Human versus mouse eosinophils: "that which we call an eosinophil, by any other name would stain as red"

Eosinophils: old cells, new directions

Eosinophils are polymorphonuclear cells that have progressively gained attention due to their involvement in multiple diseases and, more recently, in various homeostatic processes. Their well-known roles range from asthma and parasitic infections to less prevalent diseases such as eosinophilic granulomatosis with polyangiitis, eosinophilic esophagitis, and hypereosinophilic syndrome. In recent years, various biological therapies targeting these cells have been developed, altering the course of eosinophilic pathologies. Recent research has demonstrated differences in eosinophil subtypes and their functions. The presence of distinct classes of eosinophils has led to the theory of resident eosinophils (rEos) and inflammatory eosinophils (iEos). Subtype differences are determined by the pattern of protein expression on the cell membrane and the localization of eosinophils. Most of this research has been conducted in murine models, but several studies confirm these findings in peripheral blood and tissue. The objective of this review is to provide a comprehensive analysis of eosinophils, by recent findings that divide this cell line into two distinct populations with different functions and purposes.

CCL24 and Fibrosis: A Narrative Review of Existing Evidence and Mechanisms

Tissue fibrosis results from a dysregulated and chronic wound healing response accompanied by chronic inflammation and angiogenesis. Regardless of the affected organ, fibrosis shares the following common hallmarks: the recruitment of immune cells, fibroblast activation/proliferation, and excessive extracellular matrix deposition. Chemokines play a pivotal role in initiating and advancing these fibrotic processes. CCL24 (eotaxin-2) is a chemokine secreted by immune cells and epithelial cells, which promotes the trafficking of immune cells and the activation of profibrotic cells through CCR3 receptor binding. Higher levels of CCL24 and CCR3 were found in the tissue and sera of patients with fibro-inflammatory diseases, including primary sclerosing cholangitis (PSC), systemic sclerosis (SSc), and metabolic dysfunction-associated steatohepatitis (MASH). This review delves into the intricate role of CCL24 in fibrotic diseases, highlighting its impact on fibrotic, immune, and vascular pathways. We focus on the preclinical and clinical evidence supporting the therapeutic potential of blocking CCL24 in diseases that involve excessive inflammation and fibrosis.

Eosinopenia in patients with acute myocardial infarction- longitudinal imaging insights from the CAPRI study

Eosinophils are recruited to the heart during acute myocardial infarction (MI) and are considered part of the inflammatory response associated with adverse clinical outcomes. We assessed the impact of eosinopenia on cardiac imaging biomarkers in patients presenting with ST-segment elevation MI. This is a post-hoc analysis of the Evaluating the effectiveness of intravenous Ciclosporin on reducing reperfusion injury in pAtients undergoing PRImary percutaneous coronary intervention (CAPRI) trial. Patients underwent cardiac MRI within 1 week and 12 weeks and low eosinophil was defined as less than 40 cells/ml. The study included 52 patients and 38% had low eosinophil. Ciclosporin administration was comparable between patients with low versus normal eosinophils. The ischaemia time was significantly longer in low eosinophil patients [262 (205-325) vs. 138 (102-195) minutes, P < 0.001]. At 12 weeks, patients with eosinopenia had larger infarct size [9.8% (5.7-18.4) vs. 7.4% (1.9-10.2), P = 0.045], larger left ventricle (LV) end systolic volume (89 ± 28 vs. 68 ± 23, P = 0.02), and lower LV ejection fraction (EF) (49 ± 9 vs. 58 ± 7, P < 0.001). After adjustments for significant predictors, including ischaemia time, low eosinophil count was an independent predictor of worse LVEF at 12 weeks [-5.78, 95% CI (-11.22 to -0.34), P = 0.038] but not infarct size [1.83, 95% CI (-2.77 to 6.43), P = 0.43]. Patients with low eosinophil count had larger infarct size and LV volumes and worse adverse remodeling compared to those with normal eosinophil count. At 12 weeks, eosinopenia was an independent predictor of worse LVEF but not infarct size.

Long-Term Eosinophil Depletion: A Real-World Perspective on the Safety and Durability of Benralizumab Treatment in Severe Eosinophilic Asthma

Background/Objectives: Benralizumab is an anti-IL-5 receptor alpha monoclonal antibody that induces the near-complete depletion of eosinophils. This study aimed to evaluate the long-term safety and effectiveness of benralizumab in patients with severe eosinophilic asthma (SEA) over an extended 48-month follow-up period, offering one of the longest real-world perspectives available. Methods: This was a single-arm, retrospective, observational, multicenter study involving 123 SEA patients treated with benralizumab at a dosage of 30 mg every 4 weeks for the first 3 doses and then every 8 weeks. The safety endpoints focused on the frequency and nature of adverse events and the likelihood that they were induced by benralizumab. The efficacy endpoints focused on lung function, asthma exacerbations and control, and oral corticosteroid use. Results: Benralizumab, consistent with its mechanism of action, led to the rapid and nearly complete depletion of eosinophils. In total, 26 adverse events (21.1%) were observed, with 1.6% related to the treatment and 0.8% categorized as serious (vagal hypotension). Bronchitis was the most common unrelated adverse event (15.4%), occurring between months 36 and 38. Importantly, benralizumab effectiveness and safety were maintained consistently across the 48-month duration, resulting in significant improvements in lung function and reductions in oral corticosteroid use and exacerbation frequency. Conclusions: Benralizumab demonstrated a favorable safety profile, comparable to previously published studies, with perdurable effectiveness in controlling SEA and reducing oral corticosteroid use. Finally, this study provides evidence that near-complete eosinophil depletion does not increase long-term safety risks and supports benralizumab as a reliable treatment option for SEA patients.

A Glucose-Responsive Glucagon-Micelle for the Prevention of Hypoglycemia

While glucose-responsive insulin delivery systems are in widespread clinical use to treat insulin insufficiency, the on-demand supplementation of glucagon for acute hypoglycemia treatment remains understudied. A self-regulated glucagon release material is highly desired to mitigate the potential risks of severe insulin-induced hypoglycemia. Here, we describe a glucose-responsive polymeric nanosystem with glucagon covalently grafted to the end-group. Under normoglycemic conditions, phenylboronic acid units in the polymer chain reversibly bind glucose, triggering self-assembly of the conjugate into micelles. During hypoglycemia, however, the micelle disassembles into its original, unimeric state, revealing the active glucagon conjugate. The formulation showed a 5-fold increase in activity compared to native glucagon when tested in vitro. Glucagon-loaded micelles injected into mice prevented or reversed deep hypoglycemia when administered prior to or during an insulin challenge. Glucagon release was only observed at or below the counterregulatory threshold and not during normoglycemia or moderate hypoglycemia. The in vivo acute and chronic toxicity analysis, along with μPET/μCT imaging, established the biosafety profile of this formulation and demonstrated no organ accumulation. This proof-of-concept work is the first step toward development of a translational, stimuli-responsive glucagon delivery platform to control glycemia.

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.

DOGMA-seq and multimodal, single-cell analysis in acute myeloid leukemia

Acute myeloid leukemia (AML) is a complex cancer, yet advances in recent years from integrated genomics methods have helped improve diagnosis, treatment, and means of patient stratification. A recent example of a powerful, multimodal method is DOGMA-seq, which can measure chromatin accessibility, gene expression, and cell-surface protein levels from the same individual cell simultaneously. Previous bimodal single-cell techniques, such as CITE-seq (Cellular indexing of transcriptomes and epitopes), have only permitted the transcriptome and cell-surface protein expression measurement. DOGMA-seq, however, builds on this foundation and has implications for examining epigenomic, transcriptomic, and proteomic interactions between various cell types. This technique has the potential to be particularly useful in the study of cancers such as AML. This is because the cellular mechanisms that drive AML are rather heterogeneous and require a more complete understanding of the interplay between the genetic mutations, disruptions in RNA transcription and translation, and surface protein expression that cause these cancers to develop and evolve. This technique will hopefully contribute to a more clear and complete understanding of the growth and progression of complex cancers.

Stress-induced eosinophil activation contributes to postoperative morbidity and mortality after lung resection

Respiratory failure occurs more frequently after thoracic surgery than abdominal surgery. Although the etiology for this complication is frequently attributed to underlying lung disease present in patients undergoing thoracic surgery, this notion is often unfounded because many patients with normal preoperative pulmonary function often require prolonged oxygen supplementation even after minimal resection of lung tissue. Using a murine model of pulmonary resection and peripheral blood samples from patients undergoing resection of the lung or abdominal organs, we demonstrated that lung surgery initiates a proinflammatory loop that results in damage to the remaining lung tissue, noncardiogenic pulmonary edema, hypoxia, and even death. Specifically, we demonstrated that resection of murine lung tissue increased concentrations of the homeostatic cytokine interleukin-7, which led to local and systemic activation of type 2 innate lymphoid cells. This process activated lung-resident eosinophils and facilitated stress-induced eosinophil maturation in the bone marrow in a granulocyte-macrophage colony-stimulating factor-dependent manner, resulting in systemic eosinophilia in both mice and humans. Up-regulation of inducible nitric oxide synthase in lung-resident eosinophils led to tissue nitrosylation, pulmonary edema, hypoxia, and, at times, death. Disrupting this activation cascade at any stage ameliorated deleterious outcomes and improved survival after lung resection in the mouse model. Our data suggest that repurposing US Food and Drug Administration-approved eosinophil-targeting strategies may potentially offer a therapeutic intervention to improve outcomes for patients who require lung resection for benign or malignant etiology.

Animal models of eosinophilic esophagitis

Eosinophilic esophagitis is a chronic inflammatory disorder of the esophagus. Over the past 25 yr, great strides have been made toward understanding its pathogenesis, in part due to studies in several types of animal models. The vast majority of these models have been characterized in mice. In this review, we summarize the histopathological features of eosinophilic esophagitis recapitulated by these animal models, as well as discuss their strengths and weaknesses.

Considerations on the evolutionary biology and functions of eosinophils: what the "haeckel"?

The origins and evolution of the eosinophilic leukocyte have received only scattered attention since Paul Ehrlich first named this granulocyte. Studies suggest that myeloperoxidase, expressed by granulocytes, and eosinophil peroxidase diverged some 60 to 70 million years ago, but invertebrate to vertebrate evolution of the eosinophil lineage is unknown. Vertebrate eosinophils have been characterized extensively in representative species at light microscopic, ultrastructural, genetic, and biochemical levels. Understanding of eosinophil function continues to expand and includes to date regulation of "Local Immunity And/Or Remodeling/Repair" (the so-called LIAR hypothesis), modulation of innate and adaptive immune responses, maintenance of tissue and metabolic homeostasis, and, under pathologic conditions, inducers of tissue damage, repair, remodeling, and fibrosis. This contrasts with their classically considered primary roles in host defense against parasites and other pathogens, as well as involvement in T-helper 2 inflammatory and immune responses. The eosinophils' early appearance during evolution and continued retention within the innate immune system across taxa illustrate their importance during evolutionary biology. However, successful pregnancies in eosinophil-depleted humans/primates treated with biologics, host immune responses to parasites in eosinophil-deficient mice, and the absence of significant developmental or functional abnormalities in eosinophil-deficient mouse strains under laboratory conditions raise questions of the continuing selective advantages of the eosinophil lineage in mammals and humans. The objectives of this review are to provide an overview on evolutionary origins of eosinophils across the animal kingdom, discuss some of their main functions in the context of potential evolutionary relevance, and highlight the need for further research on eosinophil functions and functional evolution.

Single-cell proteomics and transcriptomics capture eosinophil development and identify the role of IL-5 in their lineage transit amplification

The activities, ontogeny, and mechanisms of lineage expansion of eosinophils are less well resolved than those of other immune cells, despite the use of biological therapies targeting the eosinophilia-promoting cytokine interleukin (IL)-5 or its receptor, IL-5Rα. We combined single-cell proteomics and transcriptomics and generated transgenic IL-5Rα reporter mice to revisit eosinophilopoiesis. We reconciled human and murine eosinophilopoiesis and provided extensive cell-surface immunophenotyping and transcriptomes at different stages along the continuum of eosinophil maturation. We used these resources to show that IL-5 promoted eosinophil-lineage expansion via transit amplification, while its deletion or neutralization did not compromise eosinophil maturation. Informed from our resources, we also showed that interferon response factor-8, considered an essential promoter of myelopoiesis, was not intrinsically required for eosinophilopoiesis. This work hence provides resources, methods, and insights for understanding eosinophil ontogeny, the effects of current precision therapeutics, and the regulation of eosinophil development and numbers in health and disease.

Tumor microenvironment in thyroid cancer: Immune cells, patterns, and novel treatments

The tumor immune microenvironment of thyroid cancer is the heterogeneous histological space in which tumor cells coexist with host cells. Published data from this review were identified by search and selection database of Pubmed, Elsevier, and Science Direct. Searching was made in two steps using different keywords. In thyroid pathology, the inflammatory response is very important, and might have a key role finding new diagnostic and therapeutic methods, particularly in thyroid cancer. Different immune cells may be more or less present in different types of thyroid cancer and may even have different functions, hence the importance of knowing their presence in different thyroid tumor pathologies. Cancer-related inflammation could be a useful target for new diagnostic and therapeutic strategies by analyzing peritumoral and intratumoral immune cells in different types of thyroid tumors. Moreover, novel strategies for thyroid cancer treatments, such as monoclonal antibodies targeting checkpoint inhibitors, are emerging as promising alternatives.

Stress-free single-cell transcriptomic profiling and functional genomics of murine eosinophils

Eosinophils are a class of granulocytes with pleiotropic functions in homeostasis and various human diseases. Nevertheless, they are absent from conventional single-cell RNA sequencing atlases owing to technical difficulties preventing their transcriptomic interrogation. Consequently, eosinophil heterogeneity and the gene regulatory networks underpinning their diverse functions remain poorly understood. We have developed a stress-free protocol for single-cell RNA capture from murine tissue-resident eosinophils, which revealed distinct intestinal subsets and their roles in colitis. Here we describe in detail how to enrich eosinophils from multiple tissues of residence and how to capture high-quality single-cell transcriptomes by preventing transcript degradation. By combining magnetic eosinophil enrichment with microwell-based single-cell RNA capture (BD Rhapsody), our approach minimizes shear stress and processing time. Moreover, we report how to perform genome-wide CRISPR pooled genetic screening in ex vivo-conditioned bone marrow-derived eosinophils to functionally probe pathways required for their differentiation and intestinal maturation. These protocols can be performed by any researcher with basic skills in molecular biology and flow cytometry, and can be adapted to investigate other granulocytes, such as neutrophils and mast cells, thereby offering potential insights into their roles in both homeostasis and disease pathogenesis. Single-cell transcriptomics of eosinophils can be performed in 2-3 d, while functional genomics assays may require up to 1 month.

Eosinophils, basophils and myeloid-derived suppressor cells in chronic Loa loa infection and its treatment in an endemic setting

BACKGROUND

Chronic infection by Loa loa remains an unsolved immunological paradox. Despite harboring subcutaneously migrating adult worms and often high densities of microfilariae, most patients experience only relatively mild symptoms, yet microfilaricidal treatment can trigger life-threatening inflammation. Here, we investigated innate cell populations hypothesized to play a role in these two faces of the disease, in an endemic population in Gabon.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed numbers and activation of eosinophils and basophils, as well as myeloid-derived suppressor cell (MDSC) subsets and associated circulating cytokine levels by flow cytometry in sex- and age-matched L. loa-uninfected (LL-), -amicrofilaraemic (MF-) and -microfilaraemic (MF+) individuals (n = 42), as well as microfilaraemic individuals treated with albendazole (n = 26). The percentage of eosinophils was lower in LL- (3.0%) than in the combined L. loa-infected population, but was similar in MF+ (13.1%) and MF- (12.3%). Upon treatment of MF+, eosinophilia increased from day 0 (17.2%) to day 14 (24.8%) and had decreased below baseline at day 168 (6.3%). Expression of the eosinophil activation marker CD123 followed the same pattern as the percentage of eosinophils, while the inverse was observed for CD193 and to some extent CD125. Circulating IL-5 levels after treatment followed the same pattern as eosinophil dynamics. Basophil numbers did not differ between infection states but increased after treatment of MF+. We did not observe differences in MDSC numbers between infection states or upon treatment.

CONCLUSIONS/SIGNIFICANCE

We demonstrate that both chronic infection and treatment of L. loa microfilaraemia are associated with eosinophil circulation and distinct phenotypical activation markers that might contribute to inflammatory pathways in this setting. In this first ever investigation into MDSC in L. loa infection, we found no evidence for their increased presence in chronic loiasis, suggesting that immunomodulation by L. loa is induced through other pathways.

Origins and functions of eosinophils in two non-mucosal tissues

Eosinophils are a type of granulocyte named after the presence of their eosin-stained granules. Traditionally, eosinophils have been best known to play prominent roles in anti-parasitic responses and mediating allergic reactions. Knowledge of their behaviour has expanded with time, and they are now recognized to play integral parts in the homeostasis of gastrointestinal, respiratory, skeletal muscle, adipose, and connective tissue systems. As such, they are implicated in a myriad of pathologies, and have been the target of several medical therapies. This review focuses on the lifespan of eosinophils, from their origins in the bone marrow, to their tissue-resident role. In particular, we wish to highlight the functions of eosinophils in non-mucosal tissues with skeletal muscle and the adipose tissues as examples, and to discuss the current understanding of their participation in diseased states in these tissues.

The Roles of Various Immune Cell Populations in Immune Response against Helminths

Helminths are multicellular parasites that are a substantial problem for both human and veterinary medicine. According to estimates, 1.5 billion people suffer from their infection, resulting in decreased life quality and burdens for healthcare systems. On the other hand, these infections may alleviate autoimmune diseases and allergy symptoms. The immune system is programmed to combat infections; nevertheless, its effector mechanisms may result in immunopathologies and exacerbate clinical symptoms. This review summarizes the role of the immune response against worms, with an emphasis on the Th2 response, which is a hallmark of helminth infections. We characterize non-immune cells (enteric tuft cells-ETCs) responsible for detecting parasites, as well as the role of hematopoietic-derived cells (macrophages, basophils, eosinophils, neutrophils, innate lymphoid cells group 2-ILC2s, mast cells, T cells, and B cells) in initiating and sustaining the immune response, as well as the functions they play in granulomas. The aim of this paper is to review the existing knowledge regarding the immune response against helminths, to attempt to decipher the interactions between cells engaged in the response, and to indicate the gaps in the current knowledge.

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.

OMIP-095: 40-Color spectral flow cytometry delineates all major leukocyte populations in murine lymphoid tissues

High-dimensional immunoprofiling is essential for studying host response to immunotherapy, infection, and disease in murine model systems. However, the difficulty of multiparameter panel design combined with a lack of existing murine tools has prevented the comprehensive study of all major leukocyte phenotypes in a single assay. Herein, we present a 40-color flow cytometry panel for deep immunophenotyping of murine lymphoid tissues, including the spleen, blood, Peyer's patches, inguinal lymph nodes, bone marrow, and thymus. This panel uses a robust set of surface markers capable of differentiating leukocyte subsets without the use of intracellular staining, thus allowing for the use of cells in downstream functional experiments or multiomic analyses. Our panel classifies T cells, B cells, natural killer cells, innate lymphoid cells, monocytes, macrophages, dendritic cells, basophils, neutrophils, eosinophils, progenitors, and their functional subsets by using a series of co-stimulatory, checkpoint, activation, migration, and maturation markers. This tool has a multitude of systems immunology applications ranging from serial monitoring of circulating blood signatures to complex endpoint analysis, especially in pre-clinical settings where treatments can modulate leukocyte abundance and/or function. Ultimately, this 40-color panel resolves a diverse array of immune cells on the axes of time, tissue, and treatment, filling the niche for a modern tool dedicated to murine immunophenotyping.

Hypereosinophilia causes progressive cardiac pathologies in mice

Hypereosinophilic syndrome is a progressive disease with extensive eosinophilia that results in organ damage. Cardiac pathologies are the main reason for its high mortality rate. A better understanding of the mechanisms of eosinophil-mediated tissue damage would benefit therapeutic development. Here, we describe the cardiac pathologies that developed in a mouse model of hypereosinophilic syndrome. These IL-5 transgenic mice exhibited decreased left ventricular function at a young age which worsened with age. Mechanistically, we demonstrated infiltration of activated eosinophils into the heart tissue that led to an inflammatory environment. Gene expression signatures showed tissue damage as well as repair and remodeling processes. Cardiomyocytes from IL-5Tg mice exhibited significantly reduced contractility relative to wild type (WT) controls. This impairment may result from the inflammatory stress experienced by the cardiomyocytes and suggest that dysregulation of contractility and Ca2+ reuptake in cardiomyocytes contributes to cardiac dysfunction at the whole organ level in hypereosinophilic mice.

Basis of preventive and non-pharmacological interventions in asthma

Asthma is one of the most common atopic disorders in all stages of life. Its etiology is likely due to a complex interaction between genetic, environmental, and lifestyle factors. Due to this, different non-pharmacological interventions can be implemented to reduce or alleviate the symptoms caused by this disease. Thus, the present narrative review aimed to analyze the preventive and non-pharmacological interventions such as physical exercise, physiotherapy, nutritional, ergonutritional, and psychological strategies in asthma treatment. To reach these aims, an extensive narrative review was conducted. The databases used were MedLine (PubMed), Cochrane (Wiley), Embase, PsychINFO, and CinAhl. Asthma is an immune-mediated inflammatory condition characterized by increased responsiveness to bronchoconstrictor stimuli. Different factors have been shown to play an important role in the pathogenesis of asthma, however, the treatments used to reduce its incidence are more controversial. Physical activity is focused on the benefits that aerobic training can provide, while physiotherapy interventions recommend breathing exercises to improve the quality of life of patients. Nutritional interventions are targeted on implement diets that prioritize the consumption of fruits and vegetables and supplementation with antioxidants. Psychological interventions have been proposed as an essential non-pharmacological tool to reduce the emotional problems associated with asthma.

Eosinophils and tissue remodeling: Relevance to airway disease

The ability of human tissue to reorganize and restore its existing structure underlies tissue homeostasis in the healthy airways, but in disease can persist without normal resolution, leading to an altered airway structure. Eosinophils play a cardinal role in airway remodeling both in health and disease, driving epithelial homeostasis and extracellular matrix turnover. Physiological consequences associated with eosinophil-driven remodeling include impaired lung function and reduced bronchodilator reversibility in asthma, and obstructed airflow in chronic rhinosinusitis with nasal polyps. Given the contribution of airway remodeling to the development and persistence of symptoms in airways disease, targeting remodeling is an important therapeutic consideration. Indeed, there is early evidence that eosinophil attenuation may reduce remodeling and disease progression in asthma. This review provides an overview of tissue remodeling in both health and airway disease with a particular focus on eosinophilic asthma and chronic rhinosinusitis with nasal polyps, as well as the role of eosinophils in these processes and the implications for therapeutic interventions. Areas for future research are also noted, to help improve our understanding of the homeostatic and pathological roles of eosinophils in tissue remodeling, which should aid the development of targeted and effective treatments for eosinophilic diseases of the airways.

Granulocyte development, tissue recruitment, and function during allergic inflammation

Granulocytes provide a fast innate response to pathogens and allergens. In allergy and anti-helminth immunity, epithelial cells of damaged barriers release alarmins like IL-25, IL-33, and thymic stromal lymphopoietin (TSLP) but also chemokines like CXCL1 or CCL11 to promote cell recruitment and inflammation. In addition, mast cells positioned at barrier tissue sites also quickly release mediators upon specifically sensing antigens through IgE bound to FcεR1 on their surface. Released mediators induce the recruitment of different granulocytes in a timely ordered manner. First, neutrophils extravasate from the blood vasculature to the side of alarmin release and promote a potent inflammatory response. Alarmins and activated mast cells further promote activation of ILC2s and recruitment of basophils and eosinophils, which inhibit neutrophil recruitment and enhance tissue type 2 immunity. In addition to their potent pro-inflammatory effector functions, granulocytes can also contribute to termination and resolution of inflammation. Here, we summarize the development and tissue recruitment of granulocyte subsets, and describe general effector functions and aspects of their increasingly appreciated role in limiting tissue damage. We further discuss targeting approaches for therapeutic interventions in allergic disorders.

Blood and adipose-resident eosinophils are defined by distinct transcriptional profiles

Eosinophils are granular leukocytes of the innate immune system that play important functions in host defense. Inappropriate activation of eosinophils can occur in pathologies such as asthma and esophagitis. However, eosinophils also reside within adipose tissue, where they play homeostatic roles and are important in the activation of thermogenic beige fat. Here we performed bulk RNA sequencing in mouse adipose tissue-resident eosinophils isolated from both subcutaneous and gonadal depots, for the first time, and compared gene expression to blood eosinophils. We found a predominantly conserved transcriptional landscape in eosinophils between adipose depots that is distinct from blood eosinophils in circulation. Through exploration of differentially expressed transcription factors and transcription factors with binding sites enriched in adipose-resident eosinophil genes, we identified KLF, CEBP, and Fos/Jun family members that may drive functional specialization of eosinophils in adipose tissue. These findings increase our understanding of tissue-specific eosinophil heterogeneity, with implications for targeting eosinophil function to treat metabolic disorders such as obesity.

The Pathology of Asthma: What Is Obstructing Our View?

Despite the advent of sophisticated and efficient new biologics to treat inflammation in asthma, the disease persists. Even following treatment, many patients still experience the well-known symptoms of wheezing, shortness of breath, and coughing. What are we missing? Here we examine the evidence that mucus plugs contribute to a substantial portion of disease, not only by physically obstructing the airways but also by perpetuating inflammation. In this way, mucus plugs may act as an immunogenic stimulus even in the absence of allergen or with the use of current therapeutics. The alterations of several parameters of mucus biology, driven by type 2 inflammation, result in sticky and tenacious sputum, which represents a potent threat, first due to the difficulties in expectoration and second by acting as a platform for viral, bacterial, or fungal colonization that allows exacerbations. Therefore, in this way, mucus plugs are an overlooked but critical feature of asthmatic airway disease.

Living without eosinophils: evidence from mouse and man

The enduring view of eosinophils, as immune effector cells whose primary function is host defence against infection by helminths and other microbial pathogens, sets the stage for a fundamental question regarding the safety of therapeutic eosinophil depletion. If eosinophils are significantly reduced or altogether depleted in an effort to alleviate the negative effects of tissue eosinophilia and eosinophilic inflammation in conditions such as asthma, COPD, chronic rhinosinusitis with nasal polyps, eosinophilic granulomatosis with polyangiitis and hypereosinophilic syndrome, would these patients become susceptible to infection or another illness? Development of mouse models in which the eosinophil lineage has been ablated, observations in patients naturally lacking eosinophils and data from studies of eosinophil-depleting medical therapies indicate that the absence of eosinophils is not detrimental to health. The evidence available to date, as presented in this review, supports the conclusion that even if certain homeostatic roles for the eosinophil may be demonstrable in controlled animal models and human in vitro settings, the evolution of the human species appears to have provided sufficient immune redundancy such that one may be hale and hearty without eosinophils.

Differential Activity of Human Leukocyte Extract on Systemic Immune Response and Cyst Growth in Mice with Echinococcus Multilocularis Infection After Oral, Subcutaneous and Intraperitoneal Routes of Administration

Alveolar echinococcosis (AE) caused by the larval stage of Echinococcus multilocularis is serious parasitic diseases associated with the host´s immunosuppression. The effects of human non-immune dialyzable leukocyte extract (DLE) on immune cells in blood and spleen and parasitic cysts weight in Balb/c mice after oral (PO), subcutaneous (SC) and intraperitoneal administration (IP) were compared. The reduction in cysts weight (p < 0.01) was recorded after PO route, whereas moderate reduction was found after SC and IP routes. The elevation of lymphoid populations in blood and spleen was found after PO administration (p < 0.01) in parallel with reduced myeloid population. Infection-elicited decline in B220+B cells was partially abolished by PO route, but DLE routes did not influence the CD3+ T cells. The proportions of CD3+CD4+Th lymphocytes were moderately upregulated, whereas CD3+CD8+Tc populations were reduced after all DLE routes (p < 0.01). PO administration increased CD11b+MHCII^high blood monocytes, CD11b-SigleF+ cell, but not CD11b+Si-glecF+ eosinophils in the blood, stimulated after SC and IP routes. DLE induced downregulation of NO production by LPS-stimulated adherent splenocytes ex vivo. Con A-triggered T lymphocyte proliferation was associated with the elevated IFN-γ production and transcription factor Tbet mRNA expression. The alleviation of Th2 (IL-4) and Treg (TGF-β) cytokine production by lymphocytes ex vivo paralleled with downregulation of gene transcription for cytokines, GATA and FoxP3. Reduction of myeloid cells with suppressive activity was found. The SC and IP routes affected partially the cysts weights, diminished significantly gene transcription, NO levels and Th2 and Treg cytokines production. Results showed that PO route of DLE administration was the most effective in ameliorating immunosuppression via stimulation of Th1 type, reducing Th2 and Treg type of immunity and CD3+CD8+Tc lymphocytes in the blood and spleens during E. multilocularis infection in mice.

Eosinophils: A Friend or Foe in Human Health and Diseases

Background

Since their discovery, around 150 years, eosinophils research has been a field of changing perspective, and new directions are emerging since then.

Summary

Initially, eosinophils were perceived as terminally differentiated cytotoxic effector cells. Clearly, eosinophils are capable of playing functions other than immune responses, which is not surprising given their intricate interactions with pathogens as well as other circulating leukocytes. Attempts to comprehend the eosinophil biology and functions have yielded remarkable insights into their roles in human health and sickness. The use of FDA-approved eosinophils-targeting biologics has provided exciting opportunities to directly explore the contributions of eosinophils in disease etiology in humans.

Key Messages

In this review, we will focus on the eosinophils' lifecycle and discuss the current state of knowledge from mouse models and retrospective human studies demonstrating eosinophils' roles in the pathogenesis of human diseases such as asthma, cancer, and kidney disorders. Despite three recently approved anti-eosinophil agents, a number of key questions and challenges remain far from settled, thereby generating opportunity to further explore this enigmatic cell. A comprehensive understanding of eosinophils biology and function will surely aid in developing improved therapeutic strategies against eosinophils-associated disorders.

The Immune Landscape of Papillary Thyroid Cancer in the Context of Autoimmune Thyroiditis

Simple Summary

The association between papillary thyroid cancer and Hashimoto’s thyroiditis went through a long-standing human debate recently elucidated by the establishment of a novel mouse model. Papillary thyroid carcinoma is an excellent model for studying the tumor immune microenvironment because it is naturally accompanied by immune cells, making it a good candidate for the treatment with immune checkpoint inhibitors.

Abstract

Papillary thyroid cancer (PTC) often co-occurs with Hashimoto’s thyroiditis, an association that has long been reported in clinical studies, remaining controversial. Experimental evidence has recently shown that pre-existing thyroiditis has a beneficial effect on PTC growth and progression by a distinctive expansion of effector memory CD8 T cells. Although the link between inflammation and PTC might involve different components of the immune system, a deep characterization of them which includes T cells, B cells and tertiary lymphoid structures, Mye-loid cells, Neutrophils, NK cells and dendritic cells will be desirable. The present review article considers the role of the adaptive and innate immune response surrounding PTC in the context of Hashimoto’s thyroiditis. This review will focus on the current knowledge by in vivo and in vitro studies specifically performed on animals’ models; thyroid cancer cells and human samples including (i) the dual role of tumor-infiltrating lymphocytes; (ii) the emerging role of B cells and tertiary lymphoid structures; (iii) the role of myeloid cells, dendritic cells, and natural killer cells; (iv) the current knowledge of the molecular biomarkers implicated in the complex link between thyroiditis and PTC and the potential implication of cancer immunotherapy in PTC patients in the context of thyroiditis.

High stability of blood parameters during mouse lifespan: sex-specific effects of every-other-day fasting

Every-other-day fasting (EODF) is one type of caloric restriction that is proposed to have significant health benefits, including slowing aging-related processes. The present study evaluated multiple parameters of blood homeostasis comparing mice of different ages and mice on different diet regimes: ad libitum (AL) versus EODF. Hematological and classical biochemical parameters of blood were measured in young (6-month), middle-aged (12-month) and old (18-month) C57BL/6J mice of both sexes subjected either to EODF, or AL feeding. Middle-aged AL males showed a decrease in erythrocyte and total leucocyte counts and an increase in plasma alkaline phosphatase activity, whereas old animals showed a decrease in relative levels of lymphocytes and an increase in relative levels of neutrophils, a decrease in plasma lactate and an increase in total cholesterol levels, compared to young mice. AL-fed females demonstrated higher stability of blood parameters during aging than males did. The EODF regimen did not significantly affect hematological parameters in females but prevented a decline in total leukocyte count with age in males. In both sexes, EODF partially prevented age-associated changes in levels of plasma lactate and cholesterol and activity of alkaline phosphatase. Thus, during normal aging, mice showed a sex-dependent maintenance of blood homeostasis which was not significantly affected by EODF.

Solving the Conundrum of Eosinophils in Alloimmunity

Eosinophils are bone-marrow-derived granulocytes known for their ability to facilitate clearance of parasitic infections and their association with asthma and other inflammatory diseases. The purpose of this review is to discuss the currently available human observational and animal experimental data linking eosinophils to the immunologic response in solid organ transplantation. First, we present observational human studies that demonstrate a link between transplantation and eosinophils yet were unable to define the exact role of this cell population. Next, we describe published experimental models and demonstrate a defined mechanistic role of eosinophils in downregulating the alloimmune response to murine lung transplants. The overall summary of this data suggests that further studies are needed to define the role of eosinophils in multiple solid organ allografts and points to the possibility of manipulating this cell population to improve graft survival.

Mast Cell Desensitization in Allergen Immunotherapy

Allergen immunotherapy (AIT) is the only treatment with disease-transforming potential for allergic disorders. The immunological mechanisms associated with AIT can be divided along time in two phases: short-term, involving mast cell (MC) desensitization; and long-term, with a regulatory T cell (Treg) response with significant reduction of eosinophilia. This regulatory response is induced in about 70% of patients and lasts up to 3 years after AIT cessation. MC desensitization is characteristic of the initial phase of AIT and it is often related to its success. Yet, the molecular mechanisms involved in allergen-specific MC desensitization, or the connection between MC desensitization and the development of a Treg arm, are poorly understood. The major AIT challenges are its long duration, the development of allergic reactions during AIT, and the lack of efficacy in a considerable proportion of patients. Therefore, reaching a better understanding of the immunology of AIT will help to tackle these short-comings and, particularly, to predict responder-patients. In this regard, omics strategies are empowering the identification of predictive and follow-up biomarkers in AIT. Here, we review the immunological mechanisms underlying AIT with a focus on MC desensitization and AIT-induced adverse reactions. Also, we discuss the identification of novel biomarkers with predictive potential that could improve the rational use of AIT.

Mitochondrial Population in Mouse Eosinophils: Ultrastructural Dynamics in Cell Differentiation and Inflammatory Diseases

Mitochondria are multifunctional organelles of which ultrastructure is tightly linked to cell physiology. Accumulating evidence shows that mitochondrial remodeling has an impact on immune responses, but our current understanding of the mitochondrial architecture, interactions, and morphological changes in immune cells, mainly in eosinophils, is still poorly known. Here, we applied transmission electron microscopy (TEM), single-cell imaging analysis, and electron tomography, a technique that provides three-dimensional (3D) views at high resolution, to investigate mitochondrial dynamics in mouse eosinophils developing in cultures as well as in the context of inflammatory diseases characterized by recruitment and activation of these cells (mouse models of asthma, H1N1 influenza A virus (IAV) infection, and schistosomiasis mansoni). First, quantitative analyses showed that the mitochondrial area decrease 70% during eosinophil development (from undifferentiated precursor cells to mature eosinophils). Mitophagy, a consistent process revealed by TEM in immature but not in mature eosinophils, is likely operating in mitochondrial clearance during eosinophilopoiesis. Events of mitochondria interaction (inter-organelle membrane contacts) were also detected and quantitated within developing eosinophils and included mitochondria-endoplasmic reticulum, mitochondria-mitochondria, and mitochondria-secretory granules, all of them significantly higher in numbers in immature compared to mature cells. Moreover, single-mitochondrion analyses revealed that as the eosinophil matures, mitochondria cristae significantly increase in number and reshape to lamellar morphology. Eosinophils did not change (asthma) or reduced (IAV and Schistosoma infections) their mitochondrial mass in response to inflammatory diseases. However, asthma and schistosomiasis, but not IAV infection, induced amplification of both cristae numbers and volume in individual mitochondria. Mitochondrial cristae remodeling occurred in all inflammatory conditions with the proportions of mitochondria containing only lamellar or tubular, or mixed cristae (an ultrastructural aspect seen just in tissue eosinophils) depending on the tissue/disease microenvironment. The ability of mitochondria to interact with granules, mainly mobilized ones, was remarkably captured by TEM in eosinophils participating in all inflammatory diseases. Altogether, we demonstrate that the processes of eosinophilopoiesis and inflammation-induced activation interfere with the mitochondrial dynamics within mouse eosinophils leading to cristae remodeling and inter-organelle contacts. The understanding of how mitochondrial dynamics contribute to eosinophil immune functions is an open interesting field to be explored.

Coiled Coil Crosslinked Alginate Hydrogels Dampen Macrophage-Driven Inflammation

Alginate hydrogels are widely used for tissue engineering and regenerative medicine due to their excellent biocompatibility. A facile and commonly used strategy to crosslink alginate is the addition of Ca²⁺ that leads to hydrogelation. However, extracellular Ca²⁺ is a secondary messenger in activating inflammasome pathways following physical injury or pathogenic insult, which carries the risk of persistent inflammation and scaffold rejection. Here, we present graft copolymers of charge complementary heterodimeric coiled coil (CC) peptides and alginate that undergo supramolecular self-assembly to form Ca²⁺ free alginate hydrogels. The formation of heterodimeric CCs was confirmed using circular dichroism spectroscopy, and scanning electron microscopy revealed a significant difference in crosslink density and homogeneity between Ca²⁺ and CC crosslinked gels. The resulting hydrogels were self-supporting and display shear-thinning and shear-recovery properties. In response to lipopolysaccharide (LPS) stimulation, peritoneal macrophages and bone marrow-derived dendritic cells cultured in the CC crosslinked gels exhibited a 10-fold reduction in secretion of the proinflammatory cytokine IL-1β compared to Ca²⁺ crosslinked gels. A similar response was also observed in vivo upon peritoneal delivery of Ca²⁺ or CC crosslinked gels. Analysis of peritoneal lavage showed that macrophages in mice injected with Ca²⁺ crosslinked gels display a more inflammatory phenotype compared to macrophages from mice injected with CC crosslinked gels. These results suggest that CC peptides by virtue of their tunable sequence-structure-function relationship and mild gelation conditions are promising alternative crosslinkers for alginate and other biopolymer scaffolds used in tissue engineering.

Human and Mouse Eosinophils Differ in Their Ability to Biosynthesize Eicosanoids, Docosanoids, the Endocannabinoid 2-Arachidonoyl-glycerol and Its Congeners

High eosinophil (EOS) counts are a key feature of eosinophilic asthma. EOS notably affect asthmatic response by generating several lipid mediators. Mice have been utilized in hopes of defining new pharmacological targets to treat asthma. However, many pinpointed targets in mice did not translate into clinics, underscoring that key differences exist between the two species. In this study, we compared the ability of human (h) and mouse (m) EOS to biosynthesize key bioactive lipids derived from arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). hEOS were isolated from the blood of healthy subjects and mild asthmatics, while mEOSs were differentiated from the bone marrow. EOSs were treated with fatty acids and lipid mediator biosynthesis assessed by LC-MS/MS. We found that hEOS biosynthesized leukotriene (LT) C₄ and LTB₄ in a 5:1 ratio while mEOS almost exclusively biosynthesized LTB₄. The biosynthesis of the 15-lipoxygenase (LO) metabolites 15-HETE and 12-HETE also differed, with a 15-HETE:12-HETE ratio of 6.3 for hEOS and 0.727 for mEOS. EOS biosynthesized some specialized pro-resolving mediators, and the levels from mEOS were 9-times higher than those of hEOS. In contrast, hEOS produced important amounts of the endocannabinoid 2-arachidonoyl-glycerol (2-AG) and its congeners from EPA and DHA, a biosynthetic pathway that was up to ~100-fold less prominent in mEOS. Our data show that hEOS and mEOS biosynthesize the same lipid mediators but in different amounts. Compared to asthmatics, mouse models likely have an amplified involvement of LTB₄ and specialized pro-resolving mediators and a diminished impact of the endocannabinoid 2-arachidonoyl-glycerol and its congeners.

Transcriptional Profiling of Mouse Eosinophils Identifies Distinct Gene Signatures Following Cellular Activation

Eosinophils are multifunctional, evolutionary conserved leukocytes that are involved in a plethora of responses ranging from regulation of tissue homeostasis to host defense and cancer. Eosinophils have been studied mostly in the context of Type 2 inflammatory responses such as those found in allergy. Nonetheless, it is now evident that they participate in Type 1 inflammatory responses and can respond to Type 1 cytokines such as IFN-γ. Recent data suggest that the pleotropic roles of eosinophils are due to heterogeneous responses to environmental cues. Despite this, the activation profile of eosinophils, in response to various stimuli is yet to be defined. To better understand the transcriptional spectrum of eosinophil activation, we exposed eosinophils to Type 1 (e.g. IFN-γ, E. coli) vs. Type 2 (e.g. IL-4) conditions and subjected them to global RNA sequencing. Our analyses show that IL-4, IFN-γ, E. coli and IFN-γ in the presence of E. coli (IFN-γ/E. coli)-stimulated eosinophils acquire distinct transcriptional profiles, which polarize them towards what we termed Type 1 and Type 2 eosinophils. Bioinformatics analyses using Gene Ontology based on biological processes revealed that different stimuli induced distinct pathways in eosinophils. These pathways were confirmed using functional assays by assessing cytokine/chemokine release (i.e. CXCL9, CCL24, TNF-α and IL-6) from eosinophils following activation. In addition, analysis of cell surface markers highlighted CD101 and CD274 as potential cell surface markers that distinguish between Type 1 and Type 2 eosinophils, respectively. Finally, the transcriptome signature of Type 1 eosinophils resembled that of eosinophils that were obtained from mice with experimental colitis whereas the transcriptome signature of Type 2 eosinophils resembled that of eosinophils from experimental asthma. Our data demonstrate that eosinophils are polarized to distinct “Type 1” and “Type 2” phenotypes following distinct stimulations. These findings provide fundamental knowledge regarding the heterogeneity of eosinophils and support the presence of transcriptional differences between Type 1 and Type 2 cells that are likely reflected by their pleotropic activities in diverse disease settings.

Are serum immunoglobulin concentrations a predictive biomarker of response to anti-IL5/IL5Rα therapies?

BACKGROUND

Approval of biologics has recently revolutionized T2 severe asthma management. However, predictive biomarkers remain highly needed to improve patient's selection.

OBJECTIVE

This study aims to determine whether serum immunoglobulins (Igs) levels might be predictive biomarkers of response to anti-interleukin-5 (IL5)/IL5Rα therapies.

METHODS

Severe asthma patients eligible for mepolizumab or benralizumab were included herein. Serum immunoglobulin quantification was performed at baseline before mepolizumab or benralizumab initiation. After a 6-month treatment of mepolizumab or benralizumab, patients presented a second serum immunoglobulin quantification. The treatment response was evaluated by the GETE (Global Evaluation of Treatment Effectiveness) score at 6 months.

RESULTS

A total of 50 patients were included. Median age was 56 [IQR 48.8-65.3] and 50% were females. Compared to baseline, a significant increase in IgG was observed at 6 months (9.2 [7.8-10.2] g/l vs 10.1 [8.8-11.1] g/l, p = 0.04). The area under the ROC curve was 0.58 [95%IC 0.40-0.77] for blood eosinophil count (p = 0.37), 0.75 [95%IC: 0.58-0.92] for serum IgG concentration (p = 0.009) for predicting the treatment response. According to the Youden index, serum IgG concentration ≥ 9.2 g/l predicts the response to anti-IL5 therapies with a sensitivity of 76.9% and a specificity of 75.7%.

CONCLUSION

Baseline serum IgG concentrations may be a useful tool to predict the response to anti-IL5/IL5Rα therapies but should be confirmed in larger clinical trials. Interestingly, anti-IL5/IL5Rα therapies are associated with a significant increase in serum IgG concentrations at 6 months.

High-dimensional profiling reveals phenotypic heterogeneity and disease-specific alterations of granulocytes in COVID-19

Accumulating evidence shows that granulocytes are key modulators of the immune response to SARS-CoV-2 infection, and their dysregulation could significantly impact COVID-19 severity and patient recovery after virus clearance. In the present study, we identify selected immune traits in neutrophil, eosinophil, and basophil subsets associated with severity of COVID-19 and with peripheral protein profiles. Moreover, computational modeling indicates that the combined use of phenotypic data and laboratory measurements can effectively predict key clinical outcomes in COVID-19 patients. Finally, patient-matched longitudinal analysis shows phenotypic normalization of granulocyte subsets 4 mo after hospitalization. Overall, in this work, we extend the current understanding of the distinct contribution of granulocyte subsets to COVID-19 pathogenesis.

Since the outset of the COVID-19 pandemic, increasing evidence suggests that the innate immune responses play an important role in the disease development. A dysregulated inflammatory state has been proposed as a key driver of clinical complications in COVID-19, with a potential detrimental role of granulocytes. However, a comprehensive phenotypic description of circulating granulocytes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)−infected patients is lacking. In this study, we used high-dimensional flow cytometry for granulocyte immunophenotyping in peripheral blood collected from COVID-19 patients during acute and convalescent phases. Severe COVID-19 was associated with increased levels of both mature and immature neutrophils, and decreased counts of eosinophils and basophils. Distinct immunotypes were evident in COVID-19 patients, with altered expression of several receptors involved in activation, adhesion, and migration of granulocytes (e.g., CD62L, CD11a/b, CD69, CD63, CXCR4). Paired sampling revealed recovery and phenotypic restoration of the granulocytic signature in the convalescent phase. The identified granulocyte immunotypes correlated with distinct sets of soluble inflammatory markers, supporting pathophysiologic relevance. Furthermore, clinical features, including multiorgan dysfunction and respiratory function, could be predicted using combined laboratory measurements and immunophenotyping. This study provides a comprehensive granulocyte characterization in COVID-19 and reveals specific immunotypes with potential predictive value for key clinical features associated with COVID-19.

Eosinophils in Health and Disease: A State-of-the-Art Review

Eosinophils play a homeostatic role in the body's immune responses. These cells are involved in combating some parasitic, bacterial, and viral infections and certain cancers and have pathologic roles in diseases including asthma, chronic rhinosinusitis with nasal polyps, eosinophilic gastrointestinal disorders, and hypereosinophilic syndromes. Treatment of eosinophilic diseases has traditionally been through nonspecific eosinophil attenuation by use of glucocorticoids. However, several novel biologic therapies targeting eosinophil maturation factors, such as interleukin (IL)-5 and the IL-5 receptor or IL-4/IL-13, have recently been approved for clinical use. Despite the success of biologic therapies, some patients with eosinophilic inflammatory disease may not achieve adequate symptom control, underlining the need to further investigate the contribution of patient characteristics, such as comorbidities and other processes, in driving ongoing disease activity. New research has shown that eosinophils are also involved in several homeostatic processes, including metabolism, tissue remodeling and development, neuronal regulation, epithelial and microbiome regulation, and immunoregulation, indicating that these cells may play a crucial role in metabolic regulation and organ function in healthy humans. Consequently, further investigation is needed into the homeostatic roles of eosinophils and eosinophil-mediated processes across different tissues and their varied microenvironments. Such work may provide important insights into the role of eosinophils not only under disease conditions but also in health. This narrative review synthesizes relevant publications retrieved from PubMed informed by author expertise to provide new insights into the diverse roles of eosinophils in health and disease, with particular emphasis on the implications for current and future development of eosinophil-targeted therapies.

Eosinophils as Drivers of Severe Eosinophilic Asthma: Endotypes or Plasticity?

Asthma is now recognized as a heterogeneous disease, encompassing different phenotypes driven by distinct pathophysiological mechanisms called endotypes. Common phenotypes of asthma, referred to as eosinophilic asthma, are characterized by the presence of eosinophilia. Eosinophils are usually considered invariant, terminally differentiated effector cells and have become a primary therapeutic target in severe eosinophilic asthma (SEA) and other eosinophil-associated diseases (EADs). Biological treatments that target eosinophils reveal an unexpectedly complex role of eosinophils in asthma, including in SEA, suggesting that "not all eosinophils are equal". In this review, we address our current understanding of the role of eosinophils in asthma with regard to asthma phenotypes and endotypes. We further address the possibility that different SEA phenotypes may involve differences in eosinophil biology. We discuss how these differences could arise through eosinophil "endotyping", viz. adaptations of eosinophil function imprinted during their development, or through tissue-induced plasticity, viz. local adaptations of eosinophil function through interaction with their lung tissue niches. In doing so, we also discuss opportunities, technical challenges, and open questions that, if addressed, might provide considerable benefits in guiding the choice of the most efficient precision therapies of SEA and, by extension, other EADs.

A lesson from the wild: The natural state of eosinophils is Ly6Ghi

With a long history of promoting pathological inflammation, eosinophils are now emerging as important regulatory cells. Yet, findings from controlled laboratory experiments so far lack translation to animals, including humans, in their natural environment. In order to appreciate the breadth of eosinophil phenotype under non‐laboratory, uncontrolled conditions, we exploit a free‐living population of the model organism Mus musculus domesticus. Eosinophils were present at significantly higher proportions in the spleen and bone marrow of wild mice compared with laboratory mice. Strikingly, the majority of eosinophils of wild mice exhibited a unique Ly6G^hi phenotype seldom described in laboratory literature. Ly6G expression correlated with activation status in spleen and bone marrow, but not peritoneal exudate cells, and is therefore likely not an activation marker per se. Intermediate Ly6G expression was transiently induced in a small proportion of eosinophils from C57BL/6 laboratory mice during acute infection with the whipworm Trichuris muris, but not during low‐dose chronic infection, which better represents parasite exposure in the wild. We conclude that the natural state of the eosinophil is not adequately reflected in the standard laboratory mouse, which compromises our attempts to dissect their functional relevance. Our findings emphasize the importance of studying the immune system in its natural context – alongside more mechanistic laboratory experiments – in order to capture the entirety of immune phenotypes and functions.

Dynamic Decrease in Eosinophil After Intravenous Thrombolysis Predicts Poor Prognosis of Acute Ischemic Stroke: A Longitudinal Study

Background and Purpose

Blood eosinophil counts are thought to be associated with atherosclerosis in acute ischemic stroke (AIS) and AIS severity. We aimed to investigate 1): the temporal profile of eosinophil in AIS patients treated with recombinant tissue plasminogen activator (r-tPA); 2): The association between dynamic eosinophil and 3-month outcomes in different AIS etiologies; 3): incremental predictive ability of dynamic eosinophil adding to conventional model; and 4): the longitudinal change of neutrophil-to-lymphocyte ratio (NLR) and compared its prognostic value with eosinophils.

Methods

A total of 623 AIS patients with intravenous thrombolysis in two hospitals were included. Blood samples were obtained on admission, within 24 h after an intravenous thrombolysis and on the seventh day. A multivariate logistic regression model with restricted cubic spline was performed to explore the association between dynamic eosinophil and a 3-month poor outcome. C-statistic, net reclassification improvement (NRI) and integrated discrimination improvement (IDI) were adopted to explore the incremental predictive ability.

Results

Percent change in eosinophil counts after intravenous thrombolysis was median -25.00% (IQR -68.25%-+14.29%). Decrease in eosinophil >75% after intravenous thrombolysis was associated with 2.585 times risk for poor outcome and 13.836 times risk for death. However, the association were weak for patients outside of cardioembolic stroke. Adding eosinophil changes to a conventional model improved the discriminatory ability of poor outcome (NRI = 53.3%; IDI = 2.2%) and death (NRI = 101.0%; IDI = 6.9%).

Conclusions

Dynamic decrease in eosinophil after intravenous thrombolysis predicts a 3-month poor outcome and death in AIS patients with r-tPA treatment and improved the predictive ability of conventional model. However, this result needs to be interpreted carefully in non-cardioembolic AIS patients.

Eosinophils and helminth infection: protective or pathogenic?

Since the earliest descriptions of this enigmatic cell, eosinophils have been implicated in both protective and pathogenic immune responses to helminth infection. Nevertheless, despite substantial data from in vitro studies, human infections, and animal models, their precise role in helminth infection remains incompletely understood. This is due to a number of factors, including the heterogeneity of the many parasites included in the designation "helminth," the complexity and redundancy in the host immune response to helminths, and the pleiotropic functions of eosinophils themselves. This review examines the consequences of helminth-associated eosinophilia in the context of protective immunity, pathogenesis, and immunoregulation.

Eosinophil Knockout Humans: Uncovering the Role of Eosinophils Through Eosinophil-Directed Biological Therapies

The enigmatic eosinophil has emerged as an exciting component of the immune system, involved in a plethora of homeostatic and inflammatory responses. Substantial progress has been achieved through experimental systems manipulating eosinophils in vivo, initially in mice and more recently in humans. Researchers using eosinophil knockout mice have identified a contributory role for eosinophils in basal and inflammatory processes and protective immunity. Primarily fueled by the purported proinflammatory role of eosinophils in eosinophil-associated diseases, a series of anti-eosinophil therapeutics have emerged as a new class of drugs. These agents, which dramatically deplete eosinophils, provide a valuable opportunity to characterize the consequences of eosinophil knockout humans. Herein, we comparatively describe mouse and human eosinophil knockouts. We put forth the view that human eosinophils negatively contribute to a variety of diseases and, unlike mouse eosinophils, do not yet have an identified role in physiological health; thus, clarifying all roles of eosinophils remains an ongoing pursuit.

Lessons learned from targeting eosinophils in human disease

Eosinophils are a minor subset of the granulocyte lineage distinguished by their unique morphology, phenotype, cytoplasmic contents, and function. Evolutionarily, these are ancient cells whose existence has been conserved within vertebrates for millions of years, suggesting that their contribution to innate immunity and other pathologic and homeostatic responses are important to the host. Knowledge regarding the role of eosinophils in health and disease took a leap forward in 2004 with the creation of mouse strains deficient in eosinophils. This advance was paralleled in humans using pharmacology, namely, with the development of drugs capable of selectively reducing and sometimes even eliminating human eosinophils in those receiving these agents. As a result, a more definitive picture of what eosinophils do, and do not do, is emerging. This review will summarize recent advances in our understanding of the role of eosinophils in human disease by focusing mainly on data from clinical studies with anti-eosinophil therapies, even though the first of such agents, mepolizumab, was only approved in the USA in November 2015. Information regarding both efficacy and safety will be highlighted, and where relevant, intriguing data from animal models will also be mentioned, especially if there are conflicting effects seen in humans.

Elevated chemokines and cytokines for eosinophils in neuromyelitis optica spectrum disorders

BACKGROUND

Eosinophil infiltration is one of the distinctive features in neuromyelitis optica spectrum disorders (NMOSD) but not in other demyelinating diseases including multiple sclerosis (MS). Eosinophils express the chemokine receptor CCR3, which is activated by eotaxins (eotaxin-1, -2, and -3) and monocyte chemoattractant protein (MCP)-4. We aimed to investigate the role of MCPs (MCP-1, -2, -3, and -4) and eotaxins in the acute phase of NMOSD.

METHODS

Levels of serum and cerebrospinal fluid (CSF) eotaxins, MCPs, interleukin (IL)-5, tumor necrosis factor (TNF)-α, granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-6 were measured using the cytokine multiplex assay from 26 patients with NMOSD (13 with immunotherapy, 13 without immunotherapy), 9 patients with MS, and 9 patients with other noninflammatory neurological diseases (OND). Glial fibrillary acidic protein was assessed using ELISA.

RESULTS

Serum MCP-1 and CSF MCP-2 levels were significantly higher in patients with NMOSD than in OND. Moreover, serum MCP-4 and CSF eotaxin-2 and -3 levels were significantly higher in NMOSD patients compared to MS and OND. Serum MCP-1, -4 and CSF eotaxin-2, -3 levels were significantly correlated with the Expanded Disability Status Scale in NMOSD. TNF-α and GM-CSF, which stimulate the above chemokines, were higher in patients with NMOSD than those in OND. Moreover, serum MCP-1 and -4 were significantly increased by IL-5 and GM-CSF stimulation, but not by TNF-α and IL-6. Only CSF eotaxin-2 was significantly increased by GM-CSF. There were no significant differences in serum MCP-1 and -4 levels between NMOSD patients with and without immunotherapy.

CONCLUSION

These findings suggest that the elevated serum MCP-1, -4 and CSF eotaxin-2, -3 may be a key step in eosinophil recruitment in the acute phase of NMOSD.

Regulatory eosinophils induce the resolution of experimental arthritis and appear in remission state of human rheumatoid arthritis

OBJECTIVES

Eosinophils possess pro-inflammatory functions in asthma. However, our recent studies have suggested that innate lymphoid cells type 2 (ILC2s) and eosinophils have proresolving properties in rheumatoid arthritis (RA). Nothing is known yet about the mechanisms determining the double-edged role of eosinophils. Therefore, we investigated whether asthma, a paradigm eosinophilic disease, can elicit resolution of chronic arthritis.

METHODS

Ovalbumin-triggered eosinophilic asthma was combined with K/BxN serum-induced arthritis, where lung and synovial eosinophil subsets were compared by single-cell RNA sequencing (scRNA-seq). To investigate the involvement of the ILC2-interleukin-5 (IL-5) axis, hydrodynamic injection (HDI) of IL-25 and IL-33 plasmids, IL-5 reporter mice and anti-IL-5 antibody treatment were used. In patients with RA, the presence of distinct eosinophil subsets was examined in peripheral blood and synovial tissue. Disease activity of patients with RA with concomitant asthma was monitored before and after mepolizumab (anti-IL-5 antibody) therapy.

RESULTS

The induction of eosinophilic asthma caused resolution of murine arthritis and joint tissue protection. ScRNA-seq revealed a specific subset of regulatory eosinophils (rEos) in the joints, distinct from inflammatory eosinophils in the lungs. Mechanistically, synovial rEos expanded on systemic upregulation of IL-5 released by lung ILC2s. Eosinophil depletion abolished the beneficial effect of asthma on arthritis. rEos were consistently present in the synovium of patients with RA in remission, but not in active stage. Remarkably, in patients with RA with concomitant asthma, mepolizumab treatment induced relapse of arthritis.

CONCLUSION

These findings point to a hitherto undiscovered proresolving signature in an eosinophil subset that stimulates arthritis resolution.

Detection of Mouse Eosinophils in Tissue by Flow Cytometry and Isolation by Fluorescence-Activated Cell Sorting (FACS)

Flow cytometry is a critical tool that can be employed to detect unique cells and to isolate cells from tissues based on their antigen profiles. While mouse eosinophils can be readily detected by one or more distinct antigen profiles, many of these strategies do not result in accurate eosinophil counts. We present here our basic protocol, which permits quantitative detection of eosinophils and isolation of eosinophils from bone marrow, spleen, and lung tissue of allergen-challenged wild-type and unchallenged IL5 transgenic mice. With small protocol variations, eosinophils can be isolated from small intestines and muscle tissue, the latter from infiltrates characteristic of muscular dystrophy (mdx) mice.

Mast Cell and Eosinophil Activation Are Associated With COVID-19 and TLR-Mediated Viral Inflammation: Implications for an Anti-Siglec-8 Antibody

Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 infection represents a global health crisis. Immune cell activation via pattern recognition receptors has been implicated as a driver of the hyperinflammatory response seen in COVID-19. However, our understanding of the specific immune responses to SARS-CoV-2 remains limited. Mast cells (MCs) and eosinophils are innate immune cells that play pathogenic roles in many inflammatory responses. Here we report MC-derived proteases and eosinophil-associated mediators are elevated in COVID-19 patient sera and lung tissues. Stimulation of viral-sensing toll-like receptors in vitro and administration of synthetic viral RNA in vivo induced features of hyperinflammation, including cytokine elevation, immune cell airway infiltration, and MC-protease production—effects suppressed by an anti-Siglec-8 monoclonal antibody which selectively inhibits MCs and depletes eosinophils. Similarly, anti-Siglec-8 treatment reduced disease severity and airway inflammation in a respiratory viral infection model. These results suggest that MC and eosinophil activation are associated with COVID-19 inflammation and anti-Siglec-8 antibodies are a potential therapeutic approach for attenuating excessive inflammation during viral infections.

Characterization of epithelial cells, connective tissue cells and immune cells in human upper airway mucosa by immunofluorescence multichannel image cytometry: a pilot study

Epithelial, connective tissue and immune cells contribute in various ways to the pathophysiology of chronic rhinosinusitis (CRS). However, data of their distribution in upper airway mucosa are sparse. We aimed to provide quantitative, purely informative data on the distribution of these cell lineages and their coexpression patterns, which might help identifying, e.g., cells in the epithelium undergoing through epithelial-mesenchymal transition (EMT). For this purpose, we used immunofluorescence multichannel image cytometry (IMIC). We examined fixed paraffin-embedded tissue samples (FFPE) of six patients with chronic rhinosinusitis (CRS) and of three patients without CRS (controls). The direct-conjugated antibodies pancytokeratin, vimentin and CD45/CD18 were used for coexpression analysis in epithelial layer and lamina propria. Image acquisition and analysis were performed with TissueFAXS and StrataQuest, respectively. To distinguish positive from negative expression, a ratio between cell-specific immunostaining intensity and background was developed. Isotype controls were used as negative controls. Per patient, a 4.5-mm2 tissue area was scanned and a median of 14,875 cells was recognized. The most common cell types were cytokeratin-single-positive (26%), vimentin-single-positive (13%) and CD45/CD18-single-positive with CD45/CD18-vimentin-double-positive cells (29%). In the patients with CRS, CD45/CD18-single-positive cells were 3-6 times higher compared to the control patients. In the epithelial layer, cytokeratin-vimentin-double-positive EMT cells were observed 3-5 times higher in the patients with CRS than in the control patients. This study provided quantitative data for the distribution of crucial cell types in CRS. Future studies may focus on the distribution and coexpression patterns of different immune cells in CRS or even cancer tissue.

ATG5 promotes eosinopoiesis but inhibits eosinophil effector functions

Eosinophils are white blood cells that contribute to the regulation of immunity and are involved in the pathogenesis of numerous inflammatory diseases. In contrast to other cells of the immune system, no information is available regarding the role of autophagy in eosinophil differentiation and functions. To study the autophagic pathway in eosinophils, we generated conditional knockout mice in which Atg5 is deleted within the eosinophil lineage only (designated Atg5eoΔ mice). Eosinophilia was provoked by crossbreeding Atg5eoΔ mice with Il5 (IL-5) overexpressing transgenic mice (designated Atg5eoΔIl5tg mice). Deletion of Atg5 in eosinophils resulted in a dramatic reduction in the number of mature eosinophils in blood and an increase of immature eosinophils in the bone marrow. Atg5-knockout eosinophil precursors exhibited reduced proliferation under both in vitro and in vivo conditions but no increased cell death. Moreover, reduced differentiation of eosinophils in the absence of Atg5 was also observed in mouse and human models of chronic eosinophilic leukemia. Atg5-knockout blood eosinophils exhibited augmented levels of degranulation and bacterial killing in vitro. Moreover, in an experimental in vivo model, we observed that Atg5eoΔ mice achieve better clearance of the local and systemic bacterial infection with Citrobacter rodentium. Evidence for increased degranulation of ATG5low-expressing human eosinophils was also obtained in both tissues and blood. Taken together, mouse and human eosinophil hematopoiesis and effector functions are regulated by ATG5, which controls the amplitude of overall antibacterial eosinophil immune responses.