Eosinophils in Autoimmune Diseases The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Diny, Nicola L., Noel R. Rose, and Daniela Čiháková. 2017. “Eosinophils in Autoimmune Diseases.” Frontiers in Immunology 8 (1): 484. doi:10.3389/fimmu.2017.00484. http://dx.doi.org/10.3389/ fimmu.2017.00484. Published Version doi:10.3389/fimmu.2017.00484 Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:33029710 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA REVIEW published: 27 April 2017 doi: 10.3389/fimmu.2017.00484 Eosinophils in Autoimmune Diseases Nicola L. Diny1, Noel R. Rose2 and Daniela Cˇiháková3* 1 W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA, 2 Department of Pathology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA, 3 Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA Eosinophils are multifunctional granulocytes that contribute to initiation and modulation of inflammation. Their role in asthma and parasitic infections has long been recognized. Growing evidence now reveals a role for eosinophils in autoimmune diseases. In this review, we summarize the function of eosinophils in inflammatory bowel diseases, neu- romyelitis optica, bullous pemphigoid, autoimmune myocarditis, primary biliary cirrhosis, eosinophilic granulomatosis with polyangiitis, and other autoimmune diseases. Clinical studies, eosinophil-targeted therapies, and experimental models have contributed to our understanding of the regulation and function of eosinophils in these diseases. By examining the role of eosinophils in autoimmune diseases of different organs, we can identify common pathogenic mechanisms. These include degranulation of cytotoxic granule proteins, induction of antibody-dependent cell-mediated cytotoxicity, release of proteases degrading extracellular matrix, immune modulation through cytokines, antigen presentation, and prothrombotic functions. The association of eosinophilic diseases with autoimmune diseases is also examined, showing a possible increase in autoimmune diseases in patients with eosinophilic esophagitis, hypereosinophilic syndrome, and Edited by: Uday Kishore, non-allergic asthma. Finally, we summarize key future research needs. Brunel University London, UK Keywords: innate immune system, autoimmune diseases, eosinophilia, bullous pemphigoid, neuromyelitis optica, Reviewed by: eosinophilic granulomatosis with polyangiitis, myocarditis, inflammatory bowel disease David Voehringer, University of Erlangen- Nuremberg, Germany INTRODUCTION Cordula M. Stover, University of Leicester, UK The cells of the innate immune system can contribute to autoimmune diseases. Activation of innate *Correspondence: immune cells by pathogen-associated molecular patterns and antigen presentation by dendritic Daniela Cˇ iháková cells can result in priming of autoreactive T and B cells and set off an adaptive immune response [email protected] against self-antigens (1–3). Possible roles for innate immune cells exist not only in the initiation stage of autoimmune diseases but also in the modulation and propagation of inflammation and Specialty section: tissue destruction. Such roles have been proposed for neutrophils (4), natural killer cells (5, 6), This article was submitted to macrophages (7), dendritic cells (8, 9), innate lymphoid cells (10), and mast cells (11). Eosinophils Molecular Innate Immunity, have been recognized as a part of the inflammatory infiltrate in several organ-specific autoimmune a section of the journal diseases, but their potential role in autoimmune diseases has not been addressed comprehensively. Frontiers in Immunology The aim of this review is to synthesize the role of eosinophils in different autoimmune diseases and Received: 10 February 2017 explore potential unifying effector mechanisms. We also address the association of autoimmune Accepted: 07 April 2017 diseases with eosinophil-associated disease like asthma and eosinophilic esophagitis. Published: 27 April 2017 Citation: EOSINOPHILS Diny NL, Rose NR and Cˇ iháková D (2017) Eosinophils in Autoimmune Diseases. Eosinophil Biology Front. Immunol. 8:484. Eosinophils are granulocytes that develop in the bone marrow in response to IL-5, with a minor role doi: 10.3389/fimmu.2017.00484 for IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-33 (12–15). IL-5 also Frontiers in Immunology | www.frontiersin.org 1 April 2017 | Volume 8 | Article 484 Diny et al. Eosinophils in Autoimmune Diseases mediates the release of mature eosinophils into the bloodstream matrix. Eosinophil granules contain four major granule proteins from where they migrate into tissues (16). In healthy individuals, and numerous cytokines, chemokines, and growth factors (31) eosinophils are found in the bone marrow, blood, spleen, thymus, (Figure 1). Cytotoxic effects to host tissues and pathogens have gastrointestinal tract, and uterus (17). Under pathological condi- been demonstrated for all major granule proteins: eosinophil tions, eosinophils can infiltrate other tissues as well. Eosinophils cationic protein (ECP), eosinophil-derived neurotoxin (EDN), are usually enumerated in the blood because tissue eosinophils are eosinophil peroxidase (EPX), and major basic protein (MBP) hard to measure. Eosinophil counts over 450–500 cells/μl blood (32). MBP can disrupt the cell membrane and is therefore highly are considered mild eosinophilia and counts over 1,500 cells/μl cytotoxic to mammalian cells, helminths, and bacteria (33–35). are characterized as hypereosinophilia (18). Other effects of MBP include altering smooth muscle contrac- The main chemotaxins for eosinophils are eotaxins, which tion, inducing mast cell and basophil degranulation, provoking homeostatically recruit eosinophils to the gastrointestinal tract, acetylcholine release from peripheral nerves, and promoting thymus, and uterus (19–21) and to other organs in disease states nerve cell survival (36–39). The granule proteins ECP and EDN (22–24). Humans express three functional eotaxins (CCL11, are ribonucleases (13, 40) with neurotoxic and strong antiviral CCL24, and CCL26), whereas mice only express two (CCL11 and activities (41, 42) and immune modulatory functions (43). EPX CCL24) (25–28). The eotaxin receptor, CCR3, is highly expressed generates reactive oxygen species that are directed extracellularly on eosinophils and to a low level on human basophils, mast cells, (44). These products have cytotoxic, prothrombotic, and pro- and Th2 cells (29, 30). Other eosinophil chemoattractants include inflammatory effects (44–46). Granule contents are generally pre- CCL5 and lipid mediators such as leukotriene B4 and prostaglan- formed in eosinophils and released upon stimulation. Piecemeal din D2, although these factors are not specific for eosinophils (31) degranulation is the most common process by which eosinophils (Figure 1). release their granule contents (47–49). Specific granule factors, A unique characteristic of eosinophils are their specific (also rather than the entire granule, are released in response to an termed secondary or secretory) granules. These are secretory activating signal. This leaves the eosinophil intact and able to vesicles with an electron-dense core and an electron-lucent respond to subsequent stimulation. FIGURE 1 | Cellular structure, receptors, and mediators of eosinophils. The pseudocolored composite electron micrograph of an eosinophil highlights cellular structures. Characteristic features of eosinophils include the multilobed nucleus, specific eosinophil granules, lipid bodies, and sombrero vesicles. Eosinophil granules contain cationic proteins, cytokines, growth factors, chemokines, and enzymes. The granule contents can be released upon stimulation. Lipid bodies are the place of synthesis for numerous lipid mediators. Granule contents can be released through sombrero vesicles. Eosinophils carry numerous cell surface receptors including chemokine receptors, Fc receptors, pattern recognition receptors, receptors for lipid mediators, cytokine receptors, complement receptors, and adhesion receptors. Abbreviations: 15-HETE, 15-hydroxyeicosatetraenoic acid; APRIL, a proliferation-inducing ligand; CCL, CC-chemokine ligand; CCR, CC-chemokine receptor; CXCL, CXC-chemokine ligand; CXCR, CXC-chemokine receptor; ECP, eosinophil cationic protein; EDN, eosinophil-derived neurotoxin; EGF, epidermal growth factor; EPX, eosinophil peroxidase; GMCSF, granulocyte-macrophage colony-stimulating factor; IFN, interferon; MBP, major basic protein; NGF, nerve growth factor; PDGF, platelet-derived growth factor; PAF, platelet-activating factor; SCF, stem cell factor; TGF, transforming growth factor; TNF, tumor necrosis factor; VEGF, vascular endothelial growth factor. The electron micrograph was generously provided by Dr. Isabelle Coppens, Johns Hopkins University, Baltimore, MD, USA. Frontiers in Immunology | www.frontiersin.org 2 April 2017 | Volume 8 | Article 484 Diny et al. Eosinophils in Autoimmune Diseases Possible Eosinophil Effector Functions Eosinophils can also influence the adaptive immune response. in Autoimmune Diseases They are capable antigen-presenting