IL-33 Precedes IL-5 in Regulating Eosinophil Commitment and Is Required for Eosinophil Homeostasis

Activated eosinophils in early life impair lung development and promote long-term lung damage

Exaggeration of type 2 immune responses promotes lung inflammation and altered lung development; however, eosinophils, despite expansion in the postnatal lung, have not been specifically assessed in the context of neonatal lung disease. Furthermore, early life factors including prematurity and respiratory infection predispose infants to chronic obstructive pulmonary disease later in life. To assess eosinophils in the developing lung and how they may contribute to chronic lung disease, we generated mice harboring eosinophil-specific deletion of the negative regulatory enzyme SH2 domain-containing inositol 5' phosphatase-1. This increased the activity and number of pulmonary eosinophils in the developing lung, which was associated with impaired lung development, expansion of activated alveolar macrophages (AMφ), multinucleated giant cell formation, enlargement of airspaces, and fibrosis. Despite regression of eosinophils following completion of lung development, AMφ-dominated inflammation persisted, alongside lung damage. Bone marrow chimera studies showed that SH2 domain-containing inositol 5' phosphatase-1-deficient eosinophils were not sufficient to drive inflammatory lung disease in adult steady-state mice but once inflammation and damage were present, it could not be resolved. Depletion of eosinophils during alveolarization alleviated pulmonary inflammation and lung pathology, demonstrating an eosinophil-intrinsic effect. These results show that the presence of activated eosinophils during alveolarization aggravates AMφs and promotes sustained inflammation and long-lasting lung pathology.

The Role of Eosinophils in Liver Disease

Previously, eosinophils were primarily regarded as effector toxic cells involved in allergic diseases and parasitic infections. Nevertheless, new research has shown that eosinophils are diverse and essential for immune regulation and tissue homeostasis. Their functional plasticity has been observed in patients with inflammatory diseases, cancer, infections, and other disorders. Although eosinophils are infrequently observed within the liver during periods of homeostasis, they are recruited to the liver in various liver diseases, including liver parasitosis, acute liver injury, autoimmune liver disease, and hepatocellular carcinoma. Furthermore, eosinophils have demonstrated the capacity to promote liver regeneration. This article explores the multifaceted roles of eosinophils in liver diseases, aiming to provide insights that could lead to more effective clinical therapies for these conditions.

Insight into IL-5 as a Potential Target for the Treatment of Allergic Diseases

Interleukin-5 functions as a B-cell differentiation factor, but more importantly, in the context of this review, it plays a variety of roles in eosinophil biology, including eosinophil differentiation and maturation in the bone marrow, and facilitates eosinophil migration to tissue sites, usually in the context of an allergic reaction. Given the availability of selective anti-IL-5 drugs such as mepolizumab and reslizumab, as well as the IL-5 receptor antagonist benralizumab, it is worth investigating whether they could be used in some cases of allergic disease. Asthma has a well-documented involvement of IL-5 in its pathophysiology and has clear benefits in the case of anti-IL-5 therapy; therefore, current knowledge is presented to provide a reference point for the study of less-described diseases such as atopic dermatitis, chronic rhinosinusitis, chronic spontaneous urticaria, and its association with both IL-5 and anti-IL-5 treatment options. We then review the current literature on these diseases, explain where appropriate potential reasons why anti-IL-5 treatments are ineffective, and then point out possible future directions for further research.

Spatial adaptation of eosinophils and their emerging roles in homeostasis, infection and disease

Eosinophils are bone marrow-derived granulocytes that are traditionally associated with type 2 immune responses, such as those that occur during parasite infections and allergy. Emerging evidence demonstrates the remarkable functional plasticity of this elusive cell type and its pleiotropic functions in diverse settings. Eosinophils broadly contribute to tissue homeostasis, host defence and immune regulation, predominantly at mucosal sites. The scope of their activities primarily reflects the breadth of their portfolio of secreted mediators, which range from cytotoxic cationic proteins and reactive oxygen species to multiple cytokines, chemokines and lipid mediators. Here, we comprehensively review basic eosinophil biology that is directly related to their activities in homeostasis, protective immunity, regeneration and cancer. We examine how dysregulation of these functions contributes to the physiopathology of a broad range of inflammatory diseases. Furthermore, we discuss recent findings regarding the tissue compartmentalization and adaptation of eosinophils, shedding light on the factors that likely drive their functional diversification within tissues.

Eosinophil-Epithelial Cell Interactions in Asthma

BACKGROUND

Eosinophils have numerous roles in type 2 inflammation depending on their activation states in the blood and airway or after encounter with inflammatory mediators. Airway epithelial cells have a sentinel role in the lung and, by instructing eosinophils, likely have a foundational role in asthma pathogenesis.

SUMMARY

In this review, we discuss various topics related to eosinophil-epithelial cell interactions in asthma, including the influence of eosinophils and eosinophil products, e.g., granule proteins, on epithelial cell function, expression, secretion, and plasticity; the effects of epithelial released factors, including oxylipins, cytokines, and other mediators on eosinophils, e.g., on their activation, expression, and survival; possible mechanisms of eosinophil-epithelial cell adhesion; and the role of intra-epithelial eosinophils in asthma.

KEY MESSAGES

We suggest that eosinophils and their products can have both injurious and beneficial effects on airway epithelial cells in asthma and that there are bidirectional interactions and signaling between eosinophils and airway epithelial cells in asthma.

Dietary fiber is a critical determinant of pathologic ILC2 responses and intestinal inflammation

Innate lymphoid cells (ILCs) can promote host defense, chronic inflammation, or tissue protection and are regulated by cytokines and neuropeptides. However, their regulation by diet and microbiota-derived signals remains unclear. We show that an inulin fiber diet promotes Tph1-expressing inflammatory ILC2s (ILC2INFLAM) in the colon, which produce IL-5 but not tissue-protective amphiregulin (AREG), resulting in the accumulation of eosinophils. This exacerbates inflammation in a murine model of intestinal damage and inflammation in an ILC2- and eosinophil-dependent manner. Mechanistically, the inulin fiber diet elevated microbiota-derived bile acids, including cholic acid (CA) that induced expression of ILC2-activating IL-33. In IBD patients, bile acids, their receptor farnesoid X receptor (FXR), IL-33, and eosinophils were all upregulated compared with controls, implicating this diet-microbiota-ILC2 axis in human IBD pathogenesis. Together, these data reveal that dietary fiber-induced changes in microbial metabolites operate as a rheostat that governs protective versus pathologic ILC2 responses with relevance to precision nutrition for inflammatory diseases.

Dupilumab and the potential risk of eosinophilic pneumonia: case report, literature review, and FAERS database analysis

Eosinophilic pneumonia (EP) is a rare but noteworthy adverse effect linked to dupilumab, an interleukin-4 (IL-4) and IL-13 inhibitor used in the managing atopic diseases. The underlying mechanisms, potential predisposing factors, clinical characteristics, and optimal management strategies for dupilumab-induced EP remain unclear. We report a 71-year-old patient who developed acute EP after the first 600-mg dose of dupilumab. Eosinophils (EOSs) were also transiently increased (up to 1,600 cells/μl). After the acute EP was effectively treated with glucocorticoids, dupilumab treatment was continued. Rash, itching, and immunoglobulin E levels continued to decrease in the patient, and no further pulmonary adverse events occurred. We combined this case with a literature review of nine articles and analyzed data from 93 cases reported in the FDA Adverse Event Reporting System (FAERS) database of patients developing EP after dupilumab use. Our findings imply that dupilumab may induce EP, particularly in individuals over 45 years old, those with a history of respiratory diseases, and those who have previously used inhaled or systemic steroids. Vigilance is required, especially when there is a persistent elevation in peripheral blood EOSs during treatment. Although steroid treatment can effectively manage EP, more data are needed to determine the safety of resuming dupilumab treatment after controlling pneumonia.

The dichotomic role of single cytokines: Fine-tuning immune responses

Cytokines are known for their pleiotropic effects. They can be classified by their function as pro-inflammatory, such as tumor necrosis factor (TNF), interleukin (IL) 1 and IL-12, or anti-inflammatory, like IL-10, IL-35 and transforming growth factor β (TGF-β). Though this type of classification is an important simplification for the understanding of the general cytokine's role, it can be misleading. Here, we discuss recent studies that show a dichotomic role of the so-called pro and anti-inflammatory cytokines, highlighting that their function can be dependent on the microenvironment and their concentrations. Furthermore, we discuss how the back-and-forth interplay between cytokines and immunometabolism can influence the dichotomic role of inflammatory responses as an important target to complement cytokine-based therapies.

How inhaled corticosteroids target inflammation in COPD

Inhaled corticosteroids (ICS) are the most commonly used anti-inflammatory drugs for the treatment of COPD. COPD has been previously described as a "corticosteroid-resistant" condition, but current clinical trial evidence shows that selected COPD patients, namely those with increased exacerbation risk plus higher blood eosinophil count (BEC), can benefit from ICS treatment. This review describes the components of inflammation modulated by ICS in COPD and the reasons for the variation in response to ICS between individuals. There are corticosteroid-insensitive inflammatory pathways in COPD, such as bacteria-induced macrophage interleukin-8 production and resultant neutrophil recruitment, but also corticosteroid-sensitive pathways including the reduction of type 2 markers and mast cell numbers. The review also describes the mechanisms whereby ICS can skew the lung microbiome, with reduced diversity and increased relative abundance, towards an excess of proteobacteria. BEC is a biomarker used to enable the selective use of ICS in COPD, but the clinical outcome in an individual is decided by a complex interacting network involving the microbiome and airway inflammation.

Eosinophils-from cradle to grave: An EAACI task force paper on new molecular insights and clinical functions of eosinophils and the clinical effects of targeted eosinophil depletion

Over the past years, eosinophils have become a focus of scientific interest, especially in the context of their recently uncovered functions (e.g. antiviral, anti-inflammatory, regulatory). These versatile cells display both beneficial and detrimental activities under various physiological and pathological conditions. Eosinophils are involved in the pathogenesis of many diseases which can be classified into primary (clonal) and secondary (reactive) disorders and idiopathic (hyper)eosinophilic syndromes. Depending on the biological specimen, the eosinophil count in different body compartments may serve as a biomarker reflecting the underlying pathophysiology and/or activity of distinct diseases and as a therapy-driving (predictive) and monitoring tool. Personalized selection of an appropriate therapeutic strategy directly or indirectly targeting the increased number and/or activity of eosinophils should be based on the understanding of eosinophil homeostasis including their interactions with other immune and non-immune cells within different body compartments. Hence, restoring as well as maintaining homeostasis within an individual's eosinophil pool is a goal of both specific and non-specific eosinophil-targeting therapies. Despite the overall favourable safety profile of the currently available anti-eosinophil biologics, the effect of eosinophil depletion should be monitored from the perspective of possible unwanted consequences.

Eosinophils in obesity and obesity-associated disorders

Despite the rising prevalence and costs for the society, obesity etiology, and its precise cellular and molecular mechanisms are still insufficiently understood. The excessive accumulation of fat by adipocytes plays a key role in obesity progression and has many repercussions on total body physiology. In recent years the immune system as a gatekeeper of adipose tissue homeostasis has been evidenced and has become a focal point of research. Herein we focus on eosinophils, an important component of type 2 immunity, assuming fundamental, yet ill-defined, roles in the genesis, and progression of obesity and related metabolic disorders. We summarize eosinophilopoiesis and eosinophils recruitment into adipose tissue and discuss how the adipose tissue environments shape their function and vice versa. Finally, we also detail how obesity transforms the local eosinophil niche. Understanding eosinophil crosstalk with the diverse cell types within the adipose tissue environment will allow us to framework the therapeutic potential of eosinophils in obesity.

Mechanistic Insights into Eosinophilic Esophagitis: Therapies Targeting Pathophysiological Mechanisms

Eosinophilic esophagitis (EoE) is a chronic inflammatory disease characterized by eosinophilic infiltration of the esophagus. It arises from a complex interplay of genetic predisposition (susceptibility loci), environmental triggers (allergens and dietary antigens), and a dysregulated immune response, mainly mediated by type 2 T helper cell (Th2)-released cytokines, such as interleukin (IL)-4, IL-5, and IL-13. These cytokines control eosinophil recruitment and activation as well as tissue remodeling, contributing to the characteristic features of EoE. The pathogenesis of EoE includes epithelial barrier dysfunction, mast cell activation, eosinophil degranulation, and fibrosis. Epithelial barrier dysfunction allows allergen penetration and promotes immune cell infiltration, thereby perpetuating the inflammatory response. Mast cells release proinflammatory mediators and promote eosinophil recruitment and the release of cytotoxic proteins and cytokines, causing tissue damage and remodeling. Prolonged inflammation can lead to fibrosis, resulting in long-term complications such as strictures and dysmotility. Current treatment options for EoE are limited and mainly focus on dietary changes, proton-pump inhibitors, and topical corticosteroids. Novel therapies targeting key inflammatory pathways, such as monoclonal antibodies against IL-4, IL-5, and IL-13, are emerging in clinical trials. A deeper understanding of the complex pathogenetic mechanisms behind EoE will contribute to the development of more effective and personalized therapeutic strategies.

Degranulation of Mast Cells as a Target for Drug Development

Mast cells act as key effector cells of inflammatory responses through degranulation. Mast cell degranulation is induced by the activation of cell surface receptors, such as FcεRI, MRGPRX2/B2, and P2RX7. Each receptor, except FcεRI, varies in its expression pattern depending on the tissue, which contributes to their differing involvement in inflammatory responses depending on the site of occurrence. Focusing on the mechanism of allergic inflammatory responses by mast cells, this review will describe newly identified mast cell receptors in terms of their involvement in degranulation induction and patterns of tissue-specific expression. In addition, new drugs targeting mast cell degranulation for the treatment of allergy-related diseases will be introduced.

Eosinophilic Airway Diseases: From Pathophysiological Mechanisms to Clinical Practice

Eosinophils play a key role in airway inflammation in many diseases, such as allergic and non-allergic asthma, chronic rhinosinusitis with nasal polyps, and chronic obstructive pulmonary disease. In these chronic disabling conditions, eosinophils contribute to tissue damage, repair, remodeling, and disease persistence through the production a variety of mediators. With the introduction of biological drugs for the treatment of these respiratory diseases, the classification of patients based on clinical characteristics (phenotype) and pathobiological mechanisms (endotype) has become mandatory. This need is particularly evident in severe asthma, where, despite the great scientific efforts to understand the immunological pathways underlying clinical phenotypes, the identification of specific biomarkers defining endotypes or predicting pharmacological response remains unsatisfied. In addition, a significant heterogeneity also exists among patients with other airway diseases. In this review, we describe some of the immunological differences in eosinophilic airway inflammation associated with severe asthma and other airway diseases and how these factors might influence the clinical presentation, with the aim of clarifying when eosinophils play a key pathogenic role and, therefore, represent the preferred therapeutic target.

ILC2 require cell-intrinsic ST2 signals to promote type 2 immune responses

The initiation of type 2 immune responses at mucosal barriers is regulated by rapidly secreted cytokines called alarmins. The alarmins IL-33, IL-25 and TSLP are mainly secreted by stromal and epithelial cells in tissues and were linked to chronic inflammatory diseases, such as allergic lung inflammation, or to resistance against worm infections. Receptors for alarmins are expressed by a variety of immune cells, including group 2 innate lymphoid cells (ILC2s), an early source of the type 2 cytokines, such as IL-5 and IL-13, which have been linked to atopic diseases and anti-worm immunity as well. However, the precise contribution of the IL-33 receptor signals for ILC2 activation still needs to be completed due to limitations in targeting genes in ILC2. Using the newly established Nmur1 iCre-eGFP mouse model, we obtained specific conditional genetic ablation of the IL-33 receptor subunit ST2 in ILC2s. ST2-deficient ILC2s were unresponsive to IL-33 but not to stimulation with the alarmin IL-25. As a result of defective ST2 signals, ILC2s produced limited amounts of IL-5 and IL-13 and failed to support eosinophil homeostasis. Further, ST2-deficient ILC2s were unable to expand and promote the recruitment of eosinophils during allergic lung inflammation provoked by papain administration. During infection with Nippostrongylus brasiliensis, ILC2-intrinsic ST2 signals were required to mount an effective type 2 immune response against the parasite leading to higher susceptibility against worm infection in conditional knockout mice. Therefore, this study argues for a non-redundant role of cell-intrinsic ST2 signals triggering proper activation of ILC2 for initiation of type 2 immunity.

Circumvention of luteolysis reveals parturition pathways in mice dependent upon innate type 2 immunity

Although mice normally enter labor when their ovaries stop producing progesterone (luteolysis), parturition can also be triggered in this species through uterus-intrinsic pathways potentially analogous to the ones that trigger parturition in humans. Such pathways, however, remain largely undefined in both species. Here, we report that mice deficient in innate type 2 immunity experienced profound parturition delays when manipulated endocrinologically to circumvent luteolysis, thus obliging them to enter labor through uterus-intrinsic pathways. We found that these pathways were in part driven by the alarmin IL-33 produced by uterine interstitial fibroblasts. We also implicated important roles for uterine group 2 innate lymphoid cells, which demonstrated IL-33-dependent activation prior to labor onset, and eosinophils, which displayed evidence of elevated turnover in the prepartum uterus. These findings reveal a role for innate type 2 immunity in controlling the timing of labor onset through a cascade potentially relevant to human parturition.

IL-33 induces histidine decarboxylase, especially in c-kit+ cells and mast cells, and roles of histamine include negative regulation of IL-33-induced eosinophilia

OBJECTIVE AND METHODS

IL-33 is present in endothelial, epithelial, and fibroblast-like cells and released upon cell injury. IL-33 reportedly induces mast-cell degranulation and is involved in various diseases, including allergic diseases. So, IL-33-related diseases seem to overlap with histamine-related diseases. In addition to the release from mast cells, histamine is newly formed by the induction of histidine decarboxylase (HDC). Some inflammatory and/or hematopoietic cytokines (IL-1, IL-3, etc.) are known to induce HDC, and the histamine produced by HDC induction is released without storage. We examined the involvement of HDC and histamine in the effects of IL-33.

RESULTS

A single intraperitoneal injection of IL-33 into mice induced HDC directly and/or via other cytokines (including IL-5) within a few hours in various tissues, particularly strongly in hematopoietic organs. The major cells exhibiting HDC-induction were mast cells and c-kit⁺ cells in the bone marrow. HDC was also induced in non-mast cells in non-hematopoietic organs. HDC, histamine, and histamine H4 receptors (H4Rs) contributed to the suppression of IL-33-induced eosinophilia.

CONCLUSION

IL-33 directly and indirectly (via IL-5) induces HDC in various cells, particularly potently in c-kit⁺ cells and mature mast cells, and the newly formed histamine contributes to the negative regulation of IL-33-induced eosinophilia via H4Rs.

Oral Immunotherapy in Food Allergy: Where Are We Now?

Food allergy (FA) has become more prevalent and problematic in the last 2 decades, and it poses important individual, social, and economic burdens. Besides treating reactions induced by accidental exposure and periodic evaluation for acquiring natural tolerance, the primary management approach is still allergen avoidance as a global standard. However, an active therapeutic approach that can raise the reaction threshold or accelerate tolerance is needed. This review aimed to provide an overview and the latest evidence of oral immunotherapy (OIT), which has recently been used in the active treatment of FA. FA immunotherapy, particularly OIT, is gaining considerable interest, and substantial effort has been made to integrate this active treatment into clinical practice. Consequently, growing evidence has been obtained regarding the efficacy and safety of OIT, particularly for allergens such as peanuts, eggs, and milk. However, several issues need to be addressed regarding the availability, safety, and long-term effects of this intervention. In this review, we summarize currently available information regarding tolerance-inducing immune mechanisms of OIT, data on efficacy and safety, gaps in current evidence, and ongoing research to develop new therapeutic molecules in order to enhance safety.

Targeting interleukin-33 and thymic stromal lymphopoietin pathways for novel pulmonary therapeutics in asthma and COPD

Interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP) are alarmins that are released upon airway epithelial injury from insults such as viruses and cigarette smoke, and play critical roles in the activation of immune cell populations such as mast cells, eosinophils and group 2 innate lymphoid cells. Both cytokines were previously understood to primarily drive type 2 (T2) inflammation, but there is emerging evidence for a role for these alarmins to additionally mediate non-T2 inflammation, with recent clinical trial data in asthma and COPD cohorts with non-T2 inflammation providing support. Currently available treatments for both COPD and asthma provide symptomatic relief with disease control, improving lung function and reducing exacerbation rates; however, there still remains an unmet need for further improving lung function and reducing exacerbations, particularly for those not responsive to currently available treatments. The epithelial cytokines/alarmins are involved in exacerbations; biologics targeting TSLP and IL-33 have been shown to reduce exacerbations in moderate-to-severe asthma, either in a broad population or in specific subgroups, respectively. For COPD, while there is clinical evidence for IL-33 blockade impacting exacerbations in COPD, clinical data from anti-TSLP therapies is awaited. Clinical data to date support an acceptable safety profile for patients with airway diseases for both anti-IL-33 and anti-TSLP antibodies in development. We examine the roles of IL-33 and TSLP, their potential use as drug targets, and the evidence for target patient populations for COPD and asthma, together with ongoing and future trials focused on these targets.

IL-5-producing CD4+ T cells and eosinophils cooperate to enhance response to immune checkpoint blockade in breast cancer

Immune checkpoint blockade (ICB) has heralded a new era in cancer therapy. Research into the mechanisms underlying response to ICB has predominantly focused on T cells; however, effective immune responses require tightly regulated crosstalk between innate and adaptive immune cells. Here, we combine unbiased analysis of blood and tumors from metastatic breast cancer patients treated with ICB with mechanistic studies in mouse models of breast cancer. We observe an increase in systemic and intratumoral eosinophils in patients and mice responding to ICB treatment. Mechanistically, ICB increased IL-5 production by CD4⁺ T cells, stimulating elevated eosinophil production from the bone marrow, leading to systemic eosinophil expansion. Additional induction of IL-33 by ICB-cisplatin combination or recombinant IL-33 promotes intratumoral eosinophil infiltration and eosinophil-dependent CD8⁺ T cell activation to enhance ICB response. This work demonstrates the critical role of eosinophils in ICB response and provides proof-of-principle for eosinophil engagement to enhance ICB efficacy.

Human JAK1 gain of function causes dysregulated myelopoeisis and severe allergic inflammation

Primary atopic disorders are a group of inborn errors of immunity that skew the immune system toward severe allergic disease. Defining the biology underlying these extreme monogenic phenotypes reveals shared mechanisms underlying common polygenic allergic disease and identifies potential drug targets. Germline gain-of-function (GOF) variants in JAK1 are a cause of severe atopy and eosinophilia. Modeling the JAK1GOF (p.A634D) variant in both zebrafish and human induced pluripotent stem cells (iPSCs) revealed enhanced myelopoiesis. RNA-Seq of JAK1GOF human whole blood, iPSCs, and transgenic zebrafish revealed a shared core set of dysregulated genes involved in IL-4, IL-13, and IFN signaling. Immunophenotypic and transcriptomic analysis of patients carrying a JAK1GOF variant revealed marked Th cell skewing. Moreover, long-term ruxolitinib treatment of 2 children carrying the JAK1GOF (p.A634D) variant remarkably improved their growth, eosinophilia, and clinical features of allergic inflammation. This work highlights the role of JAK1 signaling in atopic immune dysregulation and the clinical impact of JAK1/2 inhibition in treating eosinophilic and allergic disease.

Therapeutic Potential of Controlled Delivery Systems in Asthma: Preclinical Development of Flavonoid-Based Treatments

Asthma is a chronic disease with increasing prevalence and incidence, manifested by allergic inflammatory reactions, and is life-threatening for patients with severe disease. Repetitive challenges with the allergens and limitation of treatment efficacy greatly dampens successful management of asthma. The adverse events related to several drugs currently used, such as corticosteroids and β-agonists, and the low rigorous adherence to preconized protocols likely compromises a more assertive therapy. Flavonoids represent a class of natural compounds with extraordinary antioxidant and anti-inflammatory properties, with their potential benefits already demonstrated for several diseases, including asthma. Advanced technology has been used in the pharmaceutical field to improve the efficacy and safety of drugs. Notably, there is also an increasing interest for the application of these techniques using natural products as active molecules. Flavones, flavonols, flavanones, and chalcones are examples of flavonoid compounds that were tested in controlled delivery systems for asthma treatment, and which achieved better treatment results in comparison to their free forms. This review aims to provide a comprehensive understanding of the development of novel controlled delivery systems to enhance the therapeutic potential of flavonoids as active molecules for asthma treatment.

STAT6-IP-Dependent Disruption of IL-33-Mediated ILC2 Expansion and Type 2 Innate Immunity in the Murine Lung

Recent interest has focused on innate-type cytokines as promoters of type 2 immunity and targets for drug development in asthma. IL-33 induces production of IL-4 and/or IL-13, which is associated with STAT6-dependent responses in innate cells, including group 2 innate lymphoid cells (ILC2s), macrophages, and eosinophils. Our published data show that STAT6-immunomodulatory peptide (STAT6-IP), an immunomodulatory peptide designed to inhibit the STAT6 transcription factor, reduces induction of Th2 adaptive immunity in respiratory syncytial virus infection and asthma models. Nevertheless, the mechanism of STAT6-IP-dependent inhibition has remained obscure. In this study, we demonstrate that STAT6-IP reduced IL-33-induced type 2 innate lung inflammation. Specifically, our data show that STAT6-IP reduced recruitment and activation of eosinophils as well as polarization of alternatively activated macrophages. Decreases in these cells correlated with reduced levels of IL-5 and IL-13 as well as several type 2 chemokines in the bronchoalveolar lavage fluid. STAT6-IP effectively inhibited expansion of ILC2s as well as the number of IL-5- and IL-13-producing ILC2s. Our data suggest that STAT6-IP effectively disrupts IL-13-dependent positive feedback loops, initiated by ILC2 activation, to suppress IL-33-induced type 2 innate immunity in the murine lung.

Eosinophilic inflammation: An Appealing Target for Pharmacologic Treatments in Severe Asthma

Severe asthma is characterized by different endotypes driven by complex pathologic mechanisms. In most patients with both allergic and non-allergic asthma, predominant eosinophilic airway inflammation is present. Given the central role of eosinophilic inflammation in the pathophysiology of most cases of severe asthma and considering that severe eosinophilic asthmatic patients respond partially or poorly to corticosteroids, in recent years, research has focused on the development of targeted anti-eosinophil biological therapies; this review will focus on the unique and particular biology of the eosinophil, as well as on the current knowledge about the pathobiology of eosinophilic inflammation in asthmatic airways. Finally, current and prospective anti-eosinophil therapeutic strategies will be discussed, examining the reason why eosinophilic inflammation represents an appealing target for the pharmacological treatment of patients with severe asthma.

Hepatic recruitment of eosinophils and their protective function during acute liver injury

BACKGROUND & AIMS

Beyond the classical description of eosinophil functions in parasite infections and allergic diseases, emerging evidence supports a critical role of eosinophils in resolving inflammation and promoting tissue remodeling. However, the role of eosinophils in liver injury and the underlying mechanism of their recruitment into the liver remain unclear.

METHODS

Hepatic eosinophils were detected and quantified using flow cytometry and immunohistochemical staining. Eosinophil-deficient (ΔdblGata1) mice were used to investigate the role of eosinophils in 3 models of acute liver injury. In vivo experiments using Il33-/- mice and macrophage-depleted mice, as well as in vitro cultures of eosinophils and macrophages, were performed to interrogate the mechanism of eotaxin-2 (CCL24) production.

RESULTS

Hepatic accumulation of eosinophils was observed in patients with acetaminophen (APAP)-induced liver failure, whereas few eosinophils were detectable in healthy liver tissues. In mice treated with APAP, carbon tetrachloride or concanavalin A, eosinophils were recruited into the liver and played a profound protective role. Mice deficient of macrophages or IL-33 exhibited impaired hepatic eosinophil recruitment during acute liver injury. CCL24, but not CCL11, was increased after treatment of each hepatotoxin in an IL-33 and macrophage-dependent manner. In vitro experiments demonstrated that IL-33, by stimulating IL-4 release from eosinophils, promoted the production of CCL24 by macrophages.

CONCLUSIONS

This is the first study to demonstrate that hepatic recruitment of and protection by eosinophils occur commonly in various models of acute liver injury. Our findings support further exploration of eosinophils as a therapeutic target to treat APAP-induced acute liver injury.

LAY SUMMARY

The current study unveils that eosinophils are recruited into the liver and play a protective function during acute liver injury caused by acetaminophen overdose. The data demonstrate that IL-33-activated eosinophils trigger macrophages to release high amounts of CCL24, which promotes hepatic eosinophil recruitment. Our findings suggest that eosinophils could be an effective cell-based therapy for the treatment of acetaminophen-induced acute liver injury.

Recent advances of eosinophils and its correlated diseases

Eosinophils are differentiated by bone marrow multipotent progenitor cells and are further released into peripheral blood after maturation. Human eosinophils can exhibit unique multi-leaf nuclear morphology, which are filled with cytoplasmic granules that contain cytotoxicity and immune regulatory proteins. In recent years, many studies focused on the origin, differentiation and development process of eosinophils. It has been discovered that the eosinophils have the regulatory functions of innate and adaptive immunity, and can also function in several diseases, including asthma, chronic obstructive pulmonary diseases, acute respiratory distress syndrome, malignant tumors and so on. Hence, the role and effects of eosinophils in various diseases are emphasized. In this review, we comprehensively summarized the development and differentiation process of eosinophils, the research progress of their related cytokines, diseases and current clinical treatment options, and discussed the potential drug target, aiming to provide a theoretical and practical basis for the clinical prevention and treatment of eosinophil-related diseases, especially respiratory diseases. To conclude, the guiding significance of future disease treatment is proposed based on the recent updated understandings into the cell functions of eosinophils.

Potent CCR3 Receptor Antagonist, SB328437, Suppresses Colonic Eosinophil Chemotaxis and Inflammation in the Winnie Murine Model of Spontaneous Chronic Colitis

Eosinophils and their regulatory molecules have been associated with chronic intestinal inflammation and gastrointestinal dysfunctions; eosinophil accumulation in the gut is prominent in inflammatory bowel disease (IBD). The chemokine receptor CCR3 plays a pivotal role in local and systemic recruitment and activation of eosinophils. In this study, we targeted CCR3-ligand interactions with a potent CCR3 receptor antagonist, SB328437, to alleviate eosinophil-associated immunological responses in the Winnie model of spontaneous chronic colitis. Winnie and C57BL/6 mice were treated with SB328437 or vehicle. Clinical and histopathological parameters of chronic colitis were assessed. Flow cytometry was performed to discern changes in colonic, splenic, circulatory, and bone marrow-derived leukocytes. Changes to the serum levels of eosinophil-associated chemokines and cytokines were measured using BioPlex. Inhibition of CCR3 receptors with SB328437 attenuated disease activity and gross morphological damage to the inflamed intestines and reduced eosinophils and their regulatory molecules in the inflamed colon and circulation. SB328437 had no effect on eosinophils and their progenitor cells in the spleen and bone marrow. This study demonstrates that targeting eosinophils via the CCR3 axis has anti-inflammatory effects in the inflamed intestine, and also contributes to understanding the role of eosinophils as potential end-point targets for IBD treatment.

Rapamycin Dampens Inflammatory Properties of Bone Marrow ILC2s in IL-33-Induced Eosinophilic Airway Inflammation

The alarmin cytokine interleukin (IL)-33 plays an important proinflammatory role in type 2 immunity and can act on type 2 innate lymphoid cells (ILC2s) and type 2 T helper (T_H2) cells in eosinophilic inflammation and asthma. The mechanistic target of rapamycin (mTOR) signaling pathway drives immune responses in several inflammatory diseases, but its role in regulating bone marrow responses to IL-33 is unclear. The aim of this study was to determine the role of the mTORC1 signaling pathway in IL-33-induced bone marrow ILC2 responses and its impact on IL-33-induced eosinophilia. Wild-type mice were intranasally exposed to IL-33 only or in combination with the mTORC1 inhibitor, rapamycin, intraperitoneally. Four groups were included in the study: saline-treated (PBS)+PBS, rapamycin+PBS, PBS+IL-33 and rapamycin+IL-33. Bronchoalveolar lavage fluid (BALF), serum and bone marrow cells were collected and analyzed by differential cell count, enzyme-linked immunosorbent assay and flow cytometry. IL-33 induced phosphorylation of the mTORC1 protein rpS6 in bone marrow ILC2s both ex vivo and in vivo. The observed mTOR signal was reduced by rapamycin treatment, indicating the sensitivity of bone marrow ILC2s to mTORC1 inhibition. IL-5 production by ILC2s was reduced in cultures treated with rapamycin before stimulation with IL-33 compared to IL-33 only. Bone marrow and airway eosinophils were reduced in mice given rapamycin before IL-33-exposure compared to mice given IL-33 only. Bone marrow ILC2s responded to IL-33 in vivo with increased mTORC1 activity and rapamycin treatment successfully decreased IL-33-induced eosinophilic inflammation, possibly by inhibition of IL-5-producing bone marrow ILC2s. These findings highlight the importance of investigating specific cells and proinflammatory pathways as potential drivers of inflammatory diseases, including asthma.

Astegolimab, an anti-ST2, in chronic obstructive pulmonary disease (COPD-ST2OP): a phase 2a, placebo-controlled trial

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a heterogeneous inflammatory airway disease. The epithelial-derived IL-33 and its receptor ST2 have been implicated in airway inflammation and infection. We aimed to determine whether astegolimab, a selective ST2 IgG2 monoclonal antibody, reduces exacerbations in COPD.

METHODS

COPD-ST2OP was a single-centre, randomised, double-blinded, placebo-controlled phase 2a trial in moderate-to-very severe COPD. Participants were randomly assigned (1:1) with a web-based system to received 490 mg subcutaneous astegolimab or subcutaneous placebo, every 4 weeks for 44 weeks. The primary endpoint was exacerbation rate assessed for 48 weeks assessed with a negative binomial count model in the intention-to-treat population, with prespecified subgroup analysis by baseline blood eosinophil count. The model was the number of exacerbations over the 48-week treatment period, with treatment group as a covariate. Safety was assessed in the whole study population until week 60. Secondary endpoints included Saint George's Respiratory Questionnaire for COPD (SGRQ-C), FEV₁, and blood and sputum cell counts. The trial was registered with ClinicalTrials.gov, NCT03615040.

FINDINGS

The exacerbation rate at 48 weeks in the intention-to-treat analysis was not significantly different between the astegolimab group (2·18 [95% CI 1·59 to 2·78]) and the placebo group (2·81 [2·05 to 3·58]; rate ratio 0·78 [95% CI 0·53 to 1·14]; p=0·19]). In the prespecified analysis stratifying patients by blood eosinophil count, patients with 170 or fewer cells per μL had 0·69 exacerbations (0·39 to 1·21), whereas those with more than 170 cells per μL had 0·83 exacerbations (0·49 to 1·40). For the secondary outcomes, the mean difference between the SGRQ-C in the astegolimab group versus placebo group was -3·3 (95% CI -6·4 to -0·2; p=0·039), and mean difference in FEV₁ between the two groups was 40 mL (-10 to 90; p=0·094). The difference in geometric mean ratios between the two groups for blood eosinophil counts was 0·59 (95% CI 0·51 to 0·69; p<0·001) and 0·25 (0·19 to 0·33; p<0·001) for sputum eosinophil counts. Incidence of treatment-emergent adverse events was similar between groups.

INTERPRETATION

In patients with moderate-to-very severe COPD, astegolimab did not significantly reduce exacerbation rate, but did improve health status compared with placebo.

FUNDING

Funded by Genentech and National Institute for Health Research Biomedical Research Centres.

Elastase- and LPS-Exposed Cpa3Cre/+ and ST2-/- Mice Develop Unimpaired Obstructive Pulmonary Disease

IL-33 and its receptor ST2, as well as mast cells and their mediators, have been implicated in the development of chronic obstructive pulmonary disease (COPD). However, whether mast cells and the ST2 receptor play a critical role in COPD pathophysiology remains unclear. Here, we performed repeated intranasal administrations of porcine pancreatic elastase and LPS for four weeks to study COPD-like disease in wildtype, ST2-deficient, and Cpa3^Cre/+ mice, which lack mast cells and have a partial reduction in basophils. Alveolar enlargement and changes in spirometry-like parameters, e.g. increased dynamic compliance and decreased expiratory capacity, were evident one day after the final LPS challenge and worsened over time. The elastase/LPS model also induced mild COPD-like airway inflammation, which encompassed a transient increase in lung mast cell progenitors, but not in mature mast cells. While ST2-deficient and Cpa3^Cre/+ mice developed reduced pulmonary function uninterruptedly, they had a defective inflammatory response. Importantly, both ST2-deficient and Cpa3^Cre/+ mice had fewer alveolar macrophages, known effector cells in COPD. Elastase/LPS instillation in vivo also caused increased bronchiole contraction in precision cut lung slices challenged with methacholine ex vivo, which occurred in a mast cell-independent fashion. Taken together, our data suggest that the ST2 receptor and mast cells play a minor role in COPD pathophysiology by sustaining alveolar macrophages.

Siglec-F Promotes IL-33-Induced Cytokine Release from Bone Marrow-Derived Eosinophils Independently of the ITIM and ITIM-like Motif Phosphorylation

Eosinophils are potent innate effector cells associated mainly with type 2 immune responses elicited by helminths and allergens. Their activity needs to be tightly controlled to prevent severe inflammation and tissue damage. Eosinophil degranulation and secretion of inflammatory effector molecules, including cytokines, chemokines, and lipid mediators, can be regulated by activating and inhibitory receptors on the cell surface. In this study, we investigated the modulation of proliferation, apoptosis, gene expression, and cytokine/chemokine secretion from IL-33-activated Mus musculus eosinophils on cross-linking of the transmembrane receptor Sialic acid-binding Ig-like lectin F (Siglec-F). Siglec-F contains an ITIM plus an ITIM-like motif in its intracellular tail and is mainly regarded as an inhibitory and apoptosis-inducing receptor. In vitro costimulation of bone marrow-derived eosinophils with anti-Siglec-F and IL-33 compared with treatment with either alone led to enhanced STAT6 phosphorylation, stronger induction of hypoxia/glycolysis-related proinflammatory genes, and elevated secretion of type 2 cytokines (IL-4, IL-13) and chemokines (CCL3, CCL4) with only minor effects on proliferation and apoptosis. Using a competitive mixed bone marrow chimera approach with wild-type and Siglec-F-deficient eosinophils, we observed no evidence for Siglec-F-regulated inhibition of Aspergillus fumigatus-elicited lung eosinophilia. Truncation of the Siglec-F cytoplasmic tail, but not mutation of the ITIM and ITIM-like motifs, ablated the effect of enhanced cytokine/chemokine secretion. This provides evidence for an ITIM phosphorylation-independent signaling pathway from the cytoplasmic tail of the Siglec-F receptor that enhances effector molecule release from activated eosinophils.

Type 2 Inflammation in Eosinophilic Esophagitis: From Pathophysiology to Therapeutic Targets

Eosinophilic esophagitis (EoE) is a chronic immune-mediated disease of the esophagus characterized clinically by symptoms related to esophageal dysfunction and histologically by eosinophil-predominant inflammation, whose incidence is rising. It significantly affects patients’ quality of life and, if left untreated, results in fibrotic complications. Although broad consensus has been achieved on first-line therapy, a subset of patients remains non-responder to standard therapy. The pathogenesis of EoE is multifactorial and results from the complex, still mostly undefined, interaction between genetics and intrinsic factors, environment, and antigenic stimuli. A deep understanding of the pathophysiology of this disease is pivotal for the development of new therapies. This review provides a comprehensive description of the pathophysiology of EoE, starting from major pathogenic mechanisms (genetics, type 2 inflammation, epithelial barrier dysfunction, gastroesophageal reflux, allergens, infections and microbiota) and subsequently focusing on the single protagonists of type 2 inflammation (involved cells, cytokines, soluble effectors, surface proteins and transcription factors) that could represent present and future therapeutic targets, while summarizing previous therapeutic approaches in literature.

Trained immunity in type 2 immune responses

Immunological memory of innate immune cells, also termed "trained immunity", allows for cross-protection against distinct pathogens, but may also drive chronic inflammation. Recent studies have shown that memory responses associated with type 2 immunity do not solely rely on adaptive immune cells, such as T- and B cells, but also involve the innate immune system and epithelial cells. Memory responses have been described for monocytes, macrophages and airway epithelial cells of asthmatic patients as well as for macrophages and group 2 innate lymphoid cells (ILC2) from allergen-sensitized or helminth-infected mice. The metabolic and epigenetic mechanisms that mediate allergen- or helminth-induced reprogramming of innate immune cells are only beginning to be uncovered. Trained immunity has been implicated in helminth-driven immune regulation and allergen-specific immunotherapy, suggesting its exploitation in future therapies. Here, we discuss recent advances and key remaining questions regarding the mechanisms and functions of trained type 2 immunity in infection and inflammation.

Emerging Role of Eosinophils in Resolution of Arthritis

Eosinophils are a minor component of circulating granulocytes, which are classically viewed as end-stage effector cells in host defense against helminth infection and promoting allergic responses. However, a growing body of evidence has emerged showing that eosinophils are versatile leukocytes acting as an orchestrator in the resolution of inflammation. Rheumatoid arthritis (RA) is the most common chronic inflammatory disease characterized by persistent synovitis that hardly resolves spontaneously. Noteworthy, a specific population of eosinophils, that is, regulatory eosinophils (rEos), was identified in the synovium of RA patients, especially in disease remission. Mechanistically, the rEos in the synovium display a unique pro-resolving signature that is distinct from their counterpart in the lung. Herein, we summarize the latest understanding of eosinophils and their emerging role in promoting the resolution of arthritis. This knowledge is crucial to the design of new approaches to rebalancing immune homeostasis in RA, considering that current therapies are centered on inhibiting pro-inflammatory cytokines and mediators rather than fostering the resolution of inflammation.

The Role of CD4+ T Cells and Microbiota in the Pathogenesis of Asthma

Asthma, a chronic respiratory disease involving variable airflow limitations, exhibits two phenotypes: eosinophilic and neutrophilic. The asthma phenotype must be considered because the prognosis and drug responsiveness of eosinophilic and neutrophilic asthma differ. CD4+ T cells are the main determinant of asthma phenotype. Th2, Th9 and Tfh cells mediate the development of eosinophilic asthma, whereas Th1 and Th17 cells mediate the development of neutrophilic asthma. Elucidating the biological roles of CD4+ T cells is thus essential for developing effective asthma treatments and predicting a patient's prognosis. Commensal bacteria also play a key role in the pathogenesis of asthma. Beneficial bacteria within the host act to suppress asthma, whereas harmful bacteria exacerbate asthma. Recent literature indicates that imbalances between beneficial and harmful bacteria affect the differentiation of CD4+ T cells, leading to the development of asthma. Correcting bacterial imbalances using probiotics reportedly improves asthma symptoms. In this review, we investigate the effects of crosstalk between the microbiota and CD4+ T cells on the development of asthma.

Purified Native and Recombinant Major Alternaria alternata Allergen (Alt a 1) Induces Allergic Asthma in the Murine Model

Aeroallergens such us the spores of Alternaria alternata are described as the most important agents associated with respiratory allergies and severe asthma. Various experimental models of asthma have been developed using A. alternata extracts to study the pathogenesis of asthma, establishing the main parameters that trigger the asthmatic response. In this study, we describe a mouse model of asthma induced only by Alt a 1. To induce the allergic response, mice were challenged intranasally with the major allergen of A. alternata, Alt a 1. The presence of eosinophils in the lungs, elevated concentrations of Th2 family cytokines, lymphocyte proliferation and elevated IgE total serum levels indicated that the sensitisation and challenge with Alt a 1 induced the development of airway inflammation. Histological studies showed an eosinophilic cellular infiltrate in the lung tissue of mice instilled with Alt a 1. We demonstrate that Alt a 1 alone is capable of inducing a lung inflammatory response with an increase in IgE serum levels mimicking the allergic asthma immunoresponse when it is administered into BALB/c mice. This model will allow the evaluation of the immunoregulatory or immunotolerant capacity of several molecules that can be used in targeted immunotherapy for fungal allergic asthma.

Pharmacokinetics and pharmacodynamics of itepekimab in healthy adults and patients with asthma: Phase I first-in-human and first-in-patient trials

Itepekimab is a monoclonal antibody that targets interleukin (IL‐33) and has been shown to reduce airway inflammation and associated tissue damage in preclinical studies. We assessed the safety, tolerability, pharmacokinetics (PKs), and pharmacodynamic profiles of single‐ascending and multiple‐ascending doses of itepekimab in two randomized, double‐blind, placebo‐controlled phase I studies. Healthy adults (N = 40) were randomized to the single‐dose study and patients with moderate asthma (N = 23) to the multiple‐dose study. Itepekimab was administered intravenously (0.3, 1, 3, or 10 mg/kg infusion) or subcutaneously (150 mg) in the single‐dose study and subcutaneously (75 or 150 mg weekly for 4 weeks) in the multiple‐dose study. Itepekimab exhibited linear PKs across studies and dose‐proportional increases in mean maximum concentration in serum and area under the concentration–time curve following single intravenous or multiple subcutaneous doses. Itepekimab demonstrated mean subcutaneous bioavailability of 59–73% and a long terminal half‐life (30.0–31.6 days). IL‐33 concentrations in most healthy participants and patients with asthma were undetectable at baseline. Following administration of itepekimab in both studies, total IL‐33 concentrations increased and blood eosinophils decreased, both with durable effect. Itepekimab was well‐tolerated in both studies with no detection of treatment‐emergent anti‐drug antibody responses.

Eosinophils, a Jack of All Trades in Immunity: Therapeutic Approaches for Correcting Their Functional Disorders

BACKGROUND AND OBJECTIVE

Eosinophils are primitive myeloid cells derived from bonemarrow precursors and require the intervention of interleukin (IL)-5 for their survival and persistence in blood and tissues. Under steady-state conditions, they contribute to immune regulation and homeostasis. Under pathological circumstances, eosinophils are involved in host protection against parasites and participate in allergy and inflammation.

DISCUSSION

Mostly, in asthma, eosinophils provoke airway damage via the release of granule contents and IL-13 with mucus hypersecretion and differentiation of goblet cells. Then, tissue remodeling follows with the secretion of transforming growth factor-β. Eosinophils are able to kill helminth larvae acting as antigen-presenting cells with the involvement of T helper (h)-2 cells and subsequent antibody response. However, they also exert pro-worm activity with the production of suppressive cytokine (IL- 10 and IL-4) and inhibition of nitric oxide. Eosinophils may play a pathogenic role in the course of chronic and autoimmune disease, e.g., inflammatory bowel disease and eosinophilic gastroenteritis, regulating Th2 responses and promoting a profibrotic effect. In atopic dermatitis, eosinophils are commonly detected and may be associated with disease severity. In cutaneous spontaneous urticaria, eosinophils participate in the formation of wheals, tissue remodeling and modifications of vascular permeability. With regard to tumor growth, it seems that IgE can exert anti-neoplastic surveillance via mast cell and eosinophil-mediated cytotoxicity, the so-called allergo-oncology. From a therapeutic point of view, monoclonal antibodies directed against IL-5 or the IL-5 receptors have been shown to be very effective in patients with severe asthma. Finally, as an alternative treatment, polyphenols for their anti-inflammatory and anti-allergic activities seem to be effective in reducing serum IgE and eosinophil count in bronchoalveolar lavage in murine asthma.

CONCLUSION

Eosinophils are cells endowed with multiple functions and their modulation with monoclonal antibodies and nutraceuticals may be effective in the treatment of chronic disease.

Emerging Evidence for Pleiotropism of Eosinophils

Eosinophils are complex granulocytes with the capacity to react upon diverse stimuli due to their numerous and variable surface receptors, which allows them to respond in very different manners. Traditionally believed to be only part of parasitic and allergic/asthmatic immune responses, as scientific studies arise, the paradigm about these cells is continuously changing, adding layers of complexity to their roles in homeostasis and disease. Developing principally in the bone marrow by the action of IL-5 and granulocyte macrophage colony-stimulating factor GM-CSF, eosinophils migrate from the blood to very different organs, performing multiple functions in tissue homeostasis as in the gastrointestinal tract, thymus, uterus, mammary glands, liver, and skeletal muscle. In organs such as the lungs and gastrointestinal tract, eosinophils are able to act as immune regulatory cells and also to perform direct actions against parasites, and bacteria, where novel mechanisms of immune defense as extracellular DNA traps are key factors. Besides, eosinophils, are of importance in an effective response against viral pathogens by their nuclease enzymatic activity and have been lately described as involved in severe acute respiratory syndrome coronavirus SARS-CoV-2 immunity. The pleiotropic role of eosinophils is sustained because eosinophils can be also detrimental to human physiology, for example, in diseases like allergies, asthma, and eosinophilic esophagitis, where exosomes can be significant pathophysiologic units. These eosinophilic pathologies, require specific treatments by eosinophils control, such as new monoclonal antibodies like mepolizumab, reslizumab, and benralizumab. In this review, we describe the roles of eosinophils as effectors and regulatory cells and their involvement in pathological disorders and treatment.

Protective role of IL33 signaling in negative pregnancy outcomes associated with lipopolysaccharide exposure

Interleukin 33 (IL33) signaling has been implicated in the establishment and maintenance of pregnancy and in pregnancy disorders. The goal of this project was to evaluate the role of IL33 signaling in rat pregnancy. The rat possesses hemochorial placentation with deep intrauterine trophoblast invasion; features also characteristic of human placentation. We generated and characterized a germline mutant rat model for IL33 using CRISPR/Cas9 genome editing. IL33 deficient rats exhibited deficits in lung responses to an inflammatory stimulus (Sephadex G-200) and to estrogen-induced uterine eosinophilia. Female rats deficient in IL33 were fertile and exhibited pregnancy outcomes (gestation length and litter size) similar to wild-type rats. Placental weight was adversely affected by the disruption of IL33 signaling. A difference in pregnancy-dependent adaptations to lipopolysaccharide (LPS) exposure was observed between wild-type and IL33 deficient pregnancies. Pregnancy in wild-type rats treated with LPS did not differ significantly from pregnancy in vehicle-treated wild-type rats. In contrast, LPS treatment decreased fetal survival rate, fetal and placental weights, and increased fetal growth restriction in IL33 deficient rats. In summary, a new rat model for investigating IL33 signaling has been established. IL33 signaling participates in the regulation of placental development and protection against LPS-induced fetal and placental growth restriction.

The use of biologics in food allergy

BACKGROUND

Food allergy continues to pose problems due to its increased frequency and its increasingly high severity. In this context, alongside the traditional avoidance strategies of allergenic foods and desensitization through the cautious progression of exposure to foods in the context of oral immunotherapy (OIT), alternative strategies have made their way in the last decades. We review the possibilities of intervention in food allergy with the use of biological drugs capable of interfering with the synthesis of IgE, with their mechanisms of action, or with complex biological mechanisms that lead to the establishment of a food allergy.

METHODS

Repeated Entrez PubMed searches using the template algorithm "Food allergy" and "biologics" or "Omalizumab" or "Dupilumab" or "milk desensitization" or "oral tolerance induction" or "oral immunotherapy" or "Etokimab" or "Tezepelumab" or "Quilizumab" or "Ligelizumab" or "Tralokinumab" or "Nemolizumab" or "Mepolizumab" or "Reslizumab" or "Benralizumab". The authors' clinical experience in paediatric allergy units of University hospitals was also drawn upon.

RESULTS

The landscape in this context has changed dramatically over the past 10 years. We have acquired knowledge mainly on the effect of different types of anti-IgE treatments in poliallergic patients with food allergy, and in patients treated with OIT. However, other mediators are being targeted by specific biologic treatments. Among them, the alarmins Il-33 and TSLP, IL-4 and IL-13, eosinophil-related molecules as IL-6, IL-8, IL-10, IL-12, and mostly IL-5, and integrins involved in the pathogenesis of eosinophilic gastrointestinal diseases (EGIDs), as SIGLEC-8.

CONCLUSIONS

The ever-better knowledge of the mechanisms of food allergy allowing these developments will improve not only the perspective of patients with the most serious immediate food allergies such as anaphylaxis, but also those of patients with related diseases such as atopic dermatitis, eosinophilic esophagitis, and EGIDs. Biologics are also intended to complement OIT strategies that have developed over the years.

Regulation of eosinophil functions by autophagy

Eosinophils are granule-containing leukocytes which develop in the bone marrow. For many years, eosinophils have been recognized as cytotoxic effector cells, but recent studies suggest that they perform additional immunomodulatory and homeostatic functions. Autophagy is a conserved intracellular process which preserves cellular homeostasis. Autophagy defects have been linked to the pathogenesis of many human disorders. Evidence for abnormal regulation of autophagy, including decreased or increased expression of autophagy-related (ATG) proteins, has been reported in several eosinophilic inflammatory disorders, such as Crohn's disease, bronchial asthma, eosinophilic esophagitis, and chronic rhinosinusitis. Despite the increasing extent of research using preclinical models of immune cell-specific autophagy deficiency, the physiological relevance of autophagic pathway in eosinophils has remained unknown until recently. Owing to the increasing evidence that eosinophils play a role in keeping organismal homeostasis, the regulation of eosinophil functions is of considerable interest. Here, we discuss the most recent advances on the role of autophagy in eosinophils, placing particular emphasis on insights obtained in mouse models of infections and malignant diseases in which autophagy has genetically dismantled in the eosinophil lineage. These studies pointed to the possibility that autophagy-deficient eosinophils exaggerate inflammation. Therefore, the pharmacological modulation of the autophagic pathway in these cells could be used for therapeutic interventions.

The twilight zone: plasticity and mixed ontogeny of neutrophil and eosinophil granulocyte subsets

It is now becoming clear that neutrophils and eosinophils are heterogeneous cells with potentially multiple subsets in health and disease. With greater marker coverage by multi-color flow cytometry and single-cell level sequencing of granulocyte populations, novel phenotypes of these cells began to emerge. Intriguingly, many newly described subsets blend distinctions between classical myeloid lineage phenotypes, which are especially true for tissue resident or recruited cells in contexts of inflammation and disease. This includes reports of neutrophils with features of eosinophils, monocytes and dendritic cells, and eosinophil subsets expressing neutrophil markers. Moreover, novel studies show the ability of immature neutrophils to transdifferentiate into mature cells belonging to other myeloid lineages (eosinophils, monocytes/macrophages). In this review, we summarize novel findings in this exciting research frontier and shed light on potential processes driving the plasticity and heterogeneity of granulocyte subsets. Specifically, we discuss the hematopoietic flexibility of granulocyte precursors in bone marrow and the adaptation of myeloid cells to local tissue microenvironments. The understanding of such intermediate and developmental phenotypes is very important, as it can teach us about origins of functionally distinct myeloid cells during inflammation, and explain reasons for successes and failures of biologics targeting terminally differentiated granulocytes.

IL-33 promotes innate lymphoid cell-dependent IFN-γ production required for innate immunity to Toxoplasma gondii

IL-33 is an alarmin required for resistance to the parasite Toxoplasma gondii, but its role in innate resistance to this organism is unclear. Infection with T. gondii promotes increased stromal cell expression of IL-33, and levels of parasite replication correlate with release of IL-33 in affected tissues. In response to infection, a subset of innate lymphoid cells (ILC) emerges composed of IL-33R+ NK cells and ILC1s. In Rag1-/-mice, where NK cells and ILC1 production of IFN-γ mediate innate resistance to T. gondii, the loss of the IL-33R resulted in reduced ILC responses and increased parasite replication. Furthermore, administration of IL-33 to Rag1-/- mice resulted in a marked decrease in parasite burden, increased production of IFN-γ, and the recruitment and expansion of inflammatory monocytes associated with parasite control. These protective effects of exogenous IL-33 were dependent on endogenous IL-12p40 and the ability of IL-33 to enhance ILC production of IFN-γ. These results highlight that IL-33 synergizes with IL-12 to promote ILC-mediated resistance to T. gondii.

Role of Short Chain Fatty Acids and Apolipoproteins in the Regulation of Eosinophilia-Associated Diseases

Eosinophils are key components of our host defense and potent effectors in allergic and inflammatory diseases. Once recruited to the inflammatory site, eosinophils release their cytotoxic granule proteins as well as cytokines and lipid mediators, contributing to parasite clearance but also to exacerbation of inflammation and tissue damage. However, eosinophils have recently been shown to play an important homeostatic role in different tissues under steady state. Despite the tremendous progress in the treatment of eosinophilic disorders with the implementation of biologics, there is an unmet need for novel therapies that specifically target the cytotoxic effector functions of eosinophils without completely depleting this multifunctional immune cell type. Recent studies have uncovered several endogenous molecules that decrease eosinophil migration and activation. These include short chain fatty acids (SCFAs) such as butyrate, which are produced in large quantities in the gastrointestinal tract by commensal bacteria and enter the systemic circulation. In addition, high-density lipoprotein-associated anti-inflammatory apolipoproteins have recently been shown to attenuate eosinophil migration and activation. Here, we focus on the anti-pathogenic properties of SCFAs and apolipoproteins on eosinophil effector function and provide insights into the potential use of SCFAs and apolipoproteins (and their mimetics) as effective agents to combat eosinophilic inflammation.

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.

Biologics in food allergy: up-to-date

Introduction: In recent years, the advent of immunotherapy has remarkably improved the management of IgE-mediated food allergy. However, some barriers still exist. Therefore, the effort of researchers aims to investigate new perspectives in the field of non-allergen specific therapy, also based on the current knowledge of the pathogenesis of this disease.Areas covered: This review aims to focus on the role of biologics as a treatment option in patients with IgE-mediated food allergy. These agents are characterized by their ability to inactivate the Th2 pro-inflammatory pathways. Biologics can be used both alone and in association with immunotherapy. Monoclonal antibodies targeting IgE, the IL-4/IL-13 axis, IL-5, and alarmins have been proposed and investigated for treating food allergy.Expert opinion: The clinical efficacy and safety of biologics have been demonstrated in several preclinical studies and randomized controlled trials. Future studies are still required to address current unmet needs, including the identification of the optimal dose to be used by ensuring the effectiveness of therapy.

IL-33 promotes anemia during chronic inflammation by inhibiting differentiation of erythroid progenitors

An important comorbidity of chronic inflammation is anemia, which may be related to dysregulated activity of hematopoietic stem and progenitor cells (HSPCs) in the bone marrow (BM). Among HSPCs, we found that the receptor for IL-33, ST2, is expressed preferentially and highly on erythroid progenitors. Induction of inflammatory spondyloarthritis in mice increased IL-33 in BM plasma, and IL-33 was required for inflammation-dependent suppression of erythropoiesis in BM. Conversely, administration of IL-33 in healthy mice suppressed erythropoiesis, decreased hemoglobin expression, and caused anemia. Using purified erythroid progenitors in vitro, we show that IL-33 directly inhibited terminal maturation. This effect was dependent on NF-κB activation and associated with altered signaling events downstream of the erythropoietin receptor. Accordingly, IL-33 also suppressed erythropoietin-accelerated erythropoiesis in vivo. These results reveal a role for IL-33 in pathogenesis of anemia during inflammatory disease and define a new target for its treatment.

β-Glucosylceramide From Allergic Mothers Enhances Offspring Responsiveness to Allergen

In animals and humans, offspring of allergic mothers have increased responsiveness to allergen and the allergen-specificity of the offspring can be different than that of the mother. In our preclinical models, the mother's allergic responses influence development of the fetus and offspring by elevating numbers of cells in dendritic cell subsets. A major question is the identity of maternal factors of allergic mothers that alter offspring development of responsiveness to allergen. Lipids are altered during allergic responses and lipids are transported to the fetus for growth and formation of fetal membranes. We hypothesized that pro-inflammatory lipids, that are elevated in allergic mothers, are transported to the fetus and regulate fetal immune development. We demonstrate in this report that there was a significant 2-fold increase in β-glucosylceramides (βGlcCer) in allergic mothers, the fetal liver and her offspring. The βGlcCer were transported from mother's plasma, across the placenta, to the fetus and in breastmilk to the offspring. Administration of βGlcCer to non-allergic mothers was sufficient for offspring responses to allergen. Importantly, maternal administration of a clinically relevant pharmacological inhibitor of βGlcCer synthase returned βGlcCer to normal levels in the allergic mothers and her offspring and blocked the offspring increase in dendritic cell subsets and offspring allergen responsiveness. In summary, allergic mothers had increased βGlcCer that was transported to offspring and mediated increases in offspring DCs and responsiveness to allergen. These data have a significant impact on our understanding of mechanisms for development of allergies in offspring of allergic mothers and have the potential to lead to novel interventions that significantly impact risk for allergic disease early in life.