Combinatorial targeting of TSLP, IL-25, and IL-33 in type 2 cytokine-driven inflammation and fibrosis

Perivascular stromal cells: Directors of tissue immune niches

Perivascular niches are specialized microenvironments where stromal and immune cells interact with vasculature to monitor tissue status. Adventitial perivascular niches surround larger blood vessels and other boundary sites, supporting collections of immune cells, stromal cells, lymphatics, and neurons. Adventitial fibroblasts (AFs), a subtype of mesenchymal stromal cell, are the dominant constituents in adventitial spaces, regulating vascular integrity while organizing the accumulation and activation of a variety of interacting immune cells. In contrast, pericytes are stromal mural cells that support microvascular capillaries and surround organ-specific parenchymal cells. Here, we outline the unique immune and non-immune composition of perivascular tissue immune niches, with an emphasis on the heterogeneity and immunoregulatory functions of AFs and pericytes across diverse organs. We will discuss how perivascular stromal cells contribute to the regulation of innate and adaptive immune responses and integrate immunological signals to impact tissue health and disease.

Baicalein Protects Against Aspergillus fumigatus Keratitis by Reducing Fungal Load and Inhibiting TSLP-Induced Inflammatory Response

Purpose

To investigate the antifungal and anti-inflammatory effects of baicalein on Aspergillus fumigatus (A. fumigatus) keratitis and the underlying mechanisms.

Methods

The noncytotoxic antifungal concentration of baicalein was determined using CCK8, cell scratch assay, minimum inhibitory concentration, biofilm formation, scanning electron microscopy, propidium iodide uptake test and adherence assay in vitro and Draize test in vivo. In fungal keratitis (FK) mouse models, clinical score and plate count were used to evaluate FK severity, and myeloperoxidase assay and immunofluorescence staining were performed to examine neutrophil infiltration and activity. Real-time PCR, ELISA, and Western blot were performed to explore the anti-inflammatory activity of baicalein and the underlying mechanisms in vivo and in vitro.

Results

Baicalein at 0.25 mM (noncytotoxic) significantly inhibited A. fumigatus growth, biofilm formation, and adhesion in vitro. In A. fumigatus keratitis mice, baicalein mitigated FK severity, reduced fungal load, and inhibited neutrophil infiltration and activity. Baicalein not only suppressed mRNA and protein levels of proinflammatory factors IL-1β, IL-6, and TNF-α, but also inhibited the expression of thymic stromal lymphopoietin (TSLP) and TSLP receptor (TSLPR) in vivo and in vitro. In HCECs, mRNA and protein levels of IL-1β, IL-6, and TNF-α were significantly lower in the TSLP siRNA–treated group, while higher in the rTSLP-treated group than in the corresponding control. Baicalein treatment significantly inhibited rTSLP induced the expression of IL-1β, IL-6, and TNF-α.

Conclusions

Baicalein plays a protective role in mouse A. fumigatus keratitis by inhibiting fungal growth, biofilm formation, and adhesion, and suppressing inflammatory response via downregulation of the TSLP/TSLPR pathway.

Astegolimab (anti-ST2) efficacy and safety in adults with severe asthma: A randomized clinical trial

BACKGROUND

The IL-33/ST2 pathway is linked with asthma susceptibility. Inhaled allergens, pollutants, and respiratory viruses, which trigger asthma exacerbations, induce release of IL-33, an epithelial-derived "alarmin." Astegolimab, a human IgG₂ mAb, selectively inhibits the IL-33 receptor, ST2. Approved biologic therapies for severe asthma mainly benefit patients with elevated blood eosinophils (type 2-high), but limited options are available for patients with low blood eosinophils (type 2-low). Inhibiting IL-33 signaling may target pathogenic pathways in a wider spectrum of asthmatics.

OBJECTIVES

This study evaluated astegolimab efficacy and safety in patients with severe asthma.

METHODS

This double-blind, placebo-controlled, dose-ranging study (ZENYATTA [A Study to Assess the Efficacy and Safety of MSTT1041A in Participants With Uncontrolled Severe Asthma]) randomized 502 adults with severe asthma to subcutaneous placebo or 70-mg, 210-mg, or 490-mg doses of astegolimab every 4 weeks. The primary endpoint was the annualized asthma exacerbation rate (AER) at week 54. Enrollment caps ensured ∼30 patients who were eosinophil-high (≥300 cells/μL) and ∼95 patients who were eosinophil-low (<300 cells/μL) per arm.

RESULTS

Overall, adjusted AER reductions relative to placebo were 43% (P = .005), 22% (P = .18), and 37% (P = .01) for 490-mg, 210-mg, and 70-mg doses of astegolimab, respectively. Adjusted AER reductions for patients who were eosinophil-low were comparable to reductions in the overall population: 54% (P = .002), 14% (P = .48), and 35% (P = .05) for 490-mg, 210-mg, and 70-mg doses of astegolimab. Adverse events were similar in astegolimab- and placebo-treated groups.

CONCLUSIONS

Astegolimab reduced AER in a broad population of patients, including those who were eosinophil-low, with inadequately controlled, severe asthma. Astegolimab was safe and well tolerated.

The Concept of Pathogenic TH2 Cells: Collegium Internationale Allergologicum Update 2021

T helper (TH) cells have evolved into distinct subsets that mediate specific immune responses to protect the host against a myriad of infectious and noninfectious challenges. However, if dysregulated, TH-cell subsets can cause inflammatory disease. Emerging evidence now suggests that human allergic disease is caused by a distinct subpopulation of pathogenic TH2 cells. Pathogenic TH2 cells from different type-2-driven diseases share a core phenotype and show overlapping functional attributes. The unique differentiation requirements, activating signals, and metabolic characteristics of pathogenic TH2 cells are just being discovered. A better knowledge of this particular TH2 cell population will enable the specific targeting of disease-driving pathways in allergy. In this review, we introduce a rational for classifying TH cells into distinct subsets, discuss the current knowledge on pathogenic TH2 cells, and summarize their involvement in allergic diseases.

Novel Immune Subsets and Related Cytokines: Emerging Players in the Progression of Liver Fibrosis

Liver fibrosis is a pathological process caused by persistent chronic injury of the liver. Kupffer cells, natural killer (NK) cells, NKT cells, and dendritic cells (DCs), which are in close contact with T and B cells, serve to bridge innate and adaptive immunity in the liver. Meanwhile, an imbalanced inflammatory response constitutes a challenge in liver disease. The dichotomous roles of novel immune cells, including T helper 17 (Th17), regulatory T cells (Tregs), mucosa-associated invariant T cells (MAIT), and innate lymphoid cells (ILCs) in liver fibrosis have gradually been revealed. These cells not only induce damage during liver fibrosis but also promote tissue repair. Hence, immune cells have unique, and often opposing, roles during the various stages of fibrosis. Due to this heterogeneity, the treatment, or reversal of fibrosis through the target of immune cells have attracted much attention. Moreover, activation of hepatic stellate cells (HSCs) constitutes the core of fibrosis. This activation is regulated by various immune mediators, including Th17, Th22, and Th9, MAIT, ILCs, and γδ T cells, as well as their related cytokines. Thus, liver fibrosis results from the complex interaction of these immune mediators, thereby complicating the ability to elucidate the mechanisms of action elicited by each cell type. Future developments in biotechnology will certainly aid in this feat to inform the design of novel therapeutic targets. Therefore, the aim of this review was to summarize the role of specific immune cells in liver fibrosis, as well as biomarkers and treatment methods related to these cells.

Early Events Triggering the Initiation of a Type 2 Immune Response

Type 2 immune responses are typically associated with protection against helminth infections and also with harmful inflammation in response to allergens. Recent advances have revealed that type 2 immunity also contributes to sterile inflammation, cancer, and microbial infections. However, the early events that initiate type 2 immune responses remain poorly defined. New insights reveal major contributions from danger-associated molecular patterns (DAMPs) in the initiation of type 2 immune responses. In this review, we examine the molecules released by the host and pathogens and the role they play in mediating the initiation of mammalian innate type 2 immune responses under a variety of conditions.

Suppression of Hippo Pathway by Food Allergen Exacerbates Intestinal Epithelia Instability and Facilitates Hypersensitivity

SCOPE

Hippo signaling is a crucial pathway in innate immune responses, but the relationship between food allergy and Hippo pathway is unknown. The aim of this work is to investigate the regulation of food allergy by Hippo pathway and reveal the molecular mechanisms.

METHODS AND RESULTS

Two food allergens tropomyosin and ovalbumin are used to challenge a mouse model and CMT93 intestinal epithelia cell model. The allergic responses and the activation of Hippo pathway are tested in these models. In the mouse model, both allergens trigged significant allergic responses, and Hippo pathway is suppressed after allergen challenge. In CMT93, both allergens upregulate the expression of allergic cytokines thymic stromal lymphopoietin, interleukin (IL)-25, and IL-33. In TAZ KD CMT93, the Hippo pathway is blocked, and the expression of allergenic cytokines are also suppressed.

CONCLUSIONS

Both in vivo and in vitro data demonstrate that the two food allergens suppressed Hippo pathway by downregulating TAZ expression, resulting in intestinal epithelia instability, and finally leading to hypersensitivity reactions. These findings provide potential therapeutic targets and molecular markers for food allergy, and provide dietary guidelines for allergenic individuals.

Interleukin (IL)-33 is dispensable for Schistosoma mansoni worm maturation and the maintenance of egg-induced pathology in intestines of infected mice

BACKGROUND

Schistosomes are trematode worms that dwell in their definitive host's blood vessels, where females lay eggs that need to be discharged into the environment with host excreta to maintain their life-cycle. Both worms and eggs require type 2 immunity for their maturation and excretion, respectively. However, the immune molecules that orchestrate such immunity remain unclear. Interleukin (IL)-33 is one of the epithelium-derived cytokines that induce type 2 immunity in tissues. The aim of this study was to determine the role of IL-33 in the maturation, reproduction and excretion of Schistosoma mansoni eggs, and in the maintenance of egg-induced pathology in the intestines of mice.

METHODS

The morphology of S. mansoni worms and the number of eggs in intestinal tissues were studied at different time points post-infection in S. mansoni-infected IL-33-deficient (IL-33-/-) and wild-type (WT) mice. IL-5 and IL-13 production in the spleens and mesenteric lymph nodes were measured. Tissue histology was performed on the terminal ilea of both infected and non-infected mice.

RESULTS

Worms from IL-33-/- and WT mice did not differ morphologically at 4 and 6 weeks post-infection (wpi). The number of eggs in intestinal tissues of IL-33-/- and WT mice differed only slightly. At 6 wpi, IL-33-/- mice presented impaired type 2 immunity in the intestines, characterized by a decreased production of IL-5 and IL-13 in mesenteric lymph nodes and fewer inflammatory infiltrates with fewer eosinophils in the ilea. There was no difference between IL-33-/- and WT mice in the levels of IL-25 and thymic stromal lymphopoietin (TSLP) in intestinal tissues.

CONCLUSIONS

Despite its ability to initiate type 2 immunity in tissues, IL-33 alone seems dispensable for S. mansoni maturation and its absence may not affect much the accumulation of eggs in intestinal tissues. The transient impairment of type 2 immunity observed in the intestines, but not spleens, highlights the importance of IL-33 over IL-25 and TSLP in initiating, but not maintaining, locally-induced type 2 immunity in intestinal tissues during schistosome infection. Further studies are needed to decipher the role of each of these molecules in schistosomiasis and clarify the possible interactions that might exist between them.

The IL-33/ST2 pathway is not essential to Th2 stimulation but is key for modulation and survival during chronic infection with Schistosoma mansoni in mice

Morbidity during chronic schistosomiasis has been associated with the induction and modulation of type-2 granulomatous inflammatory response induced by antigens secreted by the eggs, which become trapped in capillary venules of the host tissues, especially in the liver and intestines. IL-33, an alarmin released after cell damage, binds to its ST2 (suppressor of tumorigenicity 2) receptor, expressed in an variety of immune cells, including ILC2 and macrophages, and stimulates the early production of IL-5 and IL-13, which leads to eosinophil infiltration and activation of a Th2 response. However, the role of IL-33/ST2 activation on Schistosoma-induced granuloma formation and modulation is mostly unknown. In the current work, we comparatively evaluated the immune response and granuloma formation in wild-type BALB/c (WT) and BALB/c mice genetically deficient in the IL-33 receptor (ST2^-/-) experimentally infected with Schistosoma mansoni. Mice were infected with 25 or 50 S. mansoni cercariae and followed for up to 14 weeks to assess mortality. Mice from each experimental group were comparatively evaluated for parasite burden, liver immune response, and granuloma appearance during acute and chronic schistosomiasis. Our data showed that the number of circulating worms and eggs retained in the liver and eliminated in the feces was similar in WT and ST2^-/- infected mice, but infected ST2^-/- mice presented an enhanced rate of mortality. Interestingly, the production of type-2 cytokines by soluble egg antigens (SEA)-stimulated spleen cells, the serum concentrations of IL-5 and Immunoglobulin (Ig)-E, and the level of parasite-reactive IgG1 were similar in infected mice of both experimental groups. The concentrations of IL-4, IL-5, IL-13, and IFN-γ in liver homogenate of infected mice also did not differ between the strains at acute schistosomiasis, but there was a significant increase in IL-17 levels in ST2^-/- infected mice at this phase. On the other hand, IL-4, IL-13, IL-10, IL-17, and IFN-γ concentrations were reduced and the ratios of IL-4/IFN-γ and IL-17/IFN-γ were higher in liver homogenate of chronically infected ST2^-/- mice, suggesting unbalanced Th2 and Th17 responses. Moreover, liver granulomas of ST2^-/- mice were larger and disorganized, showing an intense cellular infiltrate, rich in eosinophils and neutrophils. Our results suggest that the absence of the IL-33/ST2 pathway is not essential for the Schistosoma-induced Th2 response, but is necessary to prevent host mortality by modulating granuloma-mediated pathology.

Fibrosis: from mechanisms to medicines

Fibrosis can affect any organ and is responsible for up to 45% of all deaths in the industrialized world. It has long been thought to be relentlessly progressive and irreversible, but both preclinical models and clinical trials in various organ systems have shown that fibrosis is a highly dynamic process. This has clear implications for therapeutic interventions that are designed to capitalize on this inherent plasticity. However, despite substantial progress in our understanding of the pathobiology of fibrosis, a translational gap remains between the identification of putative antifibrotic targets and conversion of this knowledge into effective treatments in humans. Here we discuss the transformative experimental strategies that are being leveraged to dissect the key cellular and molecular mechanisms that regulate fibrosis, and the translational approaches that are enabling the emergence of precision medicine-based therapies for patients with fibrosis.

The expression of interleukin-25 increases in human coronary artery disease and is associated with the severity of coronary stenosis

Objective:

Interleukin (IL) 25, also known as IL-17E, is an inflammatory cytokine and has been demonstrated to be closely related to cardiovascular diseases by regulating immunity and inflammation, including atherosclerosis. This study was aimed to evaluate the expression of IL-25 in patients with coronary artery disease (CAD).

Methods:

In this study, the expression of IL-25 in normal (n=6) and atherosclerotic (n=10) human coronary arteries was detected by immunofluorescent staining. In addition, the serum IL-25, IL-6, and tumor necrosis factor (TNF) α concentrations in stable angina pectoris (SAP, n=44), unstable angina pectoris (UAP, n=46), acute myocardial infarction (AMI, n=34), and non-CAD (control, n=36) were measured using enzyme-linked immunosorbent assay (ELISA) kits.

Results:

IL-25 was significantly increased in coronary arteries of CAD patients when compared with normal coronary arteries, with macrophages and T lymphocytes being the sources of IL-25, especially macrophages. Moreover, the serum concentrations of IL-25 were markedly elevated in CAD patients and gradually increased in SAP, UAP, and AMI groups. In addition, IL-25 levels were positively correlated with the IL-6 and TNF-α levels, and Gensini score in CAD patients. Logistic regression analysis showed that IL-25 was independently positively correlated with the occurrence of acute coronary syndrome (ACS). A receiver operator characteristic curve suggested that IL-25 presented a significant diagnosis value in ACS.

Conclusion:

IL-25 is increased in the coronary arteries and serum of CAD patients and is associated with the severity of coronary stenosis and the occurrence of ACS, suggesting that IL-25 may be one of the biomarkers of ACS. (Anatol J Cardiol 2020; 23: 151-9)

Regulation of Skin Barrier Function via Competition between AHR Axis versus IL-13/IL-4‒JAK‒STAT6/STAT3 Axis: Pathogenic and Therapeutic Implications in Atopic Dermatitis

Atopic dermatitis (AD) is characterized by skin inflammation, barrier dysfunction, and chronic pruritus. As the anti-interleukin-4 (IL-4) receptor α antibody dupilumab improves all three cardinal features of AD, the type 2 cytokines IL-4 and especially IL-13 have been indicated to have pathogenic significance in AD. Accumulating evidence has shown that the skin barrier function is regulated via competition between the aryl hydrocarbon receptor (AHR) axis (up-regulation of barrier) and the IL-13/IL-4‒JAK‒STAT6/STAT3 axis (down-regulation of barrier). This latter axis also induces oxidative stress, which exacerbates inflammation. Conventional and recently developed agents for treating AD such as steroid, calcineurin inhibitors, cyclosporine, dupilumab, and JAK inhibitors inhibit the IL-13/IL-4‒JAK‒STAT6/STAT3 axis, while older remedies such as coal tar and glyteer are antioxidative AHR agonists. In this article, I summarize the pathogenic and therapeutic implications of the IL-13/IL-4‒JAK‒STAT6/STAT3 axis and the AHR axis in AD.

Combination blockade of OX40L and CD30L inhibits allergen-driven memory TH2 cell reactivity and lung inflammation

BACKGROUND

The selective reduction of memory T_H2 cell responses could be key to affording tolerance and protection from the recurrence of damaging allergic pathology.

OBJECTIVE

We asked whether TNF family costimulatory molecules cooperated to promote accumulation and reactivity of effector memory CD4 T cells to inhaled complex allergen, and whether their neutralization could promote airway tolerance to subsequent reexposure to allergen.

METHODS

Mice were sensitized intraperitoneally or intranasally with house dust mite and challenged with intranasal allergen after memory had developed. We assessed whether single or combined blockade of OX40L/CD252 and CD30L/CD153 inhibited memory T cells from driving acute asthmatic lung inflammation and protected mice following exposure to allergen at a later time.

RESULTS

OX40- or CD30-deficient animals showed strong or partial protection against allergic airway inflammation; however, neutralizing either molecule alone during the secondary response to allergen had little effect on the frequency of effector memory CD4 T cells formed and acute lung inflammation. In contrast, a significant reduction in eosinophilic inflammation was observed when OX40L and CD30L were simultaneously neutralized, with dual blockade inhibiting effector memory T_H2 cell expansion in the lungs, whereas formation of peripherally induced regulatory T cells remained intact. Moreover, dual blockade during the secondary response resulted in a tolerogenic state such that mice did not develop a normal tertiary memory T_H2 cell and lung inflammatory response when challenged weeks later with allergen.

CONCLUSION

Memory T-cell responses to complex allergens are controlled by several TNF costimulatory interactions, and their combination targeting might represent a strategy to reduce the severity of inflammatory reactions following reexposure to allergen.

Anti-alarmins in asthma: targeting the airway epithelium with next-generation biologics

Monoclonal antibody therapies have significantly improved treatment outcomes for patients with severe asthma; however, a significant disease burden remains. Available biologic treatments, including anti-immunoglobulin (Ig)E, anti-interleukin (IL)-5, anti-IL-5Rα and anti-IL-4Rα, reduce exacerbation rates in study populations by approximately 50% only. Furthermore, there are currently no effective treatments for patients with severe, type 2-low asthma. Existing biologics target immunological pathways that are downstream in the type 2 inflammatory cascade, which may explain why exacerbations are only partly abrogated. For example, type 2 airway inflammation results from several inflammatory signals in addition to IL-5. Clinically, this can be observed in how fractional exhaled nitric oxide (F eNO), which is driven by IL-13, may remain unchanged during anti-IL-5 treatment despite reduction in eosinophils, and how eosinophils may remain unchanged during anti-IL-4Rα treatment despite reduction in F eNO The broad inflammatory response involving cytokines including IL-4, IL-5 and IL-13 that ultimately results in the classic features of exacerbations (eosinophilic inflammation, mucus production and bronchospasm) is initiated by release of "alarmins" thymic stromal lymphopoietin (TSLP), IL-33 and IL-25 from the airway epithelium in response to triggers. The central, upstream role of these epithelial cytokines has identified them as strong potential therapeutic targets to prevent exacerbations and improve lung function in patients with type 2-high and type 2-low asthma. This article describes the effects of alarmins and discusses the potential role of anti-alarmins in the context of existing biologics. Clinical phenotypes of patients who may benefit from these treatments are also discussed, including how biomarkers may help identify potential responders.

Host Immunity and Inflammation to Pulmonary Helminth Infections

Helminths, including nematodes, cestodes and trematodes, are complex parasitic organisms that infect at least one billion people globally living in extreme poverty. Helminthic infections are associated with severe morbidity particularly in young children who often harbor the highest burden of disease. While each helminth species completes a distinct life cycle within the host, several helminths incite significant lung disease. This impact on the lungs occurs either directly from larval migration and host immune activation or indirectly from a systemic inflammatory immune response. The impact of helminths on the pulmonary immune response involves a sophisticated orchestration and activation of the host innate and adaptive immune cells. The consequences of activating pulmonary host immune responses are variable with several helminthic infections leading to severe, pulmonary compromise while others providing immune tolerance and protection against the development of pulmonary diseases. Further delineation of the convoluted interface between helminth infection and the pulmonary host immune responses is critical to the development of novel therapeutics that are critically needed to prevent the significant global morbidity caused by these parasites.

Heterogeneity in the initiation, development and function of type 2 immunity

Type 2 immune responses operate under varying conditions in distinct tissue environments and are crucial for protection against helminth infections and for the maintenance of tissue homeostasis. Here we explore how different layers of heterogeneity influence type 2 immunity. Distinct insults, such as allergens or infections, can induce type 2 immune responses through diverse mechanisms, and this can have heterogeneous consequences, ranging from acute or chronic inflammation to deficits in immune regulation and tissue repair. Technological advances have provided new insights into the molecular heterogeneity of different developmental lineages of type 2 immune cells. Genetic and environmental heterogeneity also contributes to the varying magnitude and quality of the type 2 immune response during infection, which is an important determinant of the balance between pathology and disease resolution. Hence, understanding the mechanisms underlying the heterogeneity of type 2 immune responses between individuals and between different tissues will be crucial for treating diseases in which type 2 immunity is an important component.

Glutaredoxin deficiency promotes activation of the transforming growth factor beta pathway in airway epithelial cells, in association with fibrotic airway remodeling

S-glutathionylation of reactive protein cysteines is a post-translational event that plays a critical role in transducing signals from oxidants into biological responses. S-glutathionylation can be reversed by the deglutathionylating enzyme glutaredoxin (GLRX). We have previously demonstrated that ablation of Glrx sensitizes mice to the development of parenchymal lung fibrosis(1). It remains unclear whether GLRX also controls airway fibrosis, a clinical feature relevant to asthma and chronic obstructive pulmonary disease, and whether GLRX controls the biology of airway epithelial cells, which have been implicated in the pathophysiology of these diseases. In the present study we utilized a house dust mite (HDM) model of allergic airway disease in wild type (WT) and Glrx-/- mice on a C57BL/6 background prone to develop airway fibrosis, and tracheal basal stem cells derived from WT mice, global Glrx-/- mice, or bi-transgenic mice allowing conditional ablation of the Glrx gene. Herein we show that absence of Glrx led to enhanced HDM-induced collagen deposition, elevated levels of transforming growth factor beta 1 (TGFB1) in the bronchoalveolar lavage, and resulted in increases in airway hyperresponsiveness. Airway epithelial cells isolated from Glrx-/- mice or following conditional ablation of Glrx showed spontaneous increases in secretion of TGFB1. Glrx-/- basal cells also showed spontaneous TGFB pathway activation, in association with increased expression of mesenchymal genes, including collagen 1a1 and fibronectin. Overall, these findings suggest that GLRX regulates airway fibrosis via a mechanism(s) that involve the plasticity of basal cells, the stem cells of the airways.

Monocyte and Macrophage-Mediated Pathology and Protective Immunity During Schistosomiasis

Infection by Schistosoma parasites culminates in a chronic granulomatous disease characterized by intense tissue fibrosis. Along the course of schistosomiasis, diverse leukocytes are recruited for inflammatory foci. Innate immune cell accumulation in Th2-driven granulomas around Schistosoma eggs is associated with increased collagen deposition, while monocytes and macrophages exert critical roles during this process. Monocytes are recruited to damaged tissues from blood, produce TGF-β and differentiate into monocyte-derived macrophages (MDMs), which become alternatively activated by IL-4/IL-13 signaling via IL-4Rα (AAMs). AAMs are key players of tissue repair and wound healing in response to Schistosoma infection. Alternative activation of macrophages is characterized by the activation of STAT6 that coordinates the transcription of Arg1, Chi3l3, Relma, and Mrc1. In addition to these markers, monocyte-derived AAMs also express Raldh2 and Pdl2. AAMs produce high levels of IL-10 and TGF-β that minimizes tissue damage caused by Schistosoma egg accumulation in tissues. In this review, we provide support to previous findings about the host response to Schistosoma infection reusing public transcriptome data. Importantly, we discuss the role of monocytes and macrophages with emphasis on the mechanisms of alternative macrophage activation during schistosomiasis.

IL-25 Receptor Signaling Modulates Host Defense against Cryptococcus neoformans Infection

Cryptococcal meningitis is one of the most common life-threatening diseases caused by Cryptococcus infection. Increasing evidence indicates that type 2 immunity is associated with disease progression by promoting fungal growth and dissemination. However, factors that govern this pathogenic response during infection are still elusive. In this study, we investigated the role of IL-25, one of the type 2-inducing cytokines produced by epithelial cells, in contributing to the pathogenesis of cryptococcosis. We found that pulmonary but not systemic infection with a high-virulence strain of C. neoformans significantly induced pulmonary IL-25 expression in the lungs but not brains. In response to pulmonary infection, mice deficient in the surface IL-17 receptor B, a component of the IL-25R, exhibited improved survival with a decreased brain fungal burden. The absence of IL-25R signaling diminished the type 2 and enhanced the type 1 immune response that directed macrophage polarization toward M1 macrophages. Interestingly, Cryptococcus-mediated IL-25 signaling suppressed the expression of cytokines and chemokines associated with protection in the brain, including Ifng, Il1b, Ip10, and Nos2, without affecting brain cellular inflammation and microglia cell activation. Il17rb^-/- mice receiving cryptococcal-specific CD4⁺ T cells from wild-type had a shorter survival time with higher fungal burden within the brain and an elevated expression of M2 macrophage markers than those receiving cryptococcal-specific CD4⁺ T cells from Il17rb^-/- mice. Taken together, our data indicated that IL-25 signaling subverts the induction of protective immunity and amplifies the type 2 immune response that may favor the development of cryptococcal disease and the fungal dissemination to the CNS.

Single-Chain Soluble Receptor Fusion Proteins as Versatile Cytokine Inhibitors

Cytokines are small secreted proteins that among many functions also play key roles in the orchestration of inflammation in host defense and disease. Over the past years, a large number of biologics have been developed to target cytokines in disease, amongst which soluble receptor fusion proteins have shown some promise in pre-clinical studies. We have previously shown proof-of-concept for the therapeutic targeting of interleukin (IL)-33 in airway inflammation using a newly developed biologic, termed IL-33trap, comprising the ectodomains of the cognate receptor ST2 and the co-receptor IL-1RAcP fused into a single-chain recombinant fusion protein. Here we extend the biophysical and biological characterization of IL-33trap variants, and show that IL-33trap is a stable protein with a monomeric profile both at physiological temperatures and during liquid storage at 4°C. Reducing the N-glycan heterogeneity and complexity of IL-33trap via GlycoDelete engineering neither affects its stability nor its inhibitory activity against IL-33. We also report that IL-33trap specifically targets biologically active IL-33 splice variants. Finally, we document the generation and antagonistic activity of a single-chain IL-4/13trap, which inhibits both IL-4 and IL-13 signaling. Collectively, these results illustrate that single-chain soluble receptor fusion proteins against IL-4, IL-13, and IL-33 are novel biologics that might not only be of interest for research purposes and further interrogation of the role of their target cytokines in physiology and disease, but may also complement monoclonal antibodies for the treatment of allergic and other inflammatory diseases.

Combinatorial IL-17RB, ST2, and TSLPR Signaling in Dendritic Cells of Patients With Allergic Rhinitis

Objectives

Myeloid dendritic cells (DCs) in patients with allergic rhinitis (AR) express higher levels of IL-17RB, ST2, and TSLPR. However, their functional roles in DCs are much less clear. This study aimed to determine the combined effects of these three receptor signals on the T cell-polarizing function of DCs in AR patients.

Methods

Monocyte-derived DCs (mo-DCs) were generated and stimulated with Toll-like receptor (TLR) 1-9 ligands. Der.p1-induced mo-DCs were stimulated with different combinations of IL-25, IL-33, and TSLP to determine phenotypic characteristics and then co-cultured with CD4⁺ T cells to assess Th2 cytokine production. Expression levels of IL-17RB, ST2, and TSLPR on myeloid DCs (mDCs) from peripheral blood of AR and healthy subjects were detected to confirm the association of these receptors with disease severity.

Results

TLR ligands induced AR-derived mo-DCs to increase IL-17RB, ST2, and TSLPR expression by varying degrees; among these, Der.p1 was the strongest inducer. Der.p1-induced mo-DCs from AR showed increased OX40L expression. IL-25, IL-33, and TSLP (alone or in double combination) significantly increased OX40L expression on Der.p1-induced mo-DCs from AR, thereby increasing the production of IL-4, IL-5, and IL-13 in co-cultured CD4⁺ T cells; triple combination further enhanced these effects. The percentage of IL-17RB⁺ST2⁺TSLPR⁺ mDCs was increased in AR, higher in moderate to severe phase than in mild phase, and positively correlated with the percentages of IL-4⁺, IL-5⁺, and IL-13⁺ T cells.

Conclusion

A combination of IL-17RB, ST2, and TSLPR signals amplified the Th2-polarizing function of DCs and was associated with disease severity in AR patients.

Bcl6 and Blimp1 reciprocally regulate ST2+ Treg-cell development in the context of allergic airway inflammation

BACKGROUND

Bcl6 is required for the development of T follicular helper cells and T follicular regulatory (Tfr) cells that regulate germinal center responses. Bcl6 also affects the function of regulatory T (Treg) cells.

OBJECTIVE

The goal of this study was to define the functions of Bcl6 in Treg cells, including Tfr cells, in the context of allergic airway inflammation.

METHODS

We used a model of house dust mite sensitization to challenge wild-type, Bcl6^fl/fl Foxp3-Cre, and Prdm1 (Blimp1)^fl/fl Foxp3-Cre mice to study the reciprocal roles of Bcl6 and Blimp1 in allergic airway inflammation.

RESULTS

In the house dust mite model, Tfr cells repress the production of IgE and Bcl6⁺ Treg cells suppress the generation of type 2 cytokine-producing cells in the lungs. In mice with Bcl6-deficient Treg cells, twice as many ST2⁺ (IL-33R⁺) Treg cells develop as are observed in wild-type mice. ST2⁺ Treg cells in the context of allergic airway inflammation are Blimp1 dependent, express type 2 cytokines, and share features of visceral adipose tissue Treg cells. Bcl6-deficient Treg cells are more susceptible, and Blimp1-deficient Treg cells are resistant, to acquiring the ST2⁺ Treg-cell phenotype in vitro and in vivo in response to IL-33. Bcl6-deficient ST2⁺ Treg cells, but not Bcl6-deficient ST2⁺ conventional T cells, strongly promote allergic airway inflammation when transferred into recipient mice. Lastly, ST2 is required for the exacerbated allergic airway inflammation in Bcl6^fl/fl Foxp3-Cre mice.

CONCLUSIONS

During allergic airway inflammation, Bcl6 and Blimp1 play dual roles in regulating Tfr-cell activity in the germinal center and in the development of ST2⁺ Treg cells that promote type 2 cytokine responses.

Tuft-Cell-Derived Leukotrienes Drive Rapid Anti-helminth Immunity in the Small Intestine but Are Dispensable for Anti-protist Immunity

Helminths, allergens, and certain protists induce type 2 immune responses, but the underlying mechanisms of immune activation remain poorly understood. In the small intestine, chemosensing by epithelial tuft cells results in the activation of group 2 innate lymphoid cells (ILC2s), which subsequently drive increased tuft cell frequency. This feedforward circuit is essential for intestinal remodeling and helminth clearance. ILC2 activation requires tuft-cell-derived interleukin-25 (IL-25), but whether additional signals regulate the circuit is unclear. Here, we show that tuft cells secrete cysteinyl leukotrienes (cysLTs) to rapidly activate type 2 immunity following chemosensing of helminth infection. CysLTs cooperate with IL-25 to activate ILC2s, and tuft-cell-specific ablation of leukotriene synthesis attenuates type 2 immunity and delays helminth clearance. Conversely, cysLTs are dispensable for the tuft cell response induced by intestinal protists. Our findings identify an additional tuft cell effector function and suggest context-specific regulation of tuft-ILC2 circuits within the small intestine.

T Lymphocyte-Mediated Liver Immunopathology of Schistosomiasis

The parasitic worms, Schistosoma mansoni and Schistosoma japonicum, reside in the mesenteric veins, where they release eggs that induce a dramatic granulomatous response in the liver and intestines. Subsequently, infection may further develop into significant fibrosis and portal hypertension. Over the past several years, uncovering the mechanism of immunopathology in schistosomiasis has become a major research objective. It is known that T lymphocytes, especially CD4⁺ T cells, are essential for immune responses against Schistosoma species. However, obtaining a clear understanding of how T lymphocytes regulate the pathological process is proving to be a daunting challenge. To date, CD4⁺ T cell subsets have been classified into several distinct T helper (Th) phenotypes including Th1, Th2, Th17, T follicular helper cells (Tfh), Th9, and regulatory T cells (Tregs). In the case of schistosomiasis, the granulomatous inflammation and the chronic liver pathology are critically regulated by the Th1/Th2 responses. Animal studies suggest that there is a moderate Th1 response to parasite antigens during the acute stage, but then, egg-derived antigens induce a sustained and dominant Th2 response that mediates granuloma formation and liver fibrosis. In addition, the newly discovered Th17 cells also play a critical role in the hepatic immunopathology of schistosomiasis. Within the liver, Tregs are recruited to hepatic granulomas and exert an immunosuppressive role to limit the granulomatous inflammation and fibrosis. Moreover, recent studies have shown that Tfh and Th9 cells might also promote liver granulomas and fibrogenesis in the murine schistosomiasis. Thus, during infection, T-cell subsets undergo complicated cross-talk with antigen presenting cells that then defines their various roles in the local microenvironment for regulating the pathological progression of schistosomiasis. This current review summarizes a vast body of literature to elucidate the contribution of T lymphocytes and their associated cytokines in the immunopathology of schistosomiasis.

Epithelial Alarmins in Serum and Exhaled Breath in Patients with Idiopathic Pulmonary Fibrosis: A Prospective One-Year Follow-Up Cohort Study

Background: Recently, epithelial alarmins have been shown to play important roles in non-allergen driven respiratory diseases like idiopathic pulmonary fibrosis (IPF). Little is known about the expression of the epithelial alarmins in IPF. Methods: This study aimed to prospectively examine interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin (TSLP) levels in the serum and exhaled breath condensate (EBC) in patients with IPF before and after one-year of antifibrotic treatment. A total of 82 volunteers, including 52 patients diagnosed with IPF that qualified for antifibrotic therapy as well as 30 controls, were examined. All study participants underwent baseline peripheral blood and EBC sampling. In 35 out of 52 IPF subjects, a follow-up sampling was performed after 12 months of antifibrotic treatment. Concentrations of alarmins in the serum and EBC were evaluated by means of ELISA. Results: Baseline TSLP concentrations were significantly elevated in patients with IPF compared to controls both in the serum (p < 0.05) and EBC (p < 0.0001). Baseline IL-25 and IL-33 serum and EBC levels did not differ significantly between IPF subjects and controls. Prospective analysis of changes in the epithelial alarmin levels showed significantly decreased IL-25 and TSLP EBC concentrations after 12 months of antifibrotic treatment (p < 0.05), which was observed in the subgroup of IPF patients treated with pirfenidone, but not in those treated with nintedanib. In stable patients with IPF over a study period (absolute forced vital capacity (FVC) % of predicted decline/year ≤ 5%, n = 25), a significant decrease in the EBC levels of both IL-25 and TSLP after 12 months of antifibrotic treatment was noted (p < 0.05), whereas, in progressor IPF patients (absolute FVC % of predicted decline/year > 5%, n = 10), a significant decrease was noted in the IL-25 EBC levels only (p < 0.05). Conclusions: Elevated TSLP levels in patients with IPF and their significant decrease in the lung compartment during antifibrotic therapy in stable patients with IPF, but not in progressors, support its significant contribution to pro-fibrotic type 2 immune responses in IPF. Noted changes in the epithelial alarmins concentration in the lung compartment during pirfenidone therapy may suggest its possible interaction with epithelial alarmins pathways in IPF.

IL-33 blockade affects mediators of persistence and exacerbation in a model of chronic airway inflammation

BACKGROUND

Severe inflammatory airway diseases are associated with inflammation that does not resolve, leading to structural changes and an overall environment primed for exacerbations.

OBJECTIVE

We sought to identify and inhibit pathways that perpetuate this heightened inflammatory state because this could lead to therapies that allow for a more quiescent lung that is less predisposed to symptoms and exacerbations.

METHODS

Using prolonged exposure to house dust mite in mice, we developed a mouse model of persistent and exacerbating airway disease characterized by a mixed inflammatory phenotype.

RESULTS

We show that lung IL-33 drives inflammation and remodeling beyond the type 2 response classically associated with IL-33 signaling. IL-33 blockade with an IL-33 neutralizing antibody normalized established inflammation and improved remodeling of both the lung epithelium and lung parenchyma. Specifically, IL-33 blockade normalized persisting and exacerbating inflammatory end points, including eosinophilic, neutrophilic, and ST2⁺CD4⁺ T-cell infiltration. Importantly, we identified a key role for IL-33 in driving lung remodeling because anti-IL-33 also re-established the presence of ciliated cells over mucus-producing cells and decreased myofibroblast numbers, even in the context of continuous allergen exposure, resulting in improved lung function.

CONCLUSION

Overall, this study shows that increased IL-33 levels drive a self-perpetuating amplification loop that maintains the lung in a state of lasting inflammation and remodeled tissue primed for exacerbations. Thus IL-33 blockade might ameliorate symptoms and prevent exacerbations by quelling persistent inflammation and airway remodeling.

Benzo(a)pyrene facilitates dermatophagoides group 1 (Der f 1)-induced epithelial cytokine release through aryl hydrocarbon receptor in asthma

BACKGROUND

Environmental pollutants, which coexist with allergens, have been associated with the exacerbation of asthma. However, the underlying molecular mechanisms remain elusive. We sought to determine whether benzo(a)pyrene (BaP) co-exposure with dermatophagoides group 1 allergen (Der f 1) can potentiate Der f 1-induced asthma and its underlying mechanisms.

METHODS

The effect of BaP was investigated in Der f 1-induced mouse model of asthma, including airway hyper-responsiveness, allergic inflammation, and epithelial-derived cytokines. The impact of BaP on Der f 1-induced airway epithelial cell oxidative stress (ROS) and cytokine release was further analyzed. The role of aryl hydrocarbon receptor (AhR) signaling in BaP-promoted Der f 1-induced ROS, cytokine production, and allergic inflammation was also investigated.

RESULTS

Compared with Der f 1, BaP co-exposure with Der f 1 led to airway hyper-responsiveness and increased lung inflammation in mouse model of asthma. Increased expression of TSLP, IL-33, and IL-25 was also found in the airways of these mice. Moreover, BaP co-exposure with Der f 1 activated AhR signaling with increased expression of AhR and CYP1A1 and promoted airway epithelial ROS generation and TSLP and IL-33, but not IL-25, expression. Interestingly, AhR antagonist CH223191 or cells with AhR knockdown abrogated the increased expression of ROS, TSLP, and IL-33. Furthermore, ROS inhibitor N-acetyl-L-cysteine (NAC) also suppressed BaP co-exposure-induced expression of epithelial TSLP, IL-33, and IL-25. Finally, AhR antagonist CH223191 and NAC inhibited BaP co-exposure with Der f 1-induced lung inflammation.

CONCLUSIONS

Our findings suggest that BaP facilitates Der f 1-induced epithelial cytokine release through the AhR-ROS axis.

Heat shock protein 70 is a positive regulator of airway inflammation and goblet cell hyperplasia in a mouse model of allergic airway inflammation

Heat shock proteins (Hsps) are highly conserved molecular chaperones that are ubiquitously expressed in all species to aid the solubilization of misfolded proteins, protein degradation, and transport. Elevated levels of Hsp70 have been found in the sputum, serum, and bronchoalveolar lavage (BAL) fluid of asthma patients and are known to correlate with disease severity. However, the function of Hsp70 in allergic airway inflammation has remained largely unknown. This study aimed to determine the role of Hsp70 in airway inflammation and remodeling using a mouse model of allergic airway inflammation. WT and Hsp70 double-knockout (Hsp70.1/.3^-/-) mice were sensitized and challenged intratracheally with Schistosoma mansoni soluble egg antigens (SEAs) to induce robust Th2 responses and airway inflammation in the lungs. The lack of Hsp70 resulted in a significant reduction in airway inflammation, goblet cell hyperplasia, and Th2 cytokine production, including IL-4, IL-5, and IL-13. An analysis of the BAL fluid suggested that Hsp70 is critically required for eosinophilic infiltration, collagen accumulation, and Th2 cytokine production in allergic airways. Furthermore, our bone marrow (BM) transfer studies show that SEA-induced airway inflammation, goblet cell hyperplasia, and Th2 cytokine production were attenuated in WT mice that were reconstituted with Hsp70-deficient BM, but these effects were not attenuated in Hsp70-deficient mice that were reconstituted with WT BM. Together, these studies identify a pathogenic role for Hsp70 in hematopoietic cells during allergic airway inflammation; this illustrates the potential utility of targeting Hsp70 to alleviate allergen-induced Th2 cytokines, goblet cell hyperplasia, and airway inflammation.

Inhibitors of class I histone deacetylases attenuate thioacetamide-induced liver fibrosis in mice by suppressing hepatic type 2 inflammation

BACKGROUND AND PURPOSE

Chronic liver diseases feature excessive collagen and matrix protein deposition or crosslinking that characterises fibrosis, leads to scar tissue, and disrupts liver functions. There is no effective treatment. This study investigated whether treatment with selective histone deacetylase (HDAC) inhibitors might specifically reduce type 2 inflammation in the injured liver, thereby attenuating fibrogenesis in mice.

EXPERIMENTAL APPROACH

Thioacetamide (TAA) was used to induce hepatic inflammation, fibrosis, and liver damage in female C57BL/6 mice, similar to the clinical features of chronic human liver disease. We used eight inhibitors of different human HDAC enzymes to probe histological (IHC and TUNEL), biochemical and immunological changes (flow cytometry, qPCR, Legendplex, and ELISA) in pathology, fibrosis, hepatic immune cell flux, and inflammatory cytokine expression.

KEY RESULTS

Inhibitors of class I, but not class II, HDAC enzymes potently suppressed chronic hepatic inflammation and fibrosis in mice, attenuating accumulation and activation of IL-33-dependent, but not IL-25-dependent, group 2 innate lymphoid cells (ILC2) and inhibiting type 2 inflammation that drives hepatic stellate cells to secrete excessive collagen and matrix proteins.

CONCLUSIONS AND IMPLICATIONS

The results show that potent and selective inhibitors of class I only HDAC enzymes profoundly inhibit hepatocyte death and type 2 inflammation to prevent TAA-induced liver fibrosis in mice. The specific HDAC enzymes identified here may be key promoters of inflammation in chronic liver fibrosis.

IL-33trap is a novel IL-33-neutralizing biologic that inhibits allergic airway inflammation

BACKGROUND

The emergence of IL-33 as a key molecular player in the development and propagation of widespread inflammatory diseases, including asthma and atopic dermatitis, has established the need for effective IL-33-neutralizing biologics.

OBJECTIVE

Here we describe the development and validation of a new antagonist of IL-33, termed IL-33trap, which combines the extracellular domains of the IL-33 receptor (ST2) and its coreceptor, IL-1 receptor accessory protein, into a single fusion protein.

METHODS

We produced and purified recombinant IL-33trap from human cells and analyzed its IL-33-binding affinity and IL-33 antagonistic activity in cultured cells and mice. IL-33trap activity was also benchmarked with a recombinant soluble ST2 corresponding to the naturally occurring IL-33 decoy receptor. Finally, we studied the effect of IL-33trap in the Alternaria alternata mouse model of allergic airway inflammation.

RESULTS

In vitro IL-33trap binds IL-33 and inhibits IL-33 activity to a much stronger degree than soluble ST2. Furthermore, IL-33trap inhibits eosinophil infiltration, splenomegaly, and production of signature cytokines in splenic lymphocytes and lung tissue on IL-33 injection. Finally, administration of IL-33trap at the time of allergen challenge inhibits inflammatory responses in a preclinical mouse model of acute allergic airway inflammation.

CONCLUSIONS

IL-33trap is a novel IL-33 antagonist that outperforms the natural IL-33 decoy receptor and shows anti-inflammatory activities in a preclinical mouse model of acute allergic airway inflammation when administered at the time of allergen challenge.

Airway mycosis in allergic airway disease

The allergic airway diseases, including chronic rhinosinusitis (CRS), asthma, allergic bronchopulmonary mycosis (ABPM) and many others, comprise a heterogeneous collection of inflammatory disorders affecting the upper and lower airways and lung parenchyma that represent the most common chronic diseases of humanity. In addition to their shared tissue tropism, the allergic airway diseases are characterized by a distinct pattern of inflammation involving the accumulation of eosinophils, type 2 macrophages, innate lymphoid cells type 2 (ILC2), IgE-secreting B cells, and T helper type 2 (Th2) cells in airway tissues, and the prominent production of type 2 cytokines including interleukin (IL-) 33, IL-4, IL-5, IL-13, and many others. These factors and related inflammatory molecules induce characteristic remodeling and other changes of the airways that include goblet cell metaplasia, enhanced mucus secretion, smooth muscle hypertrophy, tissue swelling and polyp formation that account for the major clinical manifestations of nasal obstruction, headache, hyposmia, cough, shortness of breath, chest pain, wheezing, and, in the most severe cases of lower airway disease, death due to respiratory failure or disseminated, systemic disease. The syndromic nature of the allergic airway diseases that now include many physiological variants or endotypes suggests that distinct endogenous or environmental factors underlie their expression. However, findings from different perspectives now collectively link these disorders to a single infectious source, the fungi, and a molecular pathogenesis that involves the local production of airway proteinases by these organisms. In this review, we discuss the evidence linking fungi and their proteinases to the surprisingly wide variety of chronic airway and systemic disorders and the immune pathogenesis of these conditions as they relate to environmental fungi. We further discuss the important implications these new findings have for the diagnosis and future therapy of these common conditions.

Contribution of tissue transglutaminase to the severity of hepatic fibrosis resulting from Schistosoma japonicum infection through the regulation of IL-33/ST2 expression

Background

Tissue transglutaminase (tTG)-regulating IL-13 plays an important role in the pathogenesis of liver fibrosis resulting from Schistosoma japonicum (Sj) infection. IL-33 and its receptor ST2 are involved in Th2-biased immune responses through the release of IL-5 and IL-13 and subsequent hepatic granuloma pathology induced by Sj infection. However, the relationship between tTG, IL-33/ST2, and liver fibrosis during Schistosoma infection has not been established.

Results

This study investigated the link between tTG and IL-33/ST2 in the induction of liver fibrogenesis during Sj infection in mice. The extent of liver fibrosis coincided with an increase in tTG and IL-33/ST2 expression in the liver of infected mice between five to eight weeks, with a peak of correlation at six weeks after Sj infection. The inhibition of tTG activity through cystamine administration or gene knockout alleviated the level of TLR4, NF-κB pathway molecules, IL-33/ST2, and the severity of liver fibrosis resulting from Sj infection.

Conclusions

These results indicate that during Sj infection tTG may control liver fibrosis at least partially through TLR4, NF-κB pathway activation and then IL-33/ST2. tTG, IL-33 or ST2 might be promising drug targets against liver fibrosis induced by Sj infection.

Fra-2-expressing macrophages promote lung fibrosis in mice

Idiopathic Pulmonary Fibrosis (IPF) is a deadly disease with limited therapies. Tissue fibrosis is associated with Type 2 immune response, although the causal contribution of immune cells is not defined. The AP-1 transcription factor Fra-2 is upregulated in IPF lung sections and Fra-2 transgenic mice (Fra-2tg) exhibit spontaneous lung fibrosis. Here we show that Bleomycin-induced lung fibrosis is attenuated upon myeloid-inactivation of Fra-2 and aggravated in Fra-2tg bone marrow chimeras. Type VI collagen (ColVI), a Fra-2 transcriptional target, is up-regulated in three lung fibrosis models, and macrophages promote myofibroblast activation in vitro in a ColVI- and Fra-2-dependent manner. Fra-2 or ColVI inactivation does not affect macrophage recruitment and alternative activation, suggesting that Fra-2/ColVI specifically controls the paracrine pro-fibrotic activity of macrophages. Importantly, ColVI knock-out mice (KO) and ColVI-KO bone marrow chimeras are protected from Bleomycin-induced lung fibrosis. Therapeutic administration of a Fra-2/AP-1 inhibitor reduces ColVI expression and ameliorates fibrosis in Fra-2tg mice and in the Bleomycin model. Finally, Fra-2 and ColVI positively correlate in IPF patient samples and co-localize in lung macrophages. Therefore, the Fra-2/ColVI pro-fibrotic axis is a promising biomarker and therapeutic target for lung fibrosis, and possibly other fibrotic diseases.

IL-33/IL-33R in various types of carotid artery atherosclerotic lesions

OBJECTIVE

Inflammation plays a crucial role in the progression of atherosclerotic plaques. The aim of the study was to investigate serum levels and expression of Interleukin-33 (IL-33) and ST2 receptor in atherosclerotic plaques and to analyze correlation with the type of the carotid plaques in patients with carotid disease.

METHODS

This study included 191 consecutive patients submitted for carotid endarterectomy (CEA). Preoperative serum levels of IL-33 and soluble ST2 (sST2) were measured. Atherosclerotic plaques obtained during surgery were initially histologically classified and immunohistochemical analyzes of IL-33, IL-33R, CD68 and alpha-SMA expression was performed. Ultrasound assessment of the level of carotid stenosis in each patient was performed prior to carotid surgery. Demographic and clinical data such as gender, age, smoking status, blood pressure, glycaemia, hemoglobin and creatinine levels, and comorbidities were collected and the comparisons between variables were statistically evaluated.

RESULTS

Serum levels of IL-33 (35.86 ± 7.93 pg/ml vs.12.29 ± 1.8 pg/ml, p < 0.05) and sST2 (183 ± 8.03 pg/ml vs. 122.31 ± 15.89 pg/ml, p < 0.05) were significantly higher in the group of CEA patients vs. healthy subjects. We demonstrated abundant tissue expression of IL-33 and ST2 in atherosclerotic carotid artery lesions. The levels of IL-33 and IL-33R expression were significantly higher in vulnerable plaques and significantly correlated with the degree of inflammatory cells infiltration in these plaques (R = 0.579, p = 0.049). Immunohistochemical analysis also revealed that cells responsible for IL-33 expression are not only mononuclear cells confined to inflammatory atherosclerotic lesions, but also smooth muscle cells which gained phenotypic characteristics of foam cells and were loaded with lipid droplets.

CONCLUSION

The obtained results confirm the importance of IL-33/ST2 axis in the process of atherosclerosis, and indicate its ambiguous function in immune response, whether as proinflammatory cytokine in advanced atherosclerotic lesions, or as profibrotic, in early lesions.

Type 2 Innate Lymphoid Cells in Liver and Gut: From Current Knowledge to Future Perspectives

Innate lymphoid cells (ILCs) represent a heterogeneous population of recently discovered immune cells that mirror the functions of adaptive T lymphocytes. However, ILCs are devoid of specific antigen receptors and cellular activation depends on environmental cytokines, rendering them as early regulators of immune responses. Type 2 innate lymphoid cells (ILC2s) respond to alarmins, such as interleukin-25 and -33 and shape Th2-associated immunity by expressing IL-5 and IL-13 in a GATA3-dependent manner. In addition, ILC2s express the epidermal growth factor-like molecule Amphiregulin thereby promoting regeneration of injured tissue during inflammation. The gut and liver confer nutrient metabolism and bidirectional exchange of products, known as the gut-liver axis. Accordingly, both organs are continuously exposed to a large variety of harmless antigens. This requires avoidance of immunity, which is established by a tolerogenic environment in the gut and liver. However, dysregulations within the one organ are assumed to influence vitality of the other and frequently promote chronic inflammatory settings with poor prognosis. Intensive research within the last years has revealed that ILC2s are involved in acute and chronic inflammatory settings of gut and liver. Here, we highlight the roles of ILC2s in intestinal and hepatic inflammation and discuss a regulatory potential.

Innate Lymphoid Cells in Helminth Infections-Obligatory or Accessory?

ILCs burst onto the immunological scene with their involvement in bacterial and helminth infections. As their influence has emerged, it has become clear that they play a fundamental role in regulating barrier tissue homeostasis and the immune response during inflammation. A subset of ILCs, ILC2s, has become the focus of attention for many helminth biologists-stepping into the limelight as both the elusive initiator and amplifier of the type-2 response. In many of the early reports, conclusions as to their function were based on experiments using unadapted parasites or immune-compromised hosts. In this review we re-examine the generation and function of type-2 ILCs in helminth infection and the extent to which their roles may be essential or redundant, in both primary and challenge infections. ILC2s will be discussed in terms of a broader innate network, which when in dialogue with adaptive immunity, allows the generation of the anti-parasite response. Finally, we will review how helminths manipulate ILC2 populations to benefit their survival, as well as dampen systemic inflammation in the host, and how this understanding may be used to improve strategies to control disease.

The immunopathology of lung fibrosis: amphiregulin-producing pathogenic memory T helper-2 cells control the airway fibrotic responses by inducing eosinophils to secrete osteopontin

Fibrosis is defined as excessive deposition of the extracellular matrix (ECM) in the parenchyma of various organs, and sometimes leads to irreversible organ malfunction such as idiopathic pulmonary fibrosis (IPF), a fatal disorder of the lung. Chronic inflammatory stimuli induce fibrotic responses in various organs. Various immune cells, including T helper (Th) cells in the lung, protect the host from different harmful particles, including pathogenic microorganisms. However, the dysregulation of the function of these immune cells in the lung sometimes causes inflammatory diseases, such as lung fibrosis. In this review, we will introduce an outline of the cellular and molecular mechanisms underlying the pathogenic fibrotic responses in the lung. We will also introduce the concept of the "Pathogenic Th population disease induction model," in which unique subpopulations of certain Th cell subsets control the pathology of immune-mediated inflammatory diseases. Finally, we introduce our recent findings, which demonstrate that amphiregulin-producing pathogenic memory Th2 cells control airway fibrosis through the osteopontin produced by inflammatory eosinophils. The identification of this new pathogenic Th cell population supports the concept of "Pathogenic Th population disease induction model", and will provide novel strategies for treating intractable diseases, including lung fibrosis.

ILC2s-Trailblazers in the Host Response Against Intestinal Helminths

Group 2 innate lymphoid cells (ILC2s) were first discovered in experimental studies of intestinal helminth infection—and much of our current knowledge of ILC2 activation and function is based on the use of these models. It is perhaps not surprising therefore that these cells have also been found to play a key role in mediating protection against these large multicellular parasites. ILC2s have been intensively studied over the last decade, and are known to respond quickly and robustly to the presence of helminths—both by increasing in number and producing type 2 cytokines. These mediators function to activate and repair epithelial barriers, to recruit other innate cells such as eosinophils, and to help activate T helper 2 cells. More recent investigations have focused on the mechanisms by which the host senses helminth parasites to activate ILC2s. Such studies have identified novel stromal cell types as being involved in this process—including intestinal tuft cells and enteric neurons, which respond to the presence of helminths and activate ILC2s by producing IL-25 and Neuromedin, respectively. In the current review, we will outline the latest insights into ILC2 activation and discuss the requirement for—or redundancy of—ILC2s in providing protective immunity against intestinal helminth parasites.

The use of biologics for immune modulation in allergic disease

The rising prevalence of allergies represents an increasing socioeconomic burden. A detailed understanding of the immunological mechanisms that underlie the development of allergic disease, as well as the processes that drive immune tolerance to allergens, will be instrumental in designing therapeutic strategies to treat and prevent allergic disease. Improved characterization of individual patients through the use of specific biomarkers and improved definitions of disease endotypes are paving the way for the use of targeted therapeutic approaches for personalized treatment. Allergen-specific immunotherapy and biologic therapies that target key molecules driving the Th2 response are already used in the clinic, and a wave of novel drug candidates are under development. In-depth analysis of the cells and tissues of patients treated with such targeted interventions provides a wealth of information on the mechanisms that drive allergies and tolerance to allergens. Here, we aim to deliver an overview of the current state of specific inhibitors used in the treatment of allergy, with a particular focus on asthma and atopic dermatitis, and provide insights into the roles of these molecules in immunological mechanisms of allergic disease.

Pulmonary group 2 innate lymphoid cells: surprises and challenges

Group 2 innate lymphoid cells (ILC2s) are a recently described subset of innate lymphocytes with important immune and homeostatic functions at multiple tissue sites, especially the lung. These cells expand locally after birth and during postnatal lung maturation and are present in the lung and other peripheral organs. They are modified by a variety of processes and mediate inflammatory responses to respiratory pathogens, inhaled allergens and noxious particles. Here, we review the emerging roles of ILC2s in pulmonary homeostasis and discuss recent and surprising advances in our understanding of how hormones, age, neurotransmitters, environmental challenges, and infection influence ILC2s. We also review how these responses may underpin the development, progression and severity of pulmonary inflammation and chronic lung diseases and highlight some of the remaining challenges for ILC2 biology.

Sterile particle-induced inflammation is mediated by macrophages releasing IL-33 through a Bruton's tyrosine kinase-dependent pathway

Initiation of the innate sterile inflammatory response that can develop in response to microparticle exposure is little understood. Here, we report that a potent type 2 immune response associated with the accumulation of neutrophils, eosinophils and alternatively activated (M2) macrophages was observed in response to sterile microparticles similar in size to wear debris associated with prosthetic implants. Although elevations in interleukin-33 (IL-33) and type 2 cytokines occurred independently of caspase-1 inflammasome signalling, the response was dependent on Bruton's tyrosine kinase (BTK). IL-33 was produced by macrophages and BTK-dependent expression of IL-33 by macrophages was sufficient to initiate the type 2 response. Analysis of inflammation in patient periprosthetic tissue also revealed type 2 responses under aseptic conditions in patients undergoing revision surgery. These findings indicate that microparticle-induced sterile inflammation is initiated by macrophages activated to produce IL-33. They further suggest that both BTK and IL-33 may provide therapeutic targets for wear debris-induced periprosthetic inflammation.

Schistosome Egg Migration: Mechanisms, Pathogenesis and Host Immune Responses

Many parasitic worms possess complex and intriguing life cycles, and schistosomes are no exception. To exit the human body and progress to their successive snail host, Schistosoma mansoni eggs must migrate from the mesenteric vessels, across the intestinal wall and into the feces. This process is complex and not always successful. A vast proportion of eggs fail to leave their definite host, instead becoming lodged within intestinal or hepatic tissue, where they can evoke potentially life-threatening pathology. Thus, to maximize the likelihood of successful egg passage whilst minimizing host pathology, intriguing egg exit strategies have evolved. Notably, schistosomes actively exert counter-inflammatory influences on the host immune system, discreetly compromise endothelial and epithelial barriers, and modulate granuloma formation around transiting eggs, which is instrumental to their migration. In this review, we discuss new developments in our understanding of schistosome egg migration, with an emphasis on S. mansoni and the intestine, and outline the host-parasite interactions that are thought to make this process possible. In addition, we explore the potential immune implications of egg penetration and discuss the long-term consequences for the host of unsuccessful egg transit, such as fibrosis, co-infection and cancer development.

Apoptosis and necroptosis in the liver: a matter of life and death

Cell death represents a basic biological paradigm that governs outcomes and long-term sequelae in almost every hepatic disease condition. Acute liver failure is characterized by massive loss of parenchymal cells but is usually followed by restitution ad integrum. By contrast, cell death in chronic liver diseases often occurs at a lesser extent but leads to long-term alterations in organ architecture and function, contributing to chronic hepatocyte turnover, the recruitment of immune cells and activation of hepatic stellate cells. These chronic cell death responses contribute to the development of liver fibrosis, cirrhosis and cancer. It has become evident that, besides apoptosis, necroptosis is a highly relevant form of programmed cell death in the liver. Differential activation of specific forms of programmed cell death might not only affect outcomes in liver diseases but also offer novel opportunities for therapeutic intervention. Here, we summarize the underlying molecular mechanisms and open questions about disease-specific activation and roles of programmed cell death forms, their contribution to response signatures and their detection. We focus on the role of apoptosis and necroptosis in acute liver injury, nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH) and liver cancer, and possible translations into clinical applications.

Schistosoma "Eggs-Iting" the Host: Granuloma Formation and Egg Excretion

Schistosomiasis is a major cause of morbidity in humans invoked by chronic infection with parasitic trematodes of the genus Schistosoma. Schistosomes have a complex life-cycle involving infections of an aquatic snail intermediate host and a definitive mammalian host. In humans, adult male and female worms lie within the vasculature. Here, they propagate and eggs are laid. These eggs must then be released from the host to continue the life cycle. Schistosoma mansoni and Schistosoma japonicum reside in the mesenteric circulation of the intestines with egg excreted in the feces. In contrast, S. haematobium are present in the venus plexus of the bladder, expelling eggs in the urine. In an impressive case of exploitation of the host immune system, this process of Schistosome “eggs-iting” the host is immune dependent. In this article, we review the formation of the egg granuloma and explore how S. mansoni eggs laid in vasculature must usurp immunity to induce regulated inflammation, to facilitate extravasation through the intestinal wall and to be expelled in the feces. We highlight the roles of immune cell populations, stromal factors, and egg secretions in the process of egg excretion to provide a comprehensive overview of the current state of knowledge regarding a vastly unexplored mechanism.

Helminth Infections Induce Tissue Tolerance Mitigating Immunopathology but Enhancing Microbial Pathogen Susceptibility

Helminths are ubiquitous and have chronically infected vertebrates throughout their evolution. As such helminths have likely exerted considerable selection pressure on our immune systems. The large size of multicellular helminths and their limited replicative capacity in the host necessarily elicits different host protective mechanisms than the immune response evoked by microbial pathogens such as bacteria, viruses and intracellular parasites. The cellular damage resulting from helminth migration through tissues is a major trigger of the type 2 and regulatory immune responses, which activates wound repair mechanisms that increases tissue tolerance to injury and resistance mechanisms that enhance resistance to further colonization with larval stages. While these wound healing and anti-inflammatory responses may be beneficial to the helminth infected host, they may also compromise the host's ability to mount protective immune responses to microbial pathogens. In this review we will first describe helminth-induced tolerance mechanisms that develop in specific organs including the lung and the intestine, and how adaptive immunity may contribute to these responses through differential activation of T cells in the secondary lymphoid organs. We will then integrate studies that have examined how the immune response is modulated in these specific tissues during coinfection of helminths with viruses, protozoa, and bacteria.

IL-33 drives influenza-induced asthma exacerbations by halting innate and adaptive antiviral immunity

BACKGROUND

Influenza virus triggers severe asthma exacerbations for which no adequate treatment is available. It is known that IL-33 levels correlate with exacerbation severity, but its role in the immunopathogenesis of exacerbations has remained elusive.

OBJECTIVE

We hypothesized that IL-33 is necessary to drive asthma exacerbations. We intervened with the IL-33 cascade and sought to dissect its role, also in synergy with thymic stromal lymphopoietin (TSLP), in airway inflammation, antiviral activity, and lung function. We aimed to unveil the major source of IL-33 in the airways and IL-33-dependent mechanisms that underlie severe asthma exacerbations.

METHODS

Patients with mild asthma were experimentally infected with rhinovirus. Mice were chronically exposed to house dust mite extract and then infected with influenza to resemble key features of exacerbations in human subjects. Interventions included the anti-IL-33 receptor ST2, anti-TSLP, or both.

RESULTS

We identified bronchial ciliated cells and type II alveolar cells as a major local source of IL-33 during virus-driven exacerbation in human subjects and mice, respectively. By blocking ST2, we demonstrated that IL-33 and not TSLP was necessary to drive exacerbations. IL-33 enhanced airway hyperresponsiveness and airway inflammation by suppressing innate and adaptive antiviral responses and by instructing epithelial cells and dendritic cells of house dust mite-sensitized mice to dampen IFN-β expression and prevent the T_H1-promoting dendritic cell phenotype. IL-33 also boosted luminal NETosis and halted cytolytic antiviral activities but did not affect the T_H2 response.

CONCLUSION

Interventions targeting the IL-33/ST2 axis could prove an effective acute short-term therapy for virus-induced asthma exacerbations.