Mouse neutrophils express the decoy type 2 interleukin-1 receptor (IL-1R2) constitutively and in acute inflammatory conditions

Molecular mechanisms of regulation of IL-1 and its receptors

Interleukin 1 (IL-1) is a pro-inflammatory cytokine that plays a key role in the development and regulation of nonspecific defense and specific immunity. However, its regulatory influence extends beyond inflammation and impacts a range of immune and non-immune processes. The involvement of IL-1 in numerous biological processes, including modulation of inflammation, necessitates strict regulation at multiple levels. This review focuses on these regulatory processes and discusses their underlying mechanisms. IL-1 activity is controlled at various levels, including receptor binding, gene transcription, expression as inactive proforms, and regulated post-translational processing and secretion. Regulation at the level of the receptor expression - alternative splicing, tissue-specific isoforms, and gene polymorphism - is also crucial to IL-1 functional activity. Understanding these regulatory features of IL-1 will not only continue to shape future research directions but will also highlight promising therapeutic strategies to modulate the biological effects of IL-1.

Single-cell and spatial transcriptomics of vulvar lichen sclerosus reveal multi-compartmental alterations in gene expression and signaling cross-talk

Vulvar diseases are a critical yet often neglected area of women's health, profoundly affecting patients' quality of life and frequently resulting in long-term physical and psychological challenges. Lichen sclerosus (LS) is a chronic inflammatory skin disorder that predominantly affects the vulva, leading to severe itching, pain, scarring, and an increased risk of malignancy. Despite its profound impact on affected individuals, the molecular pathogenesis of vulvar LS (VLS) is not well understood, hindering the development of FDA-approved therapies. Here, we utilize single-cell and spatial transcriptomics to analyze lesional and non-lesional skin from VLS patients, as well as healthy control vulvar skin. Our findings demonstrate histologic, cellular, and molecular heterogeneities within VLS, yet highlight unifying molecular changes across keratinocytes, fibroblasts, immune cells, and melanocytes in lesional skin. They reveal cellular stress and damage in fibroblasts and keratinocytes, enhanced T cell activation and cytotoxicity, aberrant cell-cell signaling, and increased activation of the IFN, JAK/STAT, and p53 pathways in specific cell types. Using both monolayer and organotypic culture models, we also demonstrate that knockdown of select genes, which are downregulated in VLS lesional keratinocytes, partially recapitulates VLS-like stress-associated changes. Collectively, these data provide novel insights into the pathogenesis of VLS, identifying potential biomarkers and therapeutic targets for future research.

Negative regulator IL-1 receptor 2 (IL-1R2) and its roles in immune regulation of autoimmune diseases

The decoy receptor interleukin 1 receptor 2 (IL-1R2), also known as CD121b, has different forms: membrane-bound (mIL-1R2), soluble secreted (ssIL-1R2), shedded (shIL-1R2), intracellular domain (IL-1R2ICD). The different forms of IL-1R2 exert not exactly similar functions. IL-1R2 can not only participate in the regulation of inflammatory response by competing with IL-1R1 to bind IL-1 and IL-1RAP, but also regulate IL-1 maturation and cell activation, promote cell survival, participate in IL-1-dependent internalization, and even have biological activity as a transcriptional cofactor. In this review, we provide a detailed description of the biological characteristics of IL-1R2 and discuss the expression and unique role of IL-1R2 in different immune cells. Importantly, we summarize the role of IL-1R2 in immune regulation from different autoimmune diseases, hoping to provide a new direction for in-depth studies of pathogenesis and therapeutic targets in autoimmune diseases.

Propolis Reduces Inflammation and Dyslipidemia Caused by High-Cholesterol Diet in Mice by Lowering ADAM10/17 Activities

Atherosclerosis is one of the most important causes of cardiovascular diseases. A disintegrin and metalloprotease (ADAM)10 and ADAM17 have been identified as important regulators of inflammation in recent years. Our study investigated the effect of inhibiting these enzymes with selective inhibitor and propolis on atherosclerosis. In our study, C57BL/6J mice (n = 16) were used in the control and sham groups. In contrast, ApoE-/- mice (n = 48) were used in the case, water extract of propolis (WEP), ethanolic extract of propolis (EEP), GW280264X (GW-synthetic inhibitor), and solvent (DMSO and ethanol) groups. The control group was fed a control diet, and all other groups were fed a high-cholesterol diet for 16 weeks. WEP (400 mg/kg/day), EEP (200 mg/kg/day), and GW (100 µg/kg/day) were administered intraperitoneally for the last four weeks. Animals were sacrificed, and blood, liver, aortic arch, and aortic root tissues were collected. In serum, total cholesterol (TC), triglycerides (TGs), and glucose (Glu) were measured by enzymatic colorimetric method, while interleukin-1β (IL-1β), paraoxonase-1 (PON-1), and lipoprotein-associated phospholipase-A2 (Lp-PLA2) were measured by ELISA. Tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), myeloperoxidase (MPO), interleukin-6 (IL-6), interleukin-10 (IL-10), and interleukin-12 (IL-12) levels were measured in aortic arch by ELISA and ADAM10/17 activities were measured fluorometrically. In addition, aortic root and liver tissues were examined histopathologically and immunohistochemically (ADAM10 and sortilin primary antibody). In the WEP, EEP, and GW groups compared to the case group, TC, TG, TNF-α, IL-1β, IL-6, IL-12, PLA2, MPO, ADAM10/17 activities, plaque burden, lipid accumulation, ADAM10, and sortilin levels decreased, while IL-10 and PON-1 levels increased (p < 0.003). Our study results show that propolis can effectively reduce atherosclerosis-related inflammation and dyslipidemia through ADAM10/17 inhibition.

IL-1 Receptor Dynamics in Immune Cells: Orchestrating Immune Precision and Balance

IL-1, a pleiotropic cytokine with profound effects on various cell types, particularly immune cells, plays a pivotal role in immune responses. The proinflammatory nature of IL-1 necessitates stringent control mechanisms of IL-1-mediated signaling at multiple levels, encompassing transcriptional and translational regulation, precursor processing, as well as the involvement of a receptor accessory protein, a decoy receptor, and a receptor antagonist. In T-cell immunity, IL-1 signaling is crucial during both the priming and effector phases of immune reactions. The fine-tuning of IL-1 signaling hinges upon two distinct receptor types; the functional IL-1 receptor (IL-1R) 1 and the decoy IL-1R2, accompanied by ancillary molecules such as the IL-1R accessory protein (IL-1R3) and IL-1R antagonist. IL-1R1 signaling by IL-1β is critical for the differentiation, expansion, and survival of Th17 cells, essential for defense against extracellular bacteria or fungi, yet implicated in autoimmune disease pathogenesis. Recent investigations emphasize the physiological importance of IL-1R2 expression, particularly in its capacity to modulate IL-1-dependent responses within Tregs. The precise regulation of IL-1R signaling is indispensable for orchestrating appropriate immune responses, as unchecked IL-1 signaling has been implicated in inflammatory disorders, including Th17-mediated autoimmunity. This review provides a thorough exploration of the IL-1R signaling complex and its pivotal roles in immune regulation. Additionally, it highlights recent advancements elucidating the mechanisms governing the expression of IL-1R1 and IL-1R2, underscoring their contributions to fine-tuning IL-1 signaling. Finally, the review briefly touches upon therapeutic strategies targeting IL-1R signaling, with potential clinical applications.

Loss of T follicular regulatory cell-derived IL-1R2 augments germinal center reactions via increased IL-1

Inappropriate immune activity is key in the pathogenesis of multiple diseases, and it is typically driven by excess inflammation and/or autoimmunity. IL-1 is often the effector owing to its powerful role in both innate and adaptive immunity, and, thus, it is tightly controlled at multiple levels. IL-1R2 antagonizes IL-1, but effects of losing this regulation are unknown. We found that IL-1R2 resolves inflammation by rapidly scavenging free IL-1. Specific IL-1R2 loss in germinal center (GC) T follicular regulatory (Tfr) cells increased the GC response after a first, but not booster, immunization, with an increase in T follicular helper (Tfh) cells, GC B cells, and antigen-specific antibodies, which was reversed upon IL-1 blockade. However, IL-1 signaling is not obligate for GC reactions, as WT and Il1r1-/- mice showed equivalent phenotypes, suggesting that GC IL-1 is normally restrained by IL-1R2. Fascinatingly, germline Il1r2-/- mice did not show this phenotype, but conditional Il1r2 deletion in adulthood recapitulated it, implying that compensation during development counteracts IL-1R2 loss. Finally, patients with ulcerative colitis or Crohn's disease had lower serum IL-1R2. All together, we show that IL-1R2 controls important aspects of innate and adaptive immunity and that IL-1R2 level may contribute to human disease propensity and/or progression.

IL1R2 is a Novel Prognostic Biomarker for Lung Adenocarcinoma

AIMS

The aim of this study is to figure out the role of IL1R2 in LUAD (lung adenocarcinoma).

BACKGROUND

IL1R2, a special member of IL-1 receptor family, binds to IL-1 and plays an important role in inhibiting IL-1 pathway, which seems to be involved in tumorigenesis. Emerging studies demonstrated higher IL1R2 expression levels in several malignancies.

OBJECTIVE

In the present study, we assessed the expression of IL1R2 in LUAD tissues with immunohistochemistry and explored various databases to determine whether it could be a potential prognostic biomarker and therapeutic target.

METHODS

The expression level of IL1R2 in lung adenocarcinoma was analyzed by Immunohistochemistry and UALCAN database. The correlation between IL1R2 expression and the patient prognosis was identified by Kaplan-Meier plotter. The correlation of IL1R2 expression with immune infiltrates was clarified by TIMER database. The protein-protein interaction network and gene functional enrichment analysis were constructed and performed by STRING and Metascape database.

RESULTS

Immunohistochemistry showed that the expression of IL1R2 was higher in tumor tissues of LUAD patients and that patients with lower IL1R2 level have a better prognosis than their counterparts. We validated our findings in several online databases and found that IL1R2 gene was also positively correlated with B cells and neutrophils and biomarkers of CD8+T cells and exhausted T cells. PPI network and gene enrichment analyses showed that expression of IL1R2 was also associated with complex functionspecific networks involving IL-1 signal, NF-KappaB transcription factors.

CONCLUSION

According to these findings, we demonstrated that IL1R2 was involved in the progression and prognosis of LUAD and the underlying mechanism needs further investigation.

Interleukin (IL)-1 Receptor Signaling Is Required for Complete Taste Bud Regeneration and the Recovery of Neural Taste Responses following Axotomy

Experimental or traumatic nerve injury causes the degeneration of associated taste buds. Unlike most sensory systems, the sectioned nerve and associated taste buds can then regenerate, restoring neural responses to tastants. It was previously unknown whether injury-induced immune factors mediate this process. The proinflammatory cytokines, interleukin (IL)-1α and IL-1β, and their requisite receptor are strongly expressed by anterior taste buds innervated by the chorda tympani nerve. We tested taste bud regeneration and functional recovery in mice lacking the IL-1 receptor. After axotomy, the chorda tympani nerve regenerated but was initially unresponsive to tastants in both WT and Il1r KO mice. In the absence of Il1r signaling, however, neural taste responses remained minimal even >8 weeks after injury in both male and female mice, whereas normal taste function recovered by 3 weeks in WT mice. Failed recovery was because of a 57.8% decrease in regenerated taste buds in Il1r KO compared with WT axotomized mice. Il1a gene expression was chronically dysregulated, and the subset of regenerated taste buds were reinnervated more slowly and never reached full volume as progenitor cell proliferation lagged in KO mice. Il1r signaling is thus required for complete taste bud regeneration and the recovery of normal taste transmission, likely by impairing taste progenitor cell proliferation. This is the first identification of a cytokine response that promotes taste recovery. The remarkable plasticity of the taste system makes it ideal for identifying injury-induced mechanisms mediating successful regeneration and recovery.SIGNIFICANCE STATEMENT Taste plays a critical role in nutrition and quality of life. The adult taste system is highly plastic and able to regenerate following the disappearance of most taste buds after experimental nerve injury. Several growth factors needed for taste bud regeneration have been identified, but we demonstrate the first cytokine pathway required for the recovery of taste function. In the absence of IL-1 cytokine signaling, taste bud regeneration is incomplete, preventing the transmission of taste activity to the brain. These results open a new direction in revealing injury-specific mechanisms that could be harnessed to promote the recovery of taste perception after trauma or disease.

Neutrophils and emergency granulopoiesis drive immune suppression and an extreme response endotype during sepsis

Sepsis arises from diverse and incompletely understood dysregulated host response processes following infection that leads to life-threatening organ dysfunction. Here we showed that neutrophils and emergency granulopoiesis drove a maladaptive response during sepsis. We generated a whole-blood single-cell multiomic atlas (272,993 cells, n = 39 individuals) of the sepsis immune response that identified populations of immunosuppressive mature and immature neutrophils. In co-culture, CD66b⁺ sepsis neutrophils inhibited proliferation and activation of CD4⁺ T cells. Single-cell multiomic mapping of circulating hematopoietic stem and progenitor cells (HSPCs) (29,366 cells, n = 27) indicated altered granulopoiesis in patients with sepsis. These features were enriched in a patient subset with poor outcome and a specific sepsis response signature that displayed higher frequencies of IL1R2⁺ immature neutrophils, epigenetic and transcriptomic signatures of emergency granulopoiesis in HSPCs and STAT3-mediated gene regulation across different infectious etiologies and syndromes. Our findings offer potential therapeutic targets and opportunities for stratified medicine in severe infection.

Neutrophils in host defense, healing, and hypersensitivity: Dynamic cells within a dynamic host

Neutrophils are cells of the innate immune system that are extremely abundant in vivo and respond quickly to infection, injury, and inflammation. Their constant circulation throughout the body makes them some of the first responders to infection, and indeed they play a critical role in host defense against bacterial and fungal pathogens. It is now appreciated that neutrophils also play an important role in tissue healing after injury. Their short life cycle, rapid response kinetics, and vast numbers make neutrophils a highly dynamic and potentially extremely influential cell population. It has become clear that they are highly integrated with other cells of the immune system and can thus exert critical effects on the course of an inflammatory response; they can further impact tissue homeostasis and recovery after challenge. In this review, we discuss the fundamentals of neutrophils in host defense and healing; we explore the relationship between neutrophils and the dynamic host environment, including circadian cycles and the microbiome; we survey the field of neutrophils in asthma and allergy; and we consider the question of neutrophil heterogeneity-namely, whether there could be specific subsets of neutrophils that perform different functions in vivo.

Neutrophils in aging and aging‐related pathologies

Over the past millennia, life expectancy has drastically increased. While a mere 25 years during Bronze and Iron ages, life expectancy in many European countries and in Japan is currently above 80 years. Such an increase in life expectancy is a result of improved diet, life style, and medical care. Yet, increased life span and aging also represent the most important non-modifiable risk factors for several pathologies including cardiovascular disease, neurodegenerative diseases, and cancer. In recent years, neutrophils have been implicated in all of these pathologies. Hence, this review provides an overview of how aging impacts neutrophil production and function and conversely how neutrophils drive aging-associated pathologies. Finally, we provide a perspective on how processes of neutrophil-driven pathologies in the context of aging can be targeted therapeutically.

Oxytocin ameliorates KCC2 decrease induced by oral bacteria-derived LPS that affect rat primary cultured cells and PC-12 cells

Inflammation, especially neuroinflammation, which is caused by stress, leads to central nervous system (CNS) dysfunction. Because lipopolysaccharides (LPSs) cause neuroinflammation, we investigated the effect of LPSs to CNS. In PC-12 cells, LPSs derived from oral bacteria reduced the expression of KCC2, a Cl^- transporter. LPS derived from P. gingivalis (P. g) administered to rat primary cultured cells also reduced the KCC2 expression. However, LPSs derived from E. coli did not reduce the KCC2 expression. LPS treatment activated TLR4, IL-1β, and REST gene expressions, which led to KCC2 inactivation in PC-12 cells. The mechanism of KCC2 has been shown to play an important role in brain maturation, function (such as the GABA switch), and behavioral problems, we investigated the GABA function. We found that the GABA function was changed from inhibitory to excitatory by the LPS derived from P. g treatment. We demonstrated that the GSK3β also involved in the KCC2 reduction by LPS treatment. We show that oxytocin rescued the reduction in KCC2 expression caused by LPSs by inhibiting GSK3β signaling but vasopressin could not. Considered together, our results indicate that the LPSs from oral bacteria but not the LPS from E. coli increase the risk for brain disorders and oxytocin might be a candidate to overcome the abnormal behavior caused by brain disorders such as psychiatric disorders.

The One That Got Away: How Macrophage-Derived IL-1β Escapes the Mycolactone-Dependent Sec61 Blockade in Buruli Ulcer

Buruli ulcer (BU), caused by Mycobacterium ulcerans, is a devastating necrotizing skin disease. Key to its pathogenesis is mycolactone, the exotoxin virulence factor that is both immunosuppressive and cytotoxic. The discovery that the essential Sec61 translocon is the major cellular target of mycolactone explains much of the disease pathology, including the immune blockade. Sec61 inhibition leads to a loss in production of nearly all cytokines from monocytes, macrophages, dendritic cells and T cells, as well as antigen presentation pathway proteins and costimulatory molecules. However, there has long been evidence that the immune system is not completely incapable of responding to M. ulcerans infection. In particular, IL-1β was recently shown to be present in BU lesions, and to be induced from M. ulcerans-exposed macrophages in a mycolactone-dependent manner. This has important implications for our understanding of BU, showing that mycolactone can act as the "second signal" for IL-1β production without inhibiting the pathways of unconventional secretion it uses for cellular release. In this Perspective article, we validate and discuss this recent advance, which is entirely in-line with our understanding of mycolactone's inhibition of the Sec61 translocon. However, we also show that the IL-1 receptor, which uses the conventional secretory pathway, is sensitive to mycolactone blockade at Sec61. Hence, a more complete understanding of the mechanisms regulating IL-1β function in skin tissue, including the transient intra-macrophage stage of M. ulcerans infection, is urgently needed to uncover the double-edged sword of IL-1β in BU pathogenesis, treatment and wound healing.

Network Pharmacology- and Molecular Docking-Based Identification of Potential Phytocompounds from Argyreia capitiformis in the Treatment of Inflammation

The methanolic extract of Argyreia capitiformis stem was examined for anti-inflammatory activities following network pharmacology analysis and molecular docking study. Based on gas chromatography-mass spectrometry (GC-MS) analysis, 49 compounds were identified from the methanolic extract of A. capitiformis stem. A network pharmacology analysis was conducted against the identified compounds, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene Ontology analysis of biological processes and molecular functions were performed. Six proteins (IL1R1, IRAK4, MYD88, TIRAP, TLR4, and TRAF6) were identified from the KEGG pathway analysis and subjected to molecular docking study. Additionally, six best ligand efficiency compounds and positive control (aspirin) from each protein were evaluated for their stability using the molecular dynamics simulation study. Our study suggested that IL1R1, IRAK4, MYD88, TIRAP, TLR4, and TRAF6 proteins may be targeted by compounds in the methanolic extract of A. capitiformis stem to provide anti-inflammatory effects.

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.

Cardiomyocyte IL-1R2 protects heart from ischemia/reperfusion injury by attenuating IL-17RA-mediated cardiomyocyte apoptosis

Myocardial ischemia reperfusion (I/R) injury is a complex process with intense inflammatory response and cardiomyocyte apoptosis. As a decoy receptor of IL-1β, Interleukin-1 receptor type 2 (IL-1R2) inhibits IL-1β signaling. However, its role in I/R injury remains unknown. Here we found that the serum levels of IL-1R2 were significantly increased in patients with acute myocardial infarction (AMI) following interventional therapy. Similarly, after myocardial I/R surgery, IL-1R2 expression was significantly increased in heart of wild-type mice. In addition, IL-1R2-deficient mice heart showed enlarged infarct size, increased cardiomyocyte apoptosis together with reduced cardiac systolic function. Following exposure to hypoxia and reoxygenation (H/R), neonatal rat ventricular myocytes (NRVM) significantly increased IL-1R2 expression relying on NF-κB activation. Consistently, IL-1R2-deficient mice increased immune cells infiltrating into heart after surgery, which was relevant with cardiac damage. Additionally, IL-1R2 overexpression in cardiomyocyte protected cardiomyocyte against apoptosis through reducing the IL-17RA expression both in vivo and in vitro. Our results indicate that IL-1R2 protects cardiomyocytes from apoptosis, which provides a therapeutic approach to turn down myocardial I/R injury.

Neutrophil Homeostasis and Emergency Granulopoiesis: The Example of Systemic Juvenile Idiopathic Arthritis

Neutrophils are key pathogen exterminators of the innate immune system endowed with oxidative and non-oxidative defense mechanisms. More recently, a more complex role for neutrophils as decision shaping cells that instruct other leukocytes to fine-tune innate and adaptive immune responses has come into view. Under homeostatic conditions, neutrophils are short-lived cells that are continuously released from the bone marrow. Their development starts with undifferentiated hematopoietic stem cells that pass through different immature subtypes to eventually become fully equipped, mature neutrophils capable of launching fast and robust immune responses. During severe (systemic) inflammation, there is an increased need for neutrophils. The hematopoietic system rapidly adapts to this increased demand by switching from steady-state blood cell production to emergency granulopoiesis. During emergency granulopoiesis, the de novo production of neutrophils by the bone marrow and at extramedullary sites is augmented, while additional mature neutrophils are rapidly released from the marginated pools. Although neutrophils are indispensable for host protection against microorganisms, excessive activation causes tissue damage in neutrophil-rich diseases. Therefore, tight regulation of neutrophil homeostasis is imperative. In this review, we discuss the kinetics of neutrophil ontogenesis in homeostatic conditions and during emergency myelopoiesis and provide an overview of the different molecular players involved in this regulation. We substantiate this review with the example of an autoinflammatory disease, i.e. systemic juvenile idiopathic arthritis.

Single-Cell Transcriptome Profiling Identifies Phagocytosis-Related Dual-Feature Cells in A Model of Acute Otitis Media in Rats

Background

The molecular mechanisms of acute otitis media (AOM) development, and the intercellular crosstalk within the multicellular ecosystem of AOM, are not clear.

Methods

We established a model of AOM in rats (with normal rats as controls) and undertook single-cell RNA sequencing (scRNA-seq) for the middle-ear mucosa (MEM). Cell clustering and trajectory analyses were undertaken using Seurat and Monocle 2 packages in R software. Pathway analyses were done by gene set enrichment analysis (GSEA). Cell-cell interactions were inferred by CellChat. Cell scores were calculated to identify cells with dual-feature.

Results

A total of 7023 cells from three samples of inflamed MEM and 5258 cells from three samples of healthy MEM underwent scRNA-seq, which identified 20 cell clusters belonging to eight major cell types. After exposure to lipopolysaccharide, the MEM underwent significant conversion of cell types characterized by rapid infiltration of macrophages and neutrophils. M2 macrophages seemed to play a key part in inflammatory intercellular crosstalk, which facilitated the maintenance and proliferation of macrophages, cell chemotaxis, and regulation of the proinflammatory activities of cytokines. Three rare cell clusters with phagocytosis-related dual-feature were also identified. They coexisted with professional phagocytes in the MEM, and displayed distinct immunoregulatory functions by maintaining a normal immune microenvironment or influencing inflammation progression.

Conclusions

Macrophages might be the "master" initiators and regulators of the inflammatory response of the MEM to external stimuli. And their functions are fulfilled by a specific polarization status (M2) and sophisticated intercellular crosstalk via certain signaling pathways. Besides, the coexistence of professional phagocytes and non-professional phagocytes as well as their interplay in the MEM provides new clues for deciphering the underlying pathogenic mechanisms of AOM.

MMP9 mRNA is a potential diagnostic and treatment monitoring marker for PTSD: Evidence from mice and humans

Although matrix metalloproteinase 9 (MMP9) has been found associated with various psychiatric disorders and with threat memories in humans, its role in post-traumatic stress disorder (PTSD) and related animal models is understudied. Thus, we analyzed MMP9 mRNA expression kinetics during two different stress experiments, i.e., the Trier Social Stress Test and the dexamethasone suppression test (DST), in whole blood of two independent cohorts of PTSD patients vs. non-traumatized healthy controls (HC) and, moreover, in a mouse model of PTSD and in dexamethasone-treated mice. Besides MMP9, we quantified mRNA levels of four of its regulators, i.e., interleukin (IL)-1 receptor 1 and 2 (IL1R1, IL1R2), IL-6 receptor and tumor necrosis factor receptor 1 (TNFR1) in 10 patients exposed to the DST before vs. after successful PTSD psychotherapy vs. 13 HC and, except from Il6r, also in different brain regions of the PTSD mouse model. We are the first to show that blood MMP9 mRNA concentrations were elevated after acute dexamethasone in PTSD patients, improved upon partial remission of PTSD and were, furthermore, also elevated, together with its regulator Tnfr1, in the prefrontal cortex of PTSD-like mice. In contrast, blood TNFR1 and IL1R2 were markedly underexpressed in PTSD patients. In conclusion, we found translational evidence supporting that, I, TNFR1 and MMP9 mRNA expression might be involved in PTSD pathobiology, II, might constitute potential diagnostic blood biomarkers for PTSD and, importantly, III, post-dexamethasone blood MMP9 hyperexpression, which speculatively results from post-dexamethasone underexpression of IL1R2, might serve also as potential treatment monitoring biomarker for PTSD.

IL-1 Family Antagonists in Mouse and Human Skin Inflammation

Interleukin (IL)-1 family cytokines initiate inflammatory responses, and shape innate and adaptive immunity. They play important roles in host defense, but excessive immune activation can also lead to the development of chronic inflammatory diseases. Dysregulated IL-1 family signaling is observed in a variety of skin disorders. In particular, IL-1 family cytokines have been linked to the pathogenesis of psoriasis and atopic dermatitis. The biological activity of pro-inflammatory IL-1 family agonists is controlled by the natural receptor antagonists IL-1Ra and IL-36Ra, as well as by the regulatory cytokines IL-37 and IL-38. These four anti-inflammatory IL-1 family members are constitutively and highly expressed at steady state in the epidermis, where keratinocytes are a major producing cell type. In this review, we provide an overview of the current knowledge concerning their regulatory roles in skin biology and inflammation and their therapeutic potential in human inflammatory skin diseases. We further highlight some common misunderstandings and less well-known observations, which persist in the field despite recent extensive interest for these cytokines.

High-throughput analysis of lung immune cells in a combined murine model of agriculture dust-triggered airway inflammation with rheumatoid arthritis

Rheumatoid arthritis (RA)-associated lung disease is a leading cause of mortality in RA, yet the mechanisms linking lung disease and RA remain unknown. Using an established murine model of RA-associated lung disease combining collagen-induced arthritis (CIA) with organic dust extract (ODE)-induced airway inflammation, differences among lung immune cell populations were analyzed by single cell RNA-sequencing. Additionally, four lung myeloid-derived immune cell populations including macrophages, monocytes/macrophages, monocytes, and neutrophils were isolated by fluorescence cell sorting and gene expression was determined by NanoString analysis. Unsupervised clustering revealed 14 discrete clusters among Sham, CIA, ODE, and CIA+ODE treatment groups: 3 neutrophils (inflammatory, resident/transitional, autoreactive/suppressor), 5 macrophages (airspace, differentiating/recruited, recruited, resident/interstitial, and proliferative airspace), 2 T-cells (differentiating and effector), and a single cluster each of inflammatory monocytes, dendritic cells, B-cells and natural killer cells. Inflammatory monocytes, autoreactive/suppressor neutrophils, and recruited/differentiating macrophages were predominant with arthritis induction (CIA and CIA+ODE). By specific lung cell isolation, several interferon-related and autoimmune genes were disproportionately expressed among CIA and CIA+ODE (e.g. Oasl1, Oas2, Ifit3, Gbp2, Ifi44, and Zbp1), corresponding to RA and RA-associated lung disease. Monocytic myeloid-derived suppressor cells were reduced, while complement genes (e.g. C1s1 and Cfb) were uniquely increased in CIA+ODE mice across cell populations. Recruited and inflammatory macrophages/monocytes and neutrophils expressing interferon-, autoimmune-, and complement-related genes might contribute towards pro-fibrotic inflammatory lung responses following airborne biohazard exposures in setting of autoimmune arthritis and could be predictive and/or targeted to reduce disease burden.

SiglecF(HI) Marks Late-Stage Neutrophils of the Infarcted Heart: A Single-Cell Transcriptomic Analysis of Neutrophil Diversification

Background

Neutrophils are thought to be short‐lived first responders to tissue injuries such as myocardial infarction (MI), but little is known about their diversification or dynamics.

Methods and Results

We permanently ligated the left anterior descending coronary arteries of mice and performed single‐cell RNA sequencing and analysis of >28 000 neutrophil transcriptomes isolated from the heart, peripheral blood, and bone marrow of mice on days 1 to 4 after MI or at steady‐state. Unsupervised clustering of cardiac neutrophils revealed 5 major subsets, 3 of which originated in the bone marrow, including a late‐emerging granulocyte expressing SiglecF, a marker classically used to define eosinophils. SiglecF^HI neutrophils represented ≈25% of neutrophils on day 1 and grew to account for >50% of neutrophils by day 4 post‐MI. Validation studies using quantitative polymerase chain reaction of fluorescent‐activated cell sorter sorted Ly6G⁺SiglecF^HI and Ly6G⁺SiglecF^LO neutrophils confirmed the distinct nature of these populations. To confirm that the cells were neutrophils rather than eosinophils, we infarcted GATA‐deficient mice (∆dblGATA) and observed similar quantities of infiltrating Ly6G⁺SiglecF^HI cells despite marked reductions of conventional eosinophils. In contrast to other neutrophil subsets, Ly6G⁺SiglecF^HI neutrophils expressed high levels of Myc‐regulated genes, which are associated with longevity and are consistent with the persistence of this population on day 4 after MI.

Conclusions

Overall, our data provide a spatial and temporal atlas of neutrophil specialization in response to MI and reveal a dynamic proinflammatory cardiac Ly6G⁺SigF⁺(Myc⁺NFϰB⁺) neutrophil that has been overlooked because of negative selection.

Prolonged neutrophil survival at necrotic sites is a fundamental feature for tissue recovery and resolution of hepatic inflammation

Neutrophils were classically described as powerful effectors of acute inflammation, and their main purpose was assumed to be restricted to pathogen killing through production of oxidants. As consequence, neutrophils also may lead to significant collateral damage to the healthy tissues, and after performing these tasks, these leukocytes are supposed to die within tissues. However, there is a growing body of evidence showing that neutrophils also play a pivotal role in the resolution phases of inflammation, because they can modulate tissue environment due to secretion of different kind of cytokines. Drug-induced liver injury (DILI) is a worldwide concern being one of the most prevalent causes of liver transplantation, and is well established that there is an intense neutrophil recruitment into necrotic liver during DILI. However, information if such abundant granulocyte infiltration is also linked to the tissue repairing phase of hepatic injury is still largely elusive. Here, we investigated the dynamics of neutrophil trafficking within blood, bone marrow, and liver during hepatic inflammation, and how changes in their gene expression profile could drive the resolution events during acetaminophen (APAP)-induced liver injury. We found that neutrophils remained viable during longer periods following liver damage, because they avidly patrolled necrotic areas and up-regulated pro-resolutive genes, including Tgfb, Il1r2, and Fpr2. Adoptive transference of "resolutive neutrophils" harvested from livers at 72 h after injury to mice at the initial phases of injury (6 h after APAP) significantly rescued organ injury. Thus, we provide novel insights on the role of neutrophils not only in the injury amplification, but also in the resolution phases of inflammation.

Intracellular IL-1 Receptor Antagonist Isoform 1 Released from Keratinocytes upon Cell Death Acts as an Inhibitor for the Alarmin IL-1α

The inflammatory effects of IL-1α/β are controlled by IL-1R antagonist (IL-1Ra). One IL-1Ra isoform is secreted, whereas three other isoforms (intracellular IL-1Ra [icIL-1Ra] 1, 2, and 3) are supposed to remain intracellular because of the absence of a signal peptide. In contrast to the well-characterized function of the secreted isoform, the biological role of the intracellular isoforms remains largely unclear. icIL-1Ra1 represents the major isoform in keratinocytes. We created icIL-1Ra1^-/- mice and investigated the role of icIL-1Ra1 in Aldara (5% imiquimod)-induced psoriasis-like skin inflammation. Naive icIL-1Ra1^-/- mice bred habitually and exhibited a normal phenotype. icIL-1Ra1 deficiency aggravated Aldara-induced skin inflammation, as demonstrated by increased ear thickness and increased mRNA levels of key proinflammatory cytokines. No intracellular effect of icIL-1Ra1 could be detected in isolated keratinocytes using RNA-sequencing analysis; however, Aldara treatment led to caspase 1/11-, caspase 8-, and RIPK3-independent keratinocyte cell death accompanied by the release of both icIL-1Ra1 and IL-1α. Furthermore, blocking IL-1α attenuated the clinical severity of Aldara-induced ear thickening in icIL-1Ra1^-/- mice. Our data suggest that upon keratinocyte damage icIL-1Ra1 acts extracellularly as an antagonist of the alarmin IL-1α to immediately counteract its inflammatory effects.

Evaluation of Microglia/Macrophage Cells from Rat Striatum and Prefrontal Cortex Reveals Differential Expression of Inflammatory-Related mRNA after Methamphetamine

RNA sequencing (RNAseq) can be a powerful tool in the identification of transcriptional changes after drug treatment. RNAseq was utilized to determine expression changes in Fluorescence-activated cell sorted (FACS) CD11b/c+ cells from the striatum (STR) and prefrontal cortex (PFC) of male Sprague-Dawley rats after a methamphetamine (METH) binge dosing regimen. Resident microglia and infiltrating macrophages were collected 2 h or 3 days after drug administration. Gene expression changes indicated there was an increase toward an overall pro-inflammatory state, or M1 polarization, along with what appears to be a subset of cells that differentiated toward the anti-inflammatory M2 polarization. In general, there were significantly more mRNA expression changes in the STR than the PFC and more at 2 h post-binge METH than at 3 days post-binge METH. Additionally, Ingenuity^® Pathway Analysis along with details of RNA expression changes revealed cyclo-oxygenase 2 (COX2)-driven prostaglandin (PG) E2 synthesis, glutamine uptake, and the Nuclear factor erythroid2-related factor 2 (NRF2) canonical pathway in microglia were associated with the binge administration regimen of METH.

The role of interleukin-1 in general pathology

Interleukin-1, an inflammatory cytokine, is considered to have diverse physiological functions and pathological significances and play an important role in health and disease. In this decade, interleukin-1 family members have been expanding and evidence is accumulating that highlights the importance of interleukin-1 in linking innate immunity with a broad spectrum of diseases beyond inflammatory diseases. In this review, we look back on the definition of "inflammation" in traditional general pathology and discuss new insights into interleukin-1 in view of its history and the molecular bases of diseases, as well as current progress in therapeutics.

Early pathological characterization of murine dissecting abdominal aortic aneurysms

We report here on the early pathology of a well-established murine model of dissecting abdominal aortic aneurysms (AAAs). Continuous infusion of angiotensin II (AngII) into apolipoprotein E-deficient mice induces the formation of aortic dissection and expansion at some point after implantation of miniosmotic pumps containing AngII. While this model has been studied extensively at a chronic stage, we investigated the early pathology of dissecting AAA formation at multiple scales. Using high-frequency ultrasound, we screened 12-week-old male mice daily for initial formation of these aneurysmal lesions between days 3 and 10 post-implantation. We euthanized animals on the day of diagnosis of a dissecting AAA or at day 10 if no aneurysmal lesion developed. Aortic expansion and reduced vessel wall strain occurred in animals regardless of whether a dissecting AAA developed by day 10. The aortas of mice that did not develop dissecting AAAs showed intermediate changes in morphology and biomechanical properties. RNA sequencing and gene expression analysis revealed multiple proinflammatory and matrix remodeling genes to be upregulated in the suprarenal aorta of AngII-infused mice as compared to saline-infused controls. Histology and immunohistochemistry confirmed that extracellular matrix remodeling and inflammatory cell infiltration, notably neutrophils and macrophages, occurred in AngII-infused mice with and without dissecting AAAs but not saline-infused controls. Understanding early disease processes is a critical step forward in translating experimental results in cardiovascular disease research. This work advances our understanding of this well-established murine model with applications for improving early diagnosis and therapy of acute aortic syndrome in humans.

Paradoxical Role of Matrix Metalloproteinases in Liver Injury and Regeneration after Sterile Acute Hepatic Failure

Acetaminophen (APAP) poisoning is one of the leading causes of acute hepatic failure and liver transplantation is often the only lifesaving alternative. During the course of hepatocyte necrosis, an intense accumulation of neutrophils is often observed within the liver microenvironment. Despite the classic idea that neutrophil accumulation in tissues causes collateral tissue damage, there is a growing body of evidence showing that neutrophils can also orchestrate the resolution of inflammation. In this work, drug-induced liver injury was induced by oral administration of APAP and pharmacological intervention was made 12 h after this challenge. Liver injury and repair kinetics were evaluated by a novel combination of enzyme quantifications, ELISA, specific antagonists of neutrophil enzymes and confocal intravital microscopy. We have demonstrated that neutrophil infiltration is not only involved in injury amplification, but also in liver tissue repair after APAP-induced liver injury. In fact, while neutrophil depletion led to reduced hepatic necrosis during APAP poisoning, injury recovery was also delayed in neutropenic mice. The mechanisms underlying the neutrophil reparative role involved rapid degranulation and matrix metalloproteinases (MMPs) activity. Our data highlights the crucial role of neutrophils, in particular for MMPs, in the resolution phase of APAP-induced inflammatory response.

Regulation of IL-1 signaling by the decoy receptor IL-1R2

The pleiotropic cytokine IL-1 mediates its biological functions via association with the signaling receptor IL-1R1. Despite an apparent simplicity in IL-1 signaling activation, multiple negative regulators have been identified. The decoy receptor IL-1R2 (also known as CD121b) can suppress IL-1 maturation, sequester its active forms or hinder the signaling complex assembly. IL-1R2 is differentially expressed among numerous cell types and displays cis- and trans- modes of action. In this review, we link different forms of IL-1R2 (membrane-bound (mIL-1R2), secreted (sIL-1R2), shedded (shIL-1R2), cytoplasmic, and intracellular domain (IL-1R2^ICD) restricted) with their ability to interfere with IL-1, thereby regulating immune responses. We also discuss the intriguing possible function of IL-1R2 as a transcriptional regulator. Finally, we summarize the known impact of IL-1R2 in disease pathogenesis and discuss its potential role in treatment of inflammatory conditions.

Interleukin-1 Beta-A Friend or Foe in Malignancies?

Interleukin-1 beta (IL-1β) is induced by inflammatory signals in a broad number of immune cell types. IL-1β (and IL-18) are the only cytokines which are processed by caspase-1 after inflammasome-mediated activation. This review aims to summarize current knowledge about parameters of regulation of IL-1β expression and its multi-facetted role in pathophysiological conditions. IL-1 signaling activates innate immune cells including antigen presenting cells, and drives polarization of CD4+ T cells towards T helper type (Th) 1 and Th17 cells. Therefore, IL-1β has been attributed a largely beneficial role in resolving acute inflammations, and by initiating adaptive anti-tumor responses. However, IL-1β generated in the course of chronic inflammation supports tumor development. Furthermore, IL-1β generated within the tumor microenvironment predominantly by tumor-infiltrating macrophages promotes tumor growth and metastasis via different mechanisms. These include the expression of IL-1 targets which promote neoangiogenesis and of soluble mediators in cancer-associated fibroblasts that evoke antiapoptotic signaling in tumor cells. Moreover, IL-1 promotes the propagation of myeloid-derived suppressor cells. Using genetic mouse models as well as agents for pharmacological inhibition of IL-1 signaling therapeutically applied for treatment of IL-1 associated autoimmune diseases indicate that IL-1β is a driver of tumor induction and development.

The family of the interleukin-1 receptors

The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.

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.

Interleukin-1 Receptor 2: A New Biomarker for Sepsis Diagnosis and Gram-Negative/Gram-Positive Bacterial Differentiation

This study was undertaken to explore the value of interleukin-1 receptor 2 (IL1R2) as a novel potential biomarker for diagnosis of sepsis and discrimination of gram-negative (G)/gram-positive (G) bacterial sepsis. The study was performed in Kunming mice and septic patients. Inactive Escherichia coli or Staphylococcus aureus were used to stimulate Kunming mice (10 CFU/kg). In clinical study, septic patients with different pathogen infection were studied, and healthy volunteers and patients with systemic inflammatory response syndrome without definite infection were enrolled as control. IL1R2 transcriptions of human subjects' peripheral leukocytes were measured by real-time quantitative polymerase chain reaction assay. IL1R2 serum concentrations of mice and human subjects were measured by enzyme-linked immunosorbent assay. The value of IL1R2 as a biomarker was compared with procalcitonin (PCT), C-reactive protein (CRP), and Acute Physiology and Chronic Health Evaluation II (APACHE II). The results showed that IL1R2 expression was upregulated in mice treated with inactive Escherichia coli and septic patients. The elevation of serum IL1R2 was more significant in septic patients infected by Escherichia coli or G bacteria than in those infected by Staphylococcus aureus or G bacteria. For sepsis diagnosis and G/G bacterial sepsis discrimination, serum IL1R2 was more sensitive and specific than the traditional biomarkers such as PCT, CRP, and APACHE II as shown by the receiver operating characteristic curves. It was suggested that IL1R2 was a potential biomarker for diagnosis and G/G bacterial differentiation in sepsis.

Resveratrol enhances IL-4 receptor-mediated anti-inflammatory effects in spinal cord and attenuates neuropathic pain following sciatic nerve injury

Resveratrol has been showed to relieve neuropathic pain through its anti-inflammatory effects on the peripheral nerve system. However, it is not clear whether resveratrol, especially when administered systemically, is effective in alleviating the peripheral neuropathy-induced imbalance between pro- and anti-inflammatory responses in the central nervous system. To test this, we used a rat neuropathic pain model resulting from chronic constriction injury of the sciatic nerve. Resveratrol (200 mg/kg) or vehicle (dimethylsulfoxide) were administered intraperitoneally once daily for 14 consecutive days after chronic constriction injury. We found that resveratrol attenuated mechanical allodynia and thermal hyperalgesia in rats with chronic constriction injury. After 14 days of resveratrol treatment, expression of several anti-inflammatory cytokine receptors, including IL-1RA and IL-1R2, was increased in the dorsal spinal cord of rats with chronic constriction injury, and IL-4Rα was increased in dorsal spinal cord neurons. Knockdown of IL-4Rα in a neuronal cell line reversed the resveratrol-induced upregulation of IL-1RA and IL-1R2. These results indicate that resveratrol enhances IL-4 receptor-mediated anti-inflammatory responses in the spinal cord and thus might contribute to the alleviation of central sensitization following peripheral nerve injury.

Integrative transcriptomic analysis reveals key drivers of acute peanut allergic reactions

Mechanisms driving acute food allergic reactions have not been fully characterized. We profile the dynamic transcriptome of acute peanut allergic reactions using serial peripheral blood samples obtained from 19 children before, during, and after randomized, double-blind, placebo-controlled oral challenges to peanut. We identify genes with changes in expression triggered by peanut, but not placebo, during acute peanut allergic reactions. Network analysis reveals that these genes comprise coexpression networks for acute-phase response and pro-inflammatory processes. Key driver analysis identifies six genes (LTB4R, PADI4, IL1R2, PPP1R3D, KLHL2, and ECHDC3) predicted to causally modulate the state of coregulated networks in response to peanut. Leukocyte deconvolution analysis identifies changes in neutrophil, naive CD4+ T cell, and macrophage populations during peanut challenge. Analyses in 21 additional peanut allergic subjects replicate major findings. These results highlight key genes, biological processes, and cell types that can be targeted for mechanistic study and therapeutic targeting of peanut allergy.

Deficiency in IL-1 Receptor Type 2 Aggravates K/BxN Serum Transfer-Induced Arthritis in Mice but Has No Impact on Systemic Inflammatory Responses

The biological activity of IL-1 is tightly regulated by the specific receptor antagonist (IL-1Ra) and the decoy receptor IL-1 receptor type 2 (IL-1R2). The role of IL-1Ra has been well demonstrated in IL-1Ra-deficient mice. In contrast, the role of endogenous IL-1R2 remains widely unknown. To define the functional role of endogenous IL-1R2 in the K/BxN serum transfer arthritis model and in IL-1β- or LPS-induced systemic inflammation in vivo, IL-1R2^-/- mice were created and compared with wild type mice. IL-1R2^-/- mice bred habitually and exhibited a normal phenotype. IL-1R2 deficiency aggravated arthritis severity and increased mRNA levels for key cytokines and chemokines such as IL-6, IL-1β, Cxcl-1, and Cxcl-2 significantly in ankles. There was no effect of IL-1R2 deficiency on the cell-autonomous cytokine response to IL-1β in the tested cell types, i.e., neutrophils, macrophages, and fibroblasts, but IL-1R2 deficiency on neutrophils increased the IL-1-induced response of fibroblasts in trans. Furthermore, IL-1β induced shedding of IL-1R2 in vivo. Inflammatory responses to IL-1β and LPS-induced mortality were not different in IL-1R2^-/- compared with wild type mice. Our data demonstrate that the decoy receptor IL-1R2 plays an important inhibitory role in local IL-1- and neutrophil-dependent tissue inflammation as shown in the K/BxN serum transfer arthritis model. In contrast to IL-1Ra, IL-1R2 appears to be less crucial for systemic responses to acute administration of IL-1 or LPS.

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.

Staphylococcus aureus Induces Shedding of IL-1RII in Monocytes and Neutrophils

Interleukin 1 (IL-1) β is a critical cytokine that orchestrates host defenses against Staphylococcus aureus and is crucial for the eradication of bacteria. The production and action of IL-1β are regulated by multiple control pathways. Among them, IL-1RII (the type II IL-1 receptor) acts as a decoy receptor and has been shown to regulate the biological effects of IL-1β. High levels of soluble IL-1RII are present in septic patients; however, the stimuli that regulate the expression and release of IL-1RII in pathological conditions are incompletely elucidated. In the present study, we demonstrated the ability of S. aureus and protein A to induce IL-1RII shedding in myeloid cells. The positive modulation of IL-1RII expression and cleavage was associated with the failure to detect IL-1β in response to S. aureus both in vitro and in vivo, suggesting that the soluble form of the receptor could be masking the availability of IL-1β. The absence of detectable IL-1β was associated with low levels of inflammatory cytokines and chemokines known to be regulated by IL-1β and with increased bacterial persistence. Modulation of decoy receptors during systemic S. aureus infection is proposed as a new strategy used by this bacterium to evade the immune response.

Generation and Characterization of Mice Expressing a Conditional Allele of the Interleukin-1 Receptor Type 1

The cytokines IL-1α and IL-1β exert powerful pro-inflammatory actions throughout the body, mediated primarily by the intracellular signaling capacity of the interleukin-1 receptor (IL-1R1). Although Il1r1 knockout mice have been informative with respect to a requirement for IL-1R1 signaling in inflammatory events, the constitutive nature of gene elimination has limited their utility in the assessment of temporal and spatial patterns of cytokine action. To pursue such questions, we have generated C57Bl/6J mice containing a floxed Il1r1 gene (Il1r1^loxP/loxP), with loxP sites positioned to flank exons 3 and 4 and thereby the ability to spatially and temporally eliminate Il1r1 expression and signaling. We found that Il1r1^loxP/loxP mice breed normally and exhibit no gross physical or behavioral phenotypes. Moreover, Il1r1^loxP/loxP mice exhibit normal IL-1R1 receptor expression in brain and spleen, as well as normal IL-1R1-dependent increases in serum IL-6 following IL-1α injections. Breeding of Il1r1^loxP/loxP mice to animals expressing a cytomegalovirus (CMV)-driven Cre recombinase afforded efficient excision at the Il1r1 locus. The Il1r1^loxP/loxP line should be a valuable tool for the assessment of contributions made by IL-1R1 signaling in diverse cell types across development.

The soluble interleukin-6 receptor and related proteins

Interleukin-6 is a cytokine involved in the regulation of the immune system and the central nervous system. Interleukin-6 binds to an interleukin-6 receptor, and then associates with a dimer of the ubiquitously expressed gp130 receptor subunit, which initiates intracellular signaling. The interleukin-6 receptor is found in a soluble form, which is generated by proteolytic cleavage and also to a minor extent by translation from an alternatively spliced mRNA. The complex of interleukin-6 bound to the interleukin-6 receptor can stimulate cells, which only express gp130. Such cells are not responsive to interleukin-6 alone. We have for the first time identified the molecular basis of pro-and anti-inflammatory properties of interleukin-6 and we have defined the generation of the soluble IL-6R as a crucial point in the regulation between these two properties. Furthermore, we have deduced a therapeutic principle, which enables us to exclusively block the pro-inflammatory activities of this important cytokine.

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.

Transcriptional analysis identifies key genes involved in metabolism, fibrosis/tissue repair and the immune response against Fasciola hepatica in sheep liver

BACKGROUND

Although fascioliasis has been relatively well studied, little is known about the molecular basis of this disease. This is particularly relevant, considering the very different response that sheep have to Fasciola hepatica relative to cattle. The acute phase of this disease is severe in sheep, whereas chronic fascioliasis is more common in cattle.

METHODS

To begin to explore the host-response to Fasciola in sheep and improve the understanding of the host-pathogen interactions during the parasite's migration through liver parenchyma to the bile duct, we used RNA sequencing (RNA-seq) to investigate livers from sheep infected for eight weeks compared with those from uninfected controls.

RESULTS

This study identified 572 and 42 genes that were up- and down-regulated, respectively, in infected livers relative to uninfected controls. Our molecular findings provide significant new insights into the mechanisms linked to metabolism, fibrosis and tissue-repair in sheep, and highlight the relative importance of specific components of immune response pathways, which appear to be driven toward a suppression of inflammation.

CONCLUSIONS

This study is, to our knowledge, the first detailed investigation of the transcriptomic responses in the liver tissue of any host to F. hepatica infection. It defines the involvement of specific genes associated with the host's metabolism, immune response and tissue repair/regeneration, and highlights an apparent overlapping function of many genes involved in these processes.

Microarray analysis identifies IL-1 receptor type 2 as a novel candidate biomarker in patients with acute respiratory distress syndrome

Background

Acute respiratory distress syndrome (ARDS) is a disease associated with a high mortality rate. The initial phase is characterized by induction of inflammatory cytokines and chemokines and influx of circulating inflammatory cells, including macrophages which play a pivotal role in the innate and adaptive immune responses to injury. Growing evidence points to phenotypic heterogeneity and plasticity between various macrophage activation states.

Methods

In this study, gene expression in alveolar macrophages and circulating leukocytes from healthy control subjects and patients with ARDS was assessed by mRNA microarray analysis.

Results

Both alveolar macrophages and circulating leukocytes demonstrated up-regulation of genes encoding chemotactic factors, antimicrobial peptides, chemokine receptors, and matrix metalloproteinases. Two genes, the pro-inflammatory S100A12 and the anti-inflammatory IL-1 decoy receptor IL-1R2 were significantly induced in both cell populations in ARDS patients, which was confirmed by protein quantification. Although S100A12 levels did not correlate with disease severity, there was a significant association between early plasma levels of IL-1R2 and APACHE III scores at presentation. Moreover, higher levels of IL-1R2 in plasma were observed in non-survivors as compared to survivors at later stages of ARDS.

Conclusions

These results suggest a hybrid state of alveolar macrophage activation in ARDS, with features of both alternative activation and immune tolerance/deactivation.. Furthermore, we have identified a novel plasma biomarker candidate in ARDS that correlates with the severity of systemic illness and mortality.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0190-x) contains supplementary material, which is available to authorized users.

Severe neutrophil-dominated inflammation and enhanced myelopoiesis in IL-33-overexpressing CMV/IL33 mice

IL-33 is a cytokine of the IL-1 family, which signals through the ST2 receptor. Previous studies emphasized a role for IL-33 in shaping innate and adaptive immune responses. IL-33 was also reported to modulate myelopoiesis and myeloid cell activity. In this article, we describe IL-33-overexpressing CMV/IL33 and LysM/IL33 mice, which display an inflammatory phenotype associated with growth retardation and paw swelling. The phenotype of CMV/IL33 mice is dependent on activation of the ST2 receptor and is characterized by extensive neutrophil infiltration into different organs, including the paws. Local or systemic levels of proinflammatory mediators such as IL-1β, Cxcl-1, G-CSF, and IL-6 are increased. CMV/IL-33 mice also suffer from anemia, thrombocytosis, and a marked dysregulation of myelopoiesis, leading to an important increase in myeloid cell production or accumulation in bone marrow (BM), spleen, and peripheral blood. Consistently, recombinant IL-33 induced proliferation of myeloid lineage cells in BM-derived granulocyte cultures, whereas IL-33 knockout mice exhibited minor deficiencies in spleen and BM myeloid cell populations. Our observations reveal a neutrophil-dominated inflammatory phenotype in IL-33-overexpressing CMV/IL33 and LysM/IL33 mice, and highlight important regulatory effects of IL-33 on myelopoiesis in vitro and in vivo, where excessive IL-33 signaling can translate into the occurrence of a myeloproliferative disorder.

ADAM17 regulates IL-1 signaling by selectively releasing IL-1 receptor type 2 from the cell surface

Interleukin (IL)-1 is one of the most evolutionarily conserved cytokines and plays an essential role in the regulation of innate immunity. IL-1 binds to two different receptors, IL-1R1 and IL-1R2, which share approximately 28% amino acid homology. IL-1R1 contains a cytoplasmic domain and is capable of transducing cellular signals; by contrast, IL-1R2 lacks a functional cytoplasmic domain and serves as a decoy receptor for IL-1. Interestingly, IL-1R2 is proteolytically cleaved and also functions as a soluble receptor that blocks IL-1 activity. In the present study, we examined the shedding properties of IL-1R2 and demonstrate that ADAM17 is de facto the major sheddase for IL-1R2 and that introducing a mutation into the juxta-membrane domain of IL-1R2 significantly desensitizes IL-1R2 to proteolytic cleavage. IL-1R1 was almost insensitive to ADAM17-dependent cleavage; however, the replacement of the juxta-membrane domain of IL-R1 with that of IL-1R2 significantly increased the sensitivity of IL-1R1 to shedding. Furthermore, we demonstrate that ADAM17 indirectly enhances IL-1 signaling in a cell-autonomous manner by selectively cleaving IL-1R2. Taken together, the data collected in the present study indicate that ADAM17 affects sensitivity to IL-1 by changing the balance between IL-1R1 and the decoy receptor IL-1R2.