Role of Toll interleukin-1 receptor (IL-1R) 8, a negative regulator of IL-1R/Toll-like receptor signaling, in resistance to acute Pseudomonas aeruginosa lung infection

IL-1R8: A molecular brake of anti-tumor and anti-viral activity of NK cells and ILC

Interleukin-1 receptor family members (ILRs) and Toll-Like Receptors (TLRs) play pivotal role in immunity and inflammation and are expressed by most cell types including cells of both the innate and adaptive immune system. In this context, IL-1 superfamily members are also important players in regulating function and differentiation of adaptive and innate lymphoid cells. This system is tightly regulated in order to avoid uncontrolled activation, which may lead to detrimental inflammation contributing to autoimmune or allergic responses. IL-1R8 (also known as TIR8 or SIGIRR) is a member of the IL-1R family that acts as a negative regulator dampening ILR and TLR signaling and as a co-receptor for human IL-37. Human and mouse NK cells, that are key players in immune surveillance of tumors and infections, express high level of IL-1R8. In this review, we will summarize our current understanding on the structure, expression and function of IL-1R8 and we will also discuss the emerging role of IL-1R8 as an important checkpoint regulating NK cells function in pathological conditions including cancer and viral infections.

Neutrophil-mediated delivery of the combination of colistin and azithromycin for the treatment of bacterial infection

Novel treatment strategies are in urgent need to deal with the rapid development of antibiotic-resistant superbugs. Combination therapies and targeted drug delivery have been exploited to promote treatment efficacies. In this study, we loaded neutrophils with azithromycin and colistin to combine the advantages of antibiotic combinations, targeted delivery, and immunomodulatory effect of azithromycin to treat infections caused by Gram-negative pathogens. Delivery of colistin into neutrophils was mediated by fusogenic liposome, while azithromycin was directly taken up by neutrophils. Neutrophils loaded with the drugs maintained the abilitity to generate reactive oxygen species and migrate. In vitro assays demonstrated enhanced bactericidal activity against multidrug-resistant pathogens and reduced inflammatory cytokine production by the drug-loaded neutrophils. A single intravenous administration of the drug-loaded neutrophils effectively protected mice from Pseudomonas aeruginosa infection in an acute pneumonia model. This study provides a potential effective therapeutic approach for the treatment of bacterial infections.

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Neutrophils are loaded with colistin and azithromycin in vitro

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The loaded drugs enhance the bactericidal effect and reduce the inflammatory response

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Drug-loaded neutrophils conferred effective protection against bacterial infection

Transcriptome profile of spleen tissues from locally-adapted Kenyan pigs (Sus scrofa) experimentally infected with three varying doses of a highly virulent African swine fever virus genotype IX isolate: Ken12/busia.1 (ken-1033)

Background

African swine fever (ASF) is a lethal hemorrhagic disease affecting domestic pigs resulting in up to 100% mortality rates caused by the ASF virus (ASFV). The locally-adapted pigs in South-western Kenya have been reported to be resilient to disease and harsh climatic conditions and tolerate ASF; however, the mechanisms by which this tolerance is sustained remain largely unknown. We evaluated the gene expression patterns in spleen tissues of these locally-adapted pigs in response to varying infective doses of ASFV to elucidate the virus-host interaction dynamics.

Methods

Locally adapted pigs (n = 14) were experimentally infected with a high dose (1x10⁶HAD₅₀), medium dose (1x10⁴HAD₅₀), and low dose (1x10²HAD₅₀) of the highly virulent genotype IX ASFV Ken12/busia.1 (Ken-1033) isolate diluted in PBS and followed through the course of infection for 29 days. The in vivo pig host and ASFV pathogen gene expression in spleen tissues from 10 pigs (including three from each infective group and one uninfected control) were analyzed in a dual-RNASeq fashion. We compared gene expression between three varying doses in the host and pathogen by contrasting experiment groups against the naïve control.

Results

A total of 4954 differentially expressed genes (DEGs) were detected after ASFV Ken12/1 infection, including 3055, 1771, and 128 DEGs in the high, medium, and low doses, respectively. Gene ontology and KEGG pathway analysis showed that the DEGs were enriched for genes involved in the innate immune response, inflammatory response, autophagy, and apoptosis in lethal dose groups. The surviving low dose group suppressed genes in pathways of physiopathological importance. We found a strong association between severe ASF pathogenesis in the high and medium dose groups with upregulation of proinflammatory cytokines and immunomodulation of cytokine expression possibly induced by overproduction of prostaglandin E synthase (4-fold; p < 0.05) or through downregulation of expression of M1-activating receptors, signal transductors, and transcription factors. The host-pathogen interaction resulted in induction of expression of immune-suppressive cytokines (IL-27), inactivation of autophagy and apoptosis through up-regulation of NUPR1 [5.7-fold (high dose) and 5.1-fold (medium dose) [p < 0.05] and IL7R expression. We detected repression of genes involved in MHC class II antigen processing and presentation, such as cathepsins, SLA-DQB1, SLA-DOB, SLA-DMB, SLA-DRA, and SLA-DQA in the medium and high dose groups. Additionally, the host-pathogen interaction activated the CD8⁺ cytotoxicity and neutrophil machinery by increasing the expression of neutrophils/CD8⁺ T effector cell-recruiting chemokines (CCL2, CXCL2, CXCL10, CCL23, CCL4, CXCL8, and CXCL13) in the lethal high and medium dose groups. The recovered pigs infected with ASFV at a low dose significantly repressed the expression of CXCL10, averting induction of T lymphocyte apoptosis and FUNDC1 that suppressed neutrophilia.

Conclusions

We provide the first in vivo gene expression profile data from locally-adapted pigs from south-western Kenya following experimental infection with a highly virulent ASFV genotype IX isolate at varying doses that mimic acute and mild disease. Our study showed that the locally-adapted pigs induced the expression of genes associated with tolerance to infection and repression of genes involved in inflammation at varying levels depending upon the ASFV dose administered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08754-8.

IL-1R8 as Pathoimmunological Marker for Severity of Canine Chronic Enteropathy

Chronic enteropathy (CE) is a severe multifactorial gastrointestinal disease that affects dogs and is driven by poorly characterized inflammatory pathways. Imbalance of pro-inflammatory response regulators, including IL-1R8, may be due to different factors, among which the infection with Helicobacteraceae is known to lead to a vicious circle in which excessive pro-inflammatory signaling and gastrointestinal injury reinforce each other and boost the disease. We investigated the expression of IL-1R8 in large intestine biopsies of dogs with or without clinical signs of CE and with previously assessed enterohepatic Helicobacter spp. colonization status by mean of quantitative real-time PCR. Our study revealed that IL-1R8 is downregulated in both acutely (p = 0.0074) and chronically (p = 0.0159) CE affected dogs compared to healthy controls. The data also showed that IL-1R8 expression tends to decrease with colonization by Helicobacter spp. Interestingly, a negative correlation was detected between the level of expression of IL-1R8 and the severity of macroscopic lesions identified by endoscopy and the crypt hyperplasia score. We further compared the expression levels between males and females and found no statistically significant difference between the two groups. No significant difference was observed in IL-1R8 expression profiles with the age of the animals either. Interestingly, an association was uncovered between IL-1R8 expression level and dog breed. Together, our data advance knowledge on gastrointestinal pathoimmunology in dogs and highlight the potential utilization of IL-1R8 as a diagnostic, prognostic and therapeutic biomarker for canine chronic enteropathy.

Negative Regulation of the IL-1 System by IL-1R2 and IL-1R8: Relevance in Pathophysiology and Disease

Interleukin-1 (IL-1) is a primary cytokine of innate immunity and inflammation. IL-1 belongs to a complex family including ligands with agonist activity, receptor antagonists, and an anti-inflammatory cytokine. The receptors for these ligands, the IL-1 Receptor (IL-1R) family, include signaling receptor complexes, decoy receptors, and negative regulators. Agonists and regulatory molecules co-evolved, suggesting the evolutionary relevance of a tight control of inflammatory responses, which ensures a balance between amplification of innate immunity and uncontrolled inflammation. IL-1 family members interact with innate immunity cells promoting innate immunity, as well as with innate and adaptive lymphoid cells, contributing to their differentiation and functional polarization and plasticity. Here we will review the properties of two key regulatory receptors of the IL-1 system, IL-1R2, the first decoy receptor identified, and IL-1R8, a pleiotropic regulator of different IL-1 family members and co-receptor for IL-37, the anti-inflammatory member of the IL-1 family. Their complex impact in pathology, ranging from infections and inflammatory responses, to cancer and neurologic disorders, as well as clinical implications and potential therapeutic exploitation will be presented.

Anti-Inflammatory Effects of RTD-1 in a Murine Model of Chronic Pseudomonas aeruginosa Lung Infection: Inhibition of NF-κB, Inflammasome Gene Expression, and Pro-IL-1β Biosynthesis

Vicious cycles of chronic airway obstruction, lung infections with Pseudomonas aeruginosa, and neutrophil-dominated inflammation contribute to morbidity and mortality in cystic fibrosis (CF) patients. Rhesus theta defensin-1 (RTD-1) is an antimicrobial macrocyclic peptide with immunomodulatory properties. Our objective was to investigate the anti-inflammatory effect of RTD-1 in a murine model of chronic P. aeruginosa lung infection. Mice received nebulized RTD-1 daily for 6 days. Bacterial burden, leukocyte counts, and cytokine concentrations were evaluated. Microarray analysis was performed on bronchoalveolar lavage fluid (BALF) cells and lung tissue homogenates. In vitro effects of RTD-1 in THP-1 cells were assessed using quantitative reverse transcription PCR, enzyme-linked immunosorbent assays, immunoblots, confocal microscopy, enzymatic activity assays, and NF-κB-reporter assays. RTD-1 significantly reduced lung white blood cell counts on days 3 (-54.95%; p = 0.0003) and 7 (-31.71%; p = 0.0097). Microarray analysis of lung tissue homogenates and BALF cells revealed that RTD-1 significantly reduced proinflammatory gene expression, particularly inflammasome-related genes (nod-like receptor protein 3, Mediterranean fever gene, interleukin (IL)-1α, and IL-1β) relative to the control. In vitro studies demonstrated NF-κB activation was reduced two-fold (p ≤ 0.0001) by RTD-1 treatment. Immunoblots revealed that RTD-1 treatment inhibited proIL-1β biosynthesis. Additionally, RTD-1 treatment was associated with a reduction in caspase-1 activation (FC = -1.79; p = 0.0052). RTD-1 exhibited potent anti-inflammatory activity in chronically infected mice. Importantly, RTD-1 inhibits inflammasome activity, which is possibly a downstream effect of NF-κB modulation. These findings support that this immunomodulatory peptide may be a promising therapeutic for CF-associated lung disease.

IL-37-induced activation of glycogen synthase kinase 3β promotes IL-1R8/Sigirr phosphorylation, internalization, and degradation in lung epithelial cells

Interleukin (IL)-37 diminishes a variety of inflammatory responses through ligation to its receptor IL-1R8/Sigirr. Sigirr is a Toll like receptor/IL-1R family member. We have shown that Sigirr is not stable in response to IL-37 treatment. IL-37-induced Sigirr degradation is mediated by the ubiquitin-proteasome system, and the process is reversed by a deubiquitinase, USP13. However, the molecular mechanisms by which USP13 regulates Sigirr stability have not been revealed. In this study, we investigate the roles of glycogen synthesis kinase 3β (GSK3β) in Sigirr phosphorylation and stability. IL-37 stimulation induced Sigirr phosphorylation and degradation, as well as activation of GSK3β. Inhibition of GSK3β attenuated IL-37-induced Sigirr phosphorylation, while exogenous expressed GSK3β promoted Sigirr phosphorylation at threonine (T)372 residue. Sigirr association with GSK3β was detected. Amino acid residues 51-101 in GSK3β were identified as the Sigirr binding domain. These data indicate that GSK3β mediates IL-37-induced threonine phosphorylation of Sigirr. Further, we investigated the role of GSK3β-mediated phosphorylation of Sigirr in Sigirr degradation. Inhibition of GSK3β attenuated IL-37-induced Sigirr degradation, while T372 mutant of Sigirr was resistant to IL-37-mediated degradation. Furthermore, inhibition of Sigirr phosphorylation prevented Sigirr internalization and association with USP13, suggesting GSK3β promotes Sigirr degradation through disrupting Sigirr association with USP13.

Inflammasome activation by Pseudomonas aeruginosa's ExlA pore-forming toxin is detrimental for the host

During acute Pseudomonas aeruginosa infection, the inflammatory response is essential for bacterial clearance. Neutrophil recruitment can be initiated following the assembly of an inflammasome within sentinel macrophages, leading to activation of caspase-1, which in turn triggers macrophage pyroptosis and IL-1β/IL-18 maturation. Inflammasome formation can be induced by a number of bacterial determinants, including Type III secretion systems (T3SSs) or pore-forming toxins, or, alternatively, by lipopolysaccharide (LPS) via caspase-11 activation. Surprisingly, previous studies indicated that a T3SS-induced inflammasome increased pathogenicity in mouse models of P. aeruginosa infection. Here, we investigated the immune reaction of mice infected with a T3SS-negative P. aeruginosa strain (IHMA879472). Virulence of this strain relies on ExlA, a secreted pore-forming toxin. IHMA879472 promoted massive neutrophil infiltration in infected lungs, owing to efficient priming of toll-like receptors, and thus enhanced the expression of inflammatory proteins including pro-IL-1β and TNF-α. However, mature-IL-1β and IL-18 were undetectable in wild-type mice, suggesting that ExlA failed to effectively activate caspase-1. Nevertheless, caspase-1/11 deficiency improved survival following infection with IHMA879472, as previously described for T3SS+ bacteria. We conclude that the detrimental effect associated with the ExlA-induced inflammasome is probably not due to hyperinflammation, rather it stems from another inflammasome-dependent process.

Immune response against Chlamydia trachomatis via toll-like receptors is negatively regulated by SIGIRR

Chlamydia trachomatis is the most common bacterial sexually-transmitted infection and the major cause of preventable blindness worldwide. The asymptomatic nature of many infections along with uncontrolled inflammation leads to irreversible damage in the upper genital tract and the tarsal conjunctivae, with the major complications of infertility and chronic pelvic pain, and blindness, respectively. Inflammation must, therefore, be tightly regulated to avoid an unrestrained immune response. The genetic factors that regulate inflammation through Toll-like receptor (TLR) signaling pathways during C. trachomatis infection have not been fully characterized. SIGIRR (also known as IL-1R8 or TIR8) can regulate inflammation in response to various pathogens and diseases. However, nothing is known about its role during C. trachomatis infection. Expression of the pro-inflammatory chemokine, IL-8, was measured in epithelial cells infected with C. trachomatis. The effect of SIGIRR was determined by depleting SIGIRR or over-expressing SIGIRR in the epithelial cells before infection. Our results indicate that, in the absence of SIGIRR, epithelial cells induce higher levels of the pro-inflammatory chemokine, IL-8, in response to C. trachomatis infection. In addition, SIGIRR associates with MyD88 in both infected and uninfected infected cells. Collectively, our data demonstrate that SIGIRR functions as a negative regulator of the immune response to C. trachomatis infection. This finding provides insights into the immuno-pathogenesis of C. trachomatis that can be used to treat and identify individuals at risk of uncontrolled inflammation during infection.

Interleukin-1 Family Cytokines: Keystones in Liver Inflammatory Diseases

The pyrogenic property being the first activity described, members of the interleukin-1 superfamily (IL-1α, IL-1β, IL-18, and the newest members: IL-33, IL-36, IL-37, and IL-38) are now known to be involved in several inflammatory diseases such as obesity, atherosclerosis, cancer, viral and parasite infections, and auto-inflammatory syndromes as well as liver diseases. Inflammation processes are keystones of chronic liver diseases, of which the etiology may be viral or toxic, as in alcoholic or non-alcoholic liver diseases. Inflammation is also at stake in acute liver failure involving massive necrosis, and in ischemia-reperfusion injury in the setting of liver transplantation. The role of the IL-1 superfamily of cytokines and receptors in liver diseases can be either protective or pro-inflammatory, depending on timing and the environment. Our review provides an overview of current understanding of the IL-1 family members in liver inflammation, highlighting recent key investigations, and therapeutic perspectives. We have tried to apply the concept of trained immunity to liver diseases, based on the role of the members of the IL-1 superfamily, first of all IL-1β but also IL-18 and IL-33, in modulating innate lymphoid immunity carried by natural killer cells, innate lymphoid cells or innate T-αβ lymphocytes.

Staphylococcus aureus intra-mammary infection affects the expression pattern of IL-R8 in goat

IL-1R8 is a member of Interleukin-1 receptor family acting as a negative regulator of inflammation reliant on ILRs and TLRs activation. IL-1R8 role has never been evaluated in acute bacterial mastitis. We first investigated IL-1R8 sequence conservation among different species and its pattern of expression in a wide panel of organs from healthy goats. Then, modulation of IL-1R8 during natural and experimental mammary infection was evaluated and compared in blood, milk and mammary tissues from healthy and Staphylococcus aureus infected goats. IL-1R8 has a highly conserved sequence among vertebrates. Goat IL-1R8 was ubiquitously expressed in epithelial and lymphoid tissues with highest levels in pancreas. IL-1R8 was down-regulated in epithelial mammary cells following S. aureus infection. Interestingly it was up-regulated in leukocytes infiltrating the infected mammary tissues suggesting that it could represent a target of S. aureus immune evasion.

Tuning inflammation and immunity by the negative regulators IL-1R2 and IL-1R8

Interleukin-1 receptor family members (ILRs) and Toll-Like Receptors (TLRs) are key players in immunity and inflammation and are tightly regulated at different levels. Most cell types, including cells of the innate and adaptive immune system express ILRs and TLRs. In addition, IL-1 family members are emerging as key players in the differentiation and function of innate and adaptive lymphoid cells. IL-1R2 and IL-1R8 (also known as TIR8 or SIGIRR) are members of the ILR family acting as negative regulators of the IL-1 system. IL-1R2 binds IL-1 and the accessory protein IL-1RAcP without activating signaling and can be released as a soluble form (sIL-1R2), thus modulating IL-1 availability for the signaling receptor. IL-1R8 dampens ILR- and TLR-mediated cell activation and it is a component of the receptor recognizing human IL-37. Here, we summarize our current understanding of the structure and function of IL-1R2 and IL-1R8, focusing on their role in different pathological conditions, ranging from infectious and sterile inflammation, to autoimmunity and cancer-related inflammation. We also address the emerging evidence regarding the role of IL-1R8 as a crucial checkpoint molecule in NK cells in anti-cancer and antiviral activity and the potential therapeutic implications of IL-1R8 blockade in specific pathological contexts.

Opposing Effects of IL-1Ra and IL-36Ra on Innate Immune Response to Pseudomonas aeruginosa Infection in C57BL/6 Mouse Corneas

Pseudomonas aeruginosa keratitis is characterized by severe corneal ulceration and may lead to blindness if not treated properly in a timely manner. Although the roles of the IL-1 subfamily of cytokines are well established, as a newly discovered subfamily, IL-36 cytokine regulation, immunological relevance, and relation with IL-1 cytokines in host defense remain largely unknown. In this study, we showed that P. aeruginosa infection induces the expression of IL-36α and IL-36γ, as well as IL-1β and secreted IL-1Ra (sIL-1Ra), but not IL-36Ra. Downregulation of IL-1Ra increases, whereas downregulation of IL-36Ra decreases the severity of P. aeruginosa keratitis. IL-1R and IL-36Ra downregulation have opposing effects on the expression of IL-1β, sIL-1Ra, IL-36γ, S100A8, and CXCL10 and on the infiltration of innate immune cells. Administration of recombinant IL-1Ra improved, whereas IL-36Ra worsened the outcome of P. aeruginosa keratitis. Local application of IL-36γ stimulated the expression of innate defense molecules S100A9, mouse β-defensin 3, but suppressed IL-1β expression in B6 mouse corneas. IL-36γ diminished the severity of P. aeruginosa keratitis, and its protective effects were abolished in the presence of S100A9 neutralizing Ab and partially affected by CXCL10 and CXCR3 neutralizations. Thus, our data reveal that IL-1Ra and IL-36Ra have opposing effects on the outcome of P. aeruginosa keratitis and suggest that IL-36 agonists may be used as an alternative therapeutic to IL-1β-neutralizing reagents in controlling microbial keratitis and other mucosal infections.

The Atypical Response Regulator AtvR Is a New Player in Pseudomonas aeruginosa Response to Hypoxia and Virulence

Two-component systems are widespread in bacteria, allowing adaptation to environmental changes. The classical pathway is composed of a histidine kinase that phosphorylates an aspartate residue in the cognate response regulator (RR). RRs lacking the phosphorylatable aspartate also occur, but their function and contribution during host-pathogen interactions are poorly characterized. AtvR (PA14_26570) is the only atypical response regulator with a DNA-binding domain in the opportunistic pathogen Pseudomonas aeruginosa Macrophage infection with the atvR mutant strain resulted in higher levels of tumor necrosis factor alpha secretion as well as increased bacterial clearance compared to those for macrophages infected with the wild-type strain. In an acute pneumonia model, mice infected with the atvR mutant presented increased amounts of proinflammatory cytokines, increased neutrophil recruitment to the lungs, reductions in bacterial burdens, and higher survival rates in comparison with the findings for mice infected with the wild-type strain. Further, several genes involved in hypoxia/anoxia adaptation were upregulated upon atvR overexpression, as seen by high-throughput transcriptome sequencing (RNA-Seq) analysis. In addition, atvR was more expressed in hypoxia in the presence of nitrate and required for full expression of nitrate reductase genes, promoting bacterial growth under this condition. Thus, AtvR would be crucial for successful infection, aiding P. aeruginosa survival under conditions of low oxygen tension in the host. Taken together, our data demonstrate that the atypical response regulator AtvR is part of the repertoire of transcriptional regulators involved in the lifestyle switch from aerobic to anaerobic conditions. This finding increases the complexity of regulation of one of the central metabolic pathways that contributes to Pseudomonas ubiquity and versatility.

Lack of IL-1R8 in neurons causes hyperactivation of IL-1 receptor pathway and induces MECP2-dependent synaptic defects

Inflammation modifies risk and/or severity of a variety of brain diseases through still elusive molecular mechanisms. Here we show that hyperactivation of the interleukin 1 pathway, through either ablation of the interleukin 1 receptor 8 (IL-1R8, also known as SIGIRR or Tir8) or activation of IL-1R, leads to up-regulation of the mTOR pathway and increased levels of the epigenetic regulator MeCP2, bringing to disruption of dendritic spine morphology, synaptic plasticity and plasticity-related gene expression. Genetic correction of MeCP2 levels in IL-1R8 KO neurons rescues the synaptic defects. Pharmacological inhibition of IL-1R activation by Anakinra corrects transcriptional changes, restores MeCP2 levels and spine plasticity and ameliorates cognitive defects in IL-1R8 KO mice. By linking for the first time neuronal MeCP2, a key player in brain development, to immune activation and demonstrating that synaptic defects can be pharmacologically reversed, these data open the possibility for novel treatments of neurological diseases through the immune system modulation.

DOI:http://dx.doi.org/10.7554/eLife.21735.001

Errors that occur while the brain is developing can lead to conditions such as autism and schizophrenia. They can also lead to rare disorders like Rett syndrome and MeCP2 duplication syndromes, which are characterized by severe cognitive and physical disabilities. Many people with these neurodevelopmental disorders have mutations in genes that encode proteins found at synapses, which are the junctions between neurons where the cells exchange information with one another. However, not everyone with these mutations develops a neurodevelopmental disorder, which indicates that other, non-genetic factors also play a part.

One of the main non-genetic factors that can influence the risk and severity of neurodevelopmental disorders is inflammation of the brain. Inflammation is a normal part of the body’s immune response to threats such as invading microorganisms or tissue damage. However, abnormal activation of the immune system in early life can trigger excessive inflammation. This increases the risk of a neurodevelopmental disorder, but it is not clear exactly how it does so.

Tomasoni et al. set out to test whether the missing link between inflammation and neurodevelopmental disorders might be damage to synapses. The experiments revealed that genetically modified mice with inflammation of the brain have abnormal synapses and are unable to learn properly. These mutant mice also have excessive levels of a protein that influences how synapses function called MeCP2, which is missing in the brains of people with Rett syndrome and abnormally increased in brains of patients affected by MeCP2 Duplication Syndrome. This is thus the first evidence that directly links inflammation of the brain to a synapse protein implicated in a disorder of brain development.

Tomasoni et al. also found that a drug called anakinra – which is used to treat an inflammatory disease called rheumatoid arthritis – reduced levels of MeCP2 in the mutant mice and improved their performance in cognitive tasks. Together, these results raise the possibility that anti-inflammatory medications may be beneficial in the treatment of neurodevelopment disorders.

DOI:http://dx.doi.org/10.7554/eLife.21735.002

Cytokine decoy and scavenger receptors as key regulators of immunity and inflammation

IL-1R2 was the first decoy receptor to be described. Subsequently receptors which act as pure decoys or scavengers or trigger dampening of cytokine signaling have been described for cytokines and chemokines. Here we review the current understanding of the mode of action and significance in pathology of the chemokine atypical receptor ACKR2, the IL-1 decoy receptor IL-1R2 and the atypical IL-1 receptor family IL-1R8. Decoy and scavenger receptors with no or atypical signaling have emerged as a general strategy conserved in evolution to tune the action of cytokines, chemokines and growth factors.

Regulatory Role of IL-1R8 in Immunity and Disease

Interleukin-1 receptor family members (ILRs) and toll-like receptors (TLRs) are characterized by the presence of a conserved intracellular domain and the toll-IL-1resistance (TIR) domain and are key players in immunity and inflammation. ILR and TLR signaling is tightly regulated at different levels. All cell types of the innate immune system express ILRs and TLRs. In addition, IL-1 family members are emerging as key players in the differentiation and function of innate and adaptive lymphoid cells. IL-1R8, also known as TIR8 or SIGIRR, is a fringe member of the ILR family and acts as a negative regulator of ILR and TLR signaling, which dampens ILR- and TLR-mediated cell activation. IL-1R8 is a component of the receptor recognizing human IL-37. Here, we summarize our current understanding of the structure and function of IL-1R8, focusing on its role in different pathological conditions, ranging from infectious and sterile inflammation to autoimmunity and cancer-related inflammation.

The role of IL-1β in Pseudomonas aeruginosa in lung infection

This mini-review examines the role of the pro-inflammatory cytokine interleukin (IL)-1β in the interaction of Pseudomonas aeruginosa and the host immune system during lung infection. Different studies show that the reduction of the inflammatory response, especially a decrease in IL-1β, leads to a better outcome in acute lung infection with this bacterium. This includes a higher survival rate, reduced damage to the lung tissue and, in particular, a better clearance of the airways and the tissue of the lungs from P. aeruginosa.

IL-1 receptor antagonist ameliorates inflammasome-dependent inflammation in murine and human cystic fibrosis

Dysregulated inflammasome activation contributes to respiratory infections and pathologic airway inflammation. Through basic and translational approaches involving murine models and human genetic epidemiology, we show here the importance of the different inflammasomes in regulating inflammatory responses in mice and humans with cystic fibrosis (CF), a life-threatening disorder of the lungs and digestive system. While both contributing to pathogen clearance, NLRP3 more than NLRC4 contributes to deleterious inflammatory responses in CF and correlates with defective NLRC4-dependent IL-1Ra production. Disease susceptibility in mice and microbial colonization in humans occurrs in conditions of genetic deficiency of NLRC4 or IL-1Ra and can be rescued by administration of the recombinant IL-1Ra, anakinra. These results indicate that pathogenic NLRP3 activity in CF could be negatively regulated by IL-1Ra and provide a proof-of-concept evidence that inflammasomes are potential targets to limit the pathological consequences of microbial colonization in CF.

IL-1-mediated inflammation contributes to the pathogenesis of cystic fibrosis. Here the authors show that this is largely due to NLRP3 activation, whereas NLRP4 induces IL-1Ra, limiting the overall inflammasome activity and providing a therapeutic angle to ameliorate the disease.

SIGIRR participates in negative regulation of LPS response and tolerance in human bladder epithelial cells

Background

The innate immune response of urinary tract is critically important in the defense to microbial attack. Toll-like receptor 4 (TLR4) controls initial mucosal response to uropathogenic Escherichia coli (UPEC). However, excessive and dysfunctional TLR signaling may result in severe inflammation and inappropriate tissue damage. Previous studies have demonstrated that single immunoglobulin IL-1R-related receptor/Toll IL-1 receptor 8 (SIGIRR/TIR8) is a member of the toll-interleukin-1 receptor (TIR) family that can negatively modulate TLR4 mediated signaling, but its role in the innate immunity of urinary tract infection remains incompletely defined. In this study, we investigated its cellular distribution and mechanisms involved within the human bladder epithelial cells after LPS stimulation.

Results

Immunostaining, reverse transcription PCR and Western blot results showed that SIGIRR was constitutively expressed in the human bladder epithelial cell lines and was downregulated after LPS stimulation. To further define the role of SIGIRR, cells were transiently transfected with SIGIRR siRNA and stimulated with LPS. SIGIRR gene silencing augmented chemokine expression in response to LPS, as indicated by increased levels of IL-6 and IL-8 secretions in the supernatants compared with negative control siRNA. Furthermore, LPS tolerance, a protective mechanism against second LPS stimulation, was significantly reduced in SIGIRR siRNA transfected cells. Moreover, transient gene silencing augmented LPS-induced NF-κB and MAPK activation.

Conclusions

In conclusion, our results suggest that SIGIRR plays an important role in the negative regulation of LPS response and tolerance in human bladder epithelial cells, possibly through its impact on TLR-mediated signaling.

IRAK-M regulates the inhibition of TLR-mediated macrophage immune response during late in vitro Leishmania donovani infection

Intramacrophage protozoan parasite Leishmania donovani, causative agent of visceral leishmaniasis, escapes Toll-like receptor (TLR) dependent early host immune response by inducing the deubiquitinating enzyme A20, which is sustained up to 6 h postinfection only. Therefore, Leishmania must apply other means to deactivate late host responses. Here, we elucidated the role of IL-1 receptor-associated kinase M (IRAK-M), a negative regulator of TLR signaling, in downregulating macrophage proinflammatory response during late hours of in vitro infection. Our data reveal a sharp decline in IRAK1 and IRAK4 phosphorylation at 24 h postinfection along with markedly reduced association of IRAK1-TNF receptor associated factor 6, which is mandatory for TLR activation. In contrast, IRAK-M was induced after A20 levels decreased and reached a maximum at 24 h postinfection. IRAK-M induction coincided with increased stimulation of TGF-β, a hallmark cytokine of visceral infection. TGF-β-dependent signaling-mediated induction of SMAD family of proteins, 2, 3, and 4 plays important roles in transcriptional upregulation of IRAK-M. In infected macrophages, siRNA-mediated silencing of IRAK-M displayed enhanced IRAK1 and IRAK4 phosphorylation with a concomitant increase in downstream NF-κB activity and reduced parasite survival. Taken together, the results suggest that IRAK-M may be targeted by L. donovani to inhibit TLR-mediated proinflammatory response late during in vitro infection.

The interleukin (IL)-1 cytokine family--Balance between agonists and antagonists in inflammatory diseases

The interleukin (IL)-1 family of cytokines comprises 11 members, including 7 pro-inflammatory agonists (IL-1α, IL-1β, IL-18, IL-33, IL-36α, IL-36β, IL-36γ) and 4 defined or putative antagonists (IL-1R antagonist (IL-1Ra), IL-36Ra, IL-37, and IL-38) exerting anti-inflammatory activities. Except for IL-1Ra, IL-1 cytokines do not possess a leader sequence and are secreted via an unconventional pathway. In addition, IL-1β and IL-18 are produced as biologically inert pro-peptides that require cleavage by caspase-1 in their N-terminal region to generate active proteins. N-terminal processing is also required for full activity of IL-36 cytokines. The IL-1 receptor (IL-1R) family comprises 10 members and includes cytokine-specific receptors, co-receptors and inhibitory receptors. The signaling IL-1Rs share a common structure with three extracellular immunoglobulin (Ig) domains and an intracellular Toll-like/IL-1R (TIR) domain. IL-1 cytokines bind to their specific receptor, which leads to the recruitment of a co-receptor and intracellular signaling. IL-1 cytokines induce potent inflammatory responses and their activity is tightly controlled at the level of production, protein processing and maturation, receptor binding and post-receptor signaling by naturally occurring inhibitors. Some of these inhibitors are IL-1 family antagonists, while others are IL-1R family members acting as membrane-bound or soluble decoy receptors. An imbalance between agonist and antagonist levels can lead to exaggerated inflammatory responses. Several genetic modifications or mutations associated with dysregulated IL-1 activity and autoinflammatory disorders were identified in mouse models and in patients. These findings paved the road to the successful use of IL-1 inhibitors in diseases that were previously considered as untreatable.

α-TLR2 antibody attenuates the Aβ-mediated inflammatory response in microglia through enhanced expression of SIGIRR

The immunoregulatory function of single-Ig-interleukin-1 related receptor (SIGIRR) is derived from its ability to constrain the inflammatory consequences of interleukin (IL)-1R and toll-like receptor (TLR)4 activation. This role extends to the brain, where SIGIRR deficiency increases the synaptic and cognitive dysfunction associated with IL-1R- and TLR4-mediated signalling. The current study set out to investigate the interaction between SIGIRR and TLR2 in brain tissue and the data demonstrate that the response to the TLR2 agonist, Pam3CysSK4 (Pam3Cys4), is enhanced in glial cells from SIGIRR(-/-) animals. Consistent with the view that β-amyloid peptide (Aβ) signals through activation of TLR2, the data also show that Aβ-induced changes are exaggerated in glia from SIGIRR(-/-) animals. We report that microglia, rather than astrocytes, are the primary glial cell expressing both TLR2 and SIGIRR. While Aβ increased TLR2 expression, it decreased SIGIRR expression in microglia. This was mimicked by direct activation of TLR2 with Pam3Cys4. We investigated the effect of an anti-TLR2 antibody (αTLR2) on the Aβ-induced inflammatory responses and demonstrate that it prevented the expression and release of the pro-inflammatory cytokines TNFα and IL-6 from microglia. In addition, application of αTLR2 alleviated the Aβ-mediated impairment in long-term potentiation (LTP) of hippocampal synaptic activity. The protective effects of αTLR2 were accompanied by an up-regulation in SIGIRR expression. We propose that a mechanism involving activation of PI3 kinase/Akt and the transcription factor peroxisome proliferator-activated receptor (PPAR)γ may facilitate this increase in SIGIRR. These findings highlight a novel role of SIGIRR as a negative regulator of TLR2-mediated inflammation in the brain.

Divergent functions of Toll-like receptors during bacterial lung infections

Lower respiratory tract infections caused by bacteria are a major cause of death in humans irrespective of sex, race, or geography. Indeed, accumulated data indicate greater mortality and morbidity due to these infections than cancer, malaria, or HIV infection. Successful recognition of, followed by an appropriate response to, bacterial pathogens in the lungs is crucial for effective pulmonary host defense. Although the early recruitment and activation of neutrophils in the lungs is key in the response against invading microbial pathogens, other sentinels, such as alveolar macrophages, epithelial cells, dendritic cells, and CD4(+) T cells, also contribute to the elimination of the bacterial burden. Pattern recognition receptors, such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-like receptors, are important for recognizing and responding to microbes during pulmonary infections. However, bacterial pathogens have acquired crafty evasive strategies to circumvent the pattern recognition receptor response and thus establish infection. Increased understanding of the function of TLRs and evasive mechanisms used by pathogens during pulmonary infection will deepen our knowledge of immunopathogenesis and is crucial for developing effective therapeutic and/or prophylactic measures. This review summarizes current knowledge of the multiple roles of TLRs in bacterial lung infections and highlights the mechanisms used by pathogens to modulate or interfere with TLR signaling in the lungs.

Acute exposure to silica nanoparticles enhances mortality and increases lung permeability in a mouse model of Pseudomonas aeruginosa pneumonia

BACKGROUND

The lung epithelium constitutes the first barrier against invading pathogens and also a major surface potentially exposed to nanoparticles. In order to ensure and preserve lung epithelial barrier function, the alveolar compartment possesses local defence mechanisms that are able to control bacterial infection. For instance, alveolar macrophages are professional phagocytic cells that engulf bacteria and environmental contaminants (including nanoparticles) and secrete pro-inflammatory cytokines to effectively eliminate the invading bacteria/contaminants. The consequences of nanoparticle exposure in the context of lung infection have not been studied in detail. Previous reports have shown that sequential lung exposure to nanoparticles and bacteria may impair bacterial clearance resulting in increased lung bacterial loads, associated with a reduction in the phagocytic capacity of alveolar macrophages.

RESULTS

Here we have studied the consequences of SiO2 nanoparticle exposure on Pseudomonas aeruginosa clearance, Pseudomonas aeruginosa-induced inflammation and lung injury in a mouse model of acute pneumonia. We observed that pre-exposure to SiO2 nanoparticles increased mice susceptibility to lethal pneumonia but did not modify lung clearance of a bioluminescent Pseudomonas aeruginosa strain. Furthermore, internalisation of SiO2 nanoparticles by primary alveolar macrophages did not reduce the capacity of the cells to clear Pseudomonas aeruginosa. In our murine model, SiO2 nanoparticle pre-exposure preferentially enhanced Pseudomonas aeruginosa-induced lung permeability (the latter assessed by the measurement of alveolar albumin and IgM concentrations) rather than contributing to Pseudomonas aeruginosa-induced lung inflammation (as measured by leukocyte recruitment and cytokine concentration in the alveolar compartment).

CONCLUSIONS

We show that pre-exposure to SiO2 nanoparticles increases mice susceptibility to lethal pneumonia but independently of macrophage phagocytic function. The deleterious effects of SiO2 nanoparticle exposure during Pseudomonas aeruginosa-induced pneumonia are related to alterations of the alveolar-capillary barrier rather than to modulation of the inflammatory responses.

The decreased frequency of SIGIRR-positive CD4+ T cells in peripheral blood of patients with SLE and its correlation with disease activity

Recently, many studies have shown that Single immunoglobulin interleukin-1 receptor related protein (SIGIRR), a member of the IL-1R family acting as a negative regulator of TLR/IL-1R signaling, affects autoimmune responses in animal model of systemic lupus erythematosus (SLE). However, the role of SIGIRR in the pathogenesis of human SLE has not been widely explored. In this study, we analyzed the frequency of SIGIRR-positive CD4+ T cells in peripheral blood mononuclear cells (PBMCs) of SLE patients and its correlation with disease activity as well as the clinical data. Circulating SIGIRR-positive CD4+ T cells were quantified in 51 SLE patients and 38 healthy controls by using flow cytometer. Results showed that the percentages of SIGIRR-positive CD4+ T cells were decreased in the PBMCs of SLE patients compared with healthy controls (Z = -5.49, P < 0.001). The frequency of SIGIRR-positive CD4 + T cells were also significantly decreased in SLE patients with nephritis than those without nephritis (Z = -3.71, P < 0.001). In addition, there was significant correlation between the percentages of SIGIRR-positive CD4+ T cells and SLEDAI score (r s = -0.74, P < 0.001), 24-hour urine protein (r s = -0.62, P < 0.001), Scr (r s = -0.65, P < 0.001), ESR (r s = -0.60, P < 0.001), C3 (r s = 0.53, P < 0.001) as well as C4 (r s = 0.52, P < 0.001). However, there was no correlation between the proportion of SIGIRR-positive CD4+ T cells and glucocorticoid dose (P = 0.59). In summary, decreased numbers of SIGIRR-positive CD4+ T cells in SLE patients and its correlation with SLEDAI score as well as the clinical data suggest that SIGIRR may be involved in the pathogenesis of SLE.

Involvement of a 1-Cys peroxiredoxin in bacterial virulence

The killing of bacterial pathogens by macrophages occurs via the oxidative burst and bacteria have evolved to overcome this challenge and survive, using several virulence and defense strategies, including antioxidant mechanisms. We show here that the 1-Cys peroxiredoxin LsfA from the opportunistic pathogen Pseudomonas aeruginosa is endowed with thiol-dependent peroxidase activity that protects the bacteria from H(2)O(2) and that this protein is implicated in pathogenicity. LsfA belongs to the poorly studied Prx6 subfamily of peroxiredoxins. The function of these peroxiredoxins has not been characterized in bacteria, and their contribution to host-pathogen interactions remains unknown. Infection of macrophages with the lsfA mutant strains resulted in higher levels of the cytokine TNF-α production due to the activation of the NF-kB and MAPK pathways, that are partially inhibited by the wild-type P. aeruginosa strain. A redox fluorescent probe was more oxidized in the lsfA mutant-infected macrophages than it was in the macrophages infected with the wild-type strain, suggesting that the oxidative burst was overstimulated in the absence of LsfA. Although no differences in the phagocytosis rates were observed when macrophages were infected with wild-type and mutant bacteria in a gentamicin exclusion assay, a higher number of wild-type bacterial cells was found in the supernatant. This difference was not observed when macrophages were pre-treated with a NADPH oxidase inhibitor, confirming the role of LsfA in the bacterial resistance to ROS generated via NADPH oxidase. In an acute pneumonia model, mice infected with the mutant strains presented higher cytokine release in the lungs and increased activated neutrophil recruitment, with reduced bacterial burden and improved survival rates compared to mice infected with the wild-type bacteria. LsfA is the first bacterial 1-Cys Prx shown to modulate host immune responses and its characterization will allow a better understanding of the role of redox signaling in host-pathogen interactions.

Bone morphogenetic protein 4 inhibits liposaccharide-induced inflammation in the airway

Bone morphogenetic protein 4 (BMP4) is a multifunctional growth factor that belongs to the TGF-β superfamily. The role of BMP4 in lung diseases is not fully understood. Here, we demonstrate that BMP4 was upregulated in lungs undergoing lipopolysaccharide (LPS)-induced inflammation, and in airway epithelial cells treated with LPS or TNF-α. BMP4 mutant (BMP4(+/-) ) mice presented with more severe lung inflammation in response to LPS or Pseudomonas aeruginosa, and lower bacterial load compared with that in BMP4(+/+) mice. Knockdown of BMP4 by siRNA increased LPS and TNF-α-induced IL-8 expression in 16HBE human airway epithelial cells and in primary human bronchial epithelial cells. Similarly, peritoneal macrophages from BMP4(+/-) mice produced greater levels of TNF-α and keratinocyte chemoattractant (KC) upon LPS treatment compared with cells from BMP4(+/+) mice. Administration of exogenous BMP4 attenuated the upregulation of TNF-α, IL-8, or KC induced by LPS and/or TNF-α in airway epithelial cells, and peritoneal macrophages. Finally, partial deficiency of BMP4 in BMP4(+/-) mice protected the animals from restrictive lung function reduction upon chronic LPS exposure. These results indicate that BMP4 plays an important anti-inflammatory role, controlling the strength and facilitating the resolution of acute lung inflammation; yet, BMP4 also contributes to lung function impairment during chronic lung inflammation.

Single immunoglobulin interleukin-1 receptor-related molecule impairs host defense during pneumonia and sepsis caused by Streptococcus pneumoniae

Streptococcus pneumoniae is a common cause of pneumonia and sepsis. Toll-like receptors (TLRs) play a pivotal role in the host defense against infection. In this study, we sought to determine the role of single immunoglobulin interleukin-1 receptor-related molecule (SIGIRR a.k.a. TIR8), a negative regulator of TLR signaling, in pneumococcal pneumonia and sepsis. Wild-type and SIGIRR-deficient (sigirr-/-) mice were infected intranasally (to induce pneumonia) or intravenously (to induce primary sepsis) with S. pneumoniae and euthanized after 6, 24, or 48 h for analyses. Additionally, survival studies were performed. sigirr-/- mice showed delayed mortality during lethal pneumococcal pneumonia. Accordingly, sigirr-/- mice displayed lower bacterial loads in lungs and less dissemination of the infection 24 h after the induction of pneumonia. SIGIRR deficiency was associated with increased interstitial and perivascular inflammation in lung tissue early after infection, with no impact on neutrophil recruitment or cytokine production. sigirr-/- mice also demonstrated reduced bacterial burdens at multiple body sites during S. pneumoniae sepsis. sigirr-/- alveolar macrophages and neutrophils exhibited an increased capacity to phagocytose viable pneumococci. These results suggest that SIGIRR impairs the antibacterial host defense during pneumonia and sepsis caused by S. pneumoniae.

Negative regulatory receptors of the IL-1 family

The IL-1 family of ligands and receptors has a central role in both innate and adaptive immune responses and is tightly controlled by antagonists, decoy receptors, scavengers, dominant negative molecules, miRNAs and other mechanisms, acting extracellularly or intracellularly. During evolution, the development of multiple mechanisms of negative regulation reveals the need for tight control of the biological consequences of IL-1 family ligands in order to balance local and systemic inflammation and limit immunopathology. Indeed, studies with gene targeted mice for negative regulators and genetic studies in humans provide evidence for their non-redundant role in controlling inflammation, tissue damage and adaptive responses. In addition, studies have revealed the need of negative regulation of the IL-1 family not only in disease, but also in homeostatic conditions. In this review, the negative regulation mediated by decoy receptors are presented and include IL-1R2 and IL-IL-18BP as well as atypical receptors, which include TIR8/SIGIRR, IL-1RAcPb, TIGIRR-1 and IL-1RAPL. Particular emphasis is given to IL-1R2, since its discovery is the basis for the formulation of the decoy paradigm, now considered a general strategy to counter the primary inflammatory activities of cytokines and chemokines. Emphasis is also given to TIR8, a prototypical negative regulatory receptor having non-redundant roles in limiting inflammation and adaptive responses.

Absence of Toll-IL-1 receptor 8/single immunoglobulin IL-1 receptor-related molecule reduces house dust mite-induced allergic airway inflammation in mice

Allergic asthma is a chronic inflammatory disease predominately associated with the activation of CD4(+) T helper Type 2 (Th2) cells. Innate pattern recognition receptors are widely acknowledged to shape the adaptive immune response. For example, the activation of airway epithelial Toll-like receptor-4 (TLR4) is necessary for the generation of house dust mite (HDM)-specific Th2 responses and the development of asthma in mice. Here we sought to determine whether the absence of Toll-interleukin-1 receptor (TIR)-8, a negative regulator of TLR4 signaling that is highly expressed in airway epithelial cells, would exacerbate HDM-induced asthma in a murine model. We found that Th2 but not Th1 or Th17 cytokine expression was significantly reduced in the lung and draining lymph nodes in HDM-sensitized/challenged TIR8 gene-deleted mice. Mucus-producing goblet cells, HDM-specific IgG1, and airway hyperreactivity were also significantly reduced in HDM-exposed, TIR8-deficient mice. Consistent with the attenuated Th2 response, eotaxin-2/CCL24 expression and airway and peribronchial eosinophils were significantly reduced in the absence of TIR8. In contrast, IL-17A-responsive chemokines and neutrophil numbers were unaffected. Similar findings were obtained for cockroach allergen. HDM sensitization alone up-regulated the expression of IL-1F5, a putative TIR8 ligand and inducer of IL-4. Of note, innate IL-4, IL-5, IL-13, and IL-33 cytokine expression was reduced during HDM sensitization in the absence of TIR8, as was the recruitment of conventional dendritic cells and basophils to the draining lymph nodes. Our findings suggest that TIR8 enhances the development of HDM-induced innate and adaptive Th2, but not Th1 or Th17 type immunity.

Decoys and Regulatory "Receptors" of the IL-1/Toll-Like Receptor Superfamily

Members of the IL-1 family play a key role in innate and adaptive immunity and in the pathogenesis of diverse diseases. Members of IL-1R like receptor (ILR) family include signaling molecules and negative regulators. The latter include decoy receptors (IL-1RII; IL-18BP) and “receptors” with regulatory function (TIR8/SIGIRR; IL-1RAcPb; DIGIRR). Structural considerations suggest that also TIGIRR-1 and IL-1RAPL may have regulatory function. The presence of multiple pathways of negative regulation of members of the IL-1/IL-1R family emphasizes the need for a tight control of members of this fundamental system.

Activation of inflammasome signaling mediates pathology of acute P. aeruginosa pneumonia

The respiratory tract is exceptionally well defended against infection from inhaled bacteria, with multiple proinflammatory signaling cascades recruiting phagocytes to clear airway pathogens. However, organisms that efficiently activate damaging innate immune responses, such as those mediated by the inflammasome and caspase-1, may cause pulmonary damage and interfere with bacterial clearance. The extracellular, opportunistic pathogen Pseudomonas aeruginosa expresses not only pathogen-associated molecular patterns that activate NF-κB signaling in epithelial and immune cells, but also flagella that activate the NLRC4 inflammasome. We demonstrate that induction of inflammasome signaling, ascribed primarily to the alveolar macrophage, impaired P. aeruginosa clearance and was associated with increased apoptosis/pyroptosis and mortality in a murine model of acute pneumonia. Strategies that limited inflammasome activation, including infection by fliC mutants, depletion of macrophages, deletion of NLRC4, reduction of IL-1β and IL-18 production, inhibition of caspase-1, and inhibition of downstream signaling in IL-1R- or IL-18R-null mice, all resulted in enhanced bacterial clearance and diminished pathology. These results demonstrate that the inflammasome provides a potential target to limit the pathological consequences of acute P. aeruginosa pulmonary infection.

TIR8/SIGIRR is an Interleukin-1 Receptor/Toll Like Receptor Family Member with Regulatory Functions in Inflammation and Immunity

Interleukin-1R like receptors (ILRs) and Toll Like Receptors (TLRs) are key receptors of innate immunity, inflammation, and orientation of the adaptive response. They belong to a superfamily characterized by the presence of a conserved intracellular domain, the Toll/IL-1R (TIR) domain, which is involved in the activation of a signaling cascade leading to activation of transcription factors associated to inflammation. The activation of inflammatory responses and immunity by ILRs or TLRs signaling is potentially detrimental for the host in acute and chronic conditions and is tightly regulated at different levels by receptor antagonists, decoy receptors or signaling molecules, and miRNAs. Recent evidence suggests that the ILRs family member TIR8 (also known as SIGIRR) is a regulatory protein acting intracellularly to inhibit ILRs and TLRs signaling. In particular, current evidence suggests that TIR8/SIGIRR dampens TLRs-mediated activation and inhibits signaling receptor complexes of IL-1 family members associated with Th1 (IL-18), Th2 (IL-33), and Th17 (IL-1) differentiation. Studies with Tir8/Sigirr-deficient mice showed that the ability to dampen signaling from ILRs and TLRs family members makes TIR8/SIGIRR a key regulator of inflammation. Here, we summarize our current understanding of the structure and function of TIR8/SIGIRR, focusing on its role in different pathological conditions, ranging from infectious and sterile inflammation, to autoimmunity and cancer-related inflammation.

The toll interleukin-1 receptor (IL-1R) 8/single Ig domain IL-1R-related molecule modulates the renal response to bacterial infection

Our immune system has to constantly strike a balance between activation and inhibition of an inflammatory response to combat invading pathogens and avoid inflammation-induced collateral tissue damage. Toll interleukin-1 receptor 8 (IL-1R-8)/single Ig domain IL-1R-related molecule (TIR8/SIGIRR) is an inhibitor of Toll-like receptor (TLR)/IL-1R signaling, which is predominantly expressed in the kidney. The biological role of renal TIR8 during infection is, however, unknown. We therefore evaluated renal TIR8 expression during Escherichia coli pyelonephritis and explored its role in host defense using TIR8(-/-) versus TIR8(+/+) mice. We found that TIR8 protein is abundantly present in the majority of cortical tubular epithelial cells. Pyelonephritis resulted in a significant downregulation of TIR8 mRNA in kidneys of TIR8(+/+) mice. TIR8 inhibited an effective host response against E. coli, as indicated by diminished renal bacterial outgrowth and dysfunction in TIR8(-/-) mice. This correlated with increased amounts of circulating and intrarenal neutrophils at the early phase of infection. TIR8(-/-) tubular epithelial cells had increased cytokine/chemokine production when stimulated with lipopolysaccharide (LPS) or heat-killed E. coli, suggesting that TIR8 played an anti-inflammatory role during pathogen stimulation by inhibiting LPS signaling. These data suggest that TIR8 is an important negative regulator of an LPS-mediated inflammatory response in tubular epithelial cells and dampens an effective antibacterial host response during pyelonephritis caused by uropathogenic E. coli.

Toll-like Receptors in Chronic Lymphocytic Leukemia

Toll-like receptors belong to the pattern recognition receptors family present on a variety of immune cells including normal and malignant B-cells. They act as immediate molecular sentinels of innate immunity but also act as a molecular bridge between the innate and the adaptive immune response; distinct Toll-like receptors are able to bind specific pattern molecules of bacteria, viruses and autoantigens. In this review we will briefly introduce the Toll-like receptor family and their expression pattern, signaling and function in the B cell context; following we will summarize the published data on TLR in chronic lymphocytic leukemia, and we will discuss their emerging role in the modulation of leukemia pathobiology.