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The Consortium of Eosinophilic Gastrointestinal Diseases and The International Gastrointestinal Eosinophil Researchers organized a day-long symposium at the 2022 Annual Meeting of the American Academy of Allergy, Asthma & Immunology. The symposium featured a review of recent discoveries in the basic biology and pathogenesis of eosinophilic gastrointestinal diseases (EGIDs) in addition to advances in our understanding of the clinical features of EGIDs. Diagnostic and management approaches were reviewed and debated, and clinical trials of emerging therapies were highlighted. Herein, we briefly summarize the breakthrough discoveries in EGIDs., (Copyright © 2023 American Academy of Allergy, Asthma & Immunology. All rights reserved.)

Mast cells and eosinophils are commonly found, expectedly or unexpectedly, in human tissue biopsies. Although the clinical significance of their presence, absence, quantity, and quality continues to be investigated in homeostasis and disease, there are currently gaps in knowledge related to what constitutes quantitatively relevant increases in mast cell and eosinophil number in tissue specimens for several clinical conditions. Diagnostically relevant thresholds of mast cell and eosinophil numbers have been proposed and generally accepted by the medical community for a few conditions, such as systemic mastocytosis and eosinophilic esophagitis. However, for other mast cell- and eosinophil-associated disorders, broad discrepancies remain regarding diagnostic thresholds and how samples are processed, routinely and/or specially stained, and interpreted and/or reported by pathologists. These discrepancies can obfuscate or delay a patient's correct diagnosis. Therefore, a work group was assembled to review the literature and develop a standardized consensus for assessing the presence of mast cells and eosinophils for a spectrum of clinical conditions, including systemic mastocytosis and cutaneous mastocytosis, mast cell activation syndrome, eosinophilic esophagitis, eosinophilic gastritis/enteritis, and hypereosinophilia/hypereosinophilic syndrome. The intent of this work group is to build a consensus among pathology, allergy, dermatology, hematology/oncology, and gastroenterology stakeholders for qualitatively and quantitatively assessing mast cells and eosinophils in skin, gastrointestinal, and bone marrow pathologic specimens for the benefit of clinical practice and patients., (Copyright © 2021 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Background: Sialic acid-binding immunoglobulin-like lectin (Siglec) 8 is selectively expressed on eosinophils, mast cells, and basophils and, when engaged on eosinophils, can cause cell death., Objective: We sought to characterize surface and soluble Siglec-8 (sSiglec-8) levels in normal donors (NDs) and eosinophilic donors (EOs) and assess the efficacy of anti-Siglec-8 antibodies in inducing eosinophil cell death in vitro., Methods: Eosinophil expression of Siglec-8 was assessed by using flow cytometry and quantitative PCR. Serum sSiglec-8 levels were measured by means of ELISA. Induction of eosinophil death by IgG 4 (chimeric 2E2 IgG 4 ) and afucosylated IgG 1 (chimeric 2E2 IgG 1 [c2E2 IgG 1 ]) anti-Siglec-8 antibodies was evaluated in vitro by using flow cytometry and in vivo in humanized mice., Results: Siglec-8 was consistently expressed on eosinophils from NDs and EOs and did not correlate with absolute eosinophil count or disease activity. sSiglec-8 levels were measurable in sera from most donors unrelated to absolute eosinophil counts or Siglec-8 surface expression. c2E2 IgG 1 and chimeric 2E2 IgG 4 were equally effective at inducing cell death (Annexin-V positivity) of purified eosinophils from NDs and EOs after overnight IL-5 priming. In contrast, killing of purified eosinophils without IL-5 was only seen in EOs, and natural killer cell-mediated eosinophil killing was seen only with c2E2 IgG 1 . Finally, treatment of humanized mice with anti-Siglec antibody led to robust depletion of IL-5-induced eosinophilia in vivo., Conclusions: Siglec-8 is highly expressed on blood eosinophils from EOs and NDs and represents a potential therapeutic target for eosinophilic disorders. Enhanced killing of eosinophils in the presence of IL-5 might lead to increased efficacy in patients with IL-5-driven eosinophilia., (Copyright © 2018 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Virtually all cells and extracellular material are heavily decorated by various glycans, yet our understanding of the structure and function of these moieties lags behind the understanding of nucleic acids, lipids, and proteins. Recent years have seen a tremendous acceleration of knowledge in the field of glycobiology, revealing many intricacies and functional contributions that were previously poorly appreciated or even unrecognized. This review highlights several topics relevant to glycoimmunology in which mammalian and pathogen-derived glycans displayed on glycoproteins and other scaffolds are recognized by specific glycan-binding proteins (GBPs), leading to a variety of proinflammatory and anti-inflammatory cellular responses. The focus for this review is mainly on 2 families of GBPs, sialic acid-binding immunoglobulin-like lectins (siglecs) and selectins, that are involved in multiple steps of the immune response, including distinguishing pathogens from self, cell trafficking to sites of inflammation, fine-tuning of immune responses leading to activation or tolerance, and regulation of cell survival. Importantly for the clinician, accelerated rates of discovery in the field of glycoimmunology are being translated into innovative medical approaches that harness the interaction of glycans and GBPs to the benefit of the host and might soon lead to novel diagnostics and therapeutics., (Copyright © 2014 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Background: Sialic acid-binding immunoglobulin-like lectin (Siglec)-8 is expressed on human eosinophils, where its ligation induces cell death. Paradoxically, Siglec-8-mediated cell death is markedly enhanced by the presence of the activation and survival factor IL-5 and becomes independent of caspase activity., Objective: In this report we investigate the mechanism of Siglec-8-mediated cell death in activated eosinophils., Methods: Human peripheral blood eosinophils were treated with agonistic anti-Siglec-8 antibody and IL-5, and cell death was determined by using flow cytometry and morphology. Phosphorylation of mitogen-activated protein kinase (MAPK) was determined by using phosphoLuminex, flow cytometry, and Western blotting. Reactive oxygen species (ROS) accumulation was determined by using dihydrorhodamine fluorescence., Results: Costimulation with anti-Siglec-8 and IL-5 significantly increased the rate and proportion of cell death by means of necrosis accompanied by granule release compared with that seen after stimulation with anti-Siglec-8 alone, in which apoptosis predominated. Together with the caspase-independent mode of cell death in costimulated cells, these findings suggest the activation of a specific and distinct biochemical pathway of cell death during anti-Siglec-8/IL-5 costimulation. Phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and MAPK-ERK kinase (MEK) 1 was significantly enhanced and sustained in costimulated cells compared with that seen in cells stimulated with IL-5 alone; anti-Siglec-8 alone did not cause ERK1/2 phosphorylation. MEK1 inhibitors blocked anti-Siglec-8/IL-5-induced cell death. ROS accumulation was induced by Siglec-8 ligation in a MEK-independent manner. In contrast, an ROS inhibitor prevented the anti-Siglec-8/IL-5-induced enhancement of ERK phosphorylation and cell death. Exogenous ROS mimicked stimulation by anti-Siglec-8 and was sufficient to induce enhanced cell death in IL-5-treated cells. Collectively, these data suggest that the enhancement of ERK phosphorylation is downstream of ROS generation., Conclusions: In activated eosinophils ligation of Siglec-8 leads to ROS-dependent enhancement of IL-5-induced ERK phosphorylation, which results in a novel mode of biochemically regulated eosinophil cell death., (Copyright © 2013 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.)

Background: Up to 30% of asthmatic subjects are smokers, and smoking might be an important contributor to asthma pathology. Inducible nitric oxide synthase (iNOS), ornithine decarboxylase (ODC), and arginase I are involved in the arginine pathway. We have shown that arginase I and iNOS are upregulated in asthma. Smoking asthmatic subjects are reported to have low exhaled nitric oxide levels. The effect of cigarette smoking on the expression of arginase I in asthma is unknown., Objectives: The aims of this study were to investigate the expression of arginase I, ODC, and iNOS in asthmatic airways of smokers and nonsmokers and in vitro after nicotine stimulation., Methods: Endobronchial biopsies were performed on 24 steroid-naive subjects with mild asthma: 12 smokers and 12 nonsmokers. Arginase I, ODC, and iNOS levels were assessed by means of immunohistochemistry and in situ hybridization (arginase I). In vitro stimulation of airway cells with nicotine was performed, followed by real-time PCR., Results: Arginase I, ODC, and iNOS were expressed in the epithelium and smooth muscle bundles of both subgroups of asthmatic subjects. There was an increase of arginase I and ODC immunoreactivities in smoking compared with nonsmoking asthmatic subjects. There was no significant difference in immunoreactivity for iNOS between groups. Nicotine induced a 2-fold increase in arginase I and ODC expression in airway epithelial cells and fibroblasts., Conclusion: This study demonstrates that the expression of arginase I and ODC is increased in airways of smoking compared with nonsmoking asthmatic subjects and in vitro by nicotine., Clinical Implications: Increased expression of arginase I might lead to low exhaled nitric oxide and chronic obstructive pulmonary disease-like airway remodeling in smoking asthmatic subjects.

Background: Eotaxin-2 is a member of the eotaxin subfamily of CC chemokines that display eosinophil-specific, chemotactic properties and has been associated with allergic disorders. However, the contribution of eotaxin-2 to the development of defined pathogenic features of allergic disease remains to be defined., Objective: We sought to determine whether eotaxin-2 was a cofactor with IL-5 for the regulation of pulmonary eosinophilia and to identify the combined role of these molecules in the induction of phenotypic characteristics of allergic lung disease., Methods: We instilled recombinant eotaxin-2 into the airways of wild-type mice that had been treated systemically with IL-5 or into IL-5-transgenic mice and characterized pulmonary eosinophil numbers, IL-13 production, and airway hyperreactivity (AHR) to methacholine. Mice deficient in the IL-4 receptor alpha-chain, IL-13, and signal transducers and activators of transcription 6 or mice treated with anti-CCR3 monoclonal antibody were also used., Results: Eotaxin-2 and IL-5 cooperatively promoted eosinophil accumulation, IL-13 production, and AHR to methacholine. Neither eotaxin-2 nor IL-5 alone induced these features of allergic disease. IL-13 production was critically dependent on eotaxin-2- and IL-5-regulated eosinophilia, which predisposed to the development of AHR. AHR was dependent on IL-13 and signaling through the IL-4R alpha-chain and signal transducers and activators of transcription 6 pathways and the presence of eosinophils in the lung., Conclusion: These investigations demonstrate important cooperativity between eotaxin-2, IL-5, and IL-13 signaling systems and eosinophils for the development of hallmark features of allergic disease of the lung.

The asthmatic response is characterized by elevated production of IgE, cytokines, chemokines, mucus hypersecretion, air-way obstruction, eosinophilia, and enhanced airway hyperreactivity to spasmogens. Clinical and experimental investigations have demonstrated a strong correlation between the presence of CD4+ TH2 cells, eosinophils, and disease severity, suggesting an integral role for these cells in the pathophysiology of asthma. TH2 cells are thought to induce asthma through the secretion of an array of cytokines (IL-4, -5, -9 -1),-13, -25) that activate inflammatory and residential effector pathways both directly and indirectly. In particular, IL-4 and IL-13 are produced at elevated levels in the asthmatic lung and are thought to be central regulators of many of the hallmark features of the disease. The potency of IL-13 in promoting airway hyperreactivity and mucus hypersecretion and the ability of IL-13 blockade to abrogate several critical aspects of experimental asthma have led to the view that this is a critical cytokine in disease pathogenesis. Extensive studies have also demonstrated a central role for chemokines in orchestrating multiple aspects of the asthmatic response. Chemokines are potent leukocyte chemoattractants, cellular activating factors, and histamine-releasing factors, which makes them particularly important in the pathogenesis of allergic inflammation. In particular, the eotaxin subfamily of chemokines and their receptor CC chemokine receptor 3 have emerged as central regulators of the asthmatic response. Recent studies have provided an integrated mechanism by which to explain the coordinate interaction between IL-13 and chemokines in the pathogenesis of asthma. In this regard, chemokines and IL-13 are attractive new therapeutic targets for the treatment of allergic disease. This article focuses on recently emerging data pertaining to the importance of chemokines, especially eotaxins, in promoting IL-13-associated allergic lung responses, as well as the potential for pharmacologically targeting these pathways.

Background: CC chemokine receptor 3 (CCR3) is a major chemokine receptor involved in regulating eosinophil trafficking, and therefore the elucidation of ligand-induced CCR3 events has important implications in understanding the biologic and pathologic properties of eosinophils. After ligand binding to CCR3, cellular signals include stimulatory (ie, calcium mobilization, actin polymerization, shape change, and chemotaxis) and inhibitory (ie, desensitization of the receptor) events. We have previously demonstrated that CCR3 undergoes rapid and prolonged ligand-induced internalization., Objective: Here we explore the role of internalization in downstream cellular processes, including shape change, actin polymerization, calcium mobilization, and desensitization., Methods: Peripheral blood-derived human eosinophils were pretreated with 2 mechanistically distinct inhibitors of internalization, sucrose and phenylarsine oxide, and functional responses were monitored., Results: We first demonstrate that ligand-induced internalization is required for chemokine-induced eosinophil shape change. To define which signaling components upstream of eosinophil shape change required internalization, we next studied the role of internalization in calcium mobilization and actin polymerization. Sucrose and phenylarsine oxide pretreatment inhibited actin polymerization, implicating receptor internalization in this early response. In contrast, calcium mobilization was not inhibited by blockade of internalization. Finally, we were interested in testing the role of internalization in receptor desensitization. We first demonstrated that preincubation with eotaxin induced a dose-dependent desensitization in eotaxin-induced eosinophil transepithelial migration. However, this phenomenon was not inhibited by blockade of internalization., Conclusion: These results establish that CCR3 internalization is critically involved in select eosinophil functional responses (ie, cellular shape change and actin polymerization) but not desensitization and calcium mobilization.

Background: IL-13 induces several characteristic features of asthma, including airway eosinophilia, airway hyperresponsiveness, and mucus overproduction; however, the mechanisms involved are largely unknown., Objective: We hypothesized that IL-13-induced inflammatory changes in the lung were dependent in part on IL-5 and eotaxin, two eosinophil-selective cytokines., Methods: Recombinant murine IL-13 was repeatedly administered to the lung by intranasal delivery until the characteristic features of asthma developed. To analyze the role of IL-5 and eotaxin, we subjected eotaxin gene-targeted, IL-5 gene-targeted, eotaxin/IL-5-double-deficient, IL-5 transgenic, and wild-type mice of the Balb/C background to the experimental regime., Results: The induction of IL-13-mediated airway eosinophilia was found to occur independently of eosinophilia in the blood or bone marrow, indicating that IL-13-induced airway inflammation is primarily mediated by local effects of IL-13 in the lung. Eosinophil recruitment into both the lung tissue and bronchoalveolar lavage fluid was markedly attenuated in IL-5-deficient mice in comparison with wild-type controls. Accordingly, IL-13 delivery to IL-5 transgenic mice resulted in a large increase in airway eosinophils in comparison with wild-type mice. Interestingly, IL-13-induced eosinophilia in the bronchoalveolar lavage fluid of eotaxin-deficient mice was not impaired; however, these same mice failed to mount a significant tissue eosinophilia in response to IL-13. Finally, IL-13-induced mucus production was not affected by the presence of IL-5 or eotaxin, suggesting that IL-13-induced mucus secretion is mechanistically dissociated from airway eosinophilia., Conclusion: Selective components of the IL-13-induced asthma phenotype--airway eosinophilia but not mucus secretion--are differentially regulated by IL-5 and eotaxin. IL-5 is required for IL-13 to induce eosinophilia throughout the lung, whereas eotaxin regulates the distribution of airway eosinophils.

Background: Atopic disorders, including asthma, are very prevalent, affecting up to 40% of populations, and their incidence is on the rise. Although environmental factors are important in the development of atopy, there is a strong genetic predisposition. Several genes and chromosomal regions have been linked to atopy and asthma, supporting the polygenic nature of these disorders. IL-4 and IL-13 are T(H)2 cytokines with numerous activities that contribute to allergic inflammation and asthma. Both IL-4 and IL-13 use the IL-4 receptor alpha chain (IL-4Ralpha) as a component of their respective receptor systems. Allelic variants of IL-4Ralpha have been reported, and the R576IL-4Ralpha allele was recently shown to be a risk factor for atopy., Objective: We sought to determine whether the R576 allele was associated with the prevalence or clinical severity of asthma., Methods: We developed a rapid, reliable, PCR-based assay to screen individuals for the R576IL-4Ralpha allele and used this assay to genotype prospectively recruited individuals with asthma (n = 149) and control subjects (n = 57)., Results: There was a strong association of R576IL-4Ralpha with the prevalence and clinical severity of asthma. In a prospective cohort, homozygosity for R576 was significantly increased in individuals with asthma (n = 149, P =.03; relative risk 8.2) compared with controls (n = 57). Furthermore, 1 or 2 copies R576IL-4Ralpha correlated with asthma severity establishing a genotype-phenotype relationship and suggesting a gene dosage effect., Conclusions: Thus R576IL-4Ralpha acts as an allergic asthma susceptibility and disease-modifying gene and may serve as a clinically useful marker of asthma severity.