR8. Finally, two compounds were identified, PubChem: 124126919 (A) and PubChem: 18559540 (B), each with advantages over Motolimod. As the RMSD results showed that compound A has very good flexibility, in terms of energy calculated using the MM-GBSA method, complex B and TLR8 showed the lowest energy level compared to the rest of the complexes. These observations suggest that these two compounds could be used as TLR8 agonists with the desired pharmacological features in future experimental studies.Communicated by Ramaswamy H. Sarma.

Human TLR8 induces inflammatory bone marrow erythromyeloblastic islands and anemia in SLE-prone mice

Anemia commonly occurs in systemic lupus erythematosus, a disease characterized by innate immune activation by nucleic acids. Overactivation of cytoplasmic sensors by self-DNA or RNA can cause erythroid cell death, while sparing other hematopoietic cell lineages. Whereas chronic inflammation is involved in this mechanism, less is known about the impact of systemic lupus erythematosus on the BM erythropoietic niche. We discovered that expression of the endosomal ssRNA sensor human TLR8 induces fatal anemia in Sle1.Yaa lupus mice. We observed that anemia was associated with a decrease in erythromyeloblastic islands and a block in differentiation at the CFU-E to proerythroblast transition in the BM. Single-cell RNAseq analyses of isolated BM erythromyeloblastic islands from human TLR8-expressing mice revealed that genes associated with essential central macrophage functions including adhesion and provision of nutrients were down-regulated. Although compensatory stress erythropoiesis occurred in the spleen, red blood cell half-life decreased because of hemophagocytosis. These data implicate the endosomal RNA sensor TLR8 as an additional innate receptor whose overactivation causes acquired failure of erythropoiesis via myeloid cell dysregulation.

First-in-Human Study of the Safety, Pharmacokinetics, and Pharmacodynamics of MHV370, a Dual Inhibitor of Toll-Like Receptors 7 and 8, in Healthy Adults

BACKGROUND AND OBJECTIVE

MHV370, a dual antagonist of human Toll-like receptors (TLR) 7 and 8, suppresses cytokines and interferon-stimulated genes in vitro and in vivo, and  has demonstrated efficacy in murine models of lupus. This first-in-human study aimed to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of single and multiple doses of MHV370 in healthy adults, as well as the effects of food consumption on a single dose of MHV370.

METHODS

This was a phase 1, randomised, placebo-controlled study conducted in three parts. In part A, participants received (3:1) a single ascending dose (SAD) of 1, 3, 10, 20, 40, 80, 160, 320, 640 and 1000 mg MHV370 or placebo. In part B, participants received (3:1) multiple ascending doses (MAD) of 25, 50, 100, 200 and 400 mg MHV370 twice daily (b.i.d) or placebo for 14 days. In part C, participants received an open-label single dose of 200 mg MHV370 under fasted or fed conditions. Safety, pharmacokinetic and pharmacodynamic parameters were evaluated.

RESULTS

MHV370 was well tolerated, and no safety signal was observed in the study. No dose-limiting adverse events occurred across the dose range evaluated. Plasma concentrations of MHV370 increased with dose (mean [SD] maximum plasma concentrations ranged from 0.97 [0.48] to 1670 [861.0] ng/mL for SAD of 3-1000 mg, 29.5 [7.98] to 759 [325.0] ng/mL for MAD of 25-400 mg b.i.d. on day 1). The intake of food did not have a relevant impact on the pharmacokinetics of MHV370. Pharmacodynamic data indicated time- and dose-dependent inhibition of TLR7-mediated CD69 expression on B cells (100% inhibition at 24 h post-dose starting from SAD 160 mg and MAD 50 mg b.i.d.) and TLR8-mediated TNF release after ex vivo stimulation (>90% inhibition at 24 h post-dose starting from SAD 320 mg and MAD 100 mg b.i.d.).

CONCLUSION

The safety, pharmacokinetic and pharmacodynamic data support the further development of MHV370 in systemic autoimmune diseases driven by the overactivation of TLR7 and TLR8.

TLR7/TLR8 activation and susceptibility genes synergize to breach gut barrier in a mouse model of lupus

Background

Mounting evidence suggests that increased gut permeability, or leaky gut, and the resulting translocation of pathobionts or their metabolites contributes to the pathogenesis of Systemic Lupus Erythematosus. However, the mechanisms underlying the induction of gut leakage remain unclear. In this study, we examined the effect of a treatment with a TLR7/8 agonist in the B6.Sle1.Sle2.Sle3 triple congenic (TC) mouse, a spontaneous mouse model of lupus without gut leakage.

Materials and methods

Lupus-prone mice (TC), TC.Rag1-/- mice that lack B and T cells, and congenic B6 healthy controls were treated with R848. Gut barrier integrity was assessed by measuring FITC-dextran in the serum following oral gavage. Claudin-1 and PECAM1 expression as well as the extent of CD45+ immune cells, B220+ B cells, CD3+ T cells and CD11b+ myeloid cells were measured in the ileum by immunofluorescence. NKp46+ cells were measured in the ileum and colon by immunofluorescence. Immune cells in the ileum were also analyzed by flow cytometry.

Results

R848 decreased gut barrier integrity in TC but not in congenic control B6 mice. Immunofluorescence staining of the ileum showed a reduced expression of the tight junction protein Claudin-1, endothelial cell tight junction PECAM1, as well as an increased infiltration of immune cells, including B cells and CD11b+ cells, in R848-treated TC as compared to untreated control mice. However, NKp46+ cells which play critical role in maintaining gut barrier integrity, had a lower frequency in treated TC mice. Flow cytometry showed an increased frequency of plasma cells, dendritic cells and macrophages along with a decreased frequency of NK cells in R848 treated TC mice lamina propria. In addition, we showed that the R848 treatment did not induce gut leakage in TC.Rag1-/- mice that lack mature T and B cells.

Conclusions

These results demonstrate that TLR7/8 activation induces a leaky gut in lupus-prone mice, which is mediated by adaptive immune responses. TLR7/8 activation is however not sufficient to breach gut barrier integrity in non-autoimmune mice.

Enhanced Delivery of TLR7/8 Agonists by Metal-Organic Frameworks for Hepatitis B Virus Cure

Hepatitis B virus (HBV) infection remains a major challenge to global health due to unsatisfactory treatment efficacy, side effects of current therapies, and immune tolerance. Toll-like receptors 7/8 (TLR7/8) agonists have shown great potential in chronic hepatitis B (CHB) cure, but systemic administration often induces severe side effects due to rapid dispersion into the microvasculature. Herein, we encapsulate an imidazoquinoline-based TLR7/8 agonist (IMDQ) into zeolitic imidazolate framework 8 nanoparticles (IMDQ@ZIF-8 NPs) for HBV immunotherapy. Compared with free IMDQ, IMDQ@ZIF-8 NPs efficiently accumulate in the liver and are selectively taken up by antigen-presenting cells (APCs), leading to enhanced APC activation and efficient viral elimination in HBV-infected models. Strikingly, MDQ@ZIF-8 NP treatment results in the obvious production of anti-HBs antibody and seroconversion in HBV-infected mice. Overall, this study on the convergence of a facile assembly approach and efficient therapeutic effects represents a promising strategy for HBV treatment.

Insight into the first multi-epitope-based peptide subunit vaccine against avian influenza A virus (H5N6): An immunoinformatics approach

The rampant spread of highly pathogenic avian influenza A (H5N6) virus has drawn additional concerns along with ongoing Covid-19 pandemic. Due to its migration-related diffusion, the situation is deteriorating. Without an existing effective therapy and vaccines, it will be baffling to take control measures. In this regard, we propose a revers vaccinology approach for prediction and design of a multi-epitope peptide based vaccine. The induction of humoral and cell-mediated immunity seems to be the paramount concern for a peptide vaccine candidate; thus, antigenic B and T cell epitopes were screened from the surface, membrane and envelope proteins of the avian influenza A (H5N6) virus, and passed through several immunological filters to determine the best possible one. Following that, the selected antigenic with immunogenic epitopes and adjuvant were linked to finalize the multi-epitope-based peptide vaccine by appropriate linkers. For the prediction of an effective binding, molecular docking was carried out between the vaccine and immunological receptors (TLR8). Strong binding affinity and good docking scores clarified the stringency of the vaccines. Furthermore, molecular dynamics simulation was performed within the highest binding affinity complex to observe the stability, and minimize the designed vaccine's high mobility region to order to increase its stability. Then, Codon optimization and other physicochemical properties were performed to reveal that the vaccine would be suitable for a higher expression at cloning level and satisfactory thermostability condition. In conclusion, predicting the overall in silico assessment, we anticipated that our designed vaccine would be a plausible prevention against avian influenza A (H5N6) virus.

Gain-of-function defects in toll-like receptor 8 shed light on the interface between immune system and bone marrow failure disorders

In this article, we will share lessons that patients with gain-of-function defects in Toll-like receptor 8 (TLR8-GOF) can teach us about the interface between bone marrow failure (BMF) disorders and inborn errors of immunity (IEI), subsequently referred to as “Interface Disorders”. TLR8-GOF is a relatively young entity (from a discovery standpoint) that—through both similar and dissimilar disease characteristics—can increase our understanding of interface disorders, for example, as it pertains to pathophysiology, the genetic mechanism of disease, and related diagnostics and therapeutics. From a genetics point of view, TLR8-GOF joins a growing list of (interface) disorders that can cause disease both with germline and somatic (mosaic) genetic variants. This not only has repercussions for the diagnostic workup of these disorders, inasmuch that routine genetic testing may miss somatic variants, but has therapeutic implications as well, for example, with the approach to curative treatment, such as hematopoietic stem cell transplantation. Following an introduction and schematic rendering of the interface, we will review the salient features of TLR8-GOF, with the understanding that the phenotype of this new disorder is likely not written in stone yet. In keeping with the principle of “Form Follows Function”, we will discuss specific immunological biomarkers that can be measured in clinical laboratories and highlight key disease features that pertain to TLR8-GOF, and can be found in several interface disorders. As can be seen from a schematic representation, the interface provides not only opportunities for learning and collaboration with respect to shared diagnostics but also the potential for drug repurposing and precision therapeutics. Ideally, collaboration also focuses on education and teaching, such that cross-fertilization and collaboration across these disciplines can create a framework for complementary research.

Integrated analysis of immune parameters, miRNA-mRNA interaction, and immune genes expression in the liver of rainbow trout following infectious hematopoietic necrosis virus infection

Rainbow trout (Oncorhynchus mykiss) is an important economical cold-water fish worldwide. However, infection with infectious hematopoietic necrosis virus (IHNV) has severely restricted the development of aquaculture and caused huge economic losses. Currently, little is known about the immune defense mechanisms of rainbow trout against IHNV. In this study, we detected the changes of immune parameters over different post-infection periods (6-, 12-, 24-, 48-, 72-, 96-, 120-, and 144 hours post-infection (hpi)), mRNA and miRNA expression profiles under 48 hpi (T48L) compared to control (C48L), and key immune-related genes expression patterns in rainbow trout liver following IHNV challenge through biochemical methods, RNA-seq, and qRT-PCR, and the function of miR-330-y was verified by overexpression and silencing in vitro and in vivo. The results revealed that alkaline phosphatase (AKP), alanine aminotransferase (ALT), catalase (CAT), and total superoxide dismutase (T-SOD) activities, and lysozyme (LZM) content showed significant peaks at 48 hpi, whereas malondialdehyde (MDA) content and aspartate aminotransferase (AST) activity decreased continuously during infection, and acid phosphatase (ACP) activity varied slightly. From RNA-seq, a total of 6844 genes and 86 miRNAs were differentially expressed, and numerous immune-related differentially expressed genes (DEGs) involved in RIG-I-like receptor signaling pathway, Toll-like receptor signaling pathway, NOD-like receptor signaling pathway, cytokine-cytokine receptor interaction, and antigen processing and presentation were significantly upregulated in T48Lm group, including IFIH1, DHX58, MAVS, TRAF3, IRF3, IRF7, MX1, TLR3, TLR8, MYD88, NOD1, NOD2, IL-8, CXCR1, CD209, CD83, and TAP1. Integrated analysis identified seven miRNAs (miR-425-x, miR-185-x, miR-338-x, miR-330-y, miR-361-x, miR-505-y, and miR-191-x) that target at least three key immune-related DEGs. Expression analysis showed that IFIH1, DHX58, IRF3, IRF7, MX1, TLR3, TLR8, and MYD88 showed a marked increase after 24 hpi during infection. Further research confirmed TAP1 as one of the targets of miR-330-y, overexpression of miR-330-y with mimics or agomir significantly reduced the expression levels of TAP1, IRF3, and IFN, and the opposite effects were obtained by inhibitor. These results facilitate in-depth understanding of the immune mechanisms in rainbow trout against IHNV.

Ginsenoside Rh2 Ameliorates Neuropathic Pain by inhibition of the miRNA21-TLR8-MAPK axis

Ginsenoside Rh2 is one of the major bioactive ginsenosides in Panax ginseng. Although Rh2 is known to enhance immune cells activity for treatment of cancer, its anti-inflammatory and neuroprotective effects have yet to be determined. In this study, we investigated the effects of Rh2 on spared nerve injury (SNI)-induced neuropathic pain and elucidated the potential mechanisms. We found that various doses of Rh2 intrathecal injection dose-dependently attenuated SNI-induced mechanical allodynia and thermal hyperalgesia. Rh2 also inhibited microglia and astrocyte activation in the spinal cord of a murine SNI model. Rh2 treatment inhibited SNI-induced increase of proinflammatory cytokines, including tumor necrosis factor-α, interleukin (IL)-1 and IL-6. Expression of miRNA-21, an endogenous ligand of Toll like receptor (TLR)8 was also decreased. Rh2 treatment blocked the mitogen-activated protein kinase (MAPK) signaling pathway by inhibiting of phosphorylated extracellular signal-regulated kinase expression. Finally, intrathecal injection of TLR8 agonist VTX-2337 reversed the analgesic effect of Rh2. These results indicated that Rh2 relieved SNI-induced neuropathic pain via inhibiting the miRNA-21-TLR8-MAPK signaling pathway, thus providing a potential application of Rh2 in pain therapy.

Pacritinib Inhibition of IRAK1 Blocks Aberrant TLR8 Signalling by SARS-CoV-2 and HIV-1-Derived RNA

Macrophages promote an early host response to infection by releasing pro-inflammatory cytokines such as interleukin (IL) 1β (IL-1β), tumour necrosis factor (TNF), and IL-6. One of the mechanisms through which cells sense pathogenic microorganisms is through Toll-like receptors (TLRs). IL-1 receptor-associated kinase (IRAK) 1, IRAK2, IRAK3, and IRAK4 are integral to TLR and IL-1 receptor signalling pathways. Recent studies suggest a role for aberrant TLR8 and NLRP3 inflammasome activation during both COVID-19 and HIV-1 infection. Here, we show that pacritinib inhibits the TLR8-dependent pro-inflammatory cytokine response elicited by GU-rich single-stranded RNA derived from SARS-CoV-2 and HIV-1. Using genetic and pharmacologic inhibition, we demonstrate that pacritinib inhibits IRAK1 phosphorylation and ubiquitination which then inhibits the recruitment of the TAK1 complex to IRAK1, thus inhibiting the activation of downstream signalling and the production of pro-inflammatory cytokines.

Blood DCs activated with R848 and poly(I:C) induce antigen-specific immune responses against viral and tumor-associated antigens

Monocyte-derived Dendritic cells (DCs) have successfully been employed to induce immune responses against tumor-associated antigens in patients with various cancer entities. However, objective clinical responses have only been achieved in a minority of patients. Additionally, generation of GMP-compliant DCs requires time- and labor-intensive cell differentiation. In contrast, Blood DCs (BDCs) require only minimal ex vivo handling, as differentiation occurs in vivo resulting in potentially better functional capacities and survival. We aimed to identify a protocol for optimal in vitro activation of BDCs including the three subsets pDCs, cDC1s, and cDC2s. We evaluated several TLR ligand combinations and demonstrated that polyinosinic:polycytidylic acid [poly(I:C)] and R848, ligands for TLR3 and TLR7/8, respectively, constituted the optimal combination for inducing a positive co-stimulatory profile in all BDC subsets. In addition, TLR3 and TLR7/8 activation led to high secretion of IFN-α and IL-12p70. Simultaneous as opposed to separate tailored activation of pDCs and cDCs increased immunostimulatory capacities, suggesting that BDC subsets engage in synergistic cross-talk during activation. Stimulation of BDCs with this protocol resulted in enhanced migration, high NK-cell activation, and potent antigen-specific T-cell induction.

We conclude that simultaneous activation of all BDC subsets with a combination of R848 + poly(I:C) generates highly immunostimulatory DCs. These results support further investigation and clinical testing, as standalone or in conjunction with other immunotherapeutic strategies including adoptive T-cell transfer and checkpoint inhibition.

Chronic asthma-induced airway remodeling is prevented by toll-like receptor-7/8 ligand S28463

RATIONALE

Allergic asthma is a heterogeneous disease, the pathology of which is a result of improper immune responses to innocuous antigens. We and others have previously shown that one of the Toll-like receptor (TLR)-7/8 ligands, the synthetic compound S28463 (resiquimod, R-848), is able to inhibit acute allergic asthma in mice.

OBJECTIVES

Given that the efficiency of this pharmacologic compound against the smooth muscle mass increase and goblet cell hyperplasia that are characteristic of chronic allergic asthma has not been previously assessed, we investigated the ability of this compound to prevent these aspects of chronic airway remodeling.

METHODS

The impact of S28463 treatment was assessed in a Brown Norway rat model of chronic asthma by histologic, morphometric, and molecular techniques.

MEASUREMENTS AND MAIN RESULTS

We demonstrate that treatment with S28463 is able to prevent the development of goblet cell hyperplasia and increases in airway smooth muscle mass, and that this effect is at least partially mediated by inhibiting proliferation of goblet and smooth muscle cells, respectively. Furthermore, we show that the abrogation of airway remodeling is preceded by inhibition of the inflammatory reaction normally occurring in response to allergen challenge in sensitized animals. This inhibition was associated with a reduction of both helper T cell type 1 and type 2 cytokine protein expression in the lungs, demonstrating the potent antiinflammatory effect of this pharmaceutical compound in the context of allergic reactions.

CONCLUSIONS

Taken together, our results indicate great potential for the use of S28463 as an antiinflammatory therapeutic agent for the management of chronic asthma.

Activation of innate defense against a paramyxovirus is mediated by RIG-I and TLR7 and TLR8 in a cell-type-specific manner

Recognition of pathogens by the innate immune system is mediated by pattern recognition receptors (PRRs), which recognize specific molecular structures of the infectious agents and subsequently trigger expression of genes involved in host defense. Toll-like receptors (TLRs) represent a well-characterized class of membrane-bound PRRs, and the RNA helicase retinoic acid inducible gene I (RIG-I) has recently been described as a novel cytoplasmic PRR recognizing double-stranded RNA (dsRNA). Here we show that activation of signal transduction and induction of cytokine expression by the paramyxovirus Sendai virus is dependent on virus replication and involves PRRs in a cell-type-dependent manner. While nonimmune cells relied entirely on recognition of dsRNA through RIG-I for activation of an antiviral response, myeloid cells utilized both the single-stranded RNA sensing TLR7 and TLR8 and dsRNA-dependent mechanisms independent of RIG-I, TLR3, and dsRNA-activated protein kinase R to trigger this response. Therefore, there appears to be a large degree of cell-type specificity in the mechanisms used by the host to recognize infecting viruses.

TLR ignores methylated RNA?

CpG methylation of DNA silences TLR9-mediated innate immune recognition. In this issue of Immunity, Kariko et al (2005) suggest that the innate immune recognition of RNA by TLR3, TLR7, or TLR8 is in fact controlled by modification of nucleotides, including methylation.

TLR8 and TLR7 are involved in the host's immune response to human parechovirus 1

Toll-like receptors (TLR) have a key role in regulating immunity against microbial agents. Engagement of TLR by bacterial, viral or fungal components leads to the production and release of inflammatory cytokines. In this study we show that mainly TLR8 and also TLR7 act as the host sensors for human parechovirus 1, a single-stranded RNA (ssRNA) virus. Furthermore, we see that the viral ssRNA genome is detected in endosomal compartments by these TLR, which activate signalling that lead to the synthesis of pro-inflammatory molecules by the host.

TLRs and NODs mRNA expression pattern in healthy mouse eye

AIMS

To look for TLR and NOD mRNA expression in the healthy eye and in other immune privileged and non-immune privileged mouse organs.

METHODS

Semiquantitative RT-PCR was performed to look for TLR1-9 and NOD1 and NOD2 mRNA expressions in the whole eye, in the anterior (AP) and posterior (PP) portions of the eye, in corneal fibroblasts (CF) and in ovary, brain, testis, heart, lung, and spleen.

RESULTS

All the TLR mRNAs were expressed in the whole eye of Balb/c mice. NIH and C57BL/6 did not express TLR9 and TLR8, respectively. NIH expressed higher levels of TLR1, 2, 3, and 6 than the other strains. C57BL/6 expressed the lowest levels of all TLRs. TLR9, 5, and 4 were the less expressed in all strains. All TLRs were expressed in Balb/c PP and TLR1 was not expressed in AP. In NIH and Balb/c CF the majority of TLRs were overexpressed with LPS. In testis, expression of most TLRs was absent. Non-immune privileged organs expressed most of the TLRs. All the organs expressed NOD1 and NOD2. In PP NOD2 was not expressed.

CONCLUSION

TLRs and NODs are expressed in the eye, and could have an important role in the innate immunity.

Toll-like receptor 8-mediated reversal of CD4+ regulatory T cell function

CD4+ regulatory T (Treg) cells have a profound ability to suppress host immune responses, yet little is understood about how these cells are regulated. We describe a mechanism linking Toll-like receptor (TLR) 8 signaling to the control of Treg cell function, in which synthetic and natural ligands for human TLR8 can reverse Treg cell function. This effect was independent of dendritic cells but required functional TLR8-MyD88-IRAK4 signaling in Treg cells. Adoptive transfer of TLR8 ligand-stimulated Treg cells into tumor-bearing mice enhanced anti-tumor immunity. These results suggest that TLR8 signaling could play a critical role in controlling immune responses to cancer and other diseases.

Gene expression and antiviral activity of alpha/beta interferons and interleukin-29 in virus-infected human myeloid dendritic cells

Dendritic cells (DCs) respond to microbial infections by undergoing phenotypic maturation and by producing multiple cytokines. In the present study, we analyzed the ability of influenza A and Sendai viruses to induce DC maturation and activate tumor necrosis factor alpha (TNF-alpha), alpha/beta interferon (IFN-alpha/beta), and IFN-like interleukin-28A/B (IFN-lambda2/3) and IL-29 (IFN-lambda1) gene expression in human monocyte-derived myeloid DCs (mDC). The ability of influenza A virus to induce mDC maturation or enhance the expression of TNF-alpha, IFN-alpha/beta, interleukin-28 (IL-28), and IL-29 genes was limited, whereas Sendai virus efficiently induced mDC maturation and enhanced cytokine gene expression. Influenza A virus-induced expression of TNF-alpha, IFN-alpha, IFN-beta, IL-28, and IL-29 genes was, however, dramatically enhanced when cells were pretreated with IFN-alpha. IFN-alpha priming led to increased expression of Toll-like receptor 3 (TLR3), TLR7, TLR8, MyD88, TRIF, and IFN regulatory factor 7 (IRF7) genes and enhanced influenza-induced phosphorylation and DNA binding of IRF3. Influenza A virus also enhanced the binding of NF-kappaB to the respective NF-kappaB elements of the promoters of IFN-beta and IL-29 genes. In mDC IL-29 induced MxA protein expression and possessed antiviral activity against influenza A virus, although this activity was lower than that of IFN-alpha or IFN-beta. Our results show that in human mDCs viruses can readily induce the expression of IL-28 and IL-29 genes whose gene products are likely to contribute to the host antiviral response.

Suppression of RNA recognition by Toll-like receptors: the impact of nucleoside modification and the evolutionary origin of RNA

DNA and RNA stimulate the mammalian innate immune system through activation of Toll-like receptors (TLRs). DNA containing methylated CpG motifs, however, is not stimulatory. Selected nucleosides in naturally occurring RNA are also methylated or otherwise modified, but the immunomodulatory effects of these alterations remain untested. We show that RNA signals through human TLR3, TLR7, and TLR8, but incorporation of modified nucleosides m5C, m6A, m5U, s2U, or pseudouridine ablates activity. Dendritic cells (DCs) exposed to such modified RNA express significantly less cytokines and activation markers than those treated with unmodified RNA. DCs and TLR-expressing cells are potently activated by bacterial and mitochondrial RNA, but not by mammalian total RNA, which is abundant in modified nucleosides. We conclude that nucleoside modifications suppress the potential of RNA to activate DCs. The innate immune system may therefore detect RNA lacking nucleoside modification as a means of selectively responding to bacteria or necrotic tissue.

TLR7/8-Mediated Activation of Human NK Cells Results in Accessory Cell-Dependent IFN-γ Production

NK cells express receptors that allow them to recognize pathogens and activate effector functions such as cytotoxicity and cytokine production. Among these receptors are the recently identified TLRs that recognize conserved pathogen structures and initiate innate immune responses. We demonstrate that human NK cells express TLR3, TLR7, and TLR8 and that these receptors are functional. TLR3 is expressed at the cell surface where it functions as a receptor for polyinosinic acid:cytidylic acid (poly(I:C)) in a lysosomal-independent manner. TLR7/8 signaling is sensitive to chloroquine inhibition, indicating a requirement for lysosomal signaling as for other cell types. Both R848, an agonist of human TLR7 and TLR8, and poly(I:C) activate NK cell cytotoxicity against Daudi target cells. However, IFN-gamma production is differentially regulated by these TLR agonists. In contrast to poly(I:C), R848 stimulates significant IFN-gamma production by NK cells. This is accessory cell dependent and is inhibited by addition of a neutralizing anti-IL-12 Ab. Moreover, stimulation of purified monocyte populations with R848 results in IL-12 production, and reconstitution of purified NK cells with monocytes results in increased IFN-gamma production in response to R848. In addition, we demonstrate that while resting NK cells do not transduce signals directly in response to R848, they can be primed to do so by prior exposure to either IL-2 or IFN-alpha. Therefore, although NK cells can be directly activated by TLRs, accessory cells play an important and sometimes essential role in the activation of effector functions such as IFN-gamma production and cytotoxicity.

Selected Toll-like receptor agonist combinations synergistically trigger a T helper type 1-polarizing program in dendritic cells

Toll-like receptors (TLRs) sense microbial products and initiate adaptive immune responses by activating dendritic cells (DCs). As pathogens may contain several TLR agonists, we sought to determine whether different TLRs cooperate in DC activation. In human and mouse DCs, TLR3 and TLR4 potently acted in synergy with TLR7, TLR8 and TLR9 in the induction of a selected set of genes. Synergic TLR stimulation increased production of interleukins 12 and 23 and increased the Delta-4/Jagged-1 ratio, leading to DCs with enhanced and sustained T helper type 1-polarizing capacity. Global gene transcriptional analysis showed that TLR synergy 'boosted' only approximately 1% of the transcripts induced by single TLR agonists. These results identify a 'combinatorial code' by which DCs discriminate pathogens and suggest new strategies for promoting T helper type 1 responses.

Toll-like receptor-dependent activation of several human blood cell types by protamine-condensed mRNA

We reported that RNA condensed on protamine is protected from RNase-mediated degradation and can be used for vaccination. Here, we show that such complexes are also danger signals that activate mouse cells through a MyD88-dependent pathway. Moreover, mRNA-protamine complexes stimulate human blood cells. They strongly activate DC and monocytes, leading to TNF-alpha and IFN-alpha secretion. In addition, protamine-RNA complexes directly activate B cells, NK cells and granulocytes. The detailed analysis of the activated cell types, the study of the cytokines released from PBMC cultured with protamine-RNA complexes and recently published results suggest that TLR-7 and TLR-8 may be involved in the recognition of protamine-stabilized RNA. Our data indicate that protamine-stabilized RNA, which may be similar to RNA condensed in the nucleocapsids of RNA viruses, is a strong danger signal. Thus, similarly to plasmid DNA, protamine-RNA combines antigen production and non-specific immunostimulation. The studies presented here explain the capacity of protamine-RNA to act as a vaccine, and pave the way towards the development of safe and efficient mRNA-based immunotherapies.

Identification and characterization of a functional, alternatively spliced Toll-like receptor 7 (TLR7) and genomic disruption of TLR8 in chickens

Based upon the recognition of antiviral compounds and single stranded viral RNA the Toll-like receptors TLR7 and TLR8 are suggested to play a significant role in initiating antiviral immune responses. Here we report the molecular characterization of the chicken TLR7/8 loci which revealed an intact TLR7 gene and fragments of a TLR8-like gene with a 6-kilobase insertion containing chicken repeat 1 (CR1) retroviral-like insertion elements. The chicken TLR7 gene encodes a 1047-amino-acid protein with 62% identity to human TLR7 and a conserved pattern of predicted leucine-rich repeats. Highest levels of chicken TLR7 mRNA were detected in immune-related tissues and cells, especially the spleen, caecal, tonsil and splenic B cells. Alternative spliced forms of TLR7 mRNA were identified in chicken, mouse and human and expressed in similar tissues and cell types to the major form of chicken TLR7. The chicken TLR7+ HD11 cell line and fresh splenocytes produced elevated levels of interleukin-1beta (IL-1beta) mRNA after exposure to the agonists R848 and loxoribine. Interestingly, none of the TLR7 agonists stimulated increased type I interferon (IFN) mRNA whereas poly(I:C) (a TLR3 agonist) up-regulated both chicken IFN-alpha and chicken IFN-beta mRNA. In contrast, TLR7 agonists, particularly R848 and poly(U) stimulated up-regulation of chicken IL-1beta, and chicken IL-8 mRNAs more effectively than poly(I:C). Stimulation of chicken TLR7 with R848 was chloroquine sensitive, suggesting signalling within an endosomal compartment, as for mammalian TLR7. The deletion of TLR8 in galliforms, accompanied with the differential response after exposure to TLR7 agonists, offers insight into the evolution of vertebrate TLR function.

A type I interferon autocrine-paracrine loop is involved in Toll-like receptor-induced interleukin-12p70 secretion by dendritic cells

Dendritic cells (DC) produce interleukin-12 (IL-12) in response to Toll-like receptor (TLR) activation. Two major TLR signaling pathways participate in the response to pathogens: the nuclear factor-kappaB (NF-kappaB)-dependent pathway leading to inflammatory cytokine secretion including IL-12 and the interferon (IFN)-dependent pathway inducing type I IFN and IFN-regulated genes. Here we show that the two pathways cooperate and are likely both necessary for inducing an optimal response to pathogens. R-848/Resiquimod (TLR7 ligand in the mouse and TLR7/8 ligand in human) synergized with poly(I:C) (TLR3 ligand) or lipopolysaccharide (LPS; TLR4 ligand) in inducing high levels of bioactive IL-12p70 secretion and IFN-beta mRNA accumulation by mouse bone marrow-derived DC (BM-DC). Strikingly, IL-12p70 but not IL-12p40 secretion was strongly reduced in BM-DC from STAT1(-/-) and IFNAR(-/-) mice. STAT1 tyrosine-phosphorylation, IL-12p35, and IFN-beta mRNA accumulation were strongly inhibited in IFNAR(-/-) BM-DC activated with the TLR ligand combinations. Similar observation were obtained in human TLR8-expressing monocyte-derived DC (moDC) using neutralizing anti-IFNAR2 antibodies, although results also pointed to a possible involvement of IFN-lambda1 (also known as IL-29). This suggests that TLR engagement on DC induces endogenous IFNs that further synergize with the NF-kappaB pathway for optimal IL-12p70 secretion. Moreover, analysis of interferon regulatory factors (IRF) regulation in moDC suggests a role for IRF7/8 in mediating IRF3-independent type I IFN and possibly IL-12p35 synthesis in response to TLR7/8.

The Interferon Regulatory Factor, IRF5, Is a Central Mediator of Toll-like Receptor 7 Signaling

Interferon regulatory factors (IRFs) are critical components of virus-induced immune activation and type I interferon regulation. IRF3 and IRF7 are activated in response to a variety of viruses or after engagement of Toll-like receptor (TLR) 3 and TLR4 by double-stranded RNA and lipopolysaccharide, respectively. The activation of IRF5, is much more restricted. Here we show that in contrast to IRF3 and IRF7, IRF5 is not a target of the TLR3 signaling pathway but is activated by TLR7 or TLR8 signaling. We also demonstrate that MyD88, interleukin 1 receptor-associated kinase 1, and tumor necrosis factor receptor-associated factor 6 are required for the activation of IRF5 and IRF7 in the TLR7 signaling pathway. Moreover, ectopic expression of IRF5 enabled type I interferon production in response to TLR7 signaling, whereas knockdown of IRF5 by small interfering RNA reduced type I interferon induction in response to the TLR7 ligand, R-848. IRF5 and IRF7, therefore, emerge from these studies as critical mediators of TLR7 signaling.

Use of murine embryonic fibroblasts to define Toll-like receptor activation and specificity

Toll-like receptors (TLRs) are critically involved in the innate immune response to bacterial, viral and fungal pathogens. We have studied human peripheral blood mononuclear cells, murine embryonic fibroblasts (MEFs) and a panel of human cell lines, including HEK, HeLa, AGS, ECV304 and U373 cells, for expression of TLR-specific mRNAs and for TLR-ligand dependent cytokine secretion. Peripheral blood cells expressed multiple TLRs; however, many studies have shown that blood contains multiple, heterogeneous cell populations with distinct patterns of TLR expression. Cell lines had variable expression of TLRs, and in most cases lacked TLR2 and TLR8 expression and only weakly expressed mRNAs for TLR5, TLR7 and TLR9. In contrast, MEFs expressed high levels of mRNA for TLR1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8 and TLR9. MEFs were highly responsive to TLR-ligand activation and secreted high levels of both IL-6 and MCP-1 in response to TLR ligands. MEFs from mice with targeted deletions of TLR2, TLR4 and MyD88 demonstrated profound defects in their IL-6 response to their specific ligands, consistent with studies of macrophages and tissues from adult knockout animals. MEF cultures are homogenous and amenable to biochemical analysis and should allow rigorous studies of the contribution of individual TLRs to the innate immune response.

Induction of inflammatory cytokines and interferon responses by double-stranded and single-stranded siRNAs is sequence-dependent and requires endosomal localization

The potential induction of inflammatory cytokines and interferon responses by small-interfering RNAs (siRNAs) represents a major obstacle for their use as inhibitors of gene expression. Therapeutic applications of siRNAs will require a better understanding of the mechanisms that trigger such unwanted effects, especially in freshly isolated human cells. Surprisingly, the induction of tumor necrosis factor (TNF-alpha) and interleukin-6 (IL-6) in adherent peripheral blood mononuclear cells (PBMC) was not restricted to double-stranded siRNAs, because induction was also obtained with single-stranded siRNAs (sense or antisense strands). The immunostimulatory effects were sequence-dependent, since only certain sequences are prone to induce inflammatory responses while others are not. The induction of TNF-alpha, IL-6 and interferon alpha (IFN-alpha) was chloroquine-sensitive and dependent more likely on endosomal Toll-like receptor signaling in particular TLR8. Indeed, no significant immunostimulatory effects were detected when either double or single-stranded siRNAs were delivered directly to cytoplasm via electroporation. Both RNA types activated a NF-kappaB promoter-driven luciferase gene in transiently transfected human adherent PBMC. Moreover, culture of immature dendritic cells with either double or single-stranded siRNAs stimulated interleukin-12 production and induced the expression of CD83, an activation marker. Interestingly, several double-stranded siRNAs did not induce TNF-alpha, IL-6 and IFN-alpha production, however, their single-stranded sense or antisense did. Taken together, the present data indicate for the first time that the induction of inflammatory cytokines and IFN-alpha responses by either double-stranded or single-stranded siRNAs in adherent PBMC is sequence-dependent and requires endosomal intracellular signaling. The finding that endosomal localization of self-RNAs (sense strands) can trigger Toll-like receptor signaling in adherent human PBMC is intriguing because it indicates that endosomal self-RNAs can display a molecular pattern capable for activating innate immunity.

IFN-α Enhances TLR3-Mediated Antiviral Cytokine Expression in Human Endothelial and Epithelial Cells by Up-Regulating TLR3 Expression

TLRs play a critical role in early innate immune response to virus infection. TLR3 together with TLR7 and TLR8 constitute a powerful system to detect genetic material of RNA viruses. TLR3 has been shown to bind viral dsRNA whereas TLR7 and TLR8 are receptors for viral single-stranded RNA. In this report we show that TLR7 or TLR8 are not expressed in human epithelial A549 cells or in HUVECs. Accordingly, A549 cells and HUVECs were unresponsive to TLR7/8 ligand R848. TLR3 was expressed at a higher level in HUVECs than in A549 cells. The TLR3 ligand poly(I:C) up-regulated IFN-beta, IL-28, IL-29, STAT1, and TLR3 expression in HUVECs but not in A549 cells. An enhanced TLR3 expression by transfection or by IFN-alpha stimulation conferred poly(I:C) responsiveness in A549 cells. Similarly, IFN-alpha pretreatment strongly enhanced poly(I:C)-induced activation of IFN-beta, IL-28, and IL-29 genes also in HUVECs. In conclusion, our results suggest that IFN-alpha-induced up-regulation of TLR3 expression is involved in dsRNA activated antiviral response in human epithelial and endothelial cells.

Synthetic TLR agonists reveal functional differences between human TLR7 and TLR8

Although TLR7 and TLR8 are phylogenetically and structurally related, their relative functions are largely unknown. The role of TLR7 has been established using TLR7-deficient mice and small molecule TLR7 agonists. The absence of TLR8-selective agonists has hampered our understanding of the role of TLR8. In this study TLR agonists selective for TLR7 or TLR8 were used to determine the repertoire of human innate immune cells that are activated through these TLRs. We found that TLR7 agonists directly activated purified plasmacytoid dendritic cells and, to a lesser extent, monocytes. Conversely, TLR8 agonists directly activated purified myeloid dendritic cells, monocytes, and monocyte-derived dendritic cells (GM-CSF/IL-4/TGF-beta). Accordingly, TLR7-selective agonists were more effective than TLR8-selective agonists at inducing IFN-alpha- and IFN-regulated chemokines such as IFN-inducible protein and IFN-inducible T cell alpha chemoattractant from human PBMC. In contrast, TLR8 agonists were more effective than TLR7 agonists at inducing proinflammatory cytokines and chemokines, such as TNF-alpha, IL-12, and MIP-1alpha. Thus, this study demonstrated that TLR7 and TLR8 agonists differ in their target cell selectivity and cytokine induction profile.

IFN-alpha regulates TLR-dependent gene expression of IFN-alpha, IFN-beta, IL-28, and IL-29

Toll-like receptors (TLRs) mediate host cell activation by various microbial components. TLR2, TLR3, TLR4, TLR7, TLR8, and TLR9 are the receptors that have been associated with virus-induced immune response. We have previously reported that all these TLRs, except TLR9, are expressed at mRNA levels in human monocyte-derived macrophages. Here we have studied TLR2, TLR3, TLR4, and TLR7/8 ligand-induced IFN-alpha, IFN-beta, IL-28, and IL-29 expression in human macrophages. IFN-alpha pretreatment of macrophages was required for efficient TLR3 and TLR4 agonist-induced activation of IFN-alpha, IFN-beta, IL-28, and IL-29 genes. TLR7/8 agonist weakly activated IFN-alpha, IFN-beta, IL-28, and IL-29 genes, whereas TLR2 agonist was not able to activate these genes. IFN-alpha enhanced TLR responsiveness in macrophages by up-regulating the expression of TLR3, TLR4, and TLR7. IFN-alpha also enhanced the expression of TLR signaling molecules MyD88, TIR domain-containing adaptor inducing IFN-beta, IkappaB kinase-epsilon, receptor interacting protein 1, and IFN regulatory factor 7. Furthermore, the activation of transcription factor IFN regulatory factor 3 by TLR3 and TLR4 agonists was dependent on IFN-alpha pretreatment. In conclusion, our results suggest that IFN-alpha sensitizes cells to microbial recognition by up-regulating the expression of several TLRs as well as adapter molecules and kinases involved in TLR signaling.

TLRs govern neutrophil activity in aspergillosis

Polymorphonuclear neutrophils (PMNs) are essential in initiation and execution of the acute inflammatory response and subsequent resolution of fungal infection. PMNs, however, may act as double-edged swords, as the excessive release of oxidants and proteases may be responsible for injury to organs and fungal sepsis. To identify regulatory mechanisms that may balance PMN-dependent protection and immunopathology in fungal infections, the involvement of different TLR-activation pathways was evaluated on human PMNs exposed to the fungus Aspergillus fumigatus. Recognition of Aspergillus and activation of PMNs occurred through the involvement of distinct members of the TLR family, each likely activating specialized antifungal effector functions. By affecting the balance between fungicidal oxidative and nonoxidative mechanisms, pro- and anti-inflammatory cytokine production, and apoptosis vs necrosis, the different TLRs ultimately impacted on the quality of microbicidal activity and inflammatory pathology. Signaling through TLR2 promoted the fungicidal activity of PMNs through oxidative pathways involving extracellular release of gelatinases and proinflammatory cytokines while TLR4 favored the oxidative pathways through the participation of azurophil, myeloperoxidase-positive, granules and IL-10. This translated in vivo in the occurrence of different patterns of fungal clearance and inflammatory pathology. Both pathways were variably affected by signaling through TLR3, TLR5, TLR6, TLR7, TLR8, and TLR9. The ability of selected individual TLRs to restore antifungal functions in defective PMNs suggests that the coordinated outputs of activation of multiple TLRs may contribute to PMN function in aspergillosis.

Gene expression in actinic keratoses: pharmacological modulation by imiquimod

BACKGROUND

Actinic keratoses (AKs) are premalignant lesions that can progress into squamous cell carcinoma. Imiquimod, which belongs to the new class of immune-response modifiers, was recently shown to be effective in the treatment of AKs. The underlying mechanisms are not fully understood.

OBJECTIVES

To study the expression of individual genes in uninvolved skin and AKs before therapy and to elucidate the way in which the expression of these genes is influenced by imiquimod therapy.

METHODS

We treated 13 patients with AK with imiquimod and compared gene expression before, during (five patients) and after (eight patients) therapy with that in uninvolved skin. We analysed genes coding for inflammatory cytokines or their receptors, adhesion molecules, anti-apoptotic proteins, p53 and toll-like receptors (TLRs) by reverse-transcriptase polymerase chain reaction.

RESULTS

Comparing uninvolved skin and untreated AK, we found significant differences in the expression of interleukin (IL)-6, hurpin, TLR7 and TLR8. During imiquimod therapy, we detected a further upregulation of interferon-alpha, IL-6, IL-10 receptor 1 and TLR7. In contrast, two anti-apoptotic genes, hurpin and HAX-1, were downregulated. We did not detect significant differences in gene expression for p53, tumour necrosis factor-alpha and alpha- and beta-catenins. Clinically, the upregulated expression of the proinflammatory cytokines correlated with the local inflammation induced by imiquimod.

CONCLUSIONS

Our results indicate that specific differences in gene expression are detectable between AK and uninvolved skin. Imiquimod influenced the expression of most genes analysed in this study. This work extends previous findings on the effects of imiquimod on gene regulation in AKs.

Identification and sequence analysis of chicken Toll-like receptors

Toll-like receptors (TLRs) play an important role in the recognition of microbial components. Only chicken TLR2 and -4 have been reported in the literature. The objectives of this study were to identify new chicken TLRs and to evaluate evolutionary significance of these receptors. Searching chicken genomic databases and DNA sequencing revealed five new TLRs, TLR1 (type 1 and 2), -3, -5, and -7. No chicken orthologues of mammalian TLR8, -9, or -10 were found. As in mammals, all chicken TLRs (chTLRs) share identical protein secondary structure that consists of several leucine-rich domains, a transmembrane domain, and Toll/Interleukin-1 receptor domain(s). Phylogenetic analyses indicate that the identified chTLR genes are the orthologues of TLRs in mammals. Analyses of the number of synonymous substitutions per synonymous site and nonsynonymous substitutions per nonsynonymous site indicate that the nucleotide sequences coding for the leucine-rich repeats of chicken TLR1 type 1 and type 2 were significantly under positive Darwinian selection. In contrast, the sequences of other TLRs were under purifying selection. These results support the hypothesis that one of the major evolutionary strategies of the innate immune system is to recognize a few highly conserved microbial components with several conserved TLRs. The results also indicate that the sequence changes in the ligand-binding domains of TLR1 in chickens provide adaptive advantages during evolution.

Toll-like receptors and immune response in allergic disease

Allergic reactions are dominated by the preferential development of specific Th2 responses against innocuous antigens in atopic individuals. This can reflect alterations in innate immune mechanisms. Toll-like receptors (TLRs) have evolved as key molecules in innate and adaptive immunity. Their activation by structurally distinct exogenous or endogenous ligands present at the cell microenvironment plays a critical role in antimicrobial defense. The global view is that TLR activation induces antigen-presenting cells to produce cytokines that favor Th1-type immune responses, suggesting that it might prevent the development of deleterious Th2 responses in allergy. On the basis of epidemiological studies and recent data, it has been established that TLRs play a role in the development of Th2 responses. However, more information is needed to fully understand the mechanism of TLR involvement and the implication of immune cells that express TLRs in the Th1/Th2 cytokine profiles. Several TLRs, such as TLR9, TLR7, and TLR8, can be considered as good target candidates. Some TLR ligands, such as CpG DNA, are effective adjuvants, strong inducers of both IL-5 and eosinophilia downregulation. They are also potential links to allergen epitopes that could provide new allergen-specific immunotherapy regimens for the treatment of allergic disorders.

Interferon-alpha induction through Toll-like receptors involves a direct interaction of IRF7 with MyD88 and TRAF6

Toll-like receptors (TLRs) are involved in the recognition of microbial pathogens. A subset of TLRs, TLR7, TLR8 and TLR9, induces antiviral responses by producing interferon-alpha (IFN-alpha). Production of IFN-alpha is dependent on the Toll-interleukin-1 receptor domain-containing adaptor MyD88. Here we show that MyD88 formed a complex with the transcription factor IRF7 but not with IRF3. The death domain of MyD88 interacted with an inhibitory domain of IRF7, and this interaction resulted in activation of the IFN-alpha-dependent promoters. Furthermore, the adaptor molecule TRAF6 also bound and activated IRF7. Ubiquitin ligase activity of TRAF6 was required for IRF7 activation. These results indicate that TLR-mediated IFN-alpha induction requires the formation of a complex consisting of MyD88, TRAF6 and IRF7 as well as TRAF6-dependent ubiquitination.

Species-specific recognition of single-stranded RNA via toll-like receptor 7 and 8

Double-stranded ribonucleic acid (dsRNA) serves as a danger signal associated with viral infection and leads to stimulation of innate immune cells. In contrast, the immunostimulatory potential of single-stranded RNA (ssRNA) is poorly understood and innate immune receptors for ssRNA are unknown. We report that guanosine (G)- and uridine (U)-rich ssRNA oligonucleotides derived from human immunodeficiency virus-1 (HIV-1) stimulate dendritic cells (DC) and macrophages to secrete interferon-alpha and proinflammatory, as well as regulatory, cytokines. By using Toll-like receptor (TLR)-deficient mice and genetic complementation, we show that murine TLR7 and human TLR8 mediate species-specific recognition of GU-rich ssRNA. These data suggest that ssRNA represents a physiological ligand for TLR7 and TLR8.

Ligand-regulated chimeric receptor approach reveals distinctive subcellular localization and signaling properties of the Toll-like receptors

Toll-like receptors (TLRs) are sensors for the detection of invading infectious agents and can initiate innate immune responses. Because the innate immune system induces an appropriate defense against different pathogens, different TLR signaling domains may have unique properties that are responsible for eliciting distinctive responses to different types of pathogens. To test this hypothesis, we created ligand-regulated TLR chimeric receptors composed of the extracellular region of TLR4 and the transmembrane and cytoplasmic regions of other TLRs and expressed these chimeras in macrophages lacking endogenous TLR4. Interestingly, the chimeras between TLR4 and either TLR3, TLR7, or TLR9 were localized completely intracellularly whereas other chimeras were expressed on the cell surface. Lipopolysaccharide (LPS), a ligand for these chimeras, induced the activation of nuclear factor kappa B and mitogen-activated protein kinases and the subsequent production of pro-inflammatory cytokines in macrophages expressing TLR4, TLR4/TLR5, or TLR4/TLR8 chimeras but not in macrophages expressing TLR4/TLR1, TLR4/TLR2, or TLR4/TLR6 chimeras. Co-expression of unresponsive chimeras in some combinations (chimeras with TLR1+TLR2 or TLR2+TLR6 but not TLR1+TLR6) resulted in LPS responsiveness, indicating functional complementarity. Furthermore, the pair of TLR2+TLR6 chimera required approximately 10-fold less LPS to induce the same responses compared with the TLR1+TLR2 pair. Finally, LPS induced effective interferon-beta production and subsequent Stat1 phosphorylation in macrophages expressing full-length TLR4 but not other cell surface TLR chimeras. These results suggest that the functions of TLRs are diversified not only in their extracellular regions for ligand recognition but also in their transmembrane and cytoplasmic regions for subcellular localization and signaling properties.

Toll-like receptor expression in human keratinocytes: nuclear factor kappaB controlled gene activation by Staphylococcus aureus is toll-like receptor 2 but not toll-like receptor 4 or platelet activating factor receptor dependent

Cultured primary human keratinocytes were screened for their expression of various members of the toll-like receptor (TLR) family. Keratinocytes were found to constitutively express TLR1, TLR2, TLR3, TLR5, and TLR9 but not TLR4, TLR6, TLR7, TLR8, or TLR10 as shown by polymerase chain reaction analysis. The expression of the crucial receptor for signaling of staphylococcal compounds TLR2 was also confirmed by immunohistochemistry, in contrast to TLR4, which showed a negative staining pattern. Next, we analyzed the activation of the proinflammatory nuclear transcription factor kappaB by Staphylococcus aureus strain 8325-4. Using nuclear extract gel shifts, RelA staining, and luciferase reporter transfection plasmids we found a clear induction of nuclear factor kappaB translocation by the bacteria. This translocation induced the transcription of nuclear factor kappaB controlled genes such as inducible nitric oxide synthetase, COX2, and interleukin-8. Transcription of these genes was followed by production of increased amounts of interleukin-8 protein and NO. Inhibition experiments using monoclonal antibodies and the specific platelet activating factor receptor inhibitor CV3988 showed that nuclear factor kappaB activation by S. aureus was TLR2 but not TLR4 or platelet activating factor receptor dependent. In line, the purified staphylococcal cell wall components lipoteichoic acid and peptidoglycan, known to signal through TLR2, also showed nuclear factor kappaB translocation in human keratinocytes, indicating a crucial role of the staphylococcal cell wall in the innate immune stimulation of human keratinocytes. These results help to explain the complex activation of human keratinocytes by S. aureus and its cell wall components in various inflammatory disorders of the skin.

Expression and function of Toll-like receptors in eosinophils: activation by Toll-like receptor 7 ligand

We investigated the expression of a panel of Toll-like receptors (TLRs) and their functions in human eosinophils. Eosinophils constitutively expressed TLR1, TLR4, TLR7, TLR9, and TLR10 mRNAs (TLR4 greater than TLR1, TLR7, TLR9, and TLR10 greater than TLR6). In contrast, neutrophils expressed a larger variety of TLR mRNAs (TLR1, TLR2, TLR4, TLR6, TLR8 greater than TLR5, TLR9, and TLR10 greater than TLR7). Although the expression levels in eosinophils were generally less prominent compared with those in neutrophils, eosinophils expressed a higher level of TLR7. Furthermore, among various TLR ligands (S-(2,3-bis(palmitoyloxy)-(2-RS)-propyl)-N-palmitoyl-Cys-Ser-(Lys)(4), poly(I:C), LPS, R-848, and CpG DNA), only R-848, a ligand of TLR7 and TLR8, regulated adhesion molecule (CD11b and L-selectin) expression, prolonged survival, and induced superoxide generation in eosinophils. Stimulation of eosinophils by R-848 led to p38 mitogen-activated protein kinase activation, and SB203580, a p38 mitogen-activated protein kinase inhibitor, almost completely attenuated R-848-induced superoxide generation. Although TLR8 mRNA expression was hardly detectable in freshly isolated eosinophils, mRNA expression of TLR8 as well as TLR7 was exclusively up-regulated by IFN-gamma but not by either IL-4 or IL-5. The up-regulation of the TLRs by IFN-gamma had potentially functional significance: the extent of R-848-induced modulation of adhesion molecule expression was significantly greater in cells treated with IFN-gamma compared with untreated cells. Although the natural ligands for TLR7 and TLR8 have not yet been identified, our results suggest that eosinophil TLR7/8 systems represent a potentially important mechanism of a host-defensive role against viral infection and mechanism linking exacerbation of allergic inflammation and viral infection.

Expression analysis of the Toll-like receptor and TIR domain adaptor families of zebrafish

The zebrafish genomic sequence database was analysed for the presence of genes encoding members of the Toll-like receptors (TLR) and interleukin receptors (IL-R) and associated adaptor proteins containing a TIR domain. The resulting predictions show the presence of one or more counterparts for the human TLR1, TLR2, TLR3, TLR4, TLR5, TLR7, TLR8, TLR9, IL-1R and IL-18R genes and one copy of the adaptor genes MyD88, MAL, TRIF and SARM. In contrast to data for the pufferfish Fugu rubripes, zebrafish has two genes that are highly similar to human TLR4. In addition, one fish-specific TLR group can be distinguished that is closely related to the Drosophila melanogaster Toll-9 gene. The sequence of cloned cDNAs for TLR4, TLR2 and MyD88 show the same intron-exon organisation as in the human counterparts. Expression analysis using reverse transcriptase-PCR (RT-PCR) shows that 17 of the predicted zebrafish TLR genes and all the genes encoding adaptor proteins are expressed in the adult stage. A subset of the TLR genes are expressed at higher levels in fish infected with the pathogen Mycobacterium marinum. The induced genes include the homologues of the human TLR1 and TLR2 genes, whose functions are associated with mycobacterial infections, underscoring the suitability of zebrafish as a model for analysis of the vertebrate innate immune system.

Toll-like receptor gene family and TIR-domain adapters in Danio rerio

The toll-like family of receptors (TLR) is an ancient pattern recognition receptor family, conserved from insects to mammals. We have identified in zebrafish (Danio rerio) 19 putative TLR variants, the orthologs of mammalian TLR2-5, 7-9, a fish specific receptor type group and three putative splice variants. One receptor is very close to mammalian TLR1, 6 and 10 and seems to be their common ancestor. However, in contrast to the pufferfish, Fugu rubripes, we found two receptors homologous to TLR4, showing that lack of TLR4 is not general for fish. In addition, we identified two members close to mammalian TLR8 and five members close to FuguTLR21 and goldfish TLR, a TLR group which now has only been found in fish. By RT-PCR we showed that all TLR are widely expressed in adult tissues, but also at different stages of development. All these TLRs contain very conserved toll/interleukin-1 receptor (TIR) domains able to interact with TIR-domain of adapter molecules. We demonstrate here that TIR-domain containing adapters MyD88 and SARM are present in zebrafish, showing that TLR adapter molecules are highly conserved in evolution.