Biology of the eosinophil

Eosinophils contribute to IL-4 production and shape the T-helper cytokine profile and inflammatory response in pulmonary cryptococcosis

Susceptibility to infection with Cryptococcus neoformans is tightly determined by production of IL-4. In this study, we investigated the time course of IL-4 production and its innate cellular source in mice infected intranasally with C. neoformans. We show that pulmonary IL-4 production starts surprisingly late after 6 weeks of infection. Interestingly, in the lungs of infected mice, pulmonary T helper (Th) cells and eosinophils produce significant amounts of IL-4. In eosinophil-deficient ΔdblGATA mice, IL-33 receptor-expressing Th2s are significantly reduced, albeit not absent, whereas protective Th1 and Th17 responses are enhanced. In addition, recruitment of pulmonary inflammatory cells during infection with C. neoformans is reduced in the absence of eosinophils. These data expand previous findings emphasizing an exclusively destructive effector function by eosinophilic granulocytes. Moreover, in ΔdblGATA mice, fungal control is slightly enhanced in the lung; however, dissemination of Cryptococcus is not prevented. Therefore, eosinophils play an immunoregulatory role that contributes to Th2-dependent susceptibility in allergic inflammation during bronchopulmonary mycosis.

Eosinophils contribute to IL-4 production and shape the T-helper cytokine profile and inflammatory response in pulmonary cryptococcosis

Susceptibility to infection with Cryptococcus neoformans is tightly determined by production of IL-4. In this study, we investigated the time course of IL-4 production and its innate cellular source in mice infected intranasally with C. neoformans. We show that pulmonary IL-4 production starts surprisingly late after 6 weeks of infection. Interestingly, in the lungs of infected mice, pulmonary T helper (Th) cells and eosinophils produce significant amounts of IL-4. In eosinophil-deficient ΔdblGATA mice, IL-33 receptor-expressing Th2s are significantly reduced, albeit not absent, whereas protective Th1 and Th17 responses are enhanced. In addition, recruitment of pulmonary inflammatory cells during infection with C. neoformans is reduced in the absence of eosinophils. These data expand previous findings emphasizing an exclusively destructive effector function by eosinophilic granulocytes. Moreover, in ΔdblGATA mice, fungal control is slightly enhanced in the lung; however, dissemination of Cryptococcus is not prevented. Therefore, eosinophils play an immunoregulatory role that contributes to Th2-dependent susceptibility in allergic inflammation during bronchopulmonary mycosis.

Histopathology of experimental myiasis in mice as a result of infestation and experimental implantation of Dermatobia hominis larvae

A laboratory model of myiasis as a result of Dermatobia hominis (L.) larvae was developed using mice as hosts. Mice in three groups were each infested with one newly hatched larva and skin biopsies processed for histopathology at 4, 12, and 20 d postinfestation (dpi). Mice in three other groups were each subjected to implantation of one larva collected from an infested (donor) mouse at 4, 12, and 20 dpi. Skin lesions of these receptor mice were then assessed at 10, 14, and 6 d postimplantation (dpimp), respectively. The inflammatory process in infested mice at 4 dpi was discrete, consisting of a thin necrotic layer around the larva, edema, many neutrophils, few eosinophils, mast cells, and proliferation of fibroblasts. At 12 dpi, there was a thicker necrotic layer, edema, many neutrophils and eosinophils, few mast cells, neoformation of capillaries, proliferation of the endothelium and fibroblasts, and early stages of fibrosis. These histopathological characteristics together with fibrosis were observed over a large area of the lesion at 20 dpi. Mice submitted to larval implantations demonstrated similar skin histopathology to that seen in the infested rodents, 10 dpimp corresponding to 12 dpi and 6 or 14 dpimp to 20 dpi. In all mice, the progressive acute inflammatory process followed a sequence linked to factors such as size of larvae and presence of secretory-excretory products. Both infested mice and those implanted experimentally with D. hominis larvae were shown to be suitable models for the study of the parasite-host relationship in this important zoonotic myiasis.

Targeting eosinophil biology in asthma therapy

Due to their role as main effector cells in immune reactions against invading parasites, eosinophils have a plethora of molecules available to destroy these complex pathogens. Their role in allergic diseases such as bronchial asthma, where they do not have to conquer pathogens, is discussed controversially. However, since eosinophils were identified by Paul Ehrlich in tissue and sputum of patients with asthma, it was regarded that their important defensive role turns into its direct opposite so that these cells cause destruction of the airway tissue, ultimately leading to the formation of disease phenotype. Thus, eosinophils were identified as a prime target in therapeutic intervention of bronchial asthma. Over the last years, a number of mediators and receptors involved in the regulation of eosinophil recruitment, chemotaxis, activation, survival, and apoptosis have been identified. Some of these molecules have been addressed in vitro and in animal models of experimental asthma to evaluate their therapeutic potential in asthma. A few of these candidates have been tested in clinical studies, which produced surprising results questioning the role of eosinophils in asthma pathogenesis. This article summarizes these approaches and gives a critical overview about further candidate molecules that have been recently discussed as targets for an eosinophil-specific asthma therapy.

Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro

BACKGROUND

Mast cells (MCs) and eosinophils (Eos) are the key effector cells of the allergic reaction. Although classically associated with different stages of the response, the cells co-exist in the inflamed tissue in the late and chronic phases in high numbers and are likely to cross-talk. While some mediators of MCs are known to affect Eos biology and vice versa, paracrine and physical interplay between the two cells has not been described yet. We aimed to investigate whether intercellular MC-Eos communication could take place in the allergic response and exert functional bidirectional changes on the cells.

METHODS

Tissue sections from various allergic disorders were specifically stained for both cells. Human cord blood-derived MCs and peripheral blood Eos, co-cultured under different conditions, were studied by advanced microscopy and flow cytometry.

RESULTS

Several co-localized MC-Eos pairs were detected in human nasal polyps and asthmatic bronchi, as well in mouse atopic dermatitis. In vitro, MCs and Eos formed stable conjugates at high rates, with clear membrane contact. In the presence of MCs, Eos were significantly more viable under several co-culture conditions and at both IgE-activated and steroid-inhibited settings. MC regulation of Eos survival required communication through soluble mediators but was even more dependent on physical cell-cell contact.

CONCLUSIONS

Our findings provide the first evidence for a complex network of paracrine and membrane interactions between MCs and Eos. The prosurvival phenotype induced by this MC-Eos interplay may be critical for sustaining chronic allergic inflammation.

Histopathological analysis of initial cellular response in TLR-2 deficient mice experimentally infected by Leishmania (L.) amazonensis

Tegumentary leishmaniasis is an important public health problem in several countries. The capacity of the Leishmania species, at the initial moments of the infection, to invade and survive inside the host cells involves the interaction of surface molecules that are crucial in determining the evolution of the disease. Using C57BL/6 wild-type and TLR-2(-/-) mice infected with L. (L.) amazonensis, we demonstrated that TLR-2(-/-) mice presented eosinophilic granuloma in the ear dermis, different from C57BL/6 wild-type mice that presented a cellular profile characterized mainly by mononuclear cell infiltrates, besides neutrophils and eosinophils, during the two first week of infection. When the parasite load was evaluated, we found that the absence of TLR-2 lead to a significant reduction of the infection in deficient mice, when compared with C57BL/6 mice which were more susceptible to the infection. Using TLR-2 deficient mice, it was possible to show that the absence of this receptor determined the reduction of the parasite load and the recruitment of inflammatory cells during the two first weeks after L. (L.) amazonensis infection.

Immune dysregulation in the pathogenesis of pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) is a rare disease of the lung characterized by the accumulation of surfactant-derived lipoproteins within pulmonary alveolar macrophages and alveoli, resulting in respiratory insufficiency and increased infections. The disease is caused by a disruption in surfactant catabolism by alveolar macrophages due to loss of functional granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling. The underlying molecular mechanisms causing deficiencies in GM-CSF signaling are as follows: 1) high levels of neutralizing GM-CSF autoantibodies observed in autoimmune PAP; 2) mutations in CSF2RA, the gene encoding the alpha chain of the GM-CSF receptor, observed in hereditary PAP; and 3) reduced numbers and function of alveolar macrophages as a result of other clinical diseases seen in secondary PAP. Recent studies investigating the biology of GM-CSF have revealed that not only does this cytokine have an indispensable role in lung physiology, but it is also a critical regulator of innate immunity and lung host defense.

Reslizumab for pediatric eosinophilic esophagitis

Pediatric eosinophilic esophagitis is an inflammatory condition associated with marked eosinophil accumulation in the mucosal tissues of the esophagus. Eosinophils are major proinflammatory cells thought to make a major contribution to allergic diseases that affect the upper and lower airways, skin and GI tract. IL-5 is central to eosinophil maturation and release from the bone marrow, and their subsequent accumulation, activation and persistence in the tissues. Reslizumab (Cinquil, Ception Therapeutics Inc., PA, USA) is a humanized monoclonal antibody with potent IL-5 neutralizing effects that represents a potential treatment for eosinophilic diseases. This article considers the current status of the clinical development of reslizumab for pediatric eosinophilic esophagitis.

Increased HLA-DR expression on tissue eosinophils in eosinophilic esophagitis

OBJECTIVE

The aim of the study was to investigate whether eosinophils have increased human leukocyte antigen (HLA)-DR expression in subjects with eosinophilic esophagitis (EoE) compared with controls.

PATIENTS AND METHODS

Patients who were undergoing an upper endoscopy with biopsies for suspected gastroesophageal reflux disease (GERD) or EoE at Lucile Packard Children's Hospital were enrolled. In total, the blood and tissue samples of 10 healthy controls (HC), 11 subjects with GERD, and 10 with EoE were studied. Multiple tissue staining to identify eosinophils (via eosinophil cationic protein-clone EG2) and major histocompatibility complex class II cell surface receptors (via HLA-DR) was performed via immunohistochemistry. The peripheral blood was analyzed using flow cytometry to detect eosinophil HLA-DR expression among these subjects.

RESULTS

In the tissue, a greater proportion of eosinophils expressed HLA-DR among the subjects with EoE (mean 0.83 +/- 0.14, n = 9) relative to those with GERD (mean 0.18 +/- 0.19, n = 8, P < 0.01) and HC (mean 0.18 +/- 0.13, n = 6, P < 0.01). In total, 6 participants (4 HC subjects and 2 subjects with GERD) did not have any eosinophils identified on tissue staining and were unable to be included in the present statistical analysis. In the blood, there was no statistically significant difference in eosinophil HLA-DR expression among HC subjects (mean 415 +/- 217, n = 6), subjects with GERD (mean 507 +/- 429, n = 2), and those with EoE (mean 334 +/- 181, n = 6).

CONCLUSIONS

These data demonstrate that the eosinophils from the esophagus of subjects with EoE have increased HLA-DR expression within this tissue.

Murine lung eosinophil activation and chemokine production in allergic airway inflammation

Eosinophils play important roles in asthma and lung infections. Murine models are widely used for assessing the functional significance and mechanistic basis for eosinophil involvements in these diseases. However, little is known about tissue eosinophils in homeostasis. In addition, little data on eosinophil chemokine production during allergic airway inflammation are available. In this study, the properties and functions of homeostatic and activated eosinophils were compared. Eosinophils from normal tissues expressed costimulation and adhesion molecules B7-1, B7-2 and ICAM-1 for Ag presentation but little major histocompatibility complex (MHC) class II, and were found to be poor stimulators of T-cell proliferation. However, these eosinophils expressed high levels of chemokine mRNA including C10, macrophage inflammatory protein (MIP)-1alpha, MIP-1gamma, MIP-2, eotaxin and monocyte chemoattractant protein-5 (MCP-5), and produced chemokine proteins. Eosinophil intracellular chemokines decreased rapidly with concomitant surface marker downregulation upon in vitro culturing consistent with piecemeal degranulation. Lung eosinophils from mice with induced allergic airway inflammation exhibited increased chemokines mRNA expression and chemokines protein production and upregulated MHC class II and CD11c expression. They were also found to be the predominant producers of the CCR1 ligands CCL6/C10 and CCL9/MIP-1gamma in inflamed lungs. Eosinophil production of C10 and MIP-1gamma correlated with the marked influx of CD11b(high) lung dendritic cells during allergic airway inflammation and the high expression of CCR1 on these dendritic cells (DCs). The study provided baseline information on tissue eosinophils, documented the upregulation of activation markers and chemokine production in activated eosinophils, and indicated that eosinophils were a key chemokine-producing cell type in allergic lung inflammation.

Practical approach to the patient with hypereosinophilia

Markedly increased blood eosinophilia (ie, > or =1.5 x 10(9)/L), whether discovered fortuitously or found with signs and symptoms of associated organ involvement, commands diagnostic evaluation and often therapeutic interventions. This degree of hypereosinophilia is often but not uniformly associated with eosinophilic infiltration of tissues that can potentially lead to irreversible, life-threatening organ damage. Initial approaches focus on ascertaining that eosinophilia is not secondary to other underlying disease processes, including helminthic parasite infections, varied types of adverse reactions to medications, and other eosinophil-associated syndromes, such as eosinophilic gastroenteritides, eosinophilic pneumonias, and Churg-Strauss syndrome vasculitis. If evaluations exclude eosinophilia attributable to secondary causes or other eosinophil-related syndromes or organ-specific diseases, attention must be directed to considerations of varied other forms of the hypereosinophilic syndromes, which include myeloproliferative variants, lymphocytic variants, and many of still unknown causes. Cognizant of the capacities of eosinophils to mediate tissue damage, the varied causes for hypereosinophilia are considered, and a contemporary stepwise practical approach to the diagnosis and treatment of patients with hypereosinophilia is presented.

The activity of medicinal plants and secondary metabolites on eosinophilic inflammation

Eosinophils are leukocytes that are present in several body compartments and in the blood at relatively low numbers under normal conditions. However, an increase in the number of eosinophils, in the blood or in the tissues, is observed in allergic or parasitic disorders. Although some progress has been made in understanding the development of eosinophil-mediated inflammation in allergic and parasitic diseases, the discovery of new compounds to control eosinophilia has lagged behind other advances. Plant-derived secondary metabolites are the basis for many drugs currently used to treat pathologic conditions, including eosinophilic diseases. Several studies, including our own, have demonstrated that plant extracts and secondary metabolites can reduce eosinophilia and eosinophil recruitment in different experimental animal models. In this review, we summarize these studies and describe the anti-eosinophilic activity of various plant extracts, such as Ginkgo biloba, Allium cepa, and Lafoensia pacari, as well as those of secondary metabolites (compounds isolated from plant extracts), such as quercetin and ellagic acid. In addition, we highlight the medical potential of these plant-derived compounds for treating eosinophil-mediated inflammation, such as asthma and allergy.

IgE, mast cells, basophils, and eosinophils

IgE, mast cells, basophils, and eosinophils are essential components of allergic inflammation. Antigen-specific IgE production, with subsequent fixation of IgE to FcepsilonRI receptors on mast cells and basophils, is central to the initiation and propagation of immediate hypersensitivity reactions. Mast cells, basophils, and eosinophils are central effector cells in allergic inflammation, as well as in innate and adaptive immunity. This review highlights what is known about these components and their roles in disease pathogenesis.

Mucosal immunology, eosinophilic esophagitis, and other intestinal inflammatory diseases

The gastrointestinal mucosa constitutes the largest host-environment interface of the body. It uses both innate and adaptive immune mechanisms to provide protection from the diverse onslaught of foods, microbes, and other ingested products. The innate immune system is genetically encoded and evolutionarily ancient, possesses no memory, and lacks diversity. In contrast, the adaptive immune system is quite diverse, develops memory, and undergoes expansion after stimulation. The gastrointestinal mucosa is charged with the difficult task of mounting protective responses against invading microorganisms while simultaneously maintaining an overall state of nonresponsiveness or tolerance to innocuous substances, such as commensal bacteria and food antigens. Perturbation or malfunction of these complex protective mechanisms results in diseases, such as inflammatory bowel diseases, celiac disease, or eosinophilic gastrointestinal diseases.

Cysteinyl leukotrienes acting via granule membrane-expressed receptors elicit secretion from within cell-free human eosinophil granules

BACKGROUND

Cysteinyl leukotrienes (cysLTs) are recognized to act via receptors (cysLTRs) expressed on cell surface plasma membranes. Agents that block cysLT(1) receptor (cysLT(1)R) are therapeutics for allergic disorders. Eosinophils contain multiple preformed proteins stored within their intracellular granules. Cell-free eosinophil granules are present extracellularly as intact membrane-bound organelles in sites associated with eosinophil infiltration, including asthma, rhinitis, and urticaria, but have unknown functional capabilities.

OBJECTIVE

We evaluated the expression of cysLTRs on eosinophil granule membranes and their functional roles in eliciting protein secretion from within eosinophil granules.

METHODS

We studied secretory responses of human eosinophil granules isolated by subcellular fractionation. Granules were stimulated with cysLTs, and eosinophil cationic protein and cytokines were measured in the supernatants. Receptor expression on granule membranes and eosinophils was evaluated by flow cytometry and Western blot.

RESULTS

We report that receptors for cysLTs, cysLT(1)R, cysLT(2) receptor, and the purinergic P2Y12 receptor, are expressed on eosinophil granule membranes. Leukotriene (LT) C(4) and extracellularly generated LTD(4) and LTE(4) stimulated isolated eosinophil granules to secrete eosinophil cationic protein. MRS 2395, a P2Y12 receptor antagonist, inhibited cysLT-induced eosinophil cationic protein release. Montelukast, likely not solely as an inhibitor of cysLT(1)R, inhibited eosinophil cationic protein release elicited by LTC(4) and LTD(4) as well as by LTE(4).

CONCLUSION

These studies identify previously unrecognized sites of localization, the membranes of intracellular eosinophil granule organelles, and function for cysLT-responsive receptors that mediate cysteinyl leukotriene-stimulated secretion from within eosinophil granules, including those present extracellularly.

Eosinophil survival and apoptosis in health and disease

Eosinophilia is common feature of many disorders, including allergic diseases. There are many factors that influence the production, migration, survival and death of the eosinophil. Apoptosis is the most common form of physiological cell death and a necessary process to maintain but limit cell numbers in humans and other species. It has been directly demonstrated that eosinophil apoptosis is delayed in allergic inflammatory sites, and that this mechanism contributes to the expansion of eosinophil numbers within tissues. Among the proteins known to influence hematopoiesis and survival, expression of the cytokine interleukin-5 appears to be uniquely important and specific for eosinophils. In contrast, eosinophil death can result from withdrawal of survival factors, but also by activation of pro-apoptotic pathways via death factors. Recent observations suggest a role for cell surface death receptors and mitochondria in facilitating eosinophil apoptosis, although the mechanisms that trigger each of these death pathways remain incompletely delineated. Ultimately, the control of eosinophil apoptosis may someday become another therapeutic strategy for treating allergic diseases and other eosinophil-associated disorders.

Functional extracellular eosinophil granules: novel implications in eosinophil immunobiology

Human eosinophils contain within their cytoplasmic granules multiple preformed proteins, including over three dozen cytokines with nominal Th1, Th2 and immunoregulatory capabilities, and four distinctive cationic proteins. The secretion of these granule-derived proteins within eosinophils occurs principally by a mechanism whereby selected proteins are mobilized into vesicles for transport to and release at the cell surface. In contrast, the enigmatic presence of membrane-bound cell-free granules extruded from eosinophils has been long recognized in tissues associated with eosinophilia, including allergic diseases and responses to helminths. Functional capabilities for extracellular granules have recently been demonstrated. Eosinophil granules express cytokine receptors on their membranes and function, upon extrusion from eosinophils, as independent secretory organelles releasing granule constituents in response to activating cytokines and chemokines. We provide an update on the processes that mediate selective protein secretion from within eosinophil granules both as intracellular organelles and, as novelly demonstrated, as cell-free extracellular structures.