Eosinophils and Eosinophilia

24  Eosinophils and Eosinophilia Anna Kovalszki, Peter F. Weller

Eosinophils are terminally differentiated, bone marrow–derived granulocytes that normally circulate in blood in low numbers and tend to localize in those tissues with mucosal epithelial surfaces. Increased blood or tissue eosinophils occur in helminth parasite infections, as well as in allergic diseases and a variety of other, often idiopathic, conditions. Conventionally, the major focus on eosinophils has been delineating the “effector” functions of these end-stage granulocytes, including what roles these cells play as helminthotoxic effector cells and the contribution they make to the immunopathogenesis of allergic diseases. More recent findings have indicated that eosinophil functions are considerably more extensive.1-4 Eosinophils contain stores of multiple, preformed cytokines; engage in cognate cell–cell interactions with other cell types, including lymphocytes; and have roles in varied host immune and inflammatory responses not conventionally marked by quantitatively extensive eosinophil infiltration.4

PRODUCTION AND DISTRIBUTION OF EOSINOPHILS Eosinophilopoiesis The development of eosinophils in bone marrow can be elicited by three cytokines. Granulocyte macrophage–colony-stimulating factor (GM-CSF), interleukin (IL)-3, and IL-5 all promote eosinophilopoiesis. In contrast to IL-3 and GM-CSF, which also promote the development of other lineages, IL-5 uniquely promotes the development and terminal differentiation of eosinophils. IL-5 is produced by type 2 innate lymphoid cells,5 CD8 T cells, natural killer (NK) cells, and other leukocytes, including eosinophils themselves. IL-5 is a defining cytokine product of T-helper cell-2 (Th2) CD4 T cells. The production of IL-5 by Th2 lymphocytes accounts for the eosinophilia accompanying T-helper 2 (Th2) cell–mediated immune responses characteristic of helminth infections and allergic diseases. Eosinophilopoiesis develops over about a week. Retained in bone marrow is a pool of mature eosinophils. IL-5, alone and in concert with the chemokine eotaxin-1 (CCL11), rapidly releases this pool of mature eosinophils into the circulation to acutely increase blood eosinophilia and facilitate recruitment of eosinophils to sites of inflammation.1 Blood eosinophils circulate with a half-life of about 8–18 hours. Eosinophils leave the circulation and localize in tissues, especially those with mucosal interfaces with the outside world, such as the gastrointestinal (GI) and lower genitourinary tracts. Although the mechanisms

governing this homing of eosinophils to mucosal tissues are not fully known, the chemokine eotaxin-1 is involved in the homing of eosinophils to the GI tract, but not to the respiratory tract.2 Eosinophils live longer compared with neutrophils and probably persist in tissues for several weeks. They are principally tissue-dwelling cells: as demonstrated in rodents, for every eosinophil present in the circulation, there are 300–500 in tissues.

Eosinophil Adherence Mechanisms The transit of eosinophils from bone marrow, through the circulation, and into tissues is governed, in part, by multiple adherence molecules expressed on eosinophils (Fig. 24.1). As for other leukocytes, recruitment of eosinophils into tissue sites of inflammation utilizes combinatorial interactions involving specific adhesion molecules (via their expression and altered affinity states) that mediate cellular interactions with the vascular endothelium and actions of chemoattractant molecules. Eosinophils express several adhesion molecules that they broadly share with other leukocytes. These adhesion molecules mediate their initial rolling and subsequent adherence to endothelial cells. Similar to neutrophils, eosinophils can adhere via CD11/CD18 heterodimeric β2 integrins to the intercellular adhesion molecule-1 and -2 (ICAM-1 and ICAM-2). Likewise, specific sialoglycoproteins mediate adherence between eosinophils and endothelial E- and P-selectins. Unlike neutrophils, but similar to lymphocytes, eosinophils are able to bind to vascular cell adhesion molecule-1 (VCAM-1). Eosinophils express two α4 integrins, very late activation antigen-4 (VLA-4, α4β1) and α4β7, which bind to VCAM-1. Moreover, α4β7 binds to the mucosal addressin cell adhesion molecule (MAdCAM). The β2 integrin αdβ2, which binds ICAM-3 and is expressed on other leukocytes, is an additional integrin that mediates eosinophil adhesion to VCAM-1. Enhanced expression of VCAM-1 on the vascular endothelium, as elicitable by IL-4 or IL-13 stimulation, may contribute to the localization of eosinophils in some tissue sites of inflammation. In addition to mediating interactions with the endothelium, eosinophil adherence molecules, by their interactions with extracellular matrix components, modulate the activity of eosinophils that have exited the bloodstream. Eosinophil VLA-6, α6β1, binds laminin. Both α4β1 and α4β7 interact with specific domains of tissue fibronectin, and these interactions can enhance eosinophil functional responses. Eosinophils express CD44 (PGP-1), which binds hyaluronic acid. Siglec-8, a sialic acid– binding immunoglobulin-like lectin, is expressed on eosinophils and binds sialoglycoconjugates.6

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Part two  Host Defense Mechanisms and Inflammation Extracellular matrix molecules

Eosinophil adherence molecules Integrins

Integrins VLA-6 (α6β1)

Laminin

Endothelial adherence molecules

CD11b/CD18 (Mac-1) CD11a/CD18 (LFA-1)

VLA-4 (α4β1)

Fibronectin

α4β7 Sialoglycoproteins

Hyaluronic acid

PGP-1 Siglec-8 Sialoglycoconjugates

ICAM-1 ICAM-1 ICAM-2 ICAM-3

αdβ2 VLA-4 (α4β1) α4β7

VCAM-1 MadCAM

Sialoglycoproteins Sialyl-LewisX PSGL-1

Selectins E-selectin P-selectin

Selectin L-selectin

GlyCAM-1, CD34

FIG 24.1  Adherence Mechanisms Utilized by Human Eosinophils to Bind to Vascular Endothelial Cells and the Extracellular Matrix Molecules. ICAM, intercellular adhesion molecule; VCAM, vascular cell adhesion molecule; MAdCAM, mucosal addressin cell adhesion molecule; VLA, very late activation antigen.

KEY CONCEPTS Actions of Eosinophilopoietic Cytokines Interleukin (IL)-3, Granulocyte Macrophage– Colony-Stimulating Factor (GM-CSF), IL-5 Promote eosinophil development and maturation in bone marrow (IL-5). Release a pool of mature eosinophils from bone marrow (IL-5). Sustain the viability and antagonize apoptosis of mature eosinophils, enhance multiple effector responses of mature eosinophils.

Eosinophil Chemoattractants Mobilization of eosinophils into tissues is governed by receptormediated chemoattractant stimuli. Chemoattractants promote the directed migration of eosinophils and may enhance the adhesion of eosinophils to vascular endothelium and their subsequent migration through the endothelium. Many compounds have been identified as eosinophil chemoattractants, including humoral immune mediators, such as platelet-activating factor (PAF) and the complement anaphylatoxins C5a and C3a; certain cytokines; and several chemokines, most notably the eotaxins. None of these is specific solely for eosinophils, but eotaxin-1, eotaxin-2, and eotaxin-3 exhibit the most restricted specificity.1 Eotaxins signal through CCR3 chemokine receptors that are expressed on eosinophils as well as basophils, some Th2 cells, and some mast cells. Thus recruitment of eosinophils to sites of immunological reactions is governed by their response to chemoattractants that facilitate intravascular emigration and direct migration of extravascular eosinophils, as well as by the functional states of eosinophil adherence molecules and the differential expression of endothelial cell adherence ligands.

STRUCTURE OF EOSINOPHILS Human eosinophils, unlike neutrophils, usually have a bilobed nucleus (Fig. 24.2). Defining attributes of eosinophils are their

FIG 24.2  Transmission Electron Micrograph of a Human Eosinophil. The numerous cytoplasmic specific granules contain the electron-dense crystalline cores that are unique to eosinophils. In addition, lipid bodies are visible as globular, uniformly dark structures. (Original magnification × 11,180.) (Courtesy of Dr. Ann M. Dvorak, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston.)

large, cytoplasmic “specific” granules that are morphologically distinct because of their unique content of crystalloid cores. Crystalloid cores are recognizable by transmission electron microscopy and usually appear electron dense (see Fig. 24.2). The cores and surrounding matrices of specific granules contain cationic proteins that account for the tinctorial staining of granules with eosin. Eosinophils at sites of inflammation can exhibit morphological changes in their specific granules, including loss of either matrix or core components from within intact granules, compatible with the extracellular release of granule constituents. Lipid bodies, cytoplasmic structures distinct from granules (see Fig. 24.2), are roughly globular in shape and range in size

CHAPTER 24  Eosinophils and Eosinophilia from minute to the size of specific granules. Lipid bodies are dissolved by common alcohol-based hematological stains but are preserved and stain darkly with osmium fixation. Lipid bodies lack a delimiting membrane but contain internal membranes that are often obscured by overlying lipid. Lipid bodies are found in neutrophils and other cells, especially in association with inflammation; but eosinophils typically contain more lipid bodies compared with neutrophils. Lipid body formation in eosinophils is rapidly inducible within minutes. In eosinophils, key enzymes involved in eicosanoid formation, including prostaglandin H synthase, the 5- and 15-lipoxygenases, and leukotriene (LT) C4 synthase, localize at lipid bodies; and lipid bodies are sites of eicosanoid synthesis.7

CELL-SURFACE RECEPTORS AND PROTEINS Eosinophil receptors for immunoglobulins include those for immunoglobulin G (IgG), IgE, and IgA. The receptor for IgG on eosinophils is principally the low-affinity FcγγRII (CD32), whereas neutrophils have FcγRII and FcγRIII (CD16). Eosinophil IgE receptors include the high-affinity IgE receptor FcεRI, typically found on basophils and mast cells, as well as FcεRII, the low-affinity IgE receptor, such as CD23, found on lymphocytes, monocytes, and antigen-presenting cells (APCs). Although FcεRI α-chain protein is present within eosinophils, its surface expression can be low or undetectable. Engagement of eosinophil FcεRI does not elicit exocytotic degranulation, as it does on basophils and mast cells. FcεRI may participate in IgE-mediated antigen uptake by antigen-presenting eosinophils. Eosinophil expression of IgE receptors is notable because IgE levels and eosinophil numbers frequently increase concomitantly in helminth infections as well as allergic diseases. Eosinophils express FcαRI (CD89), which binds secretory IgA more potently than other forms of IgA. Engagement of FcαRI triggers eosinophil release of granule proteins. With the characteristic localization of eosinophils to mucosal surfaces of the respiratory, GI, and genitourinary tracts, this IgA receptor enables eosinophils to engage secretory IgA present at these mucosal sites. Eosinophils have receptors for complement components, including C1q (CR1), C3b/C4b (CR1), iC3b (CR3), C3a, and C5a. Both C3a and C5a are eosinophil chemoattractants and stimulate the production of oxygen radicals by eosinophils. Eosinophils express several receptors for chemokines. CCR1 is a receptor for MIP-1α, MCP-3, and RANTES, whereas CCR3 is a receptor for eotaxin-1, eotaxin-2, eotaxin-3, MCP-3, and RANTES. Eosinophils express CXCR4 and respond to the ligand for this receptor, stromal cell–derived factor 1α. Mature eosinophils, like their immature precursors, express receptors for the three cytokines, GM-CSF, IL-3, and IL-5, which promote eosinophilopoiesis and stimulate the functioning of mature eosinophils. In addition, eosinophils have receptors for a broad range of other cytokines, including IL-1α, IL-2, IL-4, interferon (IFN)-α and IFN-γ, tumor necrosis factor (TNF)-α, stem cell factor (c-KIT), and IL-16 (which signals via CD4 on eosinophils). Thus eosinophils are subject to stimulation by many cytokines, although little is understood about how many of them affect eosinophil functioning in vivo. Of pertinence to interactions between eosinophils and B and T lymphocytes, eosinophils can express several relevant plasma membrane proteins. Class II major histocompatibility complex (MHC) proteins, generally absent on blood eosinophils, are

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induced for expression on eosinophils in sites of inflammation. In addition, eosinophils can express CD40, CD154 (CD40 ligand), CD153 (CD30 ligand), CD28 (B7–2), and CD86.4 Eosinophils express receptors for several lipid mediators, including PAF and leukotriene B4 (LTB4), which are chemoattractants for eosinophils and stimulate eosinophil degranulation and respiratory burst activity. Eosinophils also have receptors for prostaglandins D2 and E2 and for cysteinyl leukotrienes.

CONSTITUENTS OF EOSINOPHILS Eosinophil-specific granules contain preformed proteins that include both specific cationic proteins and stores of diverse cytokines and chemokines.

Cationic Granule Proteins Eosinophil granule cationic proteins have been extensively studied because of their abundance in the granules and their capacity to exert multiple effects on host cells and microbial targets. Major basic protein (MBP), named for its quantitative predominance within the granule and its markedly cationic (basic) isoelectric point of about 11, is a 13.8- to 14-kilodalton (kDa) protein. A homolog of MBP that is somewhat smaller (13.4 kDa) and less basic (pI 8.7) has been identified. MBP lacks enzymatic activity and probably exerts its varied effects via its markedly cationic nature. MBP was found to be toxic to both airway epithelium and helminths and to have antibacterial effects.8 A second granule protein is eosinophil peroxidase (EPO), an enzyme distinct from neutrophil myeloperoxidase. Cationic EPO (pI 10.8) uses hydrogen peroxide and halide ions to form hypohalous acids, which are toxic for parasites, bacteria, and tumor and host cells. EPO utilizes bromide in preference to chloride and is even more active with a pseudohalide, thiocyanate, to generate oxidant products, including hypobromous and hypothiocyanous acids. Two additional granule proteins are eosinophil cationic protein (ECP) (18 kDa, pI 10.8) and eosinophil-derived neurotoxin (EDN) (18–19 kDa, pI 8.9). EDN, never demonstrated to be neurotoxic for humans, is so named only because, after it is injected intracerebrally into test rabbits, it elicits a characteristic neuropathological response. Both ECP and EDN are ribonucleases (RNases). EDN expresses 100 times more RNase activity compared with ECP, although their toxic effects on bacterial, parasitic, and mammalian target cells are not simply a result of their RNase catalytic activities. Within the specific granule, MBP is localized to the crystalloid core and to tubulovesicular structures within and arising from the granules,8 whereas ECP, EDN, and EPO are localized in the matrix of the granule around the core (see Fig. 24.2). MBP is also found in low amounts (~3% of eosinophil levels) in basophils, but whether this reflects endocytosis or endogenous synthesis is not known. Uptake of MBP and EPO into mast cells is known to occur via endocytosis. Small amounts of EDN and ECP are present in neutrophils, and as neutrophils contain messenger RNA (mRNA) transcripts for these, EDN and ECP are likely synthesized by neutrophils. Nevertheless, eosinophils are the dominant source of these four cationic proteins. The properties of these proteins and their numerous biological effects have been reviewed,9 as these proteins have major effects not only in the potential role of eosinophils in host defense against helminth

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parasites but also in contributing to tissue dysfunction and damage in eosinophil-related allergic and other diseases.

Cytokines and Chemokines Eosinophils are capable of elaborating at least four dozen diverse cytokines and chemokines, and studies continue to identify more cytokines released by eosinophils. The potential activities of eosinophil-derived cytokines are extensive. Eosinophil-derived cytokines include those with autocrine growth factor activities for eosinophils and those with potential roles in acute and chronic inflammatory responses. A notable feature of eosinophils as a source of cytokines is that they contain stores of these cytokines preformed within eosinophil granules and secretory vesicles.10 Thus in contrast to most lymphocytes, which must be induced to synthesize de novo cytokines destined for release, eosinophils can immediately release preformed cytokine and chemokine proteins into the surrounding milieu. The local, rapid release of eosinophil-derived cytokines in tissues to effect adjacent cells could, and has been shown to, readily induce responses in varied cell types. Eosinophils synthesize the three growth factor cytokines GM-CSF, IL-3 and IL-5, which promote eosinophil survival, antagonize eosinophil apoptosis, and enhance eosinophil effector responses. Other cytokines elaborated by human eosinophils that may have activities in acute and chronic inflammatory responses include IL-1α, IL-6, IL-8, IFN-γ, TNF-α, and MIP1α. Human eosinophils can elaborate other various “growth” factors, including transforming growth factor (TGF)- α, TGF-β1, vascular endothelial growth factor, platelet-derived growth factor (PDGF)-β, heparin-binding epidermal growth factor, and a proliferation-inducing ligand (APRIL). These cytokines have roles in contributing to epithelial hyperplasia and fibrosis, as well as other immune homeostatic activities. In addition, eosinophils are recognized as sources of specific cytokines and chemokines capable of stimulating or inhibiting lymphocyte responses, including IL-2, IL-4, IL-10, IL-12, IL-16, RANTES, and TGF-β1. Of note, eosinophil cytokines include those associated with Th2 (IL-4, IL-5, IL-13), Th1 (IL-12, IFNγ), and T-regulatory (IL-10, TGF-β) responses, emphasizing the diverse immunoregulatory potentials for eosinophil-secreted cytokines.10

ACTIVATED EOSINOPHILS A well-recognized attribute of eosinophils is that, in conjunction with eosinophilic diseases, some blood and tissue eosinophils may exhibit various alterations, indicating that these cells have been “activated.” These changes include increased metabolic activity, diminished density (“hypodense”), enhanced LTC4 formation, and morphological alterations, including cytoplasmic vacuolization, alterations in granule numbers and size, and losses within specific granules of MBP-containing cores or matrices. Activated eosinophils may exhibit enhanced plasma membrane expression of some proteins, including CD69, human leukocyte antigen–D related (HLA-DR), and CD25. Features associated with in vivo “activated” eosinophils can be elicited, in part, by exposing eosinophils to specific stimuli, including GM-CSF, IL-3, and IL-5. In addition, interactions with extracellular matrix components can further contribute to eosinophil activation. Eosinophil “activation,” however, is not a singularly binary process, and some attributes of activation can

be elicited without other attributes by mediators and mechanisms that remain to be delineated.

MECHANISMS OF EOSINOPHIL DEGRANULATION As eosinophil granules contain four major cationic proteins and a multitude of preformed cytokines and chemokines, the processes by which eosinophils mobilize these granule constituents for their extracellular release are important in understanding the regulated functioning of eosinophils. Unlike mast cells or basophils that undergo acute exocytotic degranulation in response to cross-linking of their high-affinity Fcε receptors, an analogous mechanism to elicit comparable exocytotic degranulation of fluid-phase eosinophils has not been identified. Cross-linking of eosinophil IgG or IgA Fc receptors in vitro can stimulate release of eosinophil cationic proteins, but this rapid FcR-mediated acute “degranulation” process is cytolytic for eosinophils. In contrast, observations of eosinophils on the surfaces of large nonphagocytosable multicellular helminth parasites do provide evidence that eosinophils can degranulate by exocytosis to wholesale release granule contents on the surfaces of target parasites. An alternative mechanism of mobilizing granule contents for secretion that eosinophils utilize is a process of vesicular transportmediated “piecemeal” degranulation. Electron microscopic observations of lesional eosinophils provided evidence that eosinophil granule contents were mobilized in vivo by selective incorporation into small vesicles that traffic to the cell surface and release these granule contents. By this process, there may be agonist-elicited selective secretion of certain eosinophil-derived cytokines.11 Ultrastructural studies have demonstrated that secretory vesicles arise from granules and transport cytokines, such as IL-4.11 Insights into the selectivity and mechanisms of differential cytokine secretion have been gained by the finding, at least for IL-4, that a receptor for IL-4 mediates the transport of IL-4 from granules and within secretory vesicles.12 How this process of vesicular transport is regulated and functions to selectively mobilize specific eosinophil granule–derived cytokines or cationic proteins remains under investigation. In addition to regulated release of granule contents from viable eosinophils, a common, but often overlooked, occurrence is the lysis of eosinophils. Both cutaneous and pulmonary biopsy specimens of eosinophil-associated diseases contain free, extracellular, but still membrane-bound, eosinophil granules. These free extracellular granules express cytokine, chemokine, and cysteinyl leukotriene receptors and are secretion competent even outside of intact eosinophils.13,14 Cytolytic stimuli elicit both the release of nuclear DNA to form extracellular DNA “traps” and the release of free secretion-competent eosinophil granules in humans.15

FUNCTIONS OF EOSINOPHILS Conventional considerations of the roles that eosinophils may play have been guided by quantitative considerations so that those diseases characteristically marked by more prominent eosinophilia have occasioned the most interest. Thus studies have focused on the “effector” roles eosinophils play in host defense against helminth infections and in the immunopathogenesis of allergic and other eosinophilic diseases. Additional roles for eosinophils must be considered in immune or inflammatory responses not conventionally recognized to contain abundant eosinophils.4

CHAPTER 24  Eosinophils and Eosinophilia

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ROLES IN HOST DEFENSE

OTHER EOSINOPHIL FUNCTIONS

Because the host response to infections with multicellular helminth parasites is characteristically associated with eosinophilia, it is often believed that eosinophils evolved to have a role in killing helminths, especially during their larval stages. Indeed, in vitro eosinophils can kill numerous helminths, organisms too large to be phagocytosed. Eosinophils adhere to the parasite and deposit eosinophil granule contents onto its surface. Cell products that can contribute to parasite death include MBP, ECP, EDN, and EPO. As reviewed earlier,16 the helminthotoxic roles of eosinophils in vivo are less certain in humans and rodents. In eosinophildepleted mice, the intensities of primary and secondary infections with some helminths have not been greater than in eosinophilic mice, nor have IL-5 transgenic mice exhibited increased resistance to infection with some helminth species. Moreover, schistosome infections in two lines of eosinophil-ablated mice have shown no differences in measures of infection compared with normal mice.17 Nevertheless, murine studies need to be interpreted with caution. Many experimental infections involve introducing helminth infections that are often host species–restricted into unnatural host mice, in which innate immune responses may be prominent. Natural human infections are usually a consequence of repeated exposures, during which acquired, rather than innate, immunity becomes prominent. Thus eosinophil functions as helminthotoxic cells in vivo remain unclear. Eosinophils might have alternative functions in host responses to helminths, including functioning as APCs and even favoring the survival of Trichinella larvae in muscles.18,19

Other potential functions for the eosinophil are not fully defined. In addition to the acute release of lipid, peptide, and cytokine mediators of inflammation, eosinophils probably contribute to chronic inflammation, including the development of fibrosis. Eosinophils can be a major source of the fibrosis-promoting cytokine TGF-β. Additional roles of eosinophils in modulating extracellular matrix deposition and remodeling are suggested by studies of normal wound healing. During dermal wound healing, eosinophils infiltrate into wound sites and sequentially express TGF-α early and TGF-β1 later during wound healing. These findings suggest that eosinophils may contribute to the more chronic subepithelial airway fibrosis characteristic of chronic asthma. Additional functions for eosinophils are indicated by the findings that they may be induced to express class II MHC proteins and can function as APCs.20 Blood eosinophils lack HLA-DR expression, but eosinophils recovered from the airways 48 hours after segmental antigen challenge have been shown to express HLA-DR. Cytokines, including GM-CSF, IL-3, IL-4, and IFN-γ, induce eosinophil HLA-DR expression. Both murine and human eosinophils can function as HLA-DR–dependent MHC-restricted APCs in stimulating the proliferation of T cells. In vivo, murine eosinophils can process exogenous antigens in the airways, traffic to regional lymph nodes, and function as antigen-specific APCs to stimulate responses of CD4 T cells.21 Eosinophils, that normally become resident in submucosal and less prominently in other tissues, undoubtedly participate in ongoing homeostatic immune responses at these sites. Some of these responses are mediated by cytokines secreted by eosinophils, including IL-6 and APRIL to stimulate plasma cells development22 and IL-4 to activate macrophages in fat tissue and effect glucose metabolism.23 Further investigations will help delineate eosinophil’s functional roles and interactions with other cells, so that the scope of eosinophil functions will probably extend beyond its currently more defined role as an effector cell contributing to allergic inflammation.

ROLES IN DISEASE PATHOGENESIS The abilities of eosinophils to release biologically active lipids as paracrine mediators of inflammation and to release preformed cationic and cytokine granule constituents enable eosinophils to contribute to the immunopathogenesis of various diseases, including asthma.1 Eosinophils form several classes of biologically active lipids. Eosinophils may liberate PAF, whose diverse activities can be mediated either directly or by stimulating other cells to release leukotrienes, prostaglandins, and complement peptides. Stimulated eosinophils release LTC4. LTD4 and LTE4 are formed from LTC4 by the sequential enzymatic removal of glutamic acid and glycine from its tripeptide glutathione side chain. LTC4 and especially LTD4 have bronchoconstrictor activities, constrict terminal arterioles, dilate venules, and stimulate airway mucus secretion. Thus eosinophils are a potential source of two major types of mediator lipids, the sulfidopeptide leukotrienes and PAF. Oxidants released by eosinophils, including superoxide anion, hydroxyl radical, and singlet oxygen, as well as EPO-catalyzed hypothiocyanous acid and other hypohalous acids, have the potential to damage host tissues. Released eosinophil granule proteins are immunologically detectable in fluids, including blood, sputum, and synovial fluids, and in tissues, including the respiratory and GI tracts, skin, and heart, in association with various eosinophil-related diseases. The eosinophil cationic proteins, including MBP, ECP, and EPO, can damage various cell types. Thus extracellular release of eosinophil granule proteins, by degranulation or cytolysis of eosinophils, could contribute to local tissue damage by causing dysfunction and damage to adjacent cells.

EOSINOPHILIA AND EOSINOPHILIC DISORDERS Diverse infectious, allergic, neoplastic and idiopathic disease processes can be associated with increased blood and/or tissue eosinophil numbers. Blood eosinophilia, present when eosinophil numbers are in excess of their usual level of <450/µL of blood, may be intermittently, modestly, or (less frequently) markedly increased. Blood eosinophil numbers are not necessarily indicative of the extent of eosinophil involvement in affected tissues. Some patients with sustained blood eosinophilia can develop organ damage, especially cardiac damage. This cardiac involvement can include the formation of intraventricular thrombi and endomyocardial fibrosis with secondary mitral or tricuspid regurgitation (Fig. 24.3). Such damage can complicate the sustained eosinophilia of hypereosinophilic syndromes and has been noted with eosinophilias accompanying other diseases, including eosinophilia with carcinomas, lymphomas, GM-CSF, or IL-2 administration, drug reactions, and parasitic infections. Most patients with eosinophilia, however, develop no evidence of endomyocardial damage. Conversely, cardiac disease can rarely present in patients without known eosinophilia. The pathogenesis of eosinophil-mediated cardiac damage involves both usually

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INFECTIOUS DISEASES ASSOCIATED WITH EOSINOPHILIA

FIG 24.3  Eosinophil Endomyocardial Disease. A large thrombus is present in the apex of the left ventricle and the chordae tendineae are entrapped, leading to severe mitral valve regurgitation.

heightened numbers of eosinophils and some activating events, as yet ill-defined, that promote eosinophil-mediated tissue damage. Cardiac damage progresses through three stages. In the first stage, there is damage to the endocardium and infiltration of the myocardium with eosinophils and lymphocytes, with eosinophil degranulation and myocardial necrosis. Elevated plasma levels of troponin can be a sensitive assay of early eosinophil-mediated cardiac damage. A similar acute eosinophilic myocarditis can develop with drug hypersensitivity reactions and may be more fulminant. The first stage is frequently clinically occult, although subungual splinter hemorrhages may be prominent. Elevations of serum troponins as a measure of myocardial injury should be evaluated. Echocardiography usually detects no abnormalities at this stage, although cardiac magnetic resonance imaging (MRI) is evolving as a technique to potentially detect cardiac involvement at an earlier stage. Uncommonly, death due to acute progressive cardiac disease can occur. Corticosteroid therapy during the acute stage may help control and prevent the evolution of myocardial fibrosis. The second stage of heart disease, the formation of thrombi along the damaged endocardium, affects either or both ventricles and occasionally the atrium. Outflow tracts near the aortic and pulmonic valves are usually spared. These thrombi can embolize to the brain and elsewhere. Finally, in the fibrotic stage, progressive scarring leads to entrapment of chordae tendineae with the development of mitral and/or tricuspid valve regurgitation and to endomyocardial fibrosis, producing a restrictive cardiomyopathy. Echocardiography and MRI are valuable in detecting intracardiac thrombi and the manifestations of fibrosis. Patients with sustained eosinophilia should be monitored by using echocardiography and serum troponin assays for evidence of cardiac disease. In an older series of patients referred to the National Institutes of Health (NIH), much of the mortality among these patients with hypereosinophilia was attributable to end-stage congestive heart failure. In contemporary times, earlier recognition of cardiac involvement, mitral valve replacement with bioprostheses and additional therapeutic options for hypereosinophilic syndromes (see below) have largely minimized the morbidity and mortality attributable to end-stage eosinophilic endomyocardial disease.

Eosinophilia is encountered only with specific infectious diseases. With active bacterial or viral infections, eosinopenia is characteristic. This suppression of blood eosinophils is, in part, caused by heightened endogenous corticosteroid production as well as by inflammatory mediators released during these infections. This suppression of eosinophilia, with either serious bacterial infections or marked inflammation, accounts for the absence of otherwise expected eosinophilia in some patients with helminth infections, including those with hyperinfection strongyloidiasis.24 As a general clinical guideline, patients with a febrile illness and an increased or even normal blood eosinophilia are not likely to have common bacterial or viral infections, unless they have adrenal insufficiency or a confounding medication-elicited eosinophilia.

Helminth Parasites Helminth parasites are multicellular metazoan organisms—the “worm” parasites. Infections with diverse helminths elicit eosinophilia (Chapter 31).24 Although eosinophilia may provide a hematological clue to the presence of helminth infection, the absence of blood eosinophilia does not exclude such infections. The eosinophilic response to helminths is determined both by the host’s immune response and by the parasite, including its distribution, migration, and development within the infected host. The level of eosinophilia tends to parallel the magnitude and extent of tissue invasion by helminth larvae or adults. In several helminth infections, the migration of infecting larvae or subsequent developmental stages through tissues is greatest early in infection, and hence the magnitude of the elicited eosinophilia will be the greatest in these early phases. In established infections, local eosinophil infiltration will often be present around helminths within tissues, without significant blood eosinophilia. Eosinophilia may be absent in those helminth infections that are well contained within tissues (e.g., intact echinococcal cysts) or are solely intraluminal within the intestinal tract (e.g., Ascaris, tapeworms). In some established infections, increases in blood eosinophilia may be episodic. Intermittent leakage of cyst fluids from echinococcal cysts can transiently stimulate increases in blood eosinophilia and also cause symptoms attributable to allergic or anaphylactic reactions (urticaria, bronchospasm). For tissuedwelling helminths, increases in eosinophilia may occur principally in association with migration of adult parasites, as in loiasis and gnathostomiasis. Helminth infections more likely to elicit prolonged hypereosinophilia in adults include filarial and hookworm infections and strongyloidiasis (Table 24.1).24 Trichinellosis can elicit an acute hypereosinophilia. Strongyloides stercoralis infection, difficult to diagnose solely by stool examinations, is especially important to exclude, not only because it elicits modest to even marked eosinophilia but also because, unlike other helminths, it can develop into a disseminated, often fatal, disease (hyperinfection syndrome) in patients given immunosuppressive corticosteroids.24 Enzyme-linked immunosorbent assay (ELISA) serology has proved valuable in detecting strongyloidiasis and should be obtained for patients with eosinophilia likely to receive corticosteroids. Some tissue- or blood-dwelling helminths that are not diagnosable by stool examinations but that can cause marked eosinophilia require diagnostic examination of blood or biopsied tissues or specific serological tests.24 Infections with these organisms include filarial infections, trichinellosis, and visceral larva migrans. In

CHAPTER 24  Eosinophils and Eosinophilia TABLE 24.1  Parasitical Diseases Capable

of Causing Marked (>3000/µL) or LongStanding Eosinophilia Helminth Infection

Hypereosinophilia

Chronic Eosinophilia

Angiostrongyliasis costaricensis Ascariasis Hookworm infection

+ During early lung migration + During early lung migration

Strongyloidiasis

Uncommonly

Trichinellosis Visceral larva migrans Gnathostomiasis Cysticercosis Echinococcosis

+ With heavy infections + Principally in children

Filariases: Tropical pulmonary eosinophilia Loiasis Onchocerciasis Flukes:  Schistosomiasis

 Fascioliasis  Clonorchiasis  Paragonimiasis  Fasciolopsiasis

+ Common cause of low-grade eosinophilia + Self-perpetuating, may last > 50 years

+ May be episodic with cyst fluid leakage +

+

+ Especially in expatriates +

+

+ During early infection in nonimmune patients + During early infection + During early infection + During early infection + During early infection

+

+

+ + + +

Adapted from Wilson ME, Weller PF. Eosinophilia. In: Guerrant RL, Walker DH, Weller PF, eds. Tropical Infectious Diseases: Principles, Pathogens and Practice, 3rd ed. Philadelphia, Penn.: Churchill Livingstone; 2011:943.

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invasive pathogen. (ii) Coccidioidomycosis, following primary infection, especially in conjunction with erythema nodosum, and at times with progressive disseminated disease, can elicit blood eosinophilia and may cause an eosinophilic meningitis. (iii) Basidiobolomycosis infection can also be associated with eosinophilia.24

Human Immunodeficiency Virus and Retroviral Infections Eosinophilia can uncommonly accompany human immunodeficiency virus (HIV) infections for several reasons. First, leukopenia may increase eosinophil percentages without reflecting true eosinophilia. Second, adverse reactions to medications may elicit eosinophilia. Third, patients with acquired immunodeficiency syndrome (AIDS) who develop adrenal insufficiency as a result of cytomegalovirus and other infections may exhibit eosinophilia as a consequence. In addition, modest, and uncommonly marked, eosinophilia and eosinophilic pustular folliculitis can be observed in some patients with HIV infection.24 Eosinophilia more commonly develops with HTLV-1 infections.24

ALLERGIC DISEASES ASSOCIATED WITH EOSINOPHILIA Among the noninfectious diseases associated with eosinophilia (Table 24.2) are allergic diseases, notably those mediated by IgE-dependent mechanisms. In these diseases, including allergic rhinitis, conjunctivitis, and asthma, eosinophils are present in involved tissues as well as often being increased in blood.

MYELOPROLIFERATIVE AND NEOPLASTIC DISEASE Eosinophilia can occur with specific neoplastic diseases, as well as in some disorders of uncertain etiology, including some hypereosinophilic syndromes.

Hypereosinophilic Syndromes children, owing to their propensity for geophagous pica and ingestion of dirt contaminated by dog ascarid eggs, visceral larva migrans caused by Toxocara canis is a potential etiology for sustained eosinophilia. ELISA serological testing can evaluate this possibility.

Other Infections: Protozoa and Fungi Infections with single-celled protozoan parasites do not characteristically elicit eosinophilia. This is true of all intestinal, blood-, and tissue-infecting protozoa, with three exceptions. Two intestinal protozoans, Dientamoeba fragilis and Isospora belli, can at times be associated with low-grade eosinophilia. Hence, in patients with symptoms of enteric infection and eosinophilia, diagnostic trophozoites of D. fragilis or oocysts of I. belli should be sought in stool examinations. Fecal examinations for I. belli oocysts must be specifically requested, as they are not usually detected in routine stool ova and parasite examinations. Other enteric protozoa do not elicit eosinophilia and, if detected in stool examinations, should not be accepted as causes of eosinophilia. Sarcocystis, a myositis producing protozoan, can elicit modest eosinophilia. Three fungal diseases can be associated with eosinophilia. (i) Aspergillosis is accompanied by eosinophilia only in the form of allergic bronchopulmonary aspergillosis, not when it is an

A syndrome previously termed idiopathic hypereosinophilic syndrome is not a single entity but rather a constellation of leukoproliferative disorders characterized by sustained overproduction of eosinophils. The three original diagnostic criteria for this syndrome were eosinophilia in excess of 1500/µL of blood persisting for longer than 6 months; lack of an identifiable parasitic, allergic, or other etiology for eosinophilia; and signs and symptoms of organ involvement. In contemporary practice, if eosinophilia is sustained over a month and the other criteria are reliably met before the 6-month time frame, a diagnosis can be made and treatment promptly initiated. Moreover, in recent years there has been increasing recognition that hypereosinophilic syndromes (HES), even at times without evident organ damage, encompass a spectrum of disorders, and progress has been made in identifying the underlying defects in some of these (Fig. 24.4).25

KEY CONCEPTS Hypereosinophilic Syndromes Eosinophilia sustained in excess of 1500/µL. Absence of allergic, parasitic, or other etiologies for eosinophilia. Usually evidence of organ involvement.

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TABLE 24.2  Eosinophil-Associated Diseases and Disorders Allergic or Atopic Diseases Asthma Allergic rhinitis Eosinophilic esophagitis Atopic dermatitis Allergic urticaria Nasal polyps

Myeloproliferative and Neoplastic Disorders Hypereosinophilic syndromes: myeloproliferative, lymphoproliferative, and others Leukemia Lymphoma- and tumor-associated Mastocytosis

Pulmonary Syndromes Parasite-induced eosinophilic lung diseases: Loeffler syndrome: patchy migratory infiltrates, resolving over weeks, seen with transpulmonary migration of helminth parasites, especially Ascaris Tropical pulmonary eosinophilia: miliary lesions and fibrosis; heightened immune response causing one form of lymphatic filariasis; increased immunoglobulin E (IgE) and antifilarial antibodies Pulmonary parenchymal invasion: paragonimiasis Heavy hematogenous seeding with helminths: trichinellosis, schistosomiasis, larva migrans Allergic bronchopulmonary aspergillosis Chronic eosinophilic pneumonia: dense peripheral infiltrates, fever; progressive, blood eosinophilia may be absent; steroid responsive Acute eosinophilic pneumonia: acute presentation diagnosed by bronchoalveolar lavage or biopsy Eosinophilic granulomatosis with polyangiitis (Churg–Strauss syndrome) vasculitis: small- and medium-sized arteries; granulomas, necrosis; asthma often antecedent; extrapulmonary (e.g., neurological, cutaneous, cardiac, or gastrointestinal) involvement likely Drug- and toxin-induced eosinophilic lung diseases Other: hypereosinophilic syndromes, neoplasia, bronchocentric granulomatosis

Skin and Subcutaneous Diseases Skin diseases: atopic dermatitis, blistering diseases, including bullous pemphigoid, urticarias, drug reactions Diseases of pregnancy: pruritic urticarial papules and plaques syndrome, herpes gestationis Eosinophilic pustular folliculitis Eosinophilic cellulitis (Wells syndrome) Kimura disease and angiolymphoid hyperplasia with eosinophilia Shulman syndrome (eosinophilic fasciitis) Episodic angioedema with eosinophilia: recurrent periodic episodes with fever, angioedema, and secondary weight gain; may be long-standing without untoward cardiac dysfunction

Gastrointestinal Disorders Eosinophilic gastroenteritides Inflammatory bowel disease: eosinophils in lesions; occasionally blood eosinophilia with ulcerative colitis

Rheumatologic Diseases Vasculitis: Eosinophilic granulomatosis with polyangiitis (Churg–Strauss) and cutaneous necrotizing eosinophilic vasculitis

Immunological Reactions Medication-related eosinophilias Immunodeficiency diseases: Job’s syndrome and Omenn syndrome Transplant rejections

Endocrine Hypoadrenalism: Addison disease, adrenal hemorrhage, hypopituitarism

Other Causes of Eosinophilia Atheromatous cholesterol embolization Hereditary Serosal surface irritation, including peritoneal dialysis and pleural eosinophilia Adapted from Weller PF. Eosinophilia and eosinophil-related disorders. In: Adkinson NF, Jr., Yunginger JW, Busse WW, et al., eds. Allergy: Principles and Practice, 6th ed. Philadelphia, Penn.: Mosby; 2003:1105.

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Hypereosinophilic Syndromes (HESs) Eosinophils > 1,500/mm3 Persistent eosinophilia and/or end-organ damage/dysfunction Exclusion of secondary causes of eosinophilia

Myeloproliferative variant

Myeloproliferative - etiology unknown

F/P negative and clonal eosinophilia by HUMARA*** or ≥4 of the following: Dysplastic eosinophils on peripheral smear Serum B12>1000 pg/ml Anemia and/or thrombocytopenia Hepatosplenomegaly Bone marrow cellularity >80% Spindle-shaped mast cells Myelofibrosis

Lymphocytic variant

PDGFRA -associated HES

Chronic eosinophilic leukemia

F/P positive by RT - PCR or FISH

Demonstrable cytogenetic abnormalities and/or blasts on peripheral smear

Familial

Clonal lymphocyte population by flow cytometry or PCR analysis of T-cell receptor usage

Undefined

Family history of documented persistent eosinophilia of unknown cause

Benign Asymptomatic with no evidence of organ involvement

Overlap*

EGID eosinophilic pneumonia, eosinophilia myalgia syndrome, and other organrestricted eosinophilic disorders

Associated**

CSS Systemic mastocytosis, inflammatory bowel disease, sarcoidosis, HIV, and other disorders

Complex

Episodic

Symptomatic with organ dysfunction but does not meet criteria for myeloproliferative or lymphocytic variant

Cyclical angioedema and eosinophilia

FIG 24.4  Classification of Hypereosinophilic Syndromes Based on a Workshop Summary Report. Specific syndromes discussed at the workshop are indicated in bold. *Incomplete criteria, apparent restriction to specific tissues/organs. †Peripheral eosinophilia, >1500/mm3 in association with a defined diagnosis. ‡ Presence of the FLPL1/PDGFRA (F/P) mutation. § Clonality analysis based on the digestion of genomic DNA with methylation-sensitive restriction enzymes followed by polymerase chain reaction (PCR) amplification of the CAG repeat at the human androgen receptor gene (HUMARA) locus at the X chromosome. CSS, Churg-Strauss syndrome (now called eosinophilic granulomatosis with polyangiitis); EGID, eosinophil gastrointestinal diseases; FISH, fluorescence in situ hybridization. (From Klion AD, Bochner BS, Gleich GJ, et al. Approaches to the treatment of hypereosinophilic syndromes: a workshop summary report. J Allergy Clin Immunol 2006; 117:1294, with permission from the American Academy of Allergy, Asthma and Immunology.)

Some patients with HES, termed myeloproliferative variants of HES, exhibit features common to myeloproliferative disorders, including elevated vitamin B12 and lactate dehydrogenase (LDH) levels, splenomegaly, cytogenetic abnormalities, myelofibrosis, anemia, myeloid dysplasia, and often elevated serum level of mast cell tryptase. In many patients with myeloproliferative HES, the molecular defect has been identified as a chromosome 4 deletion that yields a fusion gene encoding a FIP1LI/PDGFRA (PDGF-α receptor) (F/P) protein that constitutively expresses receptor kinase activity. This fusion gene can be diagnostically evaluated by reverse transcription–polymerase chain reaction (RT-PCR) or fluorescence in situ hybridization (FISH) (Chapter 96). Importantly, the majority of patients with this fusion mutation, which constitutes a form of chronic eosinophilic leukemia (CEL), respond to therapy with imatinib, which is considered

the first line of therapy for FIP1LI/PDGFRA-positive HES.26 For patients with any evidence of cardiac involvement, including elevated troponin levels, it is recommended that glucocorticoids be administered along with initiation of imatinib therapy. Other patients with eosinophilia without F/P mutations have also responded to imatinib, indicating that other receptor tyrosine kinase mutations can underlie some of these CEL/myeloproliferative forms of HES.27 The presence of more than four myeloproliferative features commonly seen in mutation-positive disease, predicted response in those without known mutations. Some of these features included dysplastic eosinophils, vitamin B12 level >1000 picograms per milliliter (pg/mL), tryptase level ≥12 nanograms per milliliter (ng/mL), anemia/thrombocytopenia, hypercellular marrow, and spindled mast cells, reticulin fibrosis, and dysplastic megakaryocytes on bone marrow biopsy.28 In addition, clonal

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abnormalities in the eosinophil lineage have been reported in a few patients (see Fig. 24.4). Another variant form of HES is a lymphoproliferative form resulting from clonal expansions of lymphocytes, often CD4+CD3− Th2-like lymphocytes, which elaborate IL-5.29 These aberrant T cells can be sought by flow cytometry or T-cell receptor (TCR) analysis. These patients, who may have elevated IgE levels, usually do not develop eosinophilic endomyocardial disease but are at risk for developing T-cell lymphomas.29 In addition to these recognized variants, there are a substantial number of patients with HES for whom the etiologies of the eosinophilia remain unknown.26 Some such patients develop no signs or symptoms of disease and can be monitored without therapy.30 For those who require therapy, including those with lymphoproliferative variants,29 glucocorticosteroids are the mainstay of treatment.26 With glucocorticoid therapy, partial or complete remission of eosinophilia within 1 month has been reported to occur in 85% of patients.26 Second-line agents include hydroxyurea and IFN-α.26 The neutralizing anti-IL-5 monoclonal antibody (mAb), mepolizumab, has beneficial and steroid-sparing effects in those with FIP1L1-PDGFRA negative hypereosinophilic syndromes,31 but it is approved by the US Food and Drug Administration (FDA) for treating severe eosinophilic phenotype asthma but not yet approved for hypereosinophilic syndromes. Anti-CD52 mAb (alemtuzumab) and allogeneic hematopoietic cell transplantation have been used for particularly severe and refractory HES. In contrast to older reports, with earlier diagnosis and therapy and with more varied and targeted therapeutic options, morbidity and, particularly, mortality in HES syndromes have been reduced.

Eosinophilia With Tumors or Leukemias The F/P-positive and related chromosomal fusion gene mediated myeloproliferative variants of HES are forms of CEL.27 Eosinophilia is a characteristic of the M4Eo subtype of acute myeloid leukemia, having the common M4 characteristic of chromosomal 16 abnormalities. Other forms of eosinophilic leukemia, often with specific cytogenetic and molecular genetic abnormalities, have been recognized.27 Eosinophilia may accompany chronic myelogenous leukemia (often with basophilia) but is uncommon with acute lymphoblastic leukemia. Eosinophilia may be observed in some patients with lymphoma, including Hodgkin disease, especially the nodular sclerosing form, T-cell lymphoblastic lymphoma, and adult T-cell leukemia/lymphoma. A small proportion of patients with carcinomas, especially of mucin-producing epithelial cell origin, have associated blood and tissue eosinophilia. Eosinophilia may accompany angioimmunoblastic lymphadenopathy, mycosis fungoides, Sézary syndrome, and lymphomatoid papulosis. Eosinophilia occurs in about 20% of patients with systemic mastocytosis and may be the presenting finding in the absence of cutaneous manifestations.

ORGAN SYSTEM INVOLVEMENT AND EOSINOPHILIA Eosinophilic syndromes limited to specific organs, such as eosinophilic pneumonias or eosinophilic GI disorders (EGIDs; Chapter 46), characteristically do not extend beyond their own target organ, and hence lack the multiplicity of organ involvement often found with non–organ-specific hypereosinophilic syndromes. They also do not have the predilection to develop

secondary eosinophil-mediated cardiac damage, for reasons that are not known.

Pulmonary Eosinophilias Blood eosinophilia can infrequently accompany pleural fluid eosinophilia, a nonspecific response seen with various disorders, including trauma and repeated thoracenteses. In addition, several pulmonary parenchymal disorders can be associated with eosinophilia (see Table 24.2).32 Helminth parasites are responsible for four forms of eosinophilic lung disease.24,32 The first form, Loeffler syndrome, is marked by blood eosinophilia, eosinophilic patchy pulmonary infiltrates that appear and resolve over weeks, and, at times, bronchospasm, and is typically caused by those helminth parasites (Ascaris lumbricoides/Ascaris suum), and less commonly hookworm and Strongyloides that migrate through the lungs early in their developmental lifecycle.24 Stool examinations are not helpful, as the pulmonary response is elicited by infecting larval forms months before productive egg-laying from later adult stages begins in the intestines. Diagnosis is made on epidemiological grounds.24 The second form of helminth-induced lung disease is the syndrome of tropical pulmonary eosinophilia, which develops in a minority of patients infected with lymphatic-dwelling filarial species.23 This syndrome is characterized by marked blood eosinophilia, a paroxysmal nonproductive cough, wheezing, occasional weight loss, lymphadenopathy, and low-grade fevers. On chest X-rays, increased bronchovesicular markings, diffuse interstitial lesions 1–3 mm in diameter or mottled opacities, usually more prominent in lower lung fields, are common. Patients have markedly increased numbers of blood and alveolar eosinophils, and elevations in both total serum IgE and antifilarial antibodies. A third form of helminth-induced lung disease is caused by helminths that invade the pulmonary parenchyma, notably lung flukes that cause paragonimiasis. The fourth form of lung disease is caused by larger than usual numbers of helminth organisms that are carried hematogenously into the lungs. Examples include schistosomiasis, trichinellosis, and larva migrans. Bronchopulmonary aspergillosis constitutes another type of eosinophil-associated pulmonary disease. Two forms of idiopathic eosinophilic pneumonia are recognized.32 In chronic eosinophilic pneumonia, patients may exhibit peripheral pulmonary infiltrates that can extend across lobar fissures. Chronic eosinophilic pneumonia is of unknown etiology and is responsive to corticosteroids but is prone to relapse. An acute form of eosinophilic pneumonia, which manifests as fever, pulmonary infiltrates, and respiratory insufficiency, is diagnosable by finding eosinophils in bronchoalveolar lavage (BAL) fluids or on lung biopsy. Acute eosinophilic pneumonia, which often follows new exposures to cigarette or other smoke or dusts, responds to corticosteroid treatment and does not relapse. The major vasculitis associated with eosinophilia is eosinophilic granulomatosis with polyangiitis (EGPA, formerly called ChurgStrauss syndrome) (Chapter 58).33 Late-onset asthma, eosinophilia, and at times transient pulmonary infiltrates antedate the development of systemic vasculitis in about half the cases. Pulmonary involvement is seen in almost all patients, and pulmonary infiltrates occur in three-quarters of them. Nasal and sinus involvement is common. Corticosteroids, anti-IgE mAb, or anticysteinyl leukotriene agent therapies for asthma may mask

CHAPTER 24  Eosinophils and Eosinophilia the evolution of EGPA. Neurological, cutaneous, cardiac, and GI organ involvement is common.33 Cardiac involvement includes pericarditis and small vessel cardiac vasculitis, and, much less commonly, endomyocardial thrombosis and fibrosis. Diverse drugs are capable of eliciting pulmonary eosinophilia. More commonly implicated medications include nonsteroidal antiinflammatory drugs (NSAIDs) and antimicrobial medications. Likewise, toxic agents, including those from occupational exposure, can be responsible for pulmonary eosinophilia. Each of these reactions has a defined etiological stimulus and hence differs from idiopathic and other eosinophilic diseases, but the clinical presentation of drug- and toxin-elicited pulmonary eosinophilias can resemble other forms of pulmonary eosinophilia, including acute or chronic eosinophilic pneumonia.

Skin and Subcutaneous Diseases A number of cutaneous diseases can be associated with heightened blood eosinophils,34 including atopic dermatitis, blistering disorders including bullous pemphigoid, drug reactions, and two diseases associated with pregnancy: (i) herpes gestationis and (ii) the syndrome of pruritic urticarial papules and plaques of pregnancy. Eosinophilic pustular folliculitis is seen mostly in patients with HIV infections and in those treated for hematological malignancies or after bone marrow transplantation. In patients with cutaneous involvement and eosinophilia, angiolymphoid hyperplasia with eosinophilia and Kimura disease, eosinophilic cellulitis (Wells syndrome), eosinophilic fasciitis, and eosinophilic pustular folliculitis can be differentiated on the basis of histopathology of biopsied lesions. Another syndrome, episodic angioedema with eosinophilia, is characterized by recurring episodes of angioedema, urticaria, fever, and marked blood eosinophilia. This syndrome responds to glucocorticosteroid therapy.

Gastrointestinal Diseases EGIDs (Chapter 46), including eosinophilic esophagitis, eosinophilic gastroenteritis, and eosinophilic colitis, represent a heterogeneous collection of disorders in which there may be eosinophilic infiltration of the mucosa, the muscle layer or the serosa, the last of which can lead to eosinophilic ascites. Peripheral blood eosinophilia may occur in EGIDs, although with eosinophilic esophagitis, peripheral blood eosinophil counts are often normal. Eosinophils are present in the lesions of collagenous colitis and ulcerative colitis, but blood eosinophilia is usually absent. GI eosinophilia elicited by intestinal helminths and eosinophilic enterocolitis as a result of hypersensitivity reactions to medications must be excluded in patients with these diseases who have tissue eosinophilia.

Rheumatological Disorders Of the various forms of vasculitis, only two are commonly associated with eosinophilia. The principal eosinophil-related vasculitis is EGPA, formerly called Churg-Strauss syndrome (as discussed above; and in Chapter 58). Cutaneous necrotizing eosinophilic vasculitis with hypocomplementemia and eosinophilia is a distinct vasculitis of small dermal vessels that are extensively infiltrated with eosinophils. This form of vasculitis may occur in patients with connective tissue diseases. In addition, eosinophilia may uncommonly accompany rheumatoid arthritis itself but more commonly results from adverse reactions to treatment medications (including NSAIDs, gold, and tetracyclines) or concomitant vasculitis.

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Immunological Disorders CLINICAL PEARLS Eosinophilia and Drug Reactions Drug Reactions

Examples

Interstitial nephritis

Semisynthetic penicillins, cephalosporins Nitrofurantoin, sulfas, nonsteroidal antiinflammatory drugs (NSAIDs) Dantrolene Semisynthetic penicillins, tetracyclines Allopurinol, phenytoin Aspirin L-Tryptophan contaminant syndrome Ampicillin, penicillins, cephalosporins Granulocyte macrophage–colonystimulating factor (GM-CSF), interleukin (IL)-2 Minocycline, allopurinol, anticonvulsants

Pulmonary infiltrates Pleuropulmonary Hepatitis Hypersensitivity vasculitis Asthma, nasal polyps Eosinophilia–myalgia Asymptomatic Cytokine-mediated

DRESS (drug reaction with eosinophilia and systemic symptoms)

Adapted from Weller PF. Eosinophilia and eosinophil-related disorders. In: Adkinson NF, Jr., Yunginger JW, Busse WW, et al., eds. Allergy: Principles and Practice, 6th ed. Philadelphia, Penn.: Mosby; 2003:1105.

Adverse reactions to medications are a common cause of eosinophilia. Although often considered as hypersensitivity reactions, in most instances of drug-associated eosinophilia, the mechanism leading to eosinophilia is not understood. Eosinophilia may develop without other manifestations of adverse drug reactions, such as rashes or drug fevers. In addition, drug-induced eosinophilia may be associated with distinct clinicopathological patterns in which eosinophilia accompanies drug-induced diseases that are characteristically limited to specific organs with or without associated blood eosinophilia. When organ dysfunction develops, cessation of drug administration is necessary. Drug-induced interstitial nephritis may be accompanied by blood eosinophilia, and eosinophils may be detectable in urine. Unlike granulocyte–colony-stimulating factor (G-CSF) therapy, therapy with GM-CSF can lead to prominent blood and tissue eosinophilia. Administration of IL-2 or of IL-2-stimulated lymphocytes can be followed by the development of eosinophilia, most likely as a result of stimulated production of IL-5. Reactions to medications, often anticonvulsants, minocycline, and allopurinol, can elicit DRESS (drug reaction with eosinophilia and systemic symptoms).34 In addition to cutaneous eruptions, fever, lymphadenopathy, hepatitis, nephritis, atypical lymphocytosis, GI tract involvement, and eosinophilia are common but variable elements of this drug-induced syndrome, which can be fatal. The triggering medication must be stopped, and corticosteroids are often administered. Some primary immunodeficiency syndromes are associated with eosinophilia.35 Hyper-IgE syndrome is characterized by recurrent staphylococcal abscesses of the skin, lungs, and other sites; pruritic dermatitis; hyperimmunoglobulinemia E; and eosinophilia of blood, sputum, and tissues. Eosinophilia is characteristic of Omenn syndrome, combined immunodeficiency with hypereosinophilia (Chapter 35). Infiltration of eosinophils accompanies rejection of lung, kidney, and liver allografts. Tissue and blood eosinophilia occur early in the rejection process, and eosinophil counts and

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eosinophil granule protein levels (in urine, BAL fluids, and involved allograft tissues) have correlated with prognosis, severity, and response to rejection therapy.

Endocrine Diseases The loss of endogenous adrenoglucocorticosteroid production in Addison disease, adrenal hemorrhage, or hypopituitarism can cause increased blood eosinophilia, although usually not more than mild to moderate.

Other Causes of Eosinophilia The syndrome of atheromatous cholesterol embolization is at times associated with hypocomplementemia, eosinophilia, and eosinophiluria. Rarely, cases of hereditary eosinophilia among family members have been recognized. Irritation of serosal surfaces can be associated with eosinophilia, and related diseases can include Dressler syndrome; eosinophilic pleural effusions; peritoneal and, at times, blood eosinophilia developing during chronic peritoneal dialysis; and perhaps the eosinophilia that follows abdominal irradiation.

THERAPEUTIC PRINCIPLES Therapy of Specific Eosinophilic Diseases Eosinophil-Associated Diseases With Identifiable Etiologies Parasitic infections Treat causative parasite Drug-reaction related Terminate eliciting medication eosinophilias Adrenal insufficiency Corticosteroid replacement therapy Allergic/atopic diseases Varied, may include topical or inhaled corticosteroids Distinct Eosinophilic Syndromes Involving Specific Organs Eosinophilic pulmonary diseases: Acute eosinophilic pneumonia Corticosteroids Chronic eosinophilic pneumonia Corticosteroids, interferon-α Eosinophilic granulomatosis with Corticosteroids, interferon-α polyangiitis Hypereosinophilic Syndromes F/P-positive myeloproliferative Imatinib Lymphoproliferative and other Corticosteroids, interferon-α, hydroxyurea, anti–interleukin (IL)-5 monoclonal antibody (mAb), other

EVALUATION OF EOSINOPHILIA Because a diversity of disorders can be accompanied by eosinophilia, evaluation of the patient with eosinophilia requires a consideration of features based on the patient’s history, physical examination, and other laboratory, radiographic, or diagnostic tests.26,36,37 An initial approach can focus on identifying eosinophilic diseases that have a defined treatable etiology. These include infections with helminth parasites, and for these, the approach should be guided by information obtained from patient history about potential exposures; results of the history and physical examinations with regard to signs and symptoms of any clinically apparent associated illness; results of standard biochemical and radiographic tests for evidence of organ involvement; and results of specific parasitological tests, including potentially stool, urine,

blood, sputum, or tissue examinations, as well as results of serological tests.24 The duration and magnitude of the eosinophilia may suggest some entities, especially if it is prolonged or markedly elevated (see Table 24.1). Other causes of eosinophilia that are amenable to treatment include eosinophilia secondary to medications, for which cessation of the offending drug may be indicated if the eosinophilia is accompanied by organ damage. Likewise, if eosinophilia is secondary to glucocorticosteroid deficiency, diagnostic testing can corroborate this deficiency and lead to the administration of replacement corticosteroids and consequent resolution of the eosinophilia. Because allergic diseases usually are associated with at least some degree of eosinophilia, clinical and laboratory evidence of such disease should be sought. If the eosinophilia is not attributable to allergic diseases, parasitic infections, medications, or steroid deficiency, further evaluation will be guided by whether the patient has evidence of organ disease and, if so, which organs are involved (see Table 24.2). This is germane, for instance, in defining whether the patient has a distinct eosinophilic pulmonary, GI, or cutaneous syndrome. Bone marrow examinations in most patients with eosinophilia are not usually informative, revealing only evidence of enhanced eosinophilopoiesis; but bone marrow should be examined if there is suspicion of a hematological malignancy or myeloproliferative disorder. For patients with sustained eosinophilia who meet the criteria for HES, diagnostic testing should aim to identify which variant form of HES the patient may have, in which case, bone marrow examination is often needed (see Fig. 24.4).

ON THE HORIZON Identify the causes of those hypereosinophilic syndromes for which etiologies currently remain unknown. Delineation of the signaling mechanisms that govern the agonist-specific, differential secretion of cytokines that are preformed and stored within eosinophil granules and secretory vesicles. Continue to evaluate the therapeutic efficacies of anticytokine therapeutics, including anti–interleukin (IL)-5 neutralizing antibodies, in the treatment of the varied forms of eosinophilic diseases. Identify biomarkers that are predictive of eosinophil-mediated tissue damage and that can be used for clinical diagnostic and therapeutic monitoring tools.

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CHAPTER 24  Eosinophils and Eosinophilia

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MULTIPLE-CHOICE QUESTIONS 1. Which of the following may NOT contribute to or elicit eosinophilia? A. CD3−, CD4+ aberrant lymphocyte subsets B. FIP1L1-PDGFRα chromosomal gene rearrangement C. Giardia lamblia infection D. Strongyloides stercoralis infection 2. A 45-year-old male who has had eosinophilia of between 2500 and 5000/ mm3 documented for the past 6 months has been referred to you. Your evaluation could include: A. Flow cytometry for lymphocyte phenotyping B. Serum immunoglobulin E (IgE) C. Serum troponin D. Strongyloides enzyme-linked immunosorbent assay (ELISA) serology E. All of the above

3. Which three cytokines promote eosinophil development in bone marrow and sustain eosinophil viability? A. Transforming growth factor (TGF)-β, interleukin (IL)-2, IL-4 B. IL-7, IL-2, IL-13 C. Granulocyte macrophage–colony-stimulating factor (GMCSF), IL-3, IL-5 D. Interferon (INF)-γ, IL-8, IL-10