The Journal of Allergy and Clinical Immunology
Volume 126, Issue 1 , Pages 16-25, July 2010

What targeting eosinophils has taught us about their role in diseases

  • Bruce S. Bochner, MD

      Affiliations

    • Department of Medicine, Division of Allergy and Clinical Immunology, Johns Hopkins University School of Medicine, Baltimore, Md
    • Corresponding Author InformationReprint requests: Bruce S. Bochner, MD, Johns Hopkins Asthma and Allergy Center, 5501 Hopkins Bayview Circle, Baltimore, MD 21224.
    • ,
  • Gerald J. Gleich, MD

      Affiliations

    • Departments of Dermatology, Medicine, and Pediatrics, Health Sciences Center, School of Medicine, University of Utah, Salt Lake City, Utah

Received 5 January 2010; received in revised form 8 February 2010; accepted 9 February 2010. published online 03 May 2010.

Article Outline

Eosinophil-associated disease is a term used to encompass a range of disorders from hypereosinophilic syndrome to asthma. Despite the longstanding belief that eosinophils can be primary contributors to disease pathophysiology, it is only in recent years that direct and selective reduction or elimination of eosinophils can be achieved in animals or human subjects. These developments have been made possible in mice through clever targeting of eosinophil production. Antibodies and other agents that target soluble eosinophil-related molecules, such as IL-5, or cell-surface structures, such as CCR3, have also proved useful in reducing blood and tissue eosinophil counts. In human subjects the only eosinophil-selective agents tested in clinical trials thus far are neutralizing antibodies to IL-5, with promising but mixed results. At the very least, such forms of pharmacologic hypothesis testing of the role of eosinophils in certain airway, gastrointestinal, and hematologic diseases has finally provided us with new insights into disease pathogenesis. At its optimistic best, these and other targeted agents might someday become available for those afflicted with eosinophil-associated disorders. This review summarizes what has been learned in vivo in both preclinical and clinical studies of eosinophil-directed therapies, with an emphasis on recent advances.

Key words: Eosinophil, granules, asthma, hypereosinophilic syndrome, IL-5, chemokines, airways hyperreactivity, Churg-Strauss syndrome

Abbreviations used: BTS, British Thoracic Society, CSS, Churg-Strauss syndrome, EPO, Eosinophil peroxidase, HES, Hypereosinophilic syndromes, IL-5R, IL-5 receptor, MBP, Major basic protein

 

Back to Article Outline

Information for Category 1 CME Credit 

Credit can now be obtained, free for a limited time, by reading the review articles in this issue. Please note the following instructions.

Method of Physician Participation in Learning Process: The core material for these activities can be read in this issue of the Journal or online at the JACI Web site: www.jacionline.org. The accompanying tests may only be submitted online at www.jacionline.org. Fax or other copies will not be accepted.

Date of Original Release: July 2010. Credit may be obtained for these courses until June 30, 2012.

Copyright Statement: Copyright © 2010-2012. All rights reserved.

Overall Purpose/Goal: To provide excellent reviews on key aspects of allergic disease to those who research, treat, or manage allergic disease.

Target Audience: Physicians and researchers within the field of allergic disease.

Accreditation/Provider Statements and Credit Designation: The American Academy of Allergy, Asthma & Immunology (AAAAI) is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians. The AAAAI designates these educational activities for a maximum of 1 AMA PRA Category 1 Credit™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

List of Design Committee Members: Bruce S. Bochner, MD, and Gerald J. Gleich, MD

Activity Objectives

1.To become familiar with the biology of eosinophils.

2.To learn about the factors that influence eosinophils.

3.To understand the role of anti–IL-5 in current clinical practice for the allergist.

4.To understand the role of anti–IL-5 in different disease processes.

Recognition of Commercial Support: This CME activity has not received external commercial support.

Disclosure of Significant Relationships with Relevant Commercial

Companies/Organizations: B. S. Bochner has consulted for Genentech,

Amgen, Pharmacyclics, GlaxoSmithKline, Bristol-Meyers Squibb, Bayhill Therapeutics, Roche, Glycomimetics, and Sanofi-Aventis; is on a scientific advisory board for Glycomimetics, Sanofi-Aventis and Roche; and has received research support from Enobia, Sanofi-Aventis, GlaxoSmithKline, Human Genome Sciences, the National Institutes of Health, and the Dana Foundation. G. J. Gleich has equity interest in Ception Therapeutics, has received research support from GlaxoSmithKline, and is on the Board of Directors of the American Partnership for Eosinophilic Disorders.

Glossary

 

Back to Article Outline

CCR3 

CCR3 is the eotaxin family chemokine receptor. CCR3-deficient mice have decreased airway eosinophilia, mucus production, and subepithelial fibrosis, as well as protection from allergen-induced eosinophilic esophagitis.

Back to Article Outline

CHURG-STRAUSS SYNDROME (CSS) 

CSS is an eosinophilic vasculitis comprised of granulomatous inflammation with small-vessel necrosis and infiltration with eosinophils in patients with allergy and asthma.

Back to Article Outline

EOTAXIN 

Eotaxins are a family of CC chemokines that bind to CCR3 and induce eosinophil (and basophil) trafficking. Eotaxins and IL-5 work together to promote eosinophil activation and degranulation. Eotaxin-1 and eotaxin-2 are involved in airway eosinophilia, whereas eotaxin-3 is highly induced in human subjects with eosinophilic esophagitis.

Back to Article Outline

HYPEREOSINOPHILIC SYNDROME (HES) 

HES can be defined as myeloproliferative, FIP1L1-PDGFRα positive, or a lymphocytic variant. The myeloproliferative variant is associated with dysplastic eosinophils, increased serum B12 levels, increased tryptase levels, thrombocytopenia, hepatosplenomegaly, spindle-shaped mast cells, and myelofibrosis. The lymphocytic variant is associated with T-cell clones, and the FIP1L1-PDGFRα variant results in tyrosine kinase activation, leading to chronic eosinophilic leukemia.

Back to Article Outline

IL-3, IL-5, GM-CSF 

IL-3, IL-5, and GM-CSF promote the survival, activation, and chemotaxis of eosinophils. They all share a common β chain in their receptors.

Back to Article Outline

IL-5 RECEPTOR 

A heterodimer, the IL-5R shares a β chain with IL-3 and GM-CSF receptors and uses the Janus kinases and lyn (a tyrosine kinase) for signal transduction.

Back to Article Outline

MAJOR BASIC PROTEIN (MBP), EOSINOPHIL PEROXIDASE (EPO) 

MBP and EPO are eosinophil granule proteins. MBP is cytotoxic to bronchial epithelial cells and pneumocytes and causes airway dysfunction by changing the activity of parasympathetic airway nerves. EPO is highly basic, has 68% sequence identity with neutrophil myeloperoxidase, and is involved in the respiratory burst required for bacterial killing.

Back to Article Outline

PHOSPHOLIPASE A2 

Phospholipase A2 is an enzyme that releases arachidonic acid from cellular stores, leading to the generation of various metabolites, including prostaglandins and leukotrienes.

Back to Article Outline

SIGLEC-F 

The human counterpart to Siglec-F is Siglec-8, which is also involved in eosinophil apoptosis. Initially cloned from an eosinophil cDNA library, Siglec-8 is expressed on human eosinophils, mast cells, and basophils. IL-5 increases Siglec-8–mediated death.

Back to Article Outline

SIGNAL TRANSDUCER AND ACTIVATOR OF TRANSCRIPTION 6 (STAT6) 

The signal transducer and activator of transcription family of transcription factors become phosphorylated, dimerize, and bind to palindromic DNA elements in response to Janus kinase pathways. STAT6 is important for IL-4 and IL-13 signals and activates GATA3 gene expression.

Back to Article Outline

TGF-β1 

TGF-β1 is a profibrotic agent. This cytokine is found in an inactive state as a result of its being bound by latency associated-peptide. TGF-β1 can be activated by removal of latency associated-peptide by mast cell proteases, such as chymase and tryptase. TGF-β1–mediated fibrosis is implicated in many diseases, including pulmonary fibrosis, as well as nasal polyposis and severe asthma, in which TGFB1 gene single nucleotide polymorphisms can be associated with asthma.

Back to Article Outline

THYMIC STROMAL LYMPHOPOEITIN (TSLP) 

TSLP is expressed by activated epithelium and other structural cells, such as bronchial epithelial cells in asthmatic patients, and promotes antigen presentation by dendritic cells by inducing the expression of costimulatory molecules, such as OX40, CD40, and CD80. It is believed to play a critical role in initiating TH2 responses.

Back to Article Outline

VASCULAR CELL ADHESION MOLECULE 1 (VCAM-1, CD106), INTERCELLULAR ADHESION MOLECULE 1 (ICAM-1, CD54), AND MUCOSAL ADDRESSIN CELLULAR ADHESION 1 MOLECULE (MAdCAM-1) 

VCAM-1, ICAM-1, and MAdCAM-1 are endothelial inflammatory markers that allow trafficking of leukocytes into target tissues. Levels of VCAM-1 are selectively increased by IL-4 and IL-13, and it facilitates trafficking of very late antigen 4 (α4β1 integrin)–expressing cells. MAdCAM-1 specifically allows trafficking into the gastrointestinal tract and facilitates trafficking of α4β7 integrin–expressing cells. ICAM-1 is constitutively expressed on endothelium and other cells; its levels are increased by IL-1, TNF-α, and IFN-γ; and it facilitates trafficking of lymphocyte function–associated antigen 1 (αLβ2 integrin)–expressing cells.

The Editors wish to acknowledge Seema Aceves, MD, PhD, for preparing this glossary.

The role of the eosinophil in disease has long been a mystery. Paul Ehrlich, who discovered the eosinophil about 130 years ago and named it, believed that the prominent granules were storage sites, but why and for what purpose was unknown.1 Nearly 100 years ago, Schlecht and Schwenker2 observed that eosinophils infiltrated tissues of guinea pigs recovering from anaphylaxis, and they speculated that the eosinophil was recruited in response to damage. Samter et al,3 in the 1950s, transferred pieces of lung from guinea pigs having undergone severe anaphylaxis into the peritoneum of naive guinea pigs. Peritoneal eosinophilia rapidly developed in such animals, hinting at release from the transplanted lung of an eosinophil recruitment factor3 that about 40 years later was discovered to include eotaxin.4 The concept that the eosinophil functioned in tissue repair was supported by results showing that eosinophils and their products neutralized mast cell–derived mediators of anaphylaxis.5 However, a direct test of this hypothesis did not show any difference between the severity of hypersensitivity reactions in the presence and absence of the eosinophil.6 Analyses of eosinophil granule proteins revealed that they are cationic toxins able to mediate damage to tissues, and subsequent studies supported that view.7, 8, 9, 10, 11 Neutralization of major basic protein (MBP) 1 protected guinea pigs from development of airways hyperreactivity.12 However, this and other such supportive evidence is circumstantial and, in the eyes of many critics, unconvincing. In the case of human diseases, the problem was an inability to specifically ablate the eosinophil and thus to determine its role in disease. Although glucocorticoids abolish eosinophils from blood and tissues, they possess so many pharmacologic effects that one cannot ascribe any specific or unique antieosinophil role to them.13 The discovery of IL-5 as a specific eosinophil growth factor, the demonstration that the stimulatory effect of IL-5 on murine B cells does not occur on human B cells,14, 15 and the selective ability of eotaxins to promote eosinophil recruitment stimulated the development of humanized monoclonal anti–IL-5 drugs and antagonists of the eotaxin receptor CCR3.16, 17 Although the latter molecules are still in development, initial clinical trials of anti–IL-5 in patients with asthma failed to show beneficial effects,18, 19, 20, 21, 22 and reports on these results discouraged belief that the eosinophil played a significant role in this condition.23 Nonetheless, additional studies in patients with marked eosinophilia revitalized the possible role of the eosinophil in disease, and within the past 2 years, several seminal studies have shown that administration of anti–IL-5 to patients with hypereosinophilic syndrome (HES) and asthma benefits them.24, 25, 26 Meanwhile, studies of murine eosinophils have progressed with production of transgenic animals overexpressing IL-5 and others lacking IL-5, CCR3, Siglec-F, and other eosinophil-associated molecules.27, 28, 29, 30, 31, 32, 33, 34, 35, 36 These mice have been used to explore the contribution of eosinophils and their mediators to a wide variety of immune and inflammatory responses.

The purpose of this review is to discuss recent advances in animals and human subjects and thereby attempt to define the role of the eosinophil in various diseases as we know it at this time.

Back to Article Outline

Molecules critical to eosinophil hematopoiesis, trafficking to and accumulation within tissues, and survival 

For more information, see Table I.

Table I. The contribution of various molecules to eosinophil biological responses
Bone marrow maturation, egress, or bothSkin homingLung homingGut homing
Intracellular factors
GATA-1+???
C/EBPα+???
PU.1+???
FOG-1−???
FIP1L1-PDGFR+???
Soluble mediators
IL-5++++
IL-130+++
TSLP0+++
Eotaxins++++
Prostaglandin D2+++?
Leukotriene B40?+?

Surface molecules
IL-5R++++
Common γc chain0?0+
α4 Integrins/VCAM-1++++
β7 Integrin/MAdCAM-1000+
β2 Integrins/ICAM-10+++
P-selectin0+++
L-selectin0000
E-selectin0+ (weak)00
CCR3++++
CD330?0?
CD440?+?
Siglec-F0?++
Histamine H4 receptor0++?

Organ-specific conclusions are based primarily on data from animal models. Those molecules that clearly proved to be critical for the biology of human eosinophils, either based on in vitro data or in vivo pharmacology, are shown in italics.

C/EBPα, CCAAT enhancer–binding protein α; FOG-1, friend of GATA-1; ICAM-1, intercellular adhesion molecule; MAdCAM-1, mucosal addressin cellular adhesion 1 molecule; VCAM-1, vascular cell adhesion molecule 1. +, Directly involved in a positive way; −, directly involved in a negative way; 0, no effect; ?, not known or not applicable.

In the bone marrow eosinophils differentiate from stem cells in response to a specific panel of cytokine growth factors. Although the most specific is IL-5, it was initially discovered in the mouse as both an eosinophilopoietic cytokine and activator of B-cell differentiation and proliferation. It is now known that IL-5 in human subjects does not act on B cells.37 Other related cytokines, such as GM-CSF and IL-3, share eosinophil growth factor activity but act more broadly. Indeed, a murine strain deficient in the common CD131 β chain shared by the IL-3/IL-5/GM-CSF receptors was profoundly impaired in terms of lung eosinophilia in asthma models.38 An advantage for those studying eosinophil biology is the ability to grow these cells in vitro from either human or murine bone marrow by using protocols in which IL-5 is the most critical cytokine for eosinophil maturation and terminal differentiation.39, 40 Although these effects are mediated through the IL-5 heterodimeric receptor (CD125/CD131) expressed by eosinophils, basophils also express the IL-5 receptor (IL-5R),41 and therefore IL-5R–based therapies (eg, MEDI-563, a humanized mAb purportedly possessing antibody-dependent cellular cytotoxicity capabilities, see below) have the potential to affect basophil biology as well.42 The critical role of IL-5 in eosinophil differentiation is underscored in the mouse in models involving its transgenic overexpression, during which animals have profound eosinophilia and splenomegaly.27, 28 Similarly, mice genetically deficient in IL-5 have little to no blood or tissue eosinophilia, yet they maintain low basal eosinophil counts in the bone marrow.29, 30 In asthma or parasite infection models, these IL-5–deficient mice tend not to have lung injury, remodeling, or airways hyperreactivity, implicating IL-5 and eosinophils in these processes.29, 30

Eosinophil differentiation occurs as a result of the collective effects of various transcription factors, such as GATA-1, friend of GATA-1 (FOG-1), CCAAT enhancer–binding protein C/EBPα and the ETS family transcription factor PU.1.43 The role of GATA-1 is primarily in facilitating the differentiation of granulocyte-macrophage progenitors into eosinophils, whereas FOG-1 must be downregulated for eosinophil development to occur.40, 44 Indeed, GATA-1–deficient mice do not have eosinophils, and deletion of a specific GATA-binding site of the murine GATA-1 promoter (so-called ΔdblGATA mice) results in strains in which terminal differentiation of eosinophils is prevented.45, 46 Similarly, mice deficient in C/EPBα are devoid of all granulocytes,47 and mice congenitally deficient in PU.1 are unable to generate terminally differentiated eosinophils.43 Not surprisingly, many of these transcription factors are required for generation of eosinophil lineage–specific granule proteins, such as MBP1.48 The highly eosinophil-specific expression of eosinophil peroxidase (EPO) has been exploited by developing a strain of eosinophil-deficient mice (so-called PHIL mice) in which expression of a toxin is molecularly linked to EPO expression, and therefore as eosinophils undergo bone marrow differentiation, they die before ever leaving the bone marrow.49 These eosinophil-less mice have subsequently been used in various models of disease, including asthma, often with striking findings, as discussed below.

Pathways regulating mature eosinophil departure from the bone marrow are not well understood, but it appears that certain surface markers associated with migration responses and terminal differentiation, such as CCR3, are involved.50, 51, 52 Exit from the bone marrow also appears to be influenced by IL-5.53, 54 Although eosinophil-selective expression of Siglec-F plays an important role in their accumulation and survival, mice deficient in Siglec-F have normal bone marrow and circulating eosinophil counts at baseline.36 Exit from the circulation into tissue sites of eosinophils is mediated by the interaction of a variety of cell adhesion molecules expressed on the eosinophil and on endothelium and is further influenced by eosinophil-selective chemoattractants. Murine studies indicate that among various adhesion molecules, the following interactions are the most critical and selective: (1) between α4 integrins (CD49d paired as a heterodimer with CD29 or β7 integrin chains) with either vascular cell adhesion molecule 1 (CD106) or mucosal addressin cellular adhesion 1 molecule; (2) between lymphocyte function–associated antigen 1 (CD11a/CD18) and intercellular adhesion molecule 1 (CD54); and (3) between P-selectin (CD62P) and P-selectin glycoprotein ligand 1 (CD162). In comparison, interactions between E-selectin (CD62E) and its ligand, L-selectin (CD62L) and its ligand, or CD33 (platelet–endothelial cell adhesion molecule 1) contribute less, if at all, to processes of eosinophil recruitment.55, 56, 57 Among the chemoattractants most prominently involved in selective eosinophil recruitment, those active on eosinophil CCR3, such as eotaxin-1 (CCL11), eotaxin-2 (CCL24), eotaxin-3 (CCL26; present in human subjects but nonexistent in mice), RANTES (CCL5), and monocyte chemoattractant protein 4 (CCL13), are likely to be most important and selective.17 This is based on the fact that mice deficient in each of these molecules show impaired trafficking to the skin, airway, and/or gut.58 Separate studies showed that blockage of cytosolic phospholipase A2 effectively prevents eosinophil homing to the lungs,59 whereas another study implicated nonlymphoid myeloid cells in the lung that help to facilitate eosinophil recruitment through signal transducer and activator of transcription 6–inducible chemokines.60 For intestinal homing of eosinophils, β7 integrins are particularly important.61 A recent observation that mice deficient in the common γ chain that associates with receptors for IL-2, IL-4, IL-7, IL-9, and IL-15 have a unique and selective alteration in gastrointestinal, but not lung, eosinophils suggests that cytokines active through this receptor pathway play a specific role in eosinophil homing and survival in the gastrointestinal tract.62 Other studies have revealed that CCR3 is essential for maintaining basal eosinophil counts in the small intestine.63, 64 Once in tissues, eosinophil survival is primarily controlled by the presence or absence of prosurvival factors generated locally, such as IL-5 and GM-CSF.43 There might also be pathways regulating apoptosis as well. For example, mice deficient in Siglec-F show exaggerated blood, bone marrow, and tissue eosinophilia after allergen sensitization and airways challenge, strongly suggesting the presence of a pro-apoptotic Siglec-F ligand in the lung.36 Targeting Siglec-F with specific antibodies selectively induces eosinophil apoptosis and depletes eosinophils from the blood, gastrointestinal tract, and lung and reduces fibrosis and inflammation in murine models of asthma and food-associated eosinophilic gastroenteritis.65, 66, 67 In summary our knowledge of the factors that control the birth, travel, activation, and lifespan of eosinophils has been greatly expanded, and this sets the stage for manipulating these molecules for therapeutic benefit.

Back to Article Outline

Role of eosinophils in animal models of disease 

A number of murine models have been developed in which eosinophil-active cytokines or chemokines have been selectively overexpressed within a specific tissue, such as in the airways68 or the skin.69 Overexpression of IL-13 at lung sites results in profound airway remodeling associated with eosinophilia, although eosinophils in these models might not be necessary for airways remodeling. This conclusion differs from conclusions drawn from asthma models using IL-5–deficient mice, the eosinophil-deficient ΔdblGATA or PHIL murine strains, or by targeting Siglec-F, in which eosinophils are strongly associated with airways remodeling.30, 49, 67, 70, 71, 72, 73, 74 Furthermore, overexpression of IL-5 in the lung75 and even more profoundly with coexpression of eotaxin76 leads to physiologic and histologic changes resembling those of severe asthma. Indeed, the dual-transgenic IL-5 and lung eotaxin animals have pulmonary pathologies remarkably similar to those of severe asthma, including epithelial desquamation and mucus hypersecretion leading to airway obstruction, subepithelial fibrosis, airway smooth muscle hyperplasia, and striking methacholine-induced airway hyperresponsiveness. These changes are accompanied by extensive eosinophil degranulation. Data from other murine models suggest that eosinophils play a role in local antigen presentation and subepithelial fibrosis and might even be required for T-cell activation.77, 78, 79, 80, 81, 82, 83, 84 Most of the animal models implicate the eosinophil as a source of profibrotic cytokines, such as TGF-β1.74 The conclusions regarding the contribution of eosinophils in tissue remodeling are not unlike the conclusions from human studies with anti–IL-5.21, 85

Although eosinophils have long been associated with antihelminth responses, experiments have not only implicated eosinophil granules in this response but have begun to suggest that these cells might play a much broader role in immune responses. Mice deficient in eosinophils or certain eosinophil granule proteins have impaired abilities to clear a variety of helminths.35, 86, 87 More recent data, however, suggest that eosinophils also play an antibacterial role based on the ability of eosinophils to release substances with potent antibacterial and antiviral activities.88, 89, 90

Murine models of HES and eosinophilic gastrointestinal disorders have been developed and suggest a variety of pathobiologic mechanisms controlling these disorders. Models of HES include the IL-5 transgenic mouse, although in general this mouse is relatively healthy, with little evidence of eosinophil degranulation, despite the profound eosinophilia.27, 28, 37 Also, recently developed are murine models of the FIP1L1-PDGFRA fusion gene driving HES because this has been used to study chronic eosinophilic leukemia and its response to various therapies.65, 91 Regarding eosinophilic gastrointestinal disorders, eosinophil-derived EPO was implicated in a murine model of ulcerative colitis using a strain deficient in EPO.92 Oral sensitization and repetitive challenge models have been developed that yield eosinophilic inflammation of the esophagus and small intestine. Such models have highlighted the roles of chemokines, IL-13, IL-5, and β7 integrins in the development of eosinophilia, as well as a role for Siglec-F in its resolution.61, 63, 64, 65, 66, 93, 94, 95 Other molecules implicated in tissue eosinophilia, primarily through studies of deficient mice or with the use of antagonists, include prostaglandin D2 and its receptors,96, 97, 98 leukotriene B4 and its receptors,99, 100, 101, 102 the H4 histamine receptor,103, 104 and thymic stromal lymphopoietin (TSLP),105 although for some of these molecules, it is not clear whether their effects on eosinophils are direct or indirect. Unfortunately, although there is a long list of eosinophil-associated molecules to study and although there are clever ways to use eosinophil-deficient or eosinophil-depleted mice in models of disease, none fully recapitulate the human disease and thus might not be predictive of the role played by the eosinophil in its human counterpart.

Back to Article Outline

Studies in human disease 

Asthma 

Prior efforts to establish eosinophils as critical mediator cells in disease using anti–IL-5 failed, and most striking was the failure of mepolizumab, a humanized murine IgG1 monoclonal anti–IL-5 antibody, to benefit patients with asthma.18, 19 Other studies conducted on patients with mild asthma also failed, although analyses of bronchial biopsy specimens showed that mepolizumab only reduced eosinophil counts by about 50% and did not appreciably reduce the degree of eosinophil granule protein deposition (as judged by localization of granule MBP1).20, 21 These negative results cast a pall over the efforts of investigators concerned with eosinophil investigation, and for a time, it appeared that the negative view of the eosinophil in disease, as expressed in the editorial accompanying the Leckie et al18 article in the Lancet, was likely correct. However, continuing studies of anti–IL-5 with both mepolizumab and reslizumab (the latter differing from mepolizumab by being a humanized rat IgG4 anti–IL-5 mAb) showed that reslizumab reduced eosinophil counts in the blood of patients with HES53 and that mepolizumab was able to abolish eosinophils from tissues of patients with eosinophil-associated diseases, including HES, especially in the presence of cutaneous manifestations.106, 107 The latter article demonstrated that mepolizumab strikingly reduced the severity of cutaneous disease in concert with reduction in blood eosinophil counts, eosinophil counts in skin biopsy specimens, and deposition of granule eosinophil cationic protein (RNase3). These findings encouraged the belief that the negative results obtained with mepolizumab treatment of asthma might not hold for other eosinophil-associated diseases.

An important clinical experiment tested the hypothesis that measurement of sputum eosinophilia might be useful for asthma management.108 This study compared the results of asthma management by using either measurement of sputum eosinophil counts or standard asthma British Thoracic Society (BTS) treatment guidelines. Seventy-four patients with moderate-to-severe asthma were recruited and randomly allocated to a sputum management group or the BTS management group, and the patients were treated for 12 months. If sputum eosinophilia was greater than 3%, treatment was increased (mainly use of inhaled or oral glucocorticoids); if less than 1%, treatments were decreased. The most interesting outcomes at the end of the 12-month period were a reduction in severe exacerbations in the sputum management group, with 109 exacerbations in the BTS group and 35 exacerbations in the sputum management group (P = .01), and fewer rescue courses of oral glucocorticoids, with 73 courses in the BTS group and 24 in the sputum management groups (P = .008). Furthermore, change in methacholine PC20 values favored the sputum management group, with an overall reduction in methacholine responsiveness at 12 months (P = .015). In their discussion the authors stressed the following key benefits: (1) reducing severe exacerbations that require courses of oral glucocorticoids; (2) preventing asthma-related hospital admissions, morbidity, and mortality; and (3) the value of using sputum eosinophils as a guide to treatment. Their results also supported a critical role for the eosinophil in the pathogenesis of asthma. In this regard it is interesting that they recruited all patients with asthma requiring continued hospital follow-up and not a selected group with increased sputum eosinophil counts.

The above results set the stage for two studies of asthma treatment with anti–IL-5.24, 25 Although using different outcome measurements, both came to the same conclusion, namely that mepolizumab treatment benefits patients with sputum eosinophilia with reduction in prednisone requirements or asthma exacerbations and improvement of asthma quality of life. Nonetheless, these studies stirred further controversy concerning the prevalence of patients with asthma and sputum eosinophilia.

The study by Nair et al25 was based on the assumption that a rare subgroup of asthmatic patients demonstrates persistent sputum eosinophilia despite treatment with oral prednisone. Twenty adults were recruited from a population of 800 patients with severe asthma, and all but 2 had more than 3% sputum eosinophilia in spite of daily treatment with prednisone at doses from 5 to 25 mg/d for 4 weeks (in addition to inhaled fluticasone at 600-2,000 μg/d). The study period lasted up to 26 weeks, and patients were treated with 750 mg of mepolizumab or saline intravenous infusions at weeks 2, 6, 10, 14, and 18 in a randomized double-blind fashion. Oral prednisone was reduced by using a pre-established protocol, and exacerbations were defined as increased use of albuterol, nocturnal awakenings, a decrease of 15% in FEV1, or worsening of cough. The most striking outcome was a reduction in exacerbations, with 12 in the placebo group and 2 in the mepolizumab group (P = .008). FEV1 increased significantly, and both cough and Juniper asthma control questionnaire scores improved in the mepolizumab group but not in the placebo group. Prednisone was reduced by 83.8% ± 33.4% in the mepolizumab group and by 47.7% ± 40.5% in the placebo group (P = .04). As expected, eosinophil counts were significantly reduced in both blood and sputum in the mepolizumab-treated group, and eosinophil counts remained within normal limits after prednisone reductions. In contrast, reductions in prednisone levels in the placebo group were accompanied by significant increases in the eosinophil counts in sputum and blood. Adverse events in the groups appeared comparable. One limitation of this study was a higher sputum eosinophil count at baseline in the mepolizumab group, raising the possibility that patients in this group who responded were those with the greatest contribution of eosinophils to asthma. Another limitation was a failure to show a significant difference in final prednisone dosage between the groups. A final debatable shortcoming was the apparent conclusion that the favorable outcome achieved in the mepolizumab group only pertained to a rare subset of patients with asthma. Nonetheless, the authors interpreted their study as highlighting the importance of selecting patients with airway eosinophilia.

The study by Haldar et al24 focused on asthma exacerbations and is an extension of the earlier work by the same group on the use of sputum eosinophil counts for asthma management (summarized above).108 Patients studied had sputum eosinophil counts of greater than 3% on at least 1 occasion in the prior 2 years despite high-dose glucocorticoid treatment and at least 2 exacerbations in the prior 12 months. All patients were treated with oral prednisolone at 0.5 mg/kg (maximum dose, 40 mg/d) at the beginning and end of the study. Patients received 12 monthly 750-mg mepolizumab or saline infusions. At baseline, patients were well matched, and there were no significant differences between the groups, including eosinophil counts in sputum (in contrast to the Nair et al25 report). Over the treatment period (348 days for the mepolizumab group and 340 days for the placebo group), 57 severe exacerbations occurred in the mepolizumab group for a mean of 2.0 per patient and 109 in the placebo group for a mean number of 3.4 (P = .02). Patients in the mepolizumab group had 3 hospital admissions, and placebo-treated patients had 11 (P = .07). The total number of days in the hospital was significantly less in the patients receiving mepolizumab than in those receiving placebo (12 vs 48 days, P < .001). Sputum eosinophil counts were significantly reduced in the patients receiving mepolizumab, even during an exacerbation (P = .005), although sputum eosinophil counts still increased in 36% of the mepolizumab-treated patients during exacerbations. The mean asthma quality-of-life questionnaire scores favored the mepolizumab-treated patients (P = .02), but FEV1 and methacholine sensitivity did not change significantly between the groups. Interestingly, computed tomographic analyses obtained before and after active treatment showed a significant reduction in airway wall size (P = .02). Concerning safety, the numbers of adverse events were 29 in the mepolizumab-treated patients and 32 in the placebo-treated patients; 1 patient was withdrawn from the study because of a transient rash 24 hours after the first mepolizumab infusion. The authors suggest that there is dissociation between the mechanisms of exacerbations and those responsible for asthma symptoms and lung function. However, the increases in sputum eosinophil counts during exacerbations in the mepolizumab-treated patients suggest that eosinophil-mediated pathogenetic stimuli were not completely suppressed.

Editorial comment on the studies by Nair et al25 and Haldar et al24 emphasized the rarity of this eosinophil-associated asthma population, its occurrence in patients with adult-onset asthma, the relatively minimal benefit of mepolizumab therapy (even in these selected patients), and the possibility that alternative cells, presumably mast cells and neutrophils and their mediators, might play critical presently underappreciated roles in asthma.109 Overall, the editorial assumed that mepolizumab therapy sufficiently suppressed eosinophil-mediated inflammation so that it represented an adequate test of the role of the eosinophil in asthma. However, an alternative view is that mepolizumab only partially suppresses eosinophil-mediated inflammation, and therefore the effects of mepolizumab only partially show what might be expected if eosinophilic inflammation were totally abolished.110 It is the firm opinion of the authors of this review article that the clear benefit of an eosinophil-specific therapy in reducing exacerbations in selected patients with asthma, especially in a population in which about one third also had nasal polyposis, is so striking and exciting that one cannot escape the conclusion that eosinophils are critical to the pathogenesis of disease in this cohort.

HES 

Several relatively small, uncontrolled trials with anti–IL-5 antibodies in eosinophilic disorders involving the skin, esophagus, and other organs have been reported.106, 107, 111, 112, 113, 114 The reader is referred to the accompanying article in this issue of the Journal by Simon et al115 for additional details on these topics. Instead, this section will focus on the one controlled trial published to date.

The effect of mepolizumab on HES was tested in an international, randomized, multicenter, placebo-controlled, double-blind study.26 Patients entering the study required at least 20 mg of prednisone to control HES manifestations and to satisfy the Chusid criteria for HES diagnosis, including blood eosinophilia equal to or greater than 1.5 × 109, duration of disease greater than 6 months, and absence of other eosinophil-associated diseases, such as allergic or parasitic causes. A total of 85 patients were enrolled in the study and were divided into placebo and mepolizumab treatment groups. During a run-in period of up to 6 weeks, prednisone (or equivalent glucocorticoid) was tapered to the lowest level able to reduce blood eosinophil counts to less than 1 × 109/L, and patients requiring 20 mg/d or more were randomized. Prednisone reduction to 10 mg/d or less was the primary end point, and the dose was reduced by using a pre-established algorithm. Patients in whom blood eosinophilia could not be controlled were rolled over into an open mepolizumab trial. The results of the study showed that mepolizumab was an effective steroid-sparing drug and that it reduced both blood eosinophilia and the level of eosinophil participation by also reducing serum levels of the eosinophil-derived neurotoxin (RNase2). Furthermore, mepolizumab was very well tolerated, and the spectrum of adverse events in the treated patients did not differ significantly from that seen in the placebo group. Another study involving several types of patients with eosinophilic disorders (eg, HES and eosinophilic gastrointestinal disorders) treated with mepolizumab found a consistent and prolonged suppressive effect on circulating eosinophil counts and markers of eosinophil activity.116 Finally, in a retrospective study Ogbogu et al117 reported on a variety of treatments used for the treatment of HES, including the anti–IL-5 antibodies mepolizumab and reslizumab. The majority of those treated with anti–IL-5 showed favorable responses at 1 month, and discontinuation caused by intolerance was rare. Overall, these results supported the beneficial effects of anti–IL-5 in disease and a role for the eosinophil in tissue dysfunction. Regrettably, applications for registration of mepolizumab for the treatment of HES have foundered on concerns by regulators that the HES trial was not adequately blinded (the investigators should not have been aware of the eosinophil counts) and that steroid reduction was not a proper end point.118 Presently, in spite of its demonstrated usefulness and safety, it is unlikely that mepolizumab will be approved for the treatment of HES. The status of reslizumab approval at the present time is also uncertain.119

Churg-Strauss syndrome 

Scant information on the role of eosinophils in Churg-Strauss syndrome (CSS) exists in spite of their strong association with CSS and their presence as a criterion for the diagnosis. Two studies have probed the effect of mepolizumab in patients with CSS. One is a case report of a 28-year-old woman with marked peripheral blood eosinophilia, eosinophilic pneumonia, myocarditis, and peripheral neuropathy who was treated with glucocorticoids, methotrexate, IFN-α, cyclophosphamide, intravenous immunoglobulins, azathioprine, and etoposide.120 In spite of these treatments, disease activity was not controlled, and a trial of mepolizumab was begun. Improvement was noted within a month, and by 6 months, pulmonary infiltrates had cleared. By 15 months, all evidence of disease activity disappeared. However, reduction of mepolizumab resulted in a recurrence of disease, suggesting that the therapeutic benefit was not due to disease remission.

The second study administered mepolizumab to 7 patients with CSS for 4 months to assess its safety and to determine whether systemic glucocorticoids could be reduced.121 The results showed that mepolizumab reduced blood eosinophil counts, was well tolerated, and permitted reduction of glucocorticoids in all patients. After cessation of mepolizumab treatment, CSS manifestations recurred, necessitating increased glucocorticoid treatment. These studies encourage belief that anti–IL-5 might be a beneficial treatment of CSS. Clearly, additional studies in larger numbers of patients are needed to determine the place of anti–IL-5 in CSS treatment.

Back to Article Outline

Implications and future directions regarding IL-5–directed therapies 

The beneficial effects of mepolizumab on asthma can be regarded as a partial test of the eosinophil's role in disease. For example, sputum eosinophil counts still increased during exacerbations,24 and mepolizumab did not reduce deposition of eosinophil granule MBP1 in patients with mild asthma.20 Therefore the Nair et al25 and Haldar et al24 studies might have shown the effects of partial reduction of eosinophil participation and efficacy. One presumption is that more robust eosinophil suppression would show a greater degree of therapeutic benefit. This was achieved in the double-transgenic murine asthma model when these asthmatic mice were mated to eosinophil-deficient animals, and the resultant triple-transgenic animals became normal.76 Fortunately, a potential medication that might more strikingly reduce eosinophils is on the horizon. MEDI-563 is a humanized anti–IL-5Rα mAb that is presently in clinical trials.42 This antibody binds with high-affinity and mediates the lysis of IL-5Rα–positive cells, including eosinophils and basophils. A single intravenous dose of MEDI-563 was well tolerated by patients with mild asthma and decreased circulating eosinophil counts to less than detection limits within 24 to 48 hours for 8 to 12 weeks. Because this antibody mediates the lysis of eosinophils, it might be the best reagent to test the role of eosinophils in disease.

Back to Article Outline

Conclusions 

Despite the recent advancements in our understanding of the contribution of eosinophils to disease, as summarized above, it remains unclear as to whether we could live without these cells. Teleologically, something has allowed this cell type to persist. Nearly all in the eosinophil field would likely agree that the primary role of these cells is in helminth infestation, yet we still do not know whether they are essential to protecting the host from such organisms. It now appears that eosinophils can be selectively targeted with therapeutic agents, and this seems to provide clinical benefit in a subgroup of asthmatic subjects with persistent airways eosinophilia. Most subjects with HES given anti–IL-5 reduced their daily steroid requirements, but we do not know whether this provides safe and effective control of their disease in the long-term. A variety of other disorders associated with tissue eosinophilia have yet to be treated with selective eosinophil-decreasing agents, and therefore we can only continue to speculate on the role this cell plays in each of these conditions. Nevertheless, if such agents ever garner US Food and Drug Administration approval, we will be one step closer to understanding the role of this beautiful, yet enigmatic, cell in human health and disease.

What do we know?

•Eosinophils remain an enigmatic cell.

•We have learned a great deal about how to make an eosinophil from early precursor cells.

•Eosinophils have a unique pattern of cell-surface receptors, including adhesion molecules and chemokine receptors, that impart it with distinct homing capabilities.

•Survival and death signals, especially those involving cytokines and inhibitory receptors, appear to regulate the persistence of eosinophils at inflammatory sites.

•Murine strains have been developed that result in mice that are truly and specifically deficient in the eosinophil lineage, and these are yielding valuable insights into the role of the eosinophil in various murine models of disease.

•Only since the recent development of IL-5–directed therapies have we now been able to dissect the unique specific role of the eosinophil in asthma, HES, and related disorders.

•Studies with anti–IL-5 antibody therapies show consistent, profound, and prolonged suppression of eosinophil hematopoiesis and blood eosinophilia, and these treatments seem well tolerated.

•Studies with anti–IL-5 antibody therapies show improved asthma control in a subset of subjects with difficult-to-control asthma and persistent airways eosinophilia.

•Studies with anti–IL-5 antibody therapies show steroid-sparing activity in patients and HES.

What is still not known?
•Are there diseases that are purely eosinophil mediated?

•Is suppression of eosinophils safe long-term, and would it provide sustained improvement in patients with asthma and other eosinophilic diseases beyond our current treatment approaches?

•Does chronic reduction in eosinophil counts result in any permanent improvements in asthma parameters, such as lung function or airway remodeling?

•Will anti–IL-5 directed therapies receive US Food and Drug Administration approval? If so, for what indication?

•Would it be better, from an efficacy standpoint, to develop eosinophil-directed therapies that also target other cells?

Back to Article Outline

References 

  1. Ehrlich P. Beiträge zur Kenntnis der granulierten Bindegewebszellen und der eosinophilen Leucocyten. Arch Anat Physiol. 1879;3:166–182
  2. Schlecht H, Schwenker G. Über die Beziehungen der Eosinophilie zur Anaphylaxie. Dtsch Arch Klin Med. 1912;108:405–428
  3. Samter M, Kofqed MA, Pieper W. A factor in lungs of anaphylactically shocked guinea pigs which can induce eosinophilia in normal animals. J Hematol. 1953;8:1078–1090
  4. Jose PJ, Griffiths-Johnson DA, Collins PD, Walsh DT, Moqbel R, Totty NF, et al. Eotaxin: a potent eosinophil chemoattractant cytokine detected in a guinea pig model of allergic airways inflammation. J Exp Med. 1994;179:881–887
  5. Goetzl E, Wasserman S, Austen K. Eosinophil polymorphonuclear leukocyte function in immediate hypersensitivity. Arch Pathol. 1975;99:1–4
  6. Gleich GJ, Olson GM, Loegering DA. The effect of ablation of eosinophils on immediate-type hypersensitivity reactions. Immunology. 1979;38:343–353
  7. Frigas E, Loegering DA, Solley GO, Farrow GM, Gleich GJ. Elevated levels of the eosinophil granule major basic protein in the sputum of patients with bronchial asthma. Proc Mayo Clin. 1981;56:345–353
  8. Filley WV, Holley KE, Kephart GM, Gleich GJ. Identification by immunofluorescence of eosinophil granule major basic protein in lung tissues of patients with bronchial asthma. Lancet. 1982;2:11–15
  9. Ayars GH, Altman LC, Gleich GJ, Loegering DA, Baker CB. Eosinophil- and eosinophil granule-mediated pneumocyte injury. J Allergy Clin Immunol. 1985;76:595–604
  10. Dor PJ, Ackerman SJ, Gleich GJ. Charcot-Leyden crystal protein and eosinophil granule major basic protein in sputum of patients with respiratory diseases. Am Rev Respir Dis. 1984;130:1072–1077
  11. Flavahan NA, Slifman NR, Gleich GJ, Vanhoutte PM. Human eosinophil major basic protein causes hyperreactivity of respiratory smooth muscle. Am Rev Respir Dis. 1988;138:685–688
  12. Lefort J, Nahori MA, Ruffie C, Vargaftig BB, Pretolani M. In vivo neutralization of eosinophil-derived major basic protein inhibits antigen-induced bronchial hyperreactivity in sensitized guinea pigs. J Clin Invest. 1996;97:1117–1121
  13. Gleich GJ, Hunt LW, Bochner BS, Schleimer RP. Glucocorticoid effects on human eosinophils. In:  Schleimer RP,  Busse WW,  O'Byrne P editor. Inhaled glucocorticoids in asthma: mechanisms and clinical actions. New York: Marcel Dekker, Inc; 1996;p. 279–308
  14. Campbell HD, Tucker WQJ, Hort Y, Martinson ME, Mayo G, Clutterbuck EJ, et al. Molecular cloning, nucleotide sequence, and expression of the gene encoding human eosinophil differentiation factor (interleukin 5). Proc Natl Acad Sci U S A. 1987;84:6629–6633
  15. Clutterbuck E, Shields JG, Gordon J, Smith SH, Boyd A, Callard RE, et al. Recombinant human interleukin 5 is an eosinophil differentiation factor but has no activity in standard human B cell growth factor assays. Eur J Immunol. 1987;17:1743–1750
  16. Wise EL, Duchesnes C, da Fonseca PC, Allen RA, Williams TJ, Pease JE. Small molecule receptor agonists and antagonists of CCR3 provide insight into mechanisms of chemokine receptor activation. J Biol Chem. 2007;282:27935–27943
  17. Pease JE, Williams TJ. Chemokines and their receptors in allergic disease. J Allergy Clin Immunol. 2006;118:305–320
  18. Leckie MJ, Brinke A, Khan J, Diamant Z, O'Connor BJ, Walls CM, et al. Effects of an interleukin-5 blocking monoclonal antibody on eosinophils, airway hyper-responsiveness, and the late asthmatic response. Lancet. 2000;356:2144–2148
  19. Kips JC, O'Connor BJ, Langley SJ, Woodcock A, Kerstjens HA, Postma DS, et al. Effect of SCH55700, a humanized anti-human interleukin-5 antibody, in severe persistent asthma: a pilot study. Am J Respir Crit Care Med. 2003;167:1655–1659
  20. Flood-Page PT, Menzies-Gow AN, Kay AB, Robinson DS. Eosinophil's role remains uncertain as anti-interleukin-5 only partially depletes numbers in asthmatic airway. Am J Respir Crit Care Med. 2003;167:199–204
  21. Flood-Page P, Menzies-Gow A, Phipps S, Ying S, Wangoo A, Ludwig MS, et al. Anti-IL-5 treatment reduces deposition of ECM proteins in the bronchial subepithelial basement membrane of mild atopic asthmatics. J Clin Invest. 2003;112:1029–1036
  22. Flood-Page P, Swenson C, Faiferman I, Matthews J, Williams M, Brannick L, et al. A study to evaluate safety and efficacy of mepolizumab in patients with moderate persistent asthma. Am J Respir Crit Care Med. 2007;176:1062–1071
  23. Bochner BS. Verdict in the case of therapies versus eosinophils: the jury is still out. J Allergy Clin Immunol. 2004;113:3–9
  24. Haldar P, Brightling CE, Hargadon B, Gupta S, Monteiro W, Sousa A, et al. Mepolizumab and exacerbations of refractory eosinophilic asthma. N Engl J Med. 2009;360:973–984
  25. Nair P, Pizzichini MM, Kjarsgaard M, Inman MD, Efthimiadis A, Pizzichini E, et al. Mepolizumab for prednisone-dependent asthma with sputum eosinophilia. N Engl J Med. 2009;360:985–993
  26. Rothenberg ME, Klion AD, Roufosse FE, Kahn JE, Weller PF, Simon HU, et al. Treatment of patients with the hypereosinophilic syndrome with mepolizumab. N Engl J Med. 2008;358:1215–1228
  27. Dent LA, Strath M, Mellor AL, Sanderson CJ. Eosinophilia in transgenic mice expressing Interleukin-5. J Exp Med. 1990;172:1425–1431
  28. Tominaga A, Takaki S, Koyama N, Katoh S, Matsumoto R, Migita M, et al. Transgenic mice expressing a B-cell growth and differentiation factor gene (interleukin-5) develop eosinophilia and autoantibody production. J Exp Med. 1991;173:429–437
  29. Kopf M, Brombacher F, Hodgkin PD, Ramsay AJ, Milbourne EA, Dai WJ, et al. IL-5-deficient mice have a developmental defect in CD5+ B-1 cells and lack eosinophilia but have normal antibody and cytotoxic T cell responses. Immunity. 1996;4:15–24
  30. Foster PS, Hogan SP, Ramsay AJ, Matthaei KI, Young IG. Interleukin 5 deficiency abolishes eosinophilia, airways hyperreactivity, and lung damage in a mouse asthma model. J Exp Med. 1996;183:195–201
  31. Humbles AA, Lu B, Friend DS, Okinaga S, Lora J, Al-Garawi A, et al. The murine CCR3 receptor regulates both the role of eosinophils and mast cells in allergen-induced airway inflammation and hyperresponsiveness. Proc Natl Acad Sci U S A. 2002;99:1479–1484
  32. Ma W, Bryce PJ, Humbles AA, Laouini D, Yalcindag A, Alenius H, et al. CCR3 is essential for skin eosinophilia and airway hyperresponsiveness in a murine model of allergic skin inflammation. J Clin Invest. 2002;109:621–628
  33. Fulkerson PC, Fischetti CA, McBride ML, Hassman LM, Hogan SP, Rothenberg ME. A central regulatory role for eosinophils and the eotaxin/CCR3 axis in chronic experimental allergic airway inflammation. Proc Natl Acad Sci U S A. 2006;103:16418–16423
  34. Fulkerson PC, Fischetti CA, Rothenberg ME. Eosinophils and CCR3 regulate interleukin-13 transgene-induced pulmonary remodeling. Am J Pathol. 2006;169:2117–2126
  35. Gurish MF, Humbles A, Tao H, Finkelstein S, Boyce JA, Gerard C, et al. CCR3 is required for tissue eosinophilia and larval cytotoxicity after infection with Trichinella spiralis. J Immunol. 2002;168:5730–5736
  36. Zhang M, Angata T, Cho JY, Miller M, Broide DH, Varki A. Defining the in vivo function of Siglec-F, a CD33-related Siglec expressed on mouse eosinophils. Blood. 2007;109:4280–4287
  37. Takatsu K, Nakajima H. IL-5 and eosinophilia. Curr Opin Immunol. 2008;20:288–294
  38. Asquith KL, Ramshaw HS, Hansbro PM, Beagley KW, Lopez AF, Foster PS. The IL-3/IL-5/GM-CSF common receptor plays a pivotal role in the regulation of Th2 immunity and allergic airway inflammation. J Immunol. 2008;180:1199–1206
  39. Dyer KD, Moser JM, Czapiga M, Siegel SJ, Percopo CM, Rosenberg HF. Functionally competent eosinophils differentiated ex vivo in high purity from normal mouse bone marrow. J Immunol. 2008;181:4004–4009
  40. Bedi R, Du J, Sharma AK, Gomes I, Ackerman SJ. Human C/EBP-epsilon activator and repressor isoforms differentially reprogram myeloid lineage commitment and differentiation. Blood. 2009;113:317–327
  41. Yamada T, Sun QY, Zeibecoglou K, Bungre J, North J, Kay AB, et al. IL-3, IL-5, granulocyte-macrophage colony-stimulating factor receptor alpha-subunit, and common beta-subunit expression by peripheral leukocytes and blood dendritic cells. J Allergy Clin Immunol. 1998;101:677–682
  42. Reed J, Kolbeck R, Molfino N, Kozhich A, Humbles A, Erjefalt J, et al. MEDI-563, a humanized anti-IL-5Rα antibody with enhanced effector function, induces reversible blood eosinopenia in mild asthmatics. [abstract] J Allergy Clin Immunol. 2008;121(suppl):S47
  43. Ackerman SJ, Bochner BS. Mechanisms of eosinophilia in the pathogenesis of hypereosinophilic disorders. Immunol Allergy Clin North Am. 2007;27:357–375
  44. Yamaguchi Y, Nishio H, Kishi K, Ackerman SJ, Suda T. C/EBPbeta and GATA-1 synergistically regulate activity of the eosinophil granule major basic protein promoter: implication for C/EBPbeta activity in eosinophil gene expression. Blood. 1999;94:1429–1439
  45. Hirasawa R, Shimizu R, Takahashi S, Osawa M, Takayanagi S, Kato Y, et al. Essential and instructive roles of GATA factors in eosinophil development. J Exp Med. 2002;195:1379–1386
  46. Yu C, Cantor AB, Yang H, Browne C, Wells RA, Fujiwara Y, et al. Targeted deletion of a high-affinity GATA-binding site in the GATA-1 promoter leads to selective loss of the eosinophil lineage in vivo. J Exp Med. 2002;195:1387–1395
  47. Yamanaka R, Barlow C, Lekstrom-Himes J, Castilla LH, Liu PP, Eckhaus M, et al. Impaired granulopoiesis, myelodysplasia, and early lethality in CCAAT/enhancer binding protein epsilon-deficient mice. Proc Natl Acad Sci U S A. 1997;94:13187–13192
  48. Du J, Stankiewicz MJ, Liu Y, Xi Q, Schmitz JE, Lekstrom-Himes JA, et al. Novel combinatorial interactions of GATA-1, PU.1, and C/EBPepsilon isoforms regulate transcription of the gene encoding eosinophil granule major basic protein. J Biol Chem. 2002;277:43481–43494
  49. Lee JJ, Dimina D, Macias MP, Ochkur SI, McGarry MP, O'Neill KR, et al. Defining a link with asthma in mice congenitally deficient in eosinophils. Science. 2004;305:1773–1776
  50. Palframan RT, Collins PD, Severs NJ, Rothery S, Williams TJ, Rankin SM. Mechanisms of acute eosinophil mobilization from the bone marrow stimulated by interleukin 5: the role of specific adhesion molecules and phosphatidylinositol 3-kinase. J Exp Med. 1998;188:1621–1632
  51. Palframan RT, Collins PD, Williams TJ, Rankin SM. Eotaxin induces a rapid release of eosinophils and their progenitors from the bone marrow. Blood. 1998;91:2240–2248
  52. Voehringer D, van Rooijen N, Locksley RM. Eosinophils develop in distinct stages and are recruited to peripheral sites by alternatively activated macrophages. J Leukoc Biol. 2007;81:1434–1444
  53. Kay AB, Klion AD. Anti-interleukin-5 therapy for asthma and hypereosinophilic syndrome. Immunol Allergy Clin North Am. 2004;24:645–666
  54. Menzies-Gow A, Flood-Page P, Sehmi R, Burman J, Hamid Q, Robinson DS, et al. Anti-IL-5 (mepolizumab) therapy induces bone marrow eosinophil maturational arrest and decreases eosinophil progenitors in the bronchial mucosa of atopic asthmatics. J Allergy Clin Immunol. 2003;111:714–719
  55. Bochner BS. Road signs guiding leukocytes along the inflammation superhighway. J Allergy Clin Immunol. 2000;106:817–828
  56. Rosenberg HF, Phipps S, Foster PS. Eosinophil trafficking in allergy and asthma. J Allergy Clin Immunol. 2007;119:1303–1310
  57. Miller M, Sung KL, Muller WA, Cho JY, Roman M, Castaneda D, et al. Eosinophil tissue recruitment to sites of allergic inflammation in the lung is platelet endothelial cell adhesion molecule independent. J Immunol. 2001;167:2292–2297
  58. Rothenberg ME, Hogan SP. The eosinophil. Annu Rev Immunol. 2006;24:147–174
  59. Myou S, Sano H, Fujimura M, Zhu X, Kurashima K, Kita T, et al. Blockade of eosinophil migration and airway hyperresponsiveness by cPLA2-inhibition. Nat Immunol. 2001;2:145–149
  60. Medoff BD, Seung E, Hong S, Thomas SY, Sandall BP, Duffield JS, et al. CD11b+ myeloid cells are the key mediators of Th2 cell homing into the airway in allergic inflammation. J Immunol. 2009;182:623–635
  61. Brandt EB, Zimmermann N, Muntel EE, Yamada Y, Pope SM, Mishra A, et al. The α4β7-integrin is dynamically expressed on murine eosinophils and involved in eosinophil trafficking to the intestine. Clin Exp Allergy. 2006;36:543–553
  62. Carlens J, Wahl B, Ballmaier M, Bulfone-Paus S, Forster R, Pabst O. Common gamma-chain-dependent signals confer selective survival of eosinophils in the murine small intestine. J Immunol. 2009;183:5600–5607
  63. Mishra A, Hogan SP, Lee JJ, Foster PS, Rothenberg ME. Fundamental signals that regulate eosinophil homing to the gastrointestinal tract. J Clin Invest. 1999;103:1719–1727
  64. Mishra A, Hogan SP, Brandt EB, Wagner N, Crossman MW, Foster PS, et al. Enterocyte expression of the eotaxin and interleukin-5 transgenes induces compartmentalized dysregulation of eosinophil trafficking. J Biol Chem. 2002;277:4406–4412
  65. Zimmermann N, McBride ML, Yamada Y, Hudson SA, Jones C, Cromie KD, et al. Siglec-F antibody administration to mice selectively reduces blood and tissue eosinophils. Allergy. 2008;63:1156–1163
  66. Song DJ, Cho JY, Miller M, Strangman W, Zhang M, Varki A, et al. Anti-Siglec-F antibody inhibits oral egg allergen induced intestinal eosinophilic inflammation in a mouse model. Clin Immunol. 2009;131:157–169
  67. Song DJ, Cho JY, Lee SY, Miller M, Rosenthal P, Soroosh P, et al. Anti-Siglec-F antibody reduces allergen-induced eosinophilic inflammation and airway remodeling. J Immunol. 2009;183:5333–5341
  68. Zhu Z, Homer RJ, Wang Z, Chen Q, Geba GP, Wang J, et al. Pulmonary expression of interleukin-13 causes inflammation, mucus hypersecretion, subepithelial fibrosis, physiologic abnormalities, and eotaxin production. J Clin Invest. 1999;103:779–788
  69. Zheng T, Oh MH, Oh SY, Schroeder JT, Glick AB, Zhu Z. Transgenic expression of interleukin-13 in the skin induces a pruritic dermatitis and skin remodeling. J Invest Dermatol. 2009;129:742–751
  70. Hamelmann E, Cieslewicz G, Schwarze J, Ishizuka T, Joetham A, Heusser C, et al. Anti-interleukin 5 but not anti-IgE prevents airway inflammation and airway hyperresponsiveness. Am J Respir Crit Care Med. 1999;160:934–941
  71. Trifilieff A, Fujitani Y, Coyle AJ, Kopf M, Bertrand C. IL-5 deficiency abolishes aspects of airway remodelling in a murine model of lung inflammation. Clin Exp Allergy. 2001;31:934–942
  72. Cho JY, Miller M, Baek KJ, Han JW, Nayar J, Lee SY, et al. Inhibition of airway remodeling in IL-5-deficient mice. J Clin Invest. 2004;113:551–560
  73. Humbles AA, Lloyd CM, McMillan SJ, Friend DS, Xanthou G, McKenna EE, et al. A critical role for eosinophils in allergic airways remodeling. Science. 2004;305:1776–1779
  74. Broide DH. Immunologic and inflammatory mechanisms that drive asthma progression to remodeling. J Allergy Clin Immunol. 2008;121:560–570
  75. Lee JJ, McGarry MP, Farmer SC, Denzler KL, Larson KA, Carrigan PE, et al. Interleukin-5 expression in the lung epithelium of transgenic mice leads to pulmonary changes pathognomonic of asthma. J Exp Med. 1997;185:2143–2156
  76. Ochkur SI, Jacobsen EA, Protheroe CA, Biechele TL, Pero RS, McGarry MP, et al. Coexpression of IL-5 and eotaxin-2 in mice creates an eosinophil-dependent model of respiratory inflammation with characteristics of severe asthma. J Immunol. 2007;178:7879–7889
  77. Shi HZ, Humbles A, Gerard C, Jin Z, Weller PF. Lymph node trafficking and antigen presentation by endobronchial eosinophils. J Clin Invest. 2000;105:945–953
  78. Shen HH, Ochkur SI, McGarry MP, Crosby JR, Hines EM, Borchers MT, et al. A causative relationship exists between eosinophils and the development of allergic pulmonary pathologies in the mouse. J Immunol. 2003;170:3296–3305
  79. Wang HB, Ghiran I, Matthaei K, Weller PF. Airway eosinophils: allergic inflammation recruited professional antigen-presenting cells. J Immunol. 2007;179:7585–7592
  80. Padigel UM, Hess JA, Lee JJ, Lok JB, Nolan TJ, Schad GA, et al. Eosinophils act as antigen-presenting cells to induce immunity to Strongyloides stercoralis in mice. J Infect Dis. 2007;196:1844–1851
  81. Jacobsen EA, Ochkur SI, Pero RS, Taranova AG, Protheroe CA, Colbert DC, et al. Allergic pulmonary inflammation in mice is dependent on eosinophil-induced recruitment of effector T cells. J Exp Med. 2008;205:699–710
  82. Akuthota P, Wang HB, Spencer LA, Weller PF. Immunoregulatory roles of eosinophils: a new look at a familiar cell. Clin Exp Allergy. 2008;38:1254–1263
  83. Aceves SS, Broide DH. Airway fibrosis and angiogenesis due to eosinophil trafficking in chronic asthma. Curr Mol Med. 2008;8:350–358
  84. Walsh ER, August A. Eosinophils and allergic airway disease: there is more to the story. Trends Immunol. 2010;31:39–44
  85. Phipps S, Flood-Page P, Menzies-Gow A, Ong YE, Kay AB. Intravenous anti-IL-5 monoclonal antibody reduces eosinophils and tenascin deposition in allergen-challenged human atopic skin. J Invest Dermatol. 2004;122:1406–1412
  86. Specht S, Saeftel M, Arndt M, Endl E, Dubben B, Lee NA, et al. Lack of eosinophil peroxidase or major basic protein impairs defense against murine filarial infection. Infect Immun. 2006;74:5236–5243
  87. Knott ML, Matthaei KI, Foster PS, Dent LA. The roles of eotaxin and the signal transducer and activator of transcription 6 signalling pathway in eosinophil recruitment and host resistance to the nematodes Nippostrongylus brasiliensis and Heligmosomoides bakeri. Mol Immunol. 2009;46:2714–2722
  88. Yousefi S, Gold JA, Andina N, Lee JJ, Kelly AM, Kozlowski E, et al. Catapult-like release of mitochondrial DNA by eosinophils contributes to antibacterial defense. Nat Med. 2008;14:949–953
  89. Linch SN, Kelly AM, Danielson ET, Pero R, Lee JJ, Gold JA. Mouse eosinophils possess potent antibacterial properties in vivo. Infect Immun. 2009;77:4976–4982
  90. Rosenberg HF, Domachowske JB. Eosinophils, eosinophil ribonucleases, and their role in host defense against respiratory virus pathogens. J Leukoc Biol. 2001;70:691–698
  91. Yamada Y, Rothenberg ME, Lee AW, Akei HS, Brandt EB, Williams DA, et al. The FIP1L1-PDGFRA fusion gene cooperates with IL-5 to induce murine hypereosinophilic syndrome (HES)/chronic eosinophilic leukemia (CEL)-like disease. Blood. 2006;107:4071–4079
  92. Forbes E, Murase T, Yang M, Matthaei KI, Lee JJ, Lee NA, et al. Immunopathogenesis of experimental ulcerative colitis is mediated by eosinophil peroxidase. J Immunol. 2004;172:5664–5675
  93. Hogan SP, Mishra A, Brandt EB, Foster PS, Rothenberg ME. A critical role for eotaxin in experimental oral antigen-induced eosinophilic gastrointestinal allergy. Proc Natl Acad Sci U S A. 2000;97:6681–6686
  94. Hogan SP, Rosenberg HF, Moqbel R, Phipps S, Foster PS, Lacy P, et al. Eosinophils: biological properties and role in health and disease. Clin Exp Allergy. 2008;38:709–750
  95. Mishra A, Wang M, Pemmaraju VR, Collins MH, Fulkerson PC, Abonia JP, et al. Esophageal remodeling develops as a consequence of tissue specific IL-5-induced eosinophilia. Gastroenterology. 2008;134:204–214
  96. Boehme SA, Franz-Bacon K, Chen EP, Sasik R, Sprague LJ, Ly TW, et al. A small molecule CRTH2 antagonist inhibits FITC-induced allergic cutaneous inflammation. Int Immunol. 2009;21:81–93
  97. Matsuoka T, Hirata M, Tanaka H, Takahashi Y, Murata T, Kabashima K, et al. Prostaglandin D2 as a mediator of allergic asthma. Science. 2000;287:2013–2017
  98. Schratl P, Royer JF, Kostenis E, Ulven T, Sturm EM, Waldhoer M, et al. The role of the prostaglandin D2 receptor, DP, in eosinophil trafficking. J Immunol. 2007;179:4792–4799
  99. Tager AM, Dufour JH, Goodarzi K, Bercury SD, von Andrian UH, Luster AD. BLTR mediates leukotriene B(4)-induced chemotaxis and adhesion and plays a dominant role in eosinophil accumulation in a murine model of peritonitis. J Exp Med. 2000;192:439–446
  100. Reese TA, Liang HE, Tager AM, Luster AD, Van Rooijen N, Voehringer D, et al. Chitin induces accumulation in tissue of innate immune cells associated with allergy. Nature. 2007;447:92–96
  101. Cho KJ, Seo JM, Shin Y, Yoo MH, Park CS, Lee SH, et al. Blockade of airway inflammation and hyperresponsiveness by inhibition of BLT2, a low-affinity leukotriene B4 receptor. Am J Respir Cell Mol Biol. 2010;42:294–303
  102. Miyahara N, Ohnishi H, Miyahara S, Takeda K, Matsubara S, Matsuda H, et al. Leukotriene B4 release from mast cells in IgE-mediated airway hyperresponsiveness and inflammation. Am J Respir Cell Mol Biol. 2009;40:672–682
  103. Cowden JM, Zhang M, Dunford PJ, Thurmond RL. The histamine H(4) receptor mediates inflammation and pruritus in Th2-dependent dermal inflammation. J Invest Dermatol. 2009;[Epub ahead of print]
  104. Thurmond RL, Gelfand EW, Dunford PJ. The role of histamine H1 and H4 receptors in allergic inflammation: the search for new antihistamines. Nat Rev Drug Discov. 2008;7:41–53
  105. Wong CK, Hu S, Cheung PF, Lam CW. TSLP induces chemotactic and pro-survival effects in eosinophils: implications in allergic inflammation. Am J Respir Cell Mol Biol. 2009;[Epub ahead of print]
  106. Garrett JK, Jameson SC, Thomson B, Collins MH, Wagoner LE, Freese DK, et al. Anti-interleukin-5 (mepolizumab) therapy for hypereosinophilic syndromes. J Allergy Clin Immunol. 2004;113:115–119
  107. Plotz SG, Simon HU, Darsow U, Simon D, Vassina E, Yousefi S, et al. Use of an anti-interleukin-5 antibody in the hypereosinophilic syndrome with eosinophilic dermatitis. N Engl J Med. 2003;349:2334–2339
  108. Green RH, Brightling CE, McKenna S, Hargadon B, Parker D, Bradding P, et al. Asthma exacerbations and sputum eosinophil counts: a randomised controlled trial. Lancet. 2002;360:1715–1721
  109. Wenzel SE. Eosinophils in asthma—closing the loop or opening the door?. N Engl J Med. 2009;360:1026–1028
  110. Gleich GJ. Anti-interleukin-5 therapy and severe asthma. N Engl J Med. 2009;360:2577
  111. Kim YJ, Prussin C, Martin B, Law MA, Haverty TP, Nutman TB, et al. Rebound eosinophilia after treatment of hypereosinophilic syndrome and eosinophilic gastroenteritis with monoclonal anti-IL-5 antibody SCH55700. J Allergy Clin Immunol. 2004;114:1449–1455
  112. Stein ML, Collins MH, Villanueva JM, Kushner JP, Putnam PE, Buckmeier BK, et al. Anti-IL-5 (mepolizumab) therapy for eosinophilic esophagitis. J Allergy Clin Immunol. 2006;118:1312–1319
  113. Gevaert P, Lang-Loidolt D, Lackner A, Stammberger H, Staudinger H, Van Zele T, et al. Nasal IL-5 levels determine the response to anti-IL-5 treatment in patients with nasal polyps. J Allergy Clin Immunol. 2006;118:1133–1141
  114. Straumann A, Conus S, Grzonka P, Kita H, Kephart G, Bussmann C, et al. Anti-interleukin-5 antibody treatment (mepolizumab) in active eosinophilic oesophagitis: a randomised, placebo-controlled, double-blind trial. Gut. 2010;59:21–30
  115. Simon D, Wardlaw A, Rothenberg ME. Organ-specific eosinophilic disorders of the skin, lung and gastrointestinal tract. J Allergy Clin Immunol. 2010;In press
  116. Stein ML, Villanueva JM, Buckmeier BK, Yamada Y, Filipovich AH, Assa'ad AH, et al. Anti-IL-5 (mepolizumab) therapy reduces eosinophil activation ex vivo and increases IL-5 and IL-5 receptor levels. J Allergy Clin Immunol. 2008;121:1473–1483
  117. Ogbogu PU, Bochner BS, Butterfield JH, Gleich GJ, Huss-Marp J, Kahn JE, et al. Hypereosinophilic syndrome: a multicenter, retrospective analysis of clinical characteristics and response to therapy. J Allergy Clin Immunol. 2009;124:1319–1325
  118. Boucher RM, Gilbert-McClain L, Chowdhury B. Hypereosinophilic syndrome and mepolizumab. N Engl J Med. 2008;358:2838–2840
  119. Walsh GM. Reslizumab, a humanized anti-IL-5 mAb for the treatment of eosinophil-mediated inflammatory conditions. Curr Opin Mol Ther. 2009;11:329–336
  120. Kahn JE, Grandpeix-Guyodo C, Marroun I, Catherinot E, Mellot F, Roufosse F, et al. Sustained response to mepolizumab in refractory Churg-Strauss syndrome. J Allergy Clin Immunol. 2010;125:267–270
  121. Kim S, Israel E, Oren E, Wechsler M. Mepolizumab as a steroid-sparing treatment in the Churg Strauss syndrome. [abstract] Am J Respir Crit Care Med. 2009;179:A5368

 Series editors: Joshua A. Boyce, MD, Fred Finkelman, MD, William T. Shearer, MD, PhD, and Donata Vercelli, MD

 Supported in part by grant AI072265 from the National Institutes of Health. Dr Bochner also received support for human immunology research from the Dana Foundation and as a Cosner Scholar in Translational Research from the Johns Hopkins University.

 Terms in boldface and italics are defined in the glossary on page 17.

PII: S0091-6749(10)00389-1

doi:10.1016/j.jaci.2010.02.026

The Journal of Allergy and Clinical Immunology
Volume 126, Issue 1 , Pages 16-25, July 2010

Article Tools