The early history of the eosinophil

Eosinophilic mucus diseases

Eosinophilic inflammation is primarily characterized by type 2 immune responses against parasitic organisms. In the contemporary human being especially in developed countries, eosinophilic inflammation is strongly associated with allergic/sterile inflammation, and constitutes an undesired immune reaction. This situation is in stark contrast to neutrophilic inflammation, which is indispensable for the host defense against bacterial infections. Among eosinophilic inflammatory disorders, massive accumulation of eosinophils within mucus is observed in certain cases, and is often linked to the distinctive clinical finding of mucus with high viscosity. Eosinophilic mucus is found in a variety of diseases, including chronic allergic keratoconjunctivitis, chronic rhinosinusitis encompassing allergic fungal sinusitis, eosinophilic otitis media, eosinophilic sialodochitis, allergic bronchopulmonary aspergillosis/mycosis, eosinophilic plastic bronchitis, and eosinophilic asthma. In these pathological conditions, chronic inflammation and tissue remodeling coupled with irreversible organ damage due to persistent adhesion of toxic substances and luminal obstruction may impose a significant burden on the body. Eosinophils aggregate in the hyperconcentrated mucus together with cell-derived crystals, macromolecules, and polymers, thereby affecting the biophysical properties of the mucus. This review focuses on the clinically significant challenges of mucus and discusses the consequences of activated eosinophils on the mucosal surface that impact mucus and persistent inflammation.

Evolution of staining methods in neuroanatomy: Impetus for emanation of neuron doctrine during the turn of 20th century

The nervous system is distinctive as compared to other tissue systems in human body owing to intricate structural organization. Histological studies played a key role in unveiling complex details of nervous tissue. However, the process of developing suitable staining method for nerve cells was arduous and spanned across almost half a century. The present study explored details of the journey involving quest for propitious staining method in neuroanatomy culminating in promulgation of neuron doctrine at the onset of 20th century. Initial efforts involving hematoxylin (including its diverse modifications) and subsequent adoption of analogous dye-based stains (like Nissl's method) had limited success in visualization of different parts of a nerve cell and structural details of nervous tissue. This was due to inability of dye-based stains to penetrate the connective tissue sheath of nervous tissue. Eventually, advent of metallic stains in form of silver impregnation method (Golgi stain), reduced silver impregnation method with gold stain (Cajal's stain) and silver carbonate staining method of Río-Hortega unraveled the structure of nervous tissue. The evolution of staining methods catalyzed the refinement of theories pertinent to constitution of nervous tissue. Golgi's staining led to emergence of reticular theory (neurons exist as a network) and Nissl's staining was the basis of the concept of Nervösen Grau (nerve cells and glial cells are embedded in mass of gray matter). Finally, Cajal's staining method successfully elucidated the complex anatomy of nerve terminals and resulted in emanation of neuron doctrine (neurons exists as individual units with adjacent connections).

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.

Hematological Neoplasms with Eosinophilia

Eosinophils in peripheral blood account for 0.3-5% of leukocytes, which is equivalent to 0.05-0.5 × 109/L. A count above 0.5 × 109/L is considered to indicate eosinophilia, while a count equal to or above 1.5 × 109/L is defined as hypereosinophilia. In bone marrow aspirate, eosinophilia is considered when eosinophils make up more than 6% of the total nuclear cells. In daily clinical practice, the most common causes of reactive eosinophilia are non-hematologic, whether they are non-neoplastic (allergic diseases, drugs, infections, or immunological diseases) or neoplastic (solid tumors). Eosinophilia that is associated with a hematological malignancy may be reactive or secondary to the production of eosinophilopoietic cytokines, and this is mainly seen in lymphoid neoplasms (Hodgkin lymphoma, mature T-cell neoplasms, lymphocytic variant of hypereosinophilic syndrome, and B-acute lymphoblastic leukemia/lymphoma). Eosinophilia that is associated with a hematological malignancy may also be neoplastic or primary, derived from the malignant clone, usually in myeloid neoplasms or with its origin in stem cells (myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions, acute myeloid leukemia with core binding factor translocations, mastocytosis, myeloproliferative neoplasms, myelodysplastic/myeloproliferative neoplasms, and myelodysplastic neoplasms). There are no concrete data in standardized cytological and cytometric procedures that could predict whether eosinophilia is reactive or clonal. The verification is usually indirect, based on the categorization of the accompanying hematologic malignancy. This review focuses on the broad differential diagnosis of hematological malignancies with eosinophilia.

Eosinophils as potential biomarkers in respiratory viral infections

Eosinophils are bone marrow-derived granulocytes that, under homeostatic conditions, account for as much as 1-3% of peripheral blood leukocytes. During inflammation, eosinophils can rapidly expand and infiltrate inflamed tissues, guided by cytokines and alarmins (such as IL-33), adhesion molecules and chemokines. Eosinophils play a prominent role in allergic asthma and parasitic infections. Nonetheless, they participate in the immune response against respiratory viruses such as respiratory syncytial virus and influenza. Notably, respiratory viruses are associated with asthma exacerbation. Eosinophils release several molecules endowed with antiviral activity, including cationic proteins, RNases and reactive oxygen and nitrogen species. On the other hand, eosinophils release several cytokines involved in homeostasis maintenance and Th2-related inflammation. In the context of SARS-CoV-2 infection, emerging evidence indicates that eosinophils can represent possible blood-based biomarkers for diagnosis, prognosis, and severity prediction of disease. In particular, eosinopenia seems to be an indicator of severity among patients with COVID-19, whereas an increased eosinophil count is associated with a better prognosis, including a lower incidence of complications and mortality. In the present review, we provide an overview of the role and plasticity of eosinophils focusing on various respiratory viral infections and in the context of viral and allergic disease comorbidities. We will discuss the potential utility of eosinophils as prognostic/predictive immune biomarkers in emerging respiratory viral diseases, particularly COVID-19. Finally, we will revisit some of the relevant methods and tools that have contributed to the advances in the dissection of various eosinophil subsets in different pathological settings for future biomarker definition.

Blood identified and quantified in formalin fixed paraffin embedded lung sections using eosin fluorescence

Eosin Y is a common stain in histology. Although usually used for colourimetric imaging where the dye is used to stain pink/red a range of structures in the tissue, Eosin Y is also a fluorochrome, and has been used in this manner for decades. In this study our aim was to investigate the fluorescence properties of the dye to enable quantification of structures within formalin-fixed paraffin-embedded (FFPE) tissue sections. To do this, FFPE sections of hamster tissue were prepared with haematoxylin and eosin Y dyes. Spectral detection on a confocal laser scanning microscope was used to obtain the fluorescence emission spectra of the eosin Y under blue light. This showed clear spectral differences between the red blood cells and congealed blood, compared to the rest of the section. The spectra were so distinct that it was possible to discern these in fluorescence and multi-photon microscopy. An image analysis algorithm was used to quantify the red blood cells. These analyses could have broad applications in histopathology where differentiation is required, such as the analysis of clotting disorders to haemorrhage or damage from infectious disease.

Anti-IL-5 therapies for asthma

BACKGROUND

This is the second update of previously published reviews in the Cochrane Library (2015, first update 2017). Interleukin-5 (IL-5) is the main cytokine involved in the proliferation, maturation, activation and survival of eosinophils, which cause airway inflammation and are a classic feature of asthma. Studies of monoclonal antibodies targeting IL-5 or its receptor (IL-5R) suggest they reduce asthma exacerbations, improve health-related quality of life (HRQoL) and lung function in appropriately selected patients, justifying their inclusion in the latest guidelines.

OBJECTIVES

To compare the effects of therapies targeting IL-5 signalling (anti-IL-5 or anti-IL-5Rα) with placebo on exacerbations, health-related quality-of-life (HRQoL) measures and lung function in adults and children with chronic asthma, and specifically in those with eosinophilic asthma refractory to existing treatments.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, and two trials registers, manufacturers' websites, and reference lists of included studies. The most recent search was 7 February 2022.

SELECTION CRITERIA

We included randomised controlled trials comparing mepolizumab, reslizumab and benralizumab versus placebo in adults and children with asthma.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and analysed outcomes using a random-effects model. We used standard methods expected by Cochrane.

MAIN RESULTS

Seventeen studies on about 7600 participants met the inclusion criteria. Six used mepolizumab, five used reslizumab, and six used benralizumab. One study using benralizumab was terminated early due to sponsor decision and contributed no data. The studies were predominantly on people with severe eosinophilic asthma, which was similarly but variably defined. One was in children aged 6 to 17 years; nine others included children over 12 years but did not report results by age group separately. We deemed the overall risk of bias to be low, with all studies contributing data of robust methodology. We considered the certainty of the evidence for all comparisons to be high overall using the GRADE scheme, except for intravenous (IV) mepolizumab and subcutaneous (SC) reslizumab because these are not currently licensed delivery routes. The anti-IL-5 treatments assessed reduced rates of 'clinically significant' asthma exacerbation (defined by treatment with systemic corticosteroids for three days or more) by approximately half in participants with severe eosinophilic asthma on standard care (at least medium-dose inhaled corticosteroids (ICS)) with poorly controlled disease (either two or more exacerbations in the preceding year or Asthma Control Questionnaire (ACQ) score of 1.5 or more), except for reslizumab SC. The rate ratios for these effects were 0.45 (95% confidence interval (CI) 0.36 to 0.55; high-certainty evidence) for mepolizumab SC, 0.53 (95% CI 0.44 to 0.64; moderate-certainty evidence) for mepolizumab IV, 0.43 (95% CI 0.33 to 0.55; high-certainty evidence) for reslizumab IV, and 0.59 (95% CI 0.52 to 0.66; high-certainty evidence) for benralizumab SC. Non-eosinophilic participants treated with benralizumab also showed a significant reduction in exacerbation rates, an effect not seen with reslizumab IV, albeit in only one study. No data were available for non-eosinophilic participants treated with mepolizumab. There were improvements in validated HRQoL scores with all anti-IL-5 agents in severe eosinophilic asthma. This met the minimum clinically important difference (MCID) for the broader St. George's Respiratory Questionnaire (SGRQ; 4-point change) for benralizumab only, but the improvement in the ACQ and Asthma Quality of Life Questionnaire (AQLQ), which focus on asthma symptoms, fell short of the MCID (0.5 point change for both ACQ and AQLQ) for all of the interventions. The evidence for an improvement in HRQoL scores in non-eosinophilic participants treated with benralizumab and reslizumab was weak, but the tests for subgroup difference were negative. All anti-IL-5 treatments produced small improvements in mean pre-bronchodilator forced expiratory flow in one second (FEV1) of between 0.08 L and 0.15 L in eosinophilic participants, which may not be sufficient to be detected by patients. There were no excess serious adverse events with any anti-IL-5 treatment; in fact, there was a reduction in such events with benralizumab, likely arising from fewer asthma-related hospital admissions. There was no difference compared to placebo in adverse events leading to discontinuation with mepolizumab or reslizumab, but significantly more discontinued benralizumab than placebo, although the absolute numbers were small (42/2026 (2.1%) benralizumab versus 11/1227 (0.9%) placebo). The implications for efficacy or adverse events are unclear.

AUTHORS' CONCLUSIONS

Overall this analysis supports the use of anti-IL-5 treatments as an adjunct to standard care in people with severe eosinophilic asthma and poor symptom control. These treatments roughly halve the rate of asthma exacerbations in this population. There is limited evidence for improved HRQoL scores and lung function, which may not meet clinically detectable levels. The studies did not report safety concerns for mepolizumab or reslizumab, or any excess serious adverse events with benralizumab, although there remains a question over adverse events significant enough to prompt discontinuation. Further research is needed on biomarkers for assessing treatment response, optimal duration and long-term effects of treatment, risk of relapse on withdrawal, non-eosinophilic patients, children (particularly under 12 years), comparing anti-IL-5 treatments to each other and, in patients meeting relevant eligibility criteria, to other biological (monoclonal antibody) therapies. For benralizumab, future studies should closely monitor rates of adverse events prompting discontinuation.

Eosinophils and Lung Cancer: From Bench to Bedside

Eosinophils are rare, multifunctional granulocytes. Their growth, survival, and tissue migration mainly depend on interleukin (IL)-5 in physiological conditions and on IL-5 and IL-33 in inflammatory conditions. Preclinical evidence supports an immunological role for eosinophils as innate immune cells and as agents of the adaptive immune response. In addition to these data, several reports show a link between the outcomes of patients treated with immune checkpoint inhibitors (ICI) for advanced cancers and blood eosinophilia. In this review, we present, in the context of non-small cell lung cancer (NSCLC), the biological properties of eosinophils and their roles in homeostatic and pathological conditions, with a focus on their pro- and anti-tumorigenic effects. We examine the possible explanations for blood eosinophilia during NSCLC treatment with ICI. In particular, we discuss the value of eosinophils as a potential prognostic and predictive biomarker, highlighting the need for stronger clinical data. Finally, we conclude with perspectives on clinical and translational research topics on this subject.

CCR3 gene knockout in bone marrow cells ameliorates combined allergic rhinitis and asthma syndrome (CARAS) by reducing airway inflammatory cell infiltration and Th2 cytokines expression in mice model

The present study aims to investigate the effects of CCR3 gene knockout in bone marrow cells (CCR3-KO) on the mouse model of combined allergic rhinitis and asthma syndrome (CARAS). It was found that CCR3-KO significantly reduced eosinophil (EOS) migration into the nasal (NALF) and bronchoalveolar (BALF) cavities of mice, and decreased Th2 cytokines (such as, IL-4, IL-5 and IL-13) levels in nasal mucosa and lung tissues. In addition, histological analysis showed that the damage degree of nasal mucosa structure in ovalbumin (OVA) modulated CCR3-KO mice was significantly less than that in OVA modulated Wild type (WT) mice, with reduced inflammatory cell infiltration and nasal mucus secretion. The infiltration of inflammatory cells in lung tissue was significantly reduced, and the proliferation of lung smooth muscle layer and extracellular matrix (ECM) production were decreased. Symptom analysis showed that CCR3-KO can reduced allergic rhinitis (AR) signals as nose scratching and sneezing. It was also found CCR3-KO reduce OVA-induced weight loss. The results showed that CCR3-KO could reduce the symptoms of allergic inflammation in CARAS mice by reducing airway inflammatory cell infiltration and down-regulating the expression of Th2 cytokines, and CCR3 gene could be used as a target gene for the treatment of CARAS.

Eosinophil Cell Count Predicts Mortality in the Intensive Care Unit after Return of Spontaneous Circulation

BACKGROUND

Eosinophils constitute 1%-5% of peripheral blood leukocytes, less in the presence of acute infections (referred to as eosinopenia). Studies indicate that eosinopenia can be used as a prognostic predictor for chronic obstructive pulmonary disease exacerbation, sepsis, or acute myocardial infarction disease. There are only a few studies about predicting mortality in emergency departments and intensive care units (ICUs). Prognostic studies about patients in ICUs are generally carried out using different scoring systems. We aimed to analyze if the eosinophil count can estimate the prognosis among non-traumatic patients who underwent cardiopulmonary resuscitation and were hospitalized in ICU thereafter.

METHODS

The data were evaluated of 865 non-traumatic adult patients (>18 years of age) who were admitted with cardiopulmonary arrest or developed cardiopulmonary arrest during clinical follow-ups. Admission venous blood sample tests, complete blood count, and biochemical laboratory results were recorded. Arterial blood gas results were also evaluated. The mean results of the recorded laboratory results were compared between the surviving and non-surviving patients groups.

RESULTS

There was a significant difference between the two groups in regard to platelet, eosinophil count, pH, PaO₂, SaO₂, and HCO₃^- (P<0.001 for all). In the multiple linear regression analysis, eosinophil counts were found to be an independent factor (odds ratio=0.03, 95% confidence interval 0.33-0.56, P<0.001) associated with the mortality after cardiopulmonary resuscitation.

CONCLUSION

Because admission eosinophil counts can be measured easily, they are inexpensive biomarkers that can be used for predicting the prognosis among the patients who have return of spontaneous circulation and are treated in ICUs.

Pulmonary Adenocarcinoma Presenting as Acute Heart Failure and Hypereosinophilia

Hypereosinophilia is a serum eosinophil count of over 1,500 eosinophils/µL. It is an uncommon laboratory finding, and it can be asymptomatic or associated with organ damage, in which case it is referred to as hypereosinophilic syndrome. It can be primary, when the expansion of eosinophils occurs in the setting of a hematological neoplasm, or secondary, when it is caused by an external stimulus, such as a parasitic infection or a solid neoplasm. We present a case of hypereosinophilia diagnosed in a patient presenting with acute heart failure initially attributed to coronary disease and alcohol consumption. Due to persisting eosinophilia with no apparent cause, eventually reaching more than 41,000 eosinophils/µL, a full-body scan was performed, showing the presence of a peri-hilar mass partially obstructing the left main bronchus and multiple lesions in the liver and thoracic vertebrae. The liver biopsy revealed metastatic non-small cell lung carcinoma. Around the time the biopsy was performed, the patient began complaining of new-onset chest paint, and the diagnoses of pulmonary embolism and later lung abscess were made, the reasons why he had no conditions to begin chemotherapy. The medical condition of the patient deteriorated in the next few days, and the patient died six months after the initial diagnosis of hypereosinophilia.

The emerging roles of eosinophils: Implications for the targeted treatment of eosinophilic-associated inflammatory conditions

Eosinophils have multiple relevant biological functions, including the maintenance of homeostasis, host defense against infectious agents, innate immunity activities, immune regulation through Th1/Th2 balance, anti-inflammatory, and anti-tumorigenic effects. Eosinophils also have a main role in tissue damage through eosinophil-derived cytotoxic mediators that are involved in eosinophilic inflammation, as documented in Th2-high asthma and other eosinophilic-associated inflammatory conditions.

Recent evidence shows that these multiple and apparently conflicting functions may be attributed to the existence of different eosinophil subtypes (i.e.: tissue resident and inducible eosinophils). Therapeutic intervention with biological agents that totally deplete tissues and circulating eosinophils or, vice versa, maintain a minimal proportion of eosinophils, particularly the tissue-resident ones, could therefore have a very different impact on patients, especially when considering the administration of these therapies for prolonged time. In addition, the characterization of the predominant pathway underlying eosinophilic inflammation by surrogate biomarkers (circulating eosinophils, organ-specific eosinophils levels such as eosinophil count in sputum, bronchoalveolar lavage, tissue biopsy; total circulating IgE levels, or the use of FeNO) in the single patient with an eosinophilic-associated inflammatory condition could help in choosing the treatment.

These observations are crucial in light of the increasing therapeutic armamentarium effective in modulating eosinophilic inflammation through the inhibition in different, yet complementary ways of eosinophil pathways, such as the interleukin-5 one (with mepolizumab, benralizumab, reslizumab) or the interleukin-4/13 one (with dupilumab and lebrikizumab), in severe T2-high asthma as well as in other systemic eosinophilic associated diseases, such as eosinophilic granulomatosis with polyangiitis and hypereosinophilic syndrome.

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Recent evidence pointed out the existence of different eosinophil subtypes, i.e. tissue resident and inducible eosinophils, with different and apparently conflicting functions.

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Biological therapies with different mechanisms can deplete completely tissues and circulating eosinophils or maintain a minimal proportion of eosinophils, particularly the tissue-resident ones, and this could therefore have a different impact on patients, especially when considering the administration of these therapies for prolonged time.

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The identification of the predominant pathway underlying eosinophilic inflammation by surrogate biomarkers (circulating eosinophils, organ-specific eosinophils levels such as eosinophil count in sputum, bronchoalveolar lavage, tissue biopsy; total circulating IgE levels, or the use of FeNO) should be sought in the single patient with an eosinophilic-associated inflammatory condition.

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These considerations may help in choosing the best anti-eosinophilic treatment, considering the increasing therapeutic armamentarium effective in modulating eosinophilic inflammation through the inhibition of the interleukin-5 one (with mepolizumab, benralizumab, reslizumab) or the interleukin-4/13 one (with dupilumab and lebrikizumab)

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.

Eosinophils in the pathogenesis of pancreatic disorders

Eosinophils comprise approximately 1-4% of total blood leukocytes that reside in the intestine, bone marrow, mammary gland, and adipose tissues to maintain innate immunity in healthy individuals. Eosinophils have four toxic granules known as major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil peroxidase (EPO), and eosinophil-derived neurotoxin (EDN), and upon degranulation, these granules promote pathogenesis of inflammatory diseases like allergy, asthma, dermatitis, and gastrointestinal disorders. Additionally, the role of eosinophils is underscored in exocrine disorders including pancreatitis. Chronic pancreatitis (CP) is an inflammatory disorder that occurs due to the alcohol consumption, blockage of the pancreatic duct, and trypsinogen mutation. Eosinophil levels are detected in higher numbers in both CP and pancreatic cancer patients compared with healthy individuals. The mechanistic understanding of chronic inflammation-induced pancreatic malignancy has not yet been reached and requires further exploration. This review provides a comprehensive summary of the epidemiology, pathophysiology, evaluation, and management of eosinophil-associated pancreatic disorders and further summarizes current evidence regarding risk factors, pathophysiology, clinical features, diagnostic evaluation, treatment, and prognosis of eosinophilic pancreatitis (EP) and pancreatic cancer.

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.

MHTP, a synthetic alkaloid, attenuates combined allergic rhinitis and asthma syndrome through downregulation of the p38/ERK1/2 MAPK signaling pathway in mice

The combined allergic rhinitis and asthma syndrome (CARAS) is a chronic airway inflammation of allergic individuals, with a type 2 immune response. Pharmacotherapy is based on drugs with relevant side effects. Thus, the goal of this study was to evaluate the synthetic alkaloid, MHTP in the experimental model of CARAS. Therefore, BALB/c mice were ovalbumin (OVA) -sensitized and -challenged and treated with MHTP by intranasal or oral routes. Treated animals showed a decrease (p < 0.05) of sneezing, nasal rubbings, and histamine nasal hyperactivity. Besides, MHTP presented binding energy and favorable interaction for adequate anchoring in the histamine H1 receptor. MHTP treatment inhibited the eosinophil migration into the nasal (NALF) and the bronchoalveolar (BALF) fluids. Histological analysis showed that the alkaloid decreased the inflammatory cells in the subepithelial and perivascular regions of nasal tissue and in the peribronchiolar and perivascular regions of lung tissue. The MHTP treatment also reduced the pulmonary hyperactivity by decreasing the smooth muscle layer hypertrophy and the collagen fiber deposition in the extracellular matrix. The immunomodulatory effect of the alkaloid was due to the decrease of cytokines like IL-5 and IL-17A (type 2 and 3), TSLP (epithelial), and the immunoregulatory cytokine, TGF-β. These MHTP effects on granulocytes were dependent on the p38/ERK1/2 MAP kinase signaling pathway axis. Indeed, the synthetic alkaloid reduced the frequency of activation of both kinases independent of the NF-κB (p65) pathway indicating that the molecule shut down the intracellular transduction signals underlie the cytokine gene transcription.

Experimental Modeling of Eosinophil-Associated Diseases

Eosinophils are an important subtype of leukocytes derived from bone marrow multipotent hematopoietic stem cells and represent about 1% of leukocytes in circulating blood. In homeostatic conditions, eosinophils reside in the intestine to maintain the balance of immune responses by communicating with gut microbes without causing inflammation. However, under the stressed or diseased condition, eosinophils degranulate, releasing their granule-derived cytotoxic proteins that are involved in inflammatory responses. Various eosinophil-associated inflammatory diseases are eosinophilic esophagitis (EoE), eosinophilic gastroenteritis (EG), and eosinophilic colitis (EC), together called EGID, asthma, hypereosinophilic syndrome, and eosinophilic pneumonia (EP). Eosinophil degranulation results in the release of their four toxic proteins [major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil peroxidase (EPO), and eosinophil-derived neurotoxin (EDN)] which promote disease pathogenesis. Pancreatitis is the inflammatory disease of the pancreas that arises due to blockage of the pancreatic duct, trypsinogen mutation, alcohol consumption, and repeated occurrence of pancreatitis leading to chronic pancreatitis (CP); subsequently some CP patients may also develop pancreatic cancer. The presence of eosinophils is now shown in various case reports with acute, recurrent acute, and chronic pancreatitis and pancreatic cancer indicating the role of eosinophils in the pathogenesis of various pancreatic inflammatory disorders. However, the details of eosinophil accumulation during pancreatic diseases are not well explored and need further attention. Overall, the chapter provides the current understanding of reported eosinophils associated with inflammatory diseases like EGID diseases, asthma, and pancreatic disorders, i.e., acute, chronic pancreatitis, and pancreatic cancer. This knowledge will be helpful for future studies to develop novel treatment options for the eosinophils associated diseases. Therefore, more efforts are needed to perform preclinical and clinical studies in this field for the successful development of eosinophil-targeting treatments for a variety of eosinophil-associated diseases.

Heterogeneity of Intestinal Tissue Eosinophils: Potential Considerations for Next-Generation Eosinophil-Targeting Strategies

Eosinophils are implicated in the pathophysiology of a spectrum of eosinophil-associated diseases, including gastrointestinal eosinophilic diseases (EGIDs). Biologics that target the IL-5 pathway and are intended to ablate eosinophils have proved beneficial in severe eosinophilic asthma and may offer promise in treating some endotypes of EGIDs. However, destructive effector functions of eosinophils are only one side of the coin; eosinophils also play important roles in immune and tissue homeostasis. A growing body of data suggest tissue eosinophils represent a plastic and heterogeneous population of functional sub-phenotypes, shaped by environmental (systemic and local) pressures, which may differentially impact disease outcomes. This may be particularly relevant to the GI tract, wherein the highest density of eosinophils reside in the steady state, resident immune cells are exposed to an especially broad range of external and internal environmental pressures, and greater eosinophil longevity may uniquely enrich for co-expression of eosinophil sub-phenotypes. Here we review the growing evidence for functional sub-phenotypes of intestinal tissue eosinophils, with emphasis on the multifactorial pressures that shape and diversify eosinophil identity and potential targets to inform next-generation eosinophil-targeting strategies designed to restrain inflammatory eosinophil functions while sustaining homeostatic roles.

Hyper-eosinophilic syndrome: An uncommon cause of chronic abdominal pain in an elderly male

Hypereosinophilia is defined as an absolute eosinophil count of ≥1.5 × 10⁹/L, and its presence with involvement of at least one organ system defines the hypereosinophilic syndrome. It may occur with parasitic infestation, connective tissue disorder or rarely in clonal disorders such as eosinophilic leucaemia. Organ systems that may be involved include the cardiovascular, central nervous, respiratory and gastrointestinal systems. In the latter, a wide spectrum of clinical presentation may be seen from trivial, to debilitating or rarely fatal. We report an elderly male with a history of bronchial asthma, obstructive sleep apnoea and food allergy who presented with chronic abdominal pain and weight loss. Abdominal examination and routine evaluation were essentially normal other than a peripheral hyper-eosinophilia. We witnessed a brisk and lasting response to an elimination diet and corticosteroids.

Eosinophils in the Tumor Microenvironment

Eosinophils are rare blood-circulating and tissue-infiltrating immune cells studied for decades in the context of allergic diseases and parasitic infections. Eosinophils can secrete a wide array of soluble mediators and effector molecules, with potential immunoregulatory activities in the tumor microenvironment (TME). These findings imply that these cells may play a role in cancer immunity. Despite these cells were known to infiltrate tumors since many years ago, their role in TME is gaining attention only recently. In this chapter, we will review the main biological functions of eosinophils that can be relevant within the TME. We will discuss how these cells may undergo phenotypic changes acquiring pro- or antitumoricidal properties according to the surrounding stimuli. Moreover, we will analyze canonical (i.e., degranulation) and unconventional mechanisms (i.e., DNA traps, exosome secretion) employed by eosinophils in inflammatory contexts, which can be relevant for tumor immune responses. Finally, we will review the available preclinical models that could be employed for the study of the role in vivo of eosinophils in cancer.

The multiple functions and subpopulations of eosinophils in tissues under steady-state and pathological conditions

Eosinophils not only play a critical role in the pathogenesis of eosinophil-associated diseases, but they also have multiple important biological functions, including the maintenance of homeostasis, host defense against infections, immune regulation through canonical Th1/Th2 balance modulation, and anti-inflammatory and anti-tumorigenic activities. Recent studies have elucidated some emerging roles of eosinophils in steady-state conditions; for example, eosinophils contribute to adipose tissue metabolism and metabolic health through alternatively activated macrophages and the maintenance of plasma cells in intestinal tissue and bone marrow. Moreover, eosinophils exert tissue damage through eosinophil-derived cytotoxic mediators that are involved in eosinophilic airway inflammation, leading to diseases including asthma and chronic rhinosinusitis with nasal polyps characterized by fibrin deposition through excessive response by eosinophils-induced. Thus, eosinophils possessing these various effects reflect the heterogenous features of these cells, which suggests the existence of distinct different subpopulations of eosinophils between steady-state and pathological conditions. Indeed, a recent study demonstrated that instead of dividing eosinophils by classical morphological changes into normodense and hypodense eosinophils, murine eosinophils from lung tissue can be phenotypically divided into two distinct subtypes: resident eosinophils and inducible eosinophils gated by Siglec-F^int CD62L⁺ CD101^low and Siglec-F^high CD62L^- CD101^high, respectively. However, it is difficult to explain every function of eosinophils by rEos and iEos, and the relationship between the functions and subpopulations of eosinophils remains controversial. Here, we overview the multiple roles of eosinophils in the tissue and their biological behavior in steady-state and pathological conditions. We also discuss eosinophil subpopulations.

Eosinophils and COVID-19: diagnosis, prognosis, and vaccination strategies

The unprecedented impact of the coronavirus disease 2019 (COVID-19) pandemic has resulted in global challenges to our health-care systems and our economic security. As such, there has been significant research into all aspects of the disease, including diagnostic biomarkers, associated risk factors, and strategies that might be used for its treatment and prevention. Toward this end, eosinopenia has been identified as one of many factors that might facilitate the diagnosis and prognosis of severe COVID-19. However, this finding is neither definitive nor pathognomonic for COVID-19. While eosinophil-associated conditions have been misdiagnosed as COVID-19 and others are among its reported complications, patients with pre-existing eosinophil-associated disorders (e.g., asthma, eosinophilic gastrointestinal disorders) do not appear to be at increased risk for severe disease; interestingly, several recent studies suggest that a diagnosis of asthma may be associated with some degree of protection. Finally, although vaccine-associated aberrant inflammatory responses, including eosinophil accumulation in the respiratory tract, were observed in preclinical immunization studies targeting the related SARS-CoV and MERS-CoV pathogens, no similar complications have been reported clinically in response to the widespread dissemination of either of the two encapsulated mRNA-based vaccines for COVID-19.

Multiple Biological Aspects of Eosinophils in Host Defense, Eosinophil-Associated Diseases, Immunoregulation, and Homeostasis: Is Their Role Beneficial, Detrimental, Regulator, or Bystander?

Eosinophils are innate immune leukocytes and play important roles as terminal effector cells owing to their mediators, such as tissue-destructive cationic proteins, cytokines, chemokines, and lipid mediators. Historically, they are not only considered an important player in host defense against parasitic, viral, fungal, and bacterial infections but also implicated in the pathogenesis of eosinophil-associated diseases, such as allergic rhinitis, asthma, eosinophilic chronic rhinosinusitis, esophagitis, atopic dermatitis, myopathies, and hypereosinophilic syndrome. Moreover, recent studies have shown that eosinophils have an immune regulatory and homeostatic function. Interestingly, there is emerging evidence that eosinophils are accumulated through adoptive T-helper 2 (Th2) and innate Th2 responses, mechanisms of the classical allergen-specific immunoglobulin E (IgE)-mediated response, and group 2 innate lymphoid cell-derived interleukin-5, respectively. Furthermore, in agreement with current concepts of eosinophil subtypes, it has been shown that resident and phenotypically distinct eosinophils, i.e., resident and recruited inflammatory eosinophils, exist in inflamed sites, and each has different functions. Thus, the classical and novel studies suggest that eosinophils have multiple functions, and their roles may be altered by the environment. In this article, we review multiple biological aspects of eosinophils (novel and classical roles), including their beneficial and detrimental effects, immunoregulation, and homeostatic function.

Tumour-associated tissue eosinophilia (TATE) in oral squamous cell carcinoma: a comprehensive review

Oral squamous cell carcinoma is the most common head and neck malignancy, characterised by high invasive capacity, lymph node metastasis, and high recurrence rate. Among the morphological features of oral cancer, the tumour-associated tissue eosinophilia has gained growing interest in the last years. Eosinophils are a minor subpopulation of leukocytes, representing 1-3% of all circulating white blood cells. The presence of high levels of eosinophils is associated with several diseases, but their role in cancer pathophysiology is controversial. In particular, an uncertain and contradictory relationship exists between the exact role of tumour-associated tissue eosinophilia and oral cancer development. Many studies have shown that tumour-associated tissue eosinophilia increases both in the progression of oral potentially malignant disorders as well as in the grade and stage progression of oral cancer. Despite this, both negative and positive prognostic outcomes have been associated with eosinophil infiltration. The heterogeneous results may be partially due both to several methodological inconsistencies and to an incorrect interpretation of the physiological role of eosinophils. Therefore, further studies to elucidate the contribution of eosinophil infiltration are needed, focusing on the existence of eosinophil subpopulations regulated by the cancer immune microenvironment. Furthermore, the correct reporting of prognostic marker research is encouraged, in order to ensure the reproducibility and the comparability of the results from different studies.

4-Carvomenthenol ameliorates the murine combined allergic rhinitis and asthma syndrome by inhibiting IL-13 and mucus production via p38MAPK/NF-κB signaling pathway axis

The aim of this study was to analyze the 4-carvomenthenol (carvo) oral treatment on the experimental model of the combined allergic rhinitis and asthma syndrome (CARAS). BALB/c mice were OVA-sensitized on day zero and 7th (50 μg/mL OVA in 10 mg/mL Al (OH)3) and OVA-challenged (5 mg/mL, 20 μL/animal) for three weeks. In the last week, the animals were dally challenged with aerosol of OVA and the carvo treatment (12.5, 25 or 50 mg/kg) occurred one hour before each OVA-challenge. Data were analyzed and p < 0.05 was considered significant. Carvo (12.5-50 mg/kg) decreased significantly the eosinophil migration into the nasal (NALF) and bronchoalveolar (BALF) cavities as well as on the nasal and lung tissues of sick animals. The treatment also decreased mucus production on both tissue sections stained with PAS (periodic acid-Schiff satin). In addition, the histological analyzes demonstrated that sick mice presented hyperplasia and hypertrophy of the lung smooth muscle layer followed by increasing of extracellular matrix and carvo (50 mg/kg) inhibited these asthmatic parameters. We analyzed the allergic rhinitis signals as nasal frictions and sneezing and observed that carvo decreased these two signals as well as serum OVA-specific IgE titer, type 2 cytokine synthesis, mainly IL-13, with increasing of IL-10 production. Decreasing of IL-13 production corroborated with decreasing of mucus production and these effects were dependent on p38MAPK/NF-κB(p65) signaling pathway inhibition. Therefore, these data demonstrated that a monoterpene of essential oils presents anti-allergic property on an experimental model of CARAS suggesting a new drug prototype to treat this allergic syndrome.

Biologics for Severe Asthma: Treatment-Specific Effects Are Important in Choosing a Specific Agent

Patients with uncontrolled severe persistent asthma have greater morbidity, greater use of health care resources, and more impairment in health-related quality of life when compared with their peers with well-controlled disease. Fortunately, since the introduction of biological therapeutics, patients with severe eosinophilic asthma now have beneficial treatment options that they did not have just a few years ago. In addition to anti-IgE therapy for allergic asthma, 3 new biological therapeutics targeting IL-5 and 1 targeting IL-4 and IL-13 signaling have recently been approved by the Food and Drug Administration for the treatment of severe eosinophilic asthma, and approval of more biological therapeutics is on the horizon. These medications decrease the frequency of asthma exacerbations, improve lung function, reduce corticosteroid usage, and improve health-related quality of life. This article reviews the mechanisms of action, specific indications, benefits, and side effects of each of the approved biological therapies for asthma. Furthermore, this article reviews how a clinician could use specific patient characteristics to decide which biologic treatment may be optimal for a given patient.

Eosinophils and White Fat: Protection from Worms and Inflammaging

Proinflammatory alterations of white adipose tissue (WAT) with increasing age play an important role in mammalian aging. WAT produced eotaxin-1 (CCL11-C-C motif chemokine ligand 11) and monocyte chemoattractant protein 1 (MCP-1) (CCL2) are elevated in old mammals. Obese and old adipose tissues produce excessive proinflammatory cytokines such as interleukin (IL)-6, CCL2, and IL-1-beta that contribute to inflammaging. WAT-based inflammaging involves an altered homeostatic equilibrium between proinflammatory cells such as activated type 1 macrophages, B cells (high IgJ) and T cells, and anti-inflammatory eosinophils and Tregs. Specifically, young and lean individuals exhibit a high eosinophil-to-macrophage ratio with an enrichment of alternative activated tissue macrophages that is reduced in the WAT of aging mice. Eosinophils from young animals adoptively transferred to old mice, home to WAT and reverse many of the immunoinflammatory signatures associated with aging. Whether eosinophil-based therapies for inflammaging could be created remains an open question.

Promises and challenges of biologics for severe asthma

Patients with severe asthma that remain uncontrolled incur significant medical burden and healthcare costs. Severe asthma is a heterogeneous airway disorder with complex pathophysiological mechanisms which can be broadly divided into type 2 (T2)-high and T2-low inflammatory pathways. Recent advances in asthma therapeutics with the advent of biologics have heralded an era of promising targeted therapy in this group of patients. The current available biologics, including anti-IgE mAb, anti-IL-5/IL-5R mAb and anti-IL-4Rα mAb, mainly target patients with an asthma endotype characterised by T2-high inflammation. While they have delivered positive outcomes in terms of reduction in exacerbations, improving lung function and quality of life, as well as reducing the dependence on oral corticosteroids, they have not functioned as the "panacea" as a significant proportion of patients do not respond completely to these targeted therapies. In addition, there is a lack of markers that can predict treatment response and clinicians are guided only by subjective asthma symptom scores. Suboptimal treatment response is common for individual patients. There has also been a dearth of effective targeted therapy for patients with T2-low asthma and treatment options remain limited for these patients. There is a pipeline of newer biologics targeting cytokines that operate at the interface between innate and adaptive immunity (e.g. IL-17A, thymic stromal lymphopoietin (TSLP), IL-25, IL-33, IL-32 and IL-36γ) with potential of modifying and reducing the severity of asthma. This commentary provides an overview of treatment with the current biologics and highlights the limitations, challenges and unmet needs in clinical management. We also summarise up-and-coming potential targets and therapeutic biologics for severe asthma.

Intravital imaging of eosinophils: Unwrapping the enigma

Eosinophils are traditionally associated with allergic and parasitic inflammation. More recently, eosinophils have also been shown to have roles in diverse processes including development, intestinal health, thymic selection, and B-cell survival with the majority of these insights being derived from murine models and in vitro assays. Despite this, tools to measure the dynamic activity of eosinophils in situ have been lacking. Intravital microscopy is a powerful tool that enables direct visualization of leukocytes and their dynamic behavior in real-time in a wide range of processes in both health and disease. Until recently eosinophil researchers have not been able to take full advantage of this technology due to a lack of tools such as genetically encoded reporter mice. This mini-review examines the history of intravital microscopy with a focus on eosinophils. The development and use of eosinophil-specific Cre (EoCre) mice to create GFP and tdTomato fluorescent reporter animals is also described. Genetically encoded eosinophil reporter mice combined with intravital microscopy provide a powerful tool to add to the toolbox of technologies that will help us unravel the mysteries still surrounding this cell.

Eosinopenia, in Chronic Spontaneous Urticaria, Is Associated with High Disease Activity, Autoimmunity, and Poor Response to Treatment

BACKGROUND

Chronic spontaneous urticaria (CSU) is characterized by the degranulation of skin mast cells and the influx of basophils and eosinophils to affected skin sites. Blood basopenia has been linked to severe antihistamine-resistant CSU and type IIb autoimmunity, whereas the role of eosinophils in CSU is largely unknown.

OBJECTIVE

To analyze data from 1613 patients with CSU from 2 centers to study the prevalence, role, and relevance of eosinopenia in CSU.

METHODS

Peripheral blood eosinophil and basophil counts were measured by automated hematology analyzers. Patient files were screened for clinical characteristics, results of laboratory tests, the autologous serum skin test, the serum-induced basophil histamine release assay, and response to second-generation H₁-antihistamines and omalizumab.

RESULTS

Ten percent of patients with CSU had eosinopenia. Eosinopenia was associated with the female sex, high disease activity, autologous serum skin test and basophil histamine release assay positivity, low total IgE, and high levels of C-reactive protein and IgG-antithyroperoxidase (P ≤ .007). Nonresponders to second-generation H₁-antihistamines or omalizumab had significantly lower eosinophils as compared with responders (P < .05 and P < .01, respectively). Blood eosinophil counts correlated with basophil counts (r = 0.396; P < .001), and 81% of patients with CSU with undetectable eosinophils had basopenia. The combination of eosinopenia and basopenia is a better predictor of nonresponse to second-generation H₁-antihistamines than eosinopenia alone (odds ratio of 9.5 vs 4.8).

CONCLUSIONS

Eosinopenia in patients with CSU is associated with type IIb autoimmunity, high disease activity, and poor response to treatment. Eosinophils should be explored as biomarkers and investigated for their contribution to the pathogenesis of CSU.

Eosinophils in the gastrointestinal tract and their role in the pathogenesis of major colorectal disorders

Eosinophils are currently regarded as versatile mobile cells controlling and regulating multiple biological pathways and responses in health and disease. These cells store in their specific granules numerous biologically active substances (cytotoxic cationic proteins, cytokines, growth factors, chemokines, enzymes) ready for rapid release. The human gut is the main destination of eosinophils that are produced and matured in the bone marrow and then transferred to target tissues through the circulation. In health the most important functions of gut-residing eosinophils comprise their participation in the maintenance of the protective mucosal barrier and interactions with other immune cells in providing immunity to microbiota of the gut lumen. Eosinophils are closely involved in the development of inflammatory bowel disease (IBD), when their cytotoxic granule proteins cause damage to host tissues. However, their roles in Crohn’s disease and ulcerative colitis appear to follow different immune response patterns. Eosinophils in IBD are especially important in altering the structure and protective functions of the mucosal barrier and modulating massive neutrophil influx to the lamina propria followed by transepithelial migration to colorectal mucus. IBD-associated inflammatory process involving eosinophils then appears to expand to the mucus overlaying the internal gut surface. The author hypothesises that immune responses within colorectal mucus as well as ETosis exerted by both neutrophils and eosinophils on the both sides of the colonic epithelial barrier act as additional pathogenetic factors in IBD. Literature analysis also shows an association between elevated eosinophil levels and better colorectal cancer (CRC) prognosis, but mechanisms behind this effect remain to be elucidated. In conclusion, the author emphasises the importance of investigating colorectal mucus in IBD and CRC patients as a previously unexplored milieu of disease-related inflammatory responses.

Combined allergic rhinitis and asthma syndrome (CARAS)

Combined allergic rhinitis and asthma syndrome (CARAS) is a concept of "one airway - one disease" or "unified airway disease ". The upper and lower airway inflammation characterizes allergic rhinitis and asthma, respectively and both diseases have shown an intimate connection in their genesis, coexistence and similarities as triggered by the same etiological agents; the same inflammatory cell profile and share therapeutic treatment. This review highlights the concept of CARAS by its phenotype, endotype and biomarker classification. Indeed, rhinitis is divided into four major phenotypes: allergic rhinitis; infectious rhinitis; non-infective/non-allergic rhinitis and mixed rhinitis. On the other hand, asthma has no common consensus yet; however, the most accepted classification is based on the stage of life (early- or late- onset asthma) in which the clinical symptoms are presented. Experimental researches where animals develop a syndrome similar to CARAS have been contributed to better understand the pathogenesis of the syndrome. Therefore, the aim of this review is to clarify current terms related to CARAS as definition, phenotypes, endotypes/biomarkers, physiopathology and treatments.

Eosinophils: Nemeses of Pulmonary Pathogens?

PURPOSE OF REVIEW

Eosinophils are short-lived granulocytes that contain a variety of proteins and lipids traditionally associated with host defense against parasites. The primary goal of this review is to examine more recent evidence that challenged this rather outdated role of eosinophils in the context of pulmonary infections with helminths, viruses, and bacteria.

RECENT FINDINGS

While eosinophil mechanisms that counter parasites, viruses, and bacteria are similar, the kinetics and impact may differ by pathogen type. Major antiparasitic responses include direct killing and immunoregulation, as well as some mechanisms by which parasite survival/growth is supported. Antiviral defenses may be as unembellished as granule protein-induced direct killing or more urbane as serving as a conduit for better adaptive immune responses to the invading virus. Although sacrificial, eosinophil DNA emitted in response to bacteria helps trap bacteria to limit dissemination. Herein, we discuss the current research redefining eosinophils as multifunctional cells that are active participants in host defense against lung pathogens. Eosinophils recognize and differentially respond to invading pathogens, allowing them to deploy innate defense mechanisms to contain and clear the infection, or modulate the immune response. Modern technology and animal models have unraveled hitherto unknown capabilities of this surreptitious cell that indubitably has more functions awaiting discovery.

Airway Eosinophilopoietic and Autoimmune Mechanisms of Eosinophilia in Severe Asthma

Eosinophils are critical in asthma biology, contributing to symptoms, airflow obstruction, airway hyperresponsiveness, and remodeling. In severe asthma, in addition to local maturation in bone marrow, in situ eosinophilopoiesis plays a key role in the persistence of airway eosinophilia. Local milieu of structural, epithelial and inflammatory cells contribute by generating eosinophilopoietic cytokines in response to epithelial-derived alarmins. Another mechanism of persistent airway eosinophilia is glucocorticosteroid insensitivity, which is linked to recurrent airway infections and presence of local autoantibodies. Novel molecules are being developed to target specific immune pathways as potential steroid-sparing strategies.

Shall We Focus on the Eosinophil to Guide Treatment with Systemic Corticosteroids during Acute Exacerbations of COPD?: PRO

In an era of precision medicine, it seems regressive that we do not use stratified approaches to direct treatment of oral corticosteroids during an exacerbation of chronic obstructive pulmonary disease (COPD). This is despite evidence suggesting that 40% of COPD patients have eosinophilic inflammation and this is an indicator of corticosteroid response. Treatments with oral corticosteroids are not always effective and not without harm, with significant and increased risk of hyperglycemia, sepsis, and fractures. Eosinophils are innate immune cells with an incompletely understood role in the pathology of airway disease. They are detected at increased levels in some patients and can be measured using non-invasive methods during states of exacerbation and stable periods. Despite the eosinophil having an unknown mechanism in COPD, it has been shown to be a marker of length of stay in severe hospitalized exacerbations, a predictor of risk of future exacerbation and exacerbation type. Although limited, promising data has come from one prospective clinical trial investigating the eosinophil as a biomarker to direct systemic corticosteroid treatment. This identified that there were statistically significant and clinically worsened symptoms in patients with low eosinophil levels who were prescribed prednisolone, demonstrating the potential utility of the eosinophil. In an era of precision medicine our patients' needs are best served by accurate diagnosis, correct identification of maximal treatment response and the abolition of harm. The peripheral blood eosinophil count could be used towards reaching these aims.

Eosinophil Counts in the Small Intestine and Colon of Children Without Apparent Gastrointestinal Disease: A Meta-analysis

The aim of the current study was to review the available data regarding eosinophil density in healthy tissue specimen originating from lower gastrointestinal segments to support suggested diagnostic cutoffs widely used in clinical practice. A systematic search was performed in 3 different databases. Calculations were made with Comprehensive MetaAnalysis software using random-effects model. Cell number measurements were pooled using the random-effects model and displayed on forest plots. Summary point estimations, 95% confidence intervals (CIs), and 95% prediction intervals (PIs) were calculated. The cumulative mean cell numbers were 8.26 (95% CI 4.71-11.80) with PI of 0-25.32 for the duodenum, 11.52 (95% CI 7.21-15.83) with PI 0-60.64 for the terminal ileum, and 11.10/ high-power field (HPF) (95% CI 9.11-13.09) with PI of 0.96 to 21.23 in the large intestine and the rectum (HPF area = 0.2 mm). Previous studies included control patients with irritable bowel syndrome and functional gastrointestinal disorders. As mucosal eosinophils have a role in their pathomechanism, those patients should have been excluded. A critical point of interpreting reported data is that HPF is relative to the technical parameters of the microscopes; therefore, it is important to report findings in cell/mm. The present meta-analysis does not support the higher (>20) or lower (<10) cutoff values for healthy tissue eosinophil number. In contrast to the esophagus, there is no normal cutoff eosinophil density in the small intestine and the colon. A prospective, multicenter study to establish normal mucosal eosinophil density is clearly needed.

Contemporary understanding of the secretory granules in human eosinophils

Eosinophil secretory (specific) granules have a unique morphology and are both a morphologic hallmark of eosinophils and fundamental to eosinophil-mediated responses. Eosinophil mediators with multiple functional activities are presynthesized and stored within these granules, poised for very rapid, stimulus-induced secretion. The structural organization and changes of eosinophil specific granules are revealing in demonstrating the complex and diverse secretory activities of this cell. Here, we review our current knowledge on the architecture, composition, and function of eosinophil specific granules as highly elaborated organelles able to produce vesiculotubular carriers and to interplay with the intracellular vesicular trafficking. We reconsider prior identifications of eosinophil cytoplasmic granules, including "primary," "secondary," "microgranules," and "small granules"; and consonant with advances, we provide a contemporary recognition that human eosinophils contain a single population of specific granules and their developmental precursors and derived secretory vesicles.

Eosinophils: The unsung heroes in cancer?

Prolonged low-grade inflammation or smoldering inflammation is a hallmark of a cancer. Eosinophils are components of the immune microenvironment that modulates tumor initiation and progression. Although canonically associated with a detrimental role in allergic disorders, these cells can induce a protective immune response against helminthes, viral and bacterial pathogens. Eosinophils are a source of anti-tumorigenic (e.g., TNF-α, granzyme, cationic proteins, and IL-18) and protumorigenic molecules (e.g., pro-angiogenic factors) depending on the milieu. In several neoplasias (e.g., melanoma, gastric, colorectal, oral and prostate cancer) eosinophils play an anti-tumorigenic role, in others (e.g., Hodgkin's lymphoma, cervical carcinoma) have been linked to poor prognosis, whereas in yet others they are apparently innocent bystanders. These seemingly conflicting results suggest that the role of eosinophils and their mediators could be cancer-dependent. The microlocalization (e.g., peritumoral vs intratumoral) of eosinophils could be another important aspect in the initiation/progression of solid and hematological tumors. Increasing evidence in experimental models indicates that activation/recruitment of eosinophils could represent a new therapeutic strategy for certain tumors (e.g., melanoma). Many unanswered questions should be addressed before we understand whether eosinophils are an ally, adversary or neutral bystanders in different types of human cancers.

Eosinophils and eosinophil-associated diseases: An update

The goal of this series is to offer a survey of the latest literature for clinicians and scientists alike, providing a list of important recent advances relevant to the broad field of allergy and immunology. This particular assignment was to cover the topic of eosinophils. In an attempt to highlight major ideas, themes, trends, and advances relevant to basic and clinical aspects of eosinophil biology, a search of articles published since 2015 in the Journal of Allergy and Clinical Immunology and other high-impact journals was performed. Articles were then reviewed and organized, and then key findings were summarized. Given space limitations, many outstanding articles could not be included, but the hope is that what follows provides a succinct overview of recently published work that has significantly added to our knowledge of eosinophils and eosinophil-associated diseases.

Eosinophilic Otitis Media: the Aftermath of Eosinophil Extracellular Trap Cell Death

PURPOSE OF REVIEW

Eosinophilic otitis media (EOM) is a refractory disease characterized by the accumulation of eosinophils in middle ear effusion and mucosa. We summarize current knowledge regarding the clinical characteristics and management of EOM. Although eosinophil activation in inflamed foci is involved in the pathogenesis of EOM, little is known about the fate of the eosinophils and aftermath of their cell death. We discuss the possibility that eosinophils undergo non-apoptotic cell death that worsens tissue damage and increases effusion viscosity.

RECENT FINDINGS

Unlike chronic otitis media, EOM is strongly associated with an allergic background. Corticosteroids are currently the only effective pharmacological treatment, and surgical intervention is often required. Mucosal eosinophils infiltrate extensively into the middle ear cavity where they are stimulated by locally produced activators including interleukin-5 and eotaxin. The eosinophils undergo cytolysis in the effusion, which represents a major fate of activated eosinophils in vivo. Recent data revealed cytolysis could be renamed as extracellular trap cell death (ETosis). ETosis represents suicidal cell death involving total cell degranulation and development of sticky chromatin structures (extracellular traps (ETs)). The characteristics of eosinophil- and neutrophil-derived ET polymers might contribute to the difference in viscosity of secretions between EOM and common chronic otitis media. The extracellular products remaining after eosinophil ETosis are an important aspect of EOM pathology. The concept of ETosis also has novel implications for potential therapeutic modalities in various eosinophilic disorders.

Anti-IL5 therapies for asthma

BACKGROUND

This review is the first update of a previously published review in The Cochrane Library (Issue 7, 2015). Interleukin-5 (IL-5) is the main cytokine involved in the activation of eosinophils, which cause airway inflammation and are a classic feature of asthma. Monoclonal antibodies targeting IL-5 or its receptor (IL-5R) have been developed, with recent studies suggesting that they reduce asthma exacerbations, improve health-related quality of life (HRQoL) and lung function. These are being incorporated into asthma guidelines.

OBJECTIVES

To compare the effects of therapies targeting IL-5 signalling (anti-IL-5 or anti-IL-5Rα) with placebo on exacerbations, health-related qualify of life (HRQoL) measures, and lung function in adults and children with chronic asthma, and specifically in those with eosinophilic asthma refractory to existing treatments.

SEARCH METHODS

We searched the Cochrane Airways Trials Register, clinical trials registries, manufacturers' websites, and reference lists of included studies. The most recent search was March 2017.

SELECTION CRITERIA

We included randomised controlled trials comparing mepolizumab, reslizumab and benralizumab versus placebo in adults and children with asthma.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and analysed outcomes using a random-effects model. We used standard methods expected by Cochrane.

MAIN RESULTS

Thirteen studies on 6000 participants met the inclusion criteria. Four used mepolizumab, four used reslizumab, and five used benralizumab. One study in benralizumab was terminated early due to sponsor decision and contributed no data. The studies were predominantly on people with severe eosinophilic asthma, which was similarly but variably defined. Eight included children over 12 years but these results were not reported separately. We deemed the risk of bias to be low, with all studies contributing data being of robust methodology. We considered the quality of the evidence for all comparisons to be high overall using the GRADE scheme, with the exception of intravenous mepolizumab because this is not currently a licensed delivery route.All of the anti-IL-5 treatments assessed reduced rates of 'clinically significant' asthma exacerbation (defined by treatment with systemic corticosteroids for three days or more) by approximately half in participants with severe eosinophilic asthma on standard of care (at least medium-dose inhaled corticosteroids (ICS)) with poorly controlled disease (either two or more exacerbations in the preceding year or Asthma Control Questionnaire (ACQ) 1.5 or more). Non-eosinophilic participants treated with benralizumab also showed a significant reduction in exacerbation rates, but no data were available for non-eosinophilic participants, and mepolizumab or reslizumab.We saw modest improvements in validated HRQoL scores with all anti-IL-5 agents in severe eosinophilic asthma. However these did not exceed the minimum clinically important difference for ACQ and Asthma Quality of Life Questionnaire (AQLQ), with St. George's Respiratory Questionnaire (SGRQ) only assessed in two studies. The improvement in HRQoL scores in non-eosinophilic participants treated with benralizumab, the only intervention for which data were available in this subset, was not statistically significant, but the test for subgroup difference was negative.All anti-IL-5 treatments produced a small but statistically significant improvement in mean pre-bronchodilator forced expiratory flow in one second (FEV1) of between 0.08 L and 0.11 L.There were no excess serious adverse events with any anti-IL-5 treatment, and indeed a reduction in favour of mepolizumab that could be due to a beneficial effect on asthma-related serious adverse events. There was no difference compared to placebo in adverse events leading to discontinuation with mepolizumab or reslizumab, but significantly more discontinued benralizumab than placebo, although the absolute numbers were small (36/1599 benralizumab versus 9/998 placebo).Mepolizumab, reslizumab and benralizumab all markedly reduced blood eosinophils, but benralizumab resulted in almost complete depletion, whereas a small number remained with mepolizumab and reslizumab. The implications for efficacy and/or adverse events are unclear.

AUTHORS' CONCLUSIONS

Overall our study supports the use of anti-IL-5 treatments as an adjunct to standard of care in people with severe eosinophilic asthma and poor control. These treatments roughly halve the rate of asthma exacerbations in this population. There is limited evidence for improved HRQoL scores and lung function, which may not meet clinically detectable levels. There were no safety concerns regarding mepolizumab or reslizumab, and no excess serious adverse events with benralizumab, although there remains a question over adverse events significant enough to prompt discontinuation.Further research is needed on biomarkers for assessing treatment response, optimal duration and long-term effects of treatment, risk of relapse on withdrawal, non-eosinophilic patients, children (particularly under 12 years), and comparing anti-IL-5 treatments to each other and, in people eligible for both, to anti-immunoglobulin E. For benralizumab, future studies should closely monitor rates of adverse events prompting discontinuation.

Interleukin-5 Antagonists Usher in a New Generation of Asthma Therapy

Asthma is the most common chronic respiratory disease in the USA. A subset of patients with asthma have refractory symptoms, persistent eosinophilic inflammation, and recurrent exacerbations despite maximal medical therapy. The monoclonal antibodies targeting the IL-5 pathway are a new class of medications designed to target severe eosinophilic asthma. There are two medications clinically available: mepolizumab and reslizumab, both of which target IL-5. A third medication, benralizumab, is currently under development and targets the IL-5 receptor. Clinical data suggest these medications can reduce asthma exacerbations and improve lung function in patients with peripheral eosinophilia and poorly controlled asthma despite maximal medical therapy. The anti-IL-5 medications are among the first targeted molecular therapies for asthma and will usher in an exciting new era in the treatment of severe asthma.

Paul Ehrlich and the Early History of Granulocytes

Paul Ehrlich's techniques, published between 1879 and 1880, for staining blood films using coal tar dyes, and his method of differential blood cell counting, ended years of speculation regarding the classification of white cells. Acidic and basic dyes had allowed him to recognize eosinophil and basophil granules, respectively, work that was a direct continuation of his discovery of the tissue mast cell described in his doctoral thesis. Ehrlich went on to develop neutral dyes that identified epsilon granules in neutrophils ("cells with polymorphous nuclei"). He also speculated, for the most part correctly, on the formation, function, and fate of blood neutrophils and eosinophils. Before Ehrlich, a number of important observations had been made on white cells and their role in health and disease. Among the most notable were William Hewson's studies of blood and lymph; the early descriptions of leukemia by Alfred Donné, John Hughes Bennett, Rudolf Virchow, and others; as well as seminal observations on inflammation by William Addison, Friedrich von Recklinghausen, and Julius Cohnheim. Eosinophils were almost certainly recognized previously by others. In 1846, Thomas Wharton Jones (1808-1891) described "granule blood-cells" in several species including humans. The term "granule cell" had also been used by Julius Vogel (1814-1880), who had previously observed similar cells in inflammatory exudates. Vogel, in turn, was aware of the work of Gottlieb Gluge (1812-1898), who had observed "compound inflammatory globules" in pus and serum that resembled eosinophils. Almost 20 years before Ehrlich developed his staining methods, Max Johann Schultze (1825-1874) performed functional experiments on fine and coarse granular cells using a warm stage microscopic technique and showed they had amoeboid movement and phagocytic abilities. Despite these earlier observations, it was Ehrlich's use of stains that heralded the modern era of studies of leukocyte biology and pathology.