Differential regulation of human eosinophil IL-3, IL-5, and GM-CSF receptor alpha-chain expression by cytokines: IL-3, IL-5, and GM-CSF down-regulate IL-5 receptor alpha expression with loss of IL-5 responsiveness, but up-regulate IL-3 receptor alpha expression

Activation states of blood eosinophils in asthma

Asthma is characterized by airway inflammation rich in eosinophils. Airway eosinophilia is associated with exacerbations and has been suggested to play a role in airway remodelling. Recruitment of eosinophils from the circulation requires that blood eosinophils become activated, leading to their arrest on the endothelium and extravasation. Circulating eosinophils can be envisioned as potentially being in different activation states, including non-activated, pre-activated or 'primed', or fully activated. In addition, the circulation can potentially be deficient of pre-activated or activated eosinophils, because such cells have marginated on activated endothelium or extravasated into the tissue. A number of eosinophil surface proteins, including CD69, L-selectin, intercellular adhesion molecule-1 (ICAM-1, CD54), CD44, P-selectin glycoprotein ligand-1 (PSGL-1, CD162), cytokine receptors, Fc receptors, integrins including αM integrin (CD11b), and activated conformations of Fc receptors and integrins, have been proposed to report cell activation. Variation in eosinophil activation states may be associated with asthma activity. Eosinophil surface proteins proposed to be activation markers, with a particular focus on integrins, and evidence for associations between activation states of blood eosinophils and features of asthma are reviewed here. Partial activation of β1 and β2 integrins on blood eosinophils, reported by monoclonal antibodies (mAbs) N29 and KIM-127, is associated with impaired pulmonary function and airway eosinophilia, respectively, in non-severe asthma. The association with lung function does not occur in severe asthma, presumably due to greater eosinophil extravasation, specifically of activated or pre-activated cells, in severe disease.

Semaphorin 7A is expressed on airway eosinophils and upregulated by IL-5 family cytokines

Semaphorin 7A (sema7a) plays a major role in TGF-β1-induced lung fibrosis. Based on the accumulating evidence that eosinophils contribute to fibrosis/remodeling in the airway, we hypothesized that airway eosinophils may be a significant source of sema7a. In vivo, sema7a was expressed on the surface of circulating eosinophils and upregulated on bronchoalveolar lavage eosinophils obtained after segmental bronchoprovocation with allergen. Based on mRNA levels in unfractionated and isolated bronchoalveolar cells, eosinophils are the predominant source of sema7a. In vitro, among the members of the IL-5-family cytokines, sema7a protein on the surface of blood eosinophils was increased more by IL-3 than by GM-CSF or IL-5. Cytokine-induced expression of cell surface sema7a required translation of newly synthesized protein. Finally, a recombinant sema7a induced alpha-smooth muscle actin production in human bronchial fibroblasts. semaphorin 7A is a potentially important modulator of eosinophil profibrotic functions in the airway remodeling of patients with chronic asthma.

Human airway eosinophils exhibit preferential reduction in STAT signaling capacity and increased CISH expression

Allergic asthma, a chronic respiratory disorder marked by inflammation and recurrent airflow obstruction, is associated with elevated levels of IL-5 family cytokines and elevated numbers of eosinophils (EOS). IL-5 family cytokines elongate peripheral blood EOS (EOS(PB)) viability, recruit EOS(PB) to the airways, and, at higher concentrations, induce degranulation and reactive oxygen species generation. Although airway EOS (EOS(A)) remain signal ready in that GM-CSF treatment induces degranulation, treatment of EOS(A) with IL-5 family cytokines no longer confers a survival advantage. Because the IL-5 family receptors have common signaling capacity, but are uncoupled from EOS(A) survival, whereas other IL-5 family induced endpoints remain functional, we tested the hypothesis that EOS(A) possess a JAK/STAT-specific regulatory mechanism (because JAK/STAT signaling is critical to EOS survival). We found that IL-5 family-induced STAT3 and STAT5 phosphorylation is attenuated in EOS(A) relative to blood EOS from airway allergen-challenged donors. However, IL-5 family-induced ERK1/2 phosphorylation is not altered between EOS(A) and EOS from airway allergen-challenged donors. These observations suggest EOS(A) possess a regulatory mechanism for suppressing STAT signaling distinct from ERK1/2 activation. Furthermore, we found, in EOS(PB), IL-5 family cytokines induce members of the suppressors of cytokine signaling (SOCS) genes, CISH and SOCS1. Additionally, following allergen challenge, EOS(A) express significantly more CISH and SOCS1 mRNA and CISH protein than EOS(PB) counterparts. In EOS(PB), long-term pretreatment with IL-5 family cytokines, to varying degrees, attenuates IL-5 family-induced STAT5 phosphorylation. These data support a model in which IL-5 family cytokines trigger a selective downregulation mechanism in EOS(A) for JAK/STAT pathways.

Retinoic acids up-regulate functional eosinophil-driving receptor CCR3

Eotaxins and their receptor CCR3 have a definitive role for tissue accumulation of eosinophils both under homeostatic and pathologic conditions. However, physiological stimuli that can up-regulate CCR3 in blood-derived human eosinophils have not been recognized. As a prior gene microarray study revealed up-regulation of CCR3 in eosinophils stimulated with retinoic acids (RAs), the expression of functional CCR3 was examined. We found that 9-cis RA and all-trans RA (ATRA) significantly induced surface CCR3 expression regardless of the presence of IL-3 or IL-5. Pharmacological manipulations with receptor-specific agonists and antagonists indicated that retinoic acid receptor-α activation is critical for CCR3 up-regulation. RA-induced CCR3 was associated with its functional capacity, in terms of the calcium mobilization and chemotactic response to eotaxin-1 (CCL11). Our study suggests an important role of vitamin A derivatives in the tissue accumulation of eosinophils.

Toll-like receptor-mediated eosinophil-basophil differentiation: autocrine signalling by granulocyte-macrophage colony-stimulating factor in cord blood haematopoietic progenitors

Eosinophils are multi-functional leucocytes that play a role in inflammatory processes including allergy and infection. Although bone marrow (BM) inflammatory cells are the main source of eosinophil-basophil (Eo/B) differentiation-inducing cytokines, a recent role has been demonstrated for cytokine induction through Toll-like receptor (TLR)-mediated signalling in BM progenitors. Having previously demonstrated that cord blood (CB) progenitors induce Eo/B colony-forming units (CFU) after lipopolysaccharide (LPS) stimulation, we sought to investigate the intracellular mechanisms by which LPS induces Eo/B differentiation. Freshly isolated CD34-enriched human CB cells were stimulated with LPS (and/or pharmacological inhibitors) and assessed for alterations in haematopoietic cytokine receptor expression and signalling pathways by flow cytometry, Eo/B CFU in methylcellulose cultures, and cytokine secretion using Luminex assays. The LPS stimulation resulted in a significant increase in granulocyte-macrophage colony-stimulating factor (GM-CSF)-responsive, as opposed to interleukin-5-responsive, Eo/B CFU, which also correlated with significant increases in CD34(+) cell GM-CSFRα expression. Functionally, CB CD34(+) cells secrete abundant amounts of GM-CSF following LPS stimulation, via a p38 mitogen-activated protein kinase (MAPK)-dependent mechanism; this secretion was responsible for Eo/B CFU formation ex vivo, as shown by antibody blockade. We show for the first time that LPS stimulation of CB progenitor cells results in autocrine activation of p38 MAPK-dependent GM-CSF secretion facilitating Eo/B differentiation ex vivo. This work provides evidence that early life exposure to products of bacterial agents can modulate Eo/B differentiation, representing a novel mechanism by which progenitor cells can respond to microbial stimuli and so affect immune and inflammatory responses.

Eosinophils in fungus-associated allergic pulmonary disease

Asthma is frequently caused and/or exacerbated by sensitization to fungal allergens, which are ubiquitous in many indoor and outdoor environments. Severe asthma with fungal sensitization is characterized by airway hyperresponsiveness and bronchial constriction in response to an inhaled allergen that is worsened by environmental exposure to airborne fungi and which leads to a disease course that is often very difficult to treat with standard asthma therapies. As a result of complex interactions among inflammatory cells, structural cells, and the intercellular matrix of the allergic lung, patients with sensitization to fungal allergens may experience a greater degree of airway wall remodeling and progressive, accumulated pulmonary dysfunction as part of the disease sequela. From their development in the bone marrow to their recruitment to the lung via chemokine and cytokine networks, eosinophils form an important component of the inflammatory milieu that is associated with this syndrome. Eosinophils are recognized as complex multi-factorial leukocytes with diverse functions in the context of allergic fungal asthma. In this review, we will consider recent advances in our understanding of the molecular mechanisms that are associated with eosinophil development and migration to the allergic lung in response to fungal inhalation, along with the eosinophil’s function in the immune response to and the immunopathology attributed to fungus-associated allergic pulmonary disease.

The LINA cohort: indoor chemical exposure, circulating eosinophil/basophil (Eo/B) progenitors and early life skin manifestations

BACKGROUND

Hematopoietic progenitor cells, especially those committed to the Eo/B lineage, are known to contribute to allergic inflammation.

OBJECTIVE

The aim of the present study was to investigate whether environmental factors are associated with changes in numbers of circulating Eo/B progenitors at 1 year of age.

METHODS

Peripheral blood from 60 1-year-old children enrolled in the LINA (Lifestyle and environmental factors and their Influence on Newborns Allergy risk) birth cohort was assessed for Eo/B progenitor cells (Eo/B CFU) using standardized and validated methylcellulose assays. Frozen peripheral blood mononuclear cells (PBMC) were cultured in the presence of IL-3, IL-5 or GM-CSF, and Eo/B CFUs enumerated. Clinical outcomes and exposure to environmental tobacco smoke (ETS) were documented by standardized questionnaires, and indoor volatile organic compound (VOC) concentrations were assessed by passive sampling.

RESULTS

Children with skin manifestations (atopic dermatitis or cradle cap) within the first year of life had higher numbers of circulating IL-3-, IL-5- or GM-CSF-stimulated Eo/B CFUs (P < 0.05) at 1 year. In children with cradle cap, a positive correlation was found between Eo/B CFUs and exposure to ETS-related VOCs during pregnancy or at 1 year of age (P < 0.05).

CONCLUSIONS AND CLINICAL RELEVANCE

This is the first demonstration that environmental exposures are positively associated with levels of circulating Eo/B progenitors. The recruitment and differentiation of Eo/B progenitors in response to environmental triggers may play a role in the development of skin manifestations during the first year of life.

Opposing regulation of PROX1 by interleukin-3 receptor and NOTCH directs differential host cell fate reprogramming by Kaposi sarcoma herpes virus

Lymphatic endothelial cells (LECs) are differentiated from blood vascular endothelial cells (BECs) during embryogenesis and this physiological cell fate specification is controlled by PROX1, the master regulator for lymphatic development. When Kaposi sarcoma herpes virus (KSHV) infects host cells, it activates the otherwise silenced embryonic endothelial differentiation program and reprograms their cell fates. Interestingly, previous studies demonstrated that KSHV drives BECs to acquire a partial lymphatic phenotype by upregulating PROX1 (forward reprogramming), but stimulates LECs to regain some BEC-signature genes by downregulating PROX1 (reverse reprogramming). Despite the significance of this KSHV-induced bidirectional cell fate reprogramming in KS pathogenesis, its underlying molecular mechanism remains undefined. Here, we report that IL3 receptor alpha (IL3Rα) and NOTCH play integral roles in the host cell type-specific regulation of PROX1 by KSHV. In BECs, KSHV upregulates IL3Rα and phosphorylates STAT5, which binds and activates the PROX1 promoter. In LECs, however, PROX1 was rather downregulated by KSHV-induced NOTCH signal via HEY1, which binds and represses the PROX1 promoter. Moreover, PROX1 was found to be required to maintain HEY1 expression in LECs, establishing a reciprocal regulation between PROX1 and HEY1. Upon co-activation of IL3Rα and NOTCH, PROX1 was upregulated in BECs, but downregulated in LECs. Together, our study provides the molecular mechanism underlying the cell type-specific endothelial fate reprogramming by KSHV.

Kaposi's sarcoma (KS) is one of the most common neoplasms in HIV-positive individuals and organ transplant recipients. KS-associated herpes virus (KSHV), also known as human herpes virus (HHV)-8, has been identified as the causative agent and infects endothelial cells to form KS. Importantly, we and others have discovered that when KSHV infects endothelial cells of blood vessels, it reprograms host cells to resemble endothelial cells in lymphatic vessels. On the other hand, when KSHV infects endothelial cells in lymphatic vessels, the virus directs the host cells to partially obtain the phenotypes of blood vessel endothelial cells. These host cell reprogramming represent abnormal pathological processes, which are not as complete as the physiological process occurring during embryonic development. Currently, it is not clear how and why this cancer causing virus modifies the fate of its host cells. In this study, we aimed to dissect the molecular mechanism underlying the virus-induced host cell fate reprogramming and found two important cellular signaling pathways, interleukin-3 and Notch, playing key roles in the pathological events. Our current study provides a better understanding of KS tumorigenesis with a potential implication in a new KS therapy.

Role of cytokines in systemic lupus erythematosus: recent progress from GWAS and sequencing

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder, known to have a strong genetic component. Concordance between monozygotic twins is approximately 30-40%, which is 8-20 times higher than that of dizygotic twins. In the last decade, genome-wide approaches to understanding SLE have yielded many candidate genes, which are important to understanding the pathophysiology of the disease and potential targets for pharmaceutical intervention. In this paper, we focus on the role of cytokines and examine how genome-wide association studies, copy number variation studies, and next-generation sequencing are being employed to understand the etiology of SLE. Prominent genes identified by these approaches include BLK, FCγR3B, and TREX1. Our goal is to present a brief overview of genomic approaches to SLE and to introduce some of the key discussion points pertinent to the field.

Molecular and clinical rationale for therapeutic targeting of interleukin-5 and its receptor

Interleukin-5 is a Th2 homodimeric cytokine involved in the differentiation, maturation, migration, development, survival, trafficking and effector function of blood and local tissue eosinophils, in addition to basophils and mast cells. The IL-5 receptor (IL-5R) consists of an IL-5-specific α subunit that interacts in conformationally dynamic ways with the receptor's βc subunit, an aggregate of domains it shares with binding sites of IL-3 and granulocyte-macrophage colony-stimulating factor. IL-5 and IL-5R drive allergic and inflammatory immune responses characterizing numerous diseases, such as asthma, atopic dermatitis, chronic obstructive pulmonary disease, eosinophilic gastrointestinal diseases, hyper-eosinophilic syndrome, Churg-Strauss syndrome and eosinophilic nasal polyposis. Although corticosteroid therapy is the primary treatment for these diseases, a substantial number of patients exhibit incomplete responses and suffer side-effects. Two monoclonal antibodies have been designed to neutralize IL-5 (mepolizumab and reslizumab). Both antibodies have demonstrated the ability to reduce blood and tissue eosinophil counts. One additional monoclonal antibody, benralizumab (MEDI-563), has been developed to target IL-5R and attenuate eosinophilia through antibody-dependent cellular cytotoxicity. All three monoclonal antibodies are being clinically evaluated. Antisense oligonucleotide technology targeting the common βc IL-5R subunit is also being used therapeutically to inhibit IL-5-mediated effects (TPI ASM8). Small interfering RNA technology has also been used therapeutically to inhibit the expression of IL-5 in animal models. This review summarizes the structural interactions between IL-5 and IL-5R and the functional consequences of such interactions, and describes the pre-clinical and clinical evidence supporting IL-5R as a therapeutic target.

IL-5 receptor α levels in patients with marked eosinophilia or mastocytosis

BACKGROUND

IL-5 plays a central role in the development and maintenance of eosinophilia (EO) and eosinophil activation in a wide variety of eosinophilic disorders. Although IL-5, IL-3, and GM-CSF can modulate the expression of IL-5 receptor α (IL-5Rα) on eosinophils in vitro, little is known about soluble and surface IL-5Rα levels in vivo.

OBJECTIVE

To assess soluble and surface IL-5Rα levels in patients with EO and/or mastocytosis.

METHODS

Surface IL-5Rα expression was assessed by flow cytometry in blood and/or bone marrow from subjects with EO (n = 39) and systemic mastocytosis (n = 8) and from normal volunteers (n = 28). Soluble IL-5Rα (sIL-5Rα) level was measured in a cohort of 177 untreated subjects and correlated with EO, eosinophil activation, and serum tryptase and cytokine levels.

RESULTS

IL-5Rα expression on eosinophils inversely correlated with EO (r = -0.48; P < .0001), whereas serum levels of sIL-5Rα increased with the eosinophil count (r = 0.56; P < .0001) and serum IL-5 (r = 0.40; P < .0001) and IL-13 (r = 0.29; P = .004) levels. Of interest, sIL-5Rα level was significantly elevated in patients with systemic mastocytosis without EO. Although sIL-5Rα levels correlated with serum tryptase levels in these patients, eosinophil activation, assessed by CD69 expression on eosinophils and serum eosinophil-derived neurotoxin levels, was increased compared with that in normal subjects.

CONCLUSIONS

These data are consistent with an in vivo IL-5Rα regulatory pathway in human eosinophils similar to that described in vitro and involving a balance between soluble and surface receptor levels. This may have implications with respect to the use of novel therapeutic agents targeting IL-5 and its receptor in patients with EO and/or mastocytosis.

Cytokine/anti-cytokine therapy - novel treatments for asthma?

Asthma is a chronic inflammatory disease of the airways and there are no preventions or cures. Inflammatory cells through the secretion of cytokines and pro-inflammatory molecules are thought to play a critical role in pathogenesis. Type 2 CD4(+) lymphocytes (Th2 cells) and their cytokines predominate in mild to moderate allergic asthma, whereas severe steroid-resistant asthma has more of a mixed Th2/Th1 phenotype with a Th17 component. Other immune cells, particularly neutrophils, macrophages and dendritic cells, as well structural cells such as epithelial and airway smooth muscle cells also produce disease-associated cytokines in asthma. Increased levels of these immune cells and cytokines have been identified in clinical samples and their potential role in disease demonstrated in studies using mouse models of asthma. Clinical trials with inhibitors of cytokines such as interleukin (IL)-4, -5 and tumour necrosis factor-α have had success in some studies but not others. This may reflect the design of the clinical trials, including treatments regimes and the patient population included in these studies. IL-13, -9 and granulocyte-macrophage colony-stimulating factor are currently being evaluated in clinical trials or preclinically and the outcome of these studies is eagerly awaited. Roles for IL-25, -33, thymic stromal lymphopoietin, interferon-γ, IL-17 and -27 in the regulation of asthma are just emerging, identifying new ways to treat inflammation. Careful interpretation of results from mouse studies will inform the development and application of therapeutic approaches for asthma. The most effective approaches may be combination therapies that suppress multiple cytokines and a range of redundant and disconnected pathways that separately contribute to asthma pathogenesis. Astute application of these approaches may eventually lead to the development of effective asthma therapeutics. Here we review the current state of knowledge in the field.

MEDI-563, a humanized anti-IL-5 receptor alpha mAb with enhanced antibody-dependent cell-mediated cytotoxicity function

BACKGROUND

Peripheral blood eosinophilia and lung mucosal eosinophil infiltration are hallmarks of bronchial asthma. IL-5 is a critical cytokine for eosinophil maturation, survival, and mobilization. Attempts to target eosinophils for the treatment of asthma by means of IL-5 neutralization have only resulted in partial removal of airway eosinophils, and this warrants the development of more effective interventions to further explore the role of eosinophils in the clinical expression of asthma.

OBJECTIVE

We sought to develop a novel humanized anti-IL-5 receptor alpha (IL-5Ralpha) mAb with enhanced effector function (MEDI-563) that potently depletes circulating and tissue-resident eosinophils and basophils for the treatment of asthma.

METHODS

We used surface plasmon resonance to determine the binding affinity of MEDI-563 to FcgammaRIIIa. Primary human eosinophils and basophils were used to demonstrate antibody-dependent cell-mediated cytotoxicity. The binding epitope of MEDI-563 on IL-5Ralpha was determined by using site-directed mutagenesis. The consequences of MEDI-563 administration on peripheral blood and bone marrow eosinophil depletion was investigated in nonhuman primates.

RESULTS

MEDI-563 binds to an epitope on IL-5Ralpha that is in close proximity to the IL-5 binding site, and it inhibits IL-5-mediated cell proliferation. MEDI-563 potently induces antibody-dependent cell-mediated cytotoxicity of both eosinophils (half-maximal effective concentration = 0.9 pmol/L) and basophils (half-maximal effective concentration = 0.5 pmol/L) in vitro. In nonhuman primates MEDI-563 depletes blood eosinophils and eosinophil precursors in the bone marrow.

CONCLUSIONS

MEDI-563 might provide a novel approach for the treatment of asthma through active antibody-dependent cell-mediated depletion of eosinophils and basophils rather than through passive removal of IL-5.

Hemopoietic progenitors: the role of eosinophil/basophil progenitors in allergic airway inflammation

Progenitor cells play important roles in the physiology and homeostasis of the overall hemopoietic system. The majority of hemopoietic activity takes place in the bone marrow, under the influence of resident marrow stromal cells, accessory cells, and/or their products. This constitutes the complex network of the hemopoietic inductive microenvironment, which is crucial for providing signals necessary for the maintenance of populations of progenitors at varying stages of lineage commitment. Accumulation of eosinophils and basophils in tissues is characteristic of allergic inflammation. A large body of evidence now exists which confirms that these tissue inflammatory events are coincident with relevant changes in progenitors; it has thus been hypothesized that the observed changes in mature cell numbers occur directly or indirectly as a result of differentiation of lineage-committed eosinophil/basophil, and perhaps other, progenitor cells. Differentiation and maturation of hemopoietic cells have traditionally been thought to be restricted to the bone marrow microenvironment. More recently, evidence has accumulated to suggest that some hemopoietic cells present in allergic tissue may be recruited from the bone marrow, traffic through the peripheral circulation and into tissues to participate in the ongoing inflammatory process at these distal sites. The clinical administration of monotherapy with topical corticosteroids, oral cysteinyl leukotriene antagonists and cytokine antagonists such as antibodies to interleukin-5, suggest that suppression of hemopoietic contributions to allergic inflammation may be necessary for full control of allergic inflammation and disease manifestations. In addition to progenitors being targets of therapy, they may well determine how and whether allergic inflammation is generated in early life, thus serving as biomarkers of disease.

Haemopoietic processes in allergic disease: eosinophil/basophil development

Haemopoietic myeloid progenitors contribute to the ongoing recruitment of pro-inflammatory cells, such as eosinophils and basophils (Eo/B), to target tissue sites in allergic diseases. It is apparent that the development of allergic inflammation is critically dependent on the ability of the bone marrow to support the proliferation, differentiation and mobilization of haemopoietic progenitors. The haemopoietic inductive microenvironment in the bone marrow is crucial for providing signals necessary for maintenance of progenitor populations at varying stages of lineage commitment and permitting these cells to circulate in the bloodstream. Progenitors demonstrate responsiveness to specific cytokines, which varies with stage of differentiation. Pro-inflammatory signals, Th2 cytokines in particular, generated following allergen challenge, can impact on haemopoietic progenitor differentiation and mobilization, leading to accelerated Eo/B production. Allergen inhalation by allergic asthmatics induces a time-dependent change in cytokine levels within the bone marrow compartment, influencing differentiation of Eo/B progenitors, as evidenced by the relationship between increased bone marrow IL-5 levels and Eo/B production. It is proposed that inhaled allergen induces trafficking of IL-5-producing T lymphocytes to the bone marrow, further promoting eosinophilopoiesis through IL-5R signalling. In this manner, Th2 lymphocyte trafficking from the airway may regulate events occurring in the bone marrow. Negative regulators of Eo/B differentiation, including Th1 cytokines, may prove to be important for restoring homeostasis. Eo/B progenitors are also altered in cord blood of infants at risk of atopy and asthma, offering a potential biomarker for, and raising the possibility that Eo/B progenitors are directly involved in the development of allergic disease. For example, changes in the expression of haemopoietic cytokine receptors on cord blood progenitor cells are associated with maternal allergic sensitization, atopic risk and its development, suggesting that haemopoietic processes underlying the allergic phenotype may begin to evolve in the perinatal period.

Differential expression of the interleukin 5 receptor alpha isoforms in blood and tissue eosinophils of nasal polyp patients

BACKGROUND

Given the key role of interleukin-5 (IL-5) in eosinophil function, we investigated the regulated expression of the membrane-anchored (TM-IL-5Ralpha) isoform, or a secreted (SOL IL-5Ralpha) isoform, on both protein and transcript level in vitro and in vivo.

METHODS

A real-time PCR, FACS and ELISA were established to determine IL-5Ralpha isoform expression in peripheral blood and nasal tissue from control subjects and nasal polyp (NP) patients with or without asthma. Human peripheral blood eosinophils were incubated with IL-5 and were analyzed for SOL-IL-5Ralpha and TM-IL-5Ralpha mRNA and protein levels in comparison with CD-69 expression.

RESULTS

SOL-IL-5Ralpha and TM-IL-5Ralpha mRNA and protein expression was significantly increased in NP vs controls. In polyp tissue, SOL-IL-5Ralpha expression correlated to disease severity and eosinophils counts, whereas TM-IL-5Ralpha levels were inversely correlated to eosinophils counts and SOL-IL-5Ralpha expression. FACS analysis revealed increased CD-69 and decreased TM-IL-5Ralpha expression in NP tissue eosinophils vs blood eosinophils. Incubation of blood eosinophils with IL-5 caused up-regulation of CD-69 and down-regulation of TM-IL-5Ralpha after 2 and 24 h.

CONCLUSION

The expression of SOL-IL-5Ralpha and TM-IL-5Ralpha differs according to the eosinophil activation state and localization in the body (blood vs tissue) and may therefore be involved in the fine-tuning of the eosinophil homeostasis. Exposure of eosinophils to IL-5 reduces their responsiveness to IL-5 by regulated expression of the IL-5Ralpha isoforms. Since, TM-IL-5Ralpha is down-regulated and SOL-IL-5Ralpha (antagonistic) is upregulated in NP tissue, our findings are important to understand the clinical trials with anti-IL-5 in humans.

Interleukin 5 in the link between the innate and acquired immune response

Interleukin-5 (IL-5) is an interdigitating homodimeric glycoprotein that is initially identified by its ability to support the in vitro growth and differentiation of mouse B cells and eosinophils. IL-5 transgenic mouse shows two predominant features, remarkable increase in B-1 cells resulting in enhanced serum antibody levels, predominantly IgM, IgA, and IgE classes and in expansion of eosinophil numbers in the blood and eosinophil infiltration into various tissues. Conversely, mice lacking a functional gene for IL-5 or IL-5 receptor alpha chain (IL-5Ralpha) display a number of developmental and functional impairments in B cells and eosinophils. IL-5 receptor (IL-5R) comprises alpha and betac chains. IL-5 specifically binds to IL-5Ralpha and induces the recruitment of betac to IL-5R. Although precise mechanisms on cell-lineage-specific IL-5Ralpha expression remain elusive, several transcription factors including Sp1, E12/E47, Oct-2, and c/EBPbeta have been shown to regulate its expression in B cells and eosinophils. JAK2 and JAK1 tyrosine kinase are constitutively associated with IL-5Ralpha and betac, respectively, and are activated by IL-5 stimulation. IL-5 activates at least three different signaling pathways including JAK2/STAT5 pathway, Btk pathway, and Ras/ERK pathway. IL-5 is one of key cytokines for mouse B cell differentiation in general, particularly for fate-determination of terminal B cell differentiation to antibody-secreting plasma cells. IL-5 critically regulates homeostatic proliferation and survival of and natural antibody production by B-1 cells, and enhances the AID and Blimp-1 expression in activated B-2 cells leading to induce mu to gamma1 class switch recombination and terminal differentiation to IgM- and IgG1-secreting plasma cells, respectively. In humans, major target cells of IL-5 are eosinophils. IL-5 appears to play important roles in pathogenesis of asthma, hypereosinophilic syndromes, and eosinophil-dependent inflammatory diseases. Clinical studies will provide a strong impetus for investigating the means of modulating IL-5 effects. We will discuss the role of IL-5 in the link between innate and acquired immune response, particularly emphasis of the molecular basis of IL-5-dependent B cell activation, allergen-induced chronic inflammation and hypereosinophilic syndromes on a novel target for therapy.

Eosinophil progenitors in allergy and asthma - do they matter?

Allergic inflammation is associated with marked infiltration of eosinophils in affected tissues. The eosinophil is believed to be a key effector cells in allergen induced asthma pathogenesis. However, the role of eosinophils in the clinical manifestation of asthma has recently been questioned, since therapies directed against eosinophil infiltration (i.e. anti-interleukin-5) failed to improve clinical symptoms such as airways hyper-responsiveness (AHR) in patients with asthma. Although eosinophils in peripheral blood and the airways were largely depleted after anti-IL-5 treatment, residual eosinophilia in lung tissue persisted, which permits speculation that the remaining eosinophils may be sufficient to drive the asthma symptomatology. Furthermore, recent findings suggest that primitive eosinophil progenitor cells traffic from the bone marrow to sites of inflammation in response to allergen exposure. These progenitors may then differentiate in situ and thus provide an ongoing supply of mature pro-inflammatory cells and secretory mediators that augment the inflammatory response. In the present article, we will review the evidence for these findings, and discuss the rationale for targeting hematopoiesis and their migration pathways in the treatment of allergic diseases. Furthermore, this review will highlight the hypothesis that both IL-5- and CCR3-mediated signaling pathways may need to be targeted in order to control the inflammation and AHR associated with asthma.

Cross-talk between ICAM-1 and granulocyte-macrophage colony-stimulating factor receptor signaling modulates eosinophil survival and activation

Reversal of eosinophilic inflammation has been an elusive therapeutic goal in the management of asthma pathogenesis. In this regard, GM-CSF is a primary candidate cytokine regulating eosinophil activation and survival in the lung; however, its molecular mechanism of propagation and maintenance of stimulated eosinophil activation is not well understood. In this study, we elucidate those late interactions occurring between the GM-CSF receptor and activated eosinophil signaling molecules. Using coimmunoprecipitation with GM-CSF-stimulated eosinophils, we have identified that the GM-CSF receptor beta-chain (GMRbeta) interacted with ICAM-1 and Shp2 phosphatase, as well as Slp76 and ADAP adaptor proteins. Separate experiments using affinity binding with a tyrosine-phosphorylated peptide containing an ITIM (ICAM-1 residues 480-488) showed binding to Shp2 phosphatase and GMRbeta. However, the interaction of GMRbeta with the phosphorylated ICAM-1-derived peptide was observed only with stimulated eosinophil lysates, suggesting that the interaction of GMRbeta with ICAM-1 required phosphorylated Shp2 and/or phosphorylated GMRbeta. Importantly, we found that inhibition of ICAM-1 in activated eosinophils blocked GM-CSF-induced expression of c-fos, c-myc, IL-8, and TNF-alpha. Moreover, inhibition of ICAM-1 expression with either antisense oligonucleotide or an ICAM-1-blocking Ab effectively inhibited ERK activation and eosinophil survival. We concluded that the interaction between ICAM-1 and the GM-CSF receptor was essential for GM-CSF-induced eosinophil activation and survival. Taken together, these results provide novel mechanistic insights defining the interaction between ICAM-1 and the GM-CSF receptor and highlight the importance of targeting ICAM-1 and GM-CSF/IL-5/IL-3 receptor systems as a therapeutic strategy to counter eosinophilia in asthma.

IL-5 and eosinophilia

While Interleukin-5 (IL-5) is initially identified by its ability to support the growth and differentiation of activated B cells, overexpression of IL-5 significantly increases eosinophil numbers and antibody levels predominantly from an expanded population of B-1 cells in vivo. Conversely, mice lacking a functional gene for IL-5 or IL-5 receptor alpha chain (IL-5Ralpha) display a number of developmental and functional impairments in B cell and eosinophil lineages. In addition to the JAK-STAT and Btk pathway, the Ras-extracellular signal-regulated kinase (ERK) signals are important for IL-5-dependent cell survival. IL-5 critically regulates expression of genes involved in cell survival, IgH switch recombination, maturation in B cells and genes required for growth, survival, and effector function of eosinophils. IL-5Ralpha expression in B cells, but not in eosinophils is regulated by Oct-2. Eosinophilia is associated with a wide variety of conditions, including asthma and atopic diseases, helminth infections, drug hypersensitivity, and neoplastic disorders. In humans, the biologic effects of IL-5 are best characterized for eosinophils. The Sprouty-related Ena/VASP homology 1-domain containing protein (Spred)-1 negatively controls eosinophil numbers and functions by modulating IL-5 signaling in allergic asthma. We will emphasize that IL-5 plays a pivotal role in the innate and acquired immune response and eosinophilia.

Interleukin-3 does not affect the differentiation of mast cells derived from human bone marrow progenitors

Although IL-3 is commonly used for culture of human progenitor-derived mast cells together with Stem cell factor (SCF) and IL-6, the effect of IL-3 on human mast cell differentiation has not been well elucidated. Human bone marrow CD34+ progenitors were cultured for up to 12 weeks in the presence of rhSCF and rhIL-6 either with rhIL-3 (IL-3 (+)) or without rhIL-3 (IL-3 (−)) for the initial 1-week of culture. Total cell number increased at 2 weeks in IL-3 (+), as compared to IL-3 (−), but changes in the appearance of mast cells were delayed. When IL-3 was present for the initial 1-week culture, granules looked more mature with IL-3 than without IL-3. However, tryptase and chymase contents, and surface antigen expression (CD18, CD51, CD54, and CD117) were not altered by IL-3. Surface expression and mRNA level of FcεRIα and histamine release by crosslinking of FcεRIα did not differ from one preparation to the next. GeneChip analysis revealed that no significant differences were observed between IL-3 (+) and IL-3 (−) cells either when inactivated or activated by aggregation of FcεRIα. These findings indicate that initial incubation of human bone marrow CD34+ progenitors with IL-3 does not affect the differentiation of mast cells.

Influence of varying doses of granulocyte-macrophage colony-stimulating factor on pharmacokinetics and antibody-dependent cellular cytotoxicity

Recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) is used in immunotherapy for correction of neutropoenia. The optimal dose for activation of immune functions and the pharmacokinetics following repeated administrations is less analysed in depth. In this study, the pharmacokinetics and the effects on haematological functions and antibody-dependent cellular cytotoxicity (ADCC) were analysed in 50 patients with metastatic colorectal carcinoma receiving monoclonal antibody based therapy in combination with Escherichia coli-derived GM-CSF (molgramostim) administered s.c. once daily for 10 days every month over a period of 4 months. Thirty-three patients received a GM-CSF dose of 200-250 microg/m(2)/day. Seventeen patients received GM-CSF doses varying between 65 and 325 microg/m(2)/day in the different treatment cycles. Serum GM-CSF concentration was measured (ELISA) before and 3-4 h after (peak serum concentration) GM-CSF administration days 1, 5 and 10. Prior to therapy, GM-CSF was not detectable in serum. Following repeated daily administrations, the peak serum concentration of GM-CSF gradually decreased on days 5 and 10 compared to day 1 (P < 0.05). During a 10-day treatment cycle, the total number of leukocytes, neutrophils, eosinophils, monocytes and lymphocytes increased. A dose-dependent increment in total white blood cell count and neutrophils was observed. The total numbers of GM-CSF receptor (alpha-subunit) expressing cells (granulocytes and monocytes) increased significantly during treatment while a transient decline in expression intensity was observed at day 5, suggesting a receptor-mediated removal of GM-CSF as a mechanism for the elimination of GM-CSF from circulation. ADCC of peripheral mononuclear cells was decreased at day 10 compared to baseline. An inverse correlation between the dose and ADCC was noted. The data might indicate that high doses of GM-CSF may have a negative impact on ADCC.

Basal expression of bone morphogenetic protein receptor is reduced in mild asthma

RATIONALE

Despite increasing recognition of bone morphogenetic protein (BMP) signaling in tissue remodeling, the expression pattern of ligands and signaling pathways remain undefined in the asthmatic airway.

OBJECTIVES

To determine expression of BMP ligands (BMP-2, BMP-4, and BMP-7) and type I and type II receptors (ALK-2, ALK-3, ALK-6, and BMPRII) as well as evidence for activation of BMP signaling via detection of phosphorylated Smad1/5 (pSmad1/5) expression in asthmatic airways at baseline (compared with nonasthmatic controls), and after allergen challenge.

METHODS

Bronchial biopsies were obtained from 6 nonasthmatic control volunteers, and 15 atopic patients with asthma (median age, 25 yr; median FEV(1)% predicted, 97%) at baseline, then at 24 hours and 7 days after allergen challenge. Expression of BMP ligands, receptors, and signaling was analyzed using immunohistochemistry.

MEASUREMENTS AND MAIN RESULTS

BMP ligand expression did not differ between asthmatic and control airways at baseline. Compared with the normal airway, there was significant down-regulation of ALK-2 (P = 0.001), ALK-6 (P = 0.0009), and BMPRII (P = 0.009) expression in asthma. Allergen challenge was associated with marked and sustained up-regulation of BMP-7 in airway epithelium (P = 0.017) and infiltrating inflammatory cells (P = 0.071) (predominantly in eosinophils, but also CD4(+) T cells, mast cells, and macrophages). Up-regulation of pSmad1/5 expression (P = 0.031), ALK-2 (P = 0.002), and ALK-6 (P < 0.001) was observed indicating active signaling.

CONCLUSIONS

BMP receptor expression is down-regulated in the asthmatic airway, which may impede repair responses. Allergen provocation increases expression of the regulatory ligand BMP-7, activates BMP signaling, and increases receptor expression, all of which may contribute to repair and control of inflammation.

Airway eosinophils: allergic inflammation recruited professional antigen-presenting cells

The capacity of airway eosinophils, potentially pertinent to allergic diseases of the upper and lower airways, to function as professional APCs, those specifically able to elicit responses from unprimed, Ag-naive CD4(+) T cells has been uncertain. We investigated whether airway eosinophils are capable of initiating naive T cell responses in vivo. Eosinophils, isolated free of other APCs from the spleens of IL-5 transgenic mice, following culture with GM-CSF expressed MHC class II and the costimulatory proteins, CD40, CD80, and CD86. Eosinophils, incubated with OVA Ag in vitro, were instilled intratracheally into wild-type recipient mice that adoptively received i.v. infusions of OVA Ag-specific CD4(+) T cells from OVA TCR transgenic mice. OVA-exposed eosinophils elicited activation (CD69 expression), proliferation (BrdU incorporation), and IL-4, but not IFN-gamma, cytokine production by OVA-specific CD4(+) T cells in paratracheal lymph nodes (LN). Exposure of eosinophils to lysosomotropic NH(4)Cl, which inhibits Ag processing, blocked each of these eosinophil-mediated activation responses of CD4(+) T cells. By three-color fluorescence microscopy, OVA Ag-loaded eosinophil APCs were physically interacting with naive OVA-specific CD4(+) T cells in paratracheal LN after eosinophil airway instillation. Thus, recruited luminal airway eosinophils are distinct allergic "inflammatory" professional APCs able to activate primary CD4(+) T cell responses in regional LNs.

Sustained biological effects of porcine interleukin 5 delivered to pigs as recombinant protein or via a DNA vector

The ability of cytokines to act as natural immunotherapeutics to enhance the health and the disease resistance of animals is of particular interest to the intensive livestock industries. Antibiotics have been used for such purposes over a long period of time, however, there is growing concern that this practice will enhance the development of antibiotic resistance in a range of bacterial pathogens. In several species, interleukin 5 (IL-5) is known to enhance B cell activity and to increase the numbers of eosinophils in blood and tissues. In this report, IL-5 was delivered to pigs, either as a recombinant protein or via a DNA delivery vector and was shown to elevate eosinophils in blood over a sustained period. Interleukin 3, a potent haemopoietic factor, did not synergize with IL-5 when both cytokines were given together, but did prime the pigs for a stronger response to IL-5. These results demonstrate that IL-5 can readily be delivered to commercial pigs to elicit a significant biological effect.

A study to evaluate safety and efficacy of mepolizumab in patients with moderate persistent asthma

RATIONALE

Accumulation of eosinophils in the bronchial mucosa of individuals with asthma is considered to be a central event in the pathogenesis of asthma. In animal models, airway eosinophil recruitment and airway hyperresponsiveness in response to allergen challenge are reduced by specific targeting of interleukin-5. A previous small dose-finding study found that mepolizumab, a humanized anti-interleukin-5 monoclonal antibody, had no effect on allergen challenge in humans.

OBJECTIVES

To investigate the effect of three intravenous infusions of mepolizumab, 250 or 750 mg at monthly intervals, on clinical outcome measures in 362 patients with asthma experiencing persistent symptoms despite inhaled corticosteroid therapy (400-1,000 mug of beclomethasone or equivalent).

METHODS

Multicenter, randomized, double-blind, placebo-controlled study.

MEASUREMENTS AND MAIN RESULTS

Morning peak expiratory flow, forced expiratory volume in 1 second, daily beta(2)-agonist use, symptom scores, exacerbation rates, and quality of life measures. Sputum eosinophil levels were also measured in a subgroup of 37 individuals. Mepolizumab was associated with a significant reduction in blood and sputum eosinophils in both treatment groups (blood, P < 0.001 for both doses; sputum, P = 0.006 for 250 mg and P = 0.004 for 750 mg). There were no statistically significant changes in any of the clinical end points measured. There was a nonsignificant trend for decrease in exacerbation rates in the mepolizumab 750-mg treatment group (P = 0.065).

CONCLUSIONS

Mepolizumab treatment does not appear to add significant clinical benefit in patients with asthma with persistent symptoms despite inhaled corticosteroid therapy. Further studies are needed to investigate the effect of mepolizumab on exacerbation rates, using protocols specifically tailored to patients with asthma with persistent airway eosinophilia.

[Anti-interleukin-5 therapy for eosinophilic diseases]

In a number of diseases with eosinophilia, elevated interleukin (IL)-5 levels are detected in the peripheral blood and/or tissues. IL-5 plays an important role in regulating the production, differentiation, recruitment, activation, and survival of eosinophils. Therefore, neutralizing IL-5 by blocking antibodies seems a promising approach in the treatment of eosinophilic diseases. Clinical trials have demonstrated that anti-IL-5 therapy results in a rapid decrease in peripheral blood eosinophil numbers. Moreover, improvement of symptoms in patients with lymphocytic variants of hypereosinophilic syndromes, in eosinophilic esophagitis and chronic rhinitis with nasal polyposis has been observed. In contrast, in patients with bronchial asthma or atopic eczema, anti-IL-5 therapy showed only moderate or no clinical effects. Future studies will have to identify those eosinophilic diseases in which anti-IL-5 antibodies are effective, perhaps with the help of newly developed biomarkers.

Eosinophils in the pathogenesis of allergic airways disease

Eosinophils are traditionally thought to form part of the innate immune response against parasitic helminths acting through the release of cytotoxic granule proteins. However, they are also a central feature in asthma. From their development in the bone marrow to their recruitment to the lung via chemokines and cytokines, they form an important component of the inflammatory milieu observed in the asthmatic lung following allergen challenge. A wealth of studies has been performed in both patients with asthma and in mouse models of allergic pulmonary inflammation to delineate the role of eosinophils in the allergic response. Although the long-standing association between eosinophils and the induction of airway hyper-responsiveness remains controversial, recent studies have shown that eosinophils may also promote airway remodelling. In addition, emerging evidence suggests that the eosinophil may also serve to modulate the immune response. Here we review the highly co-ordinated nature of eosinophil development and trafficking and the evolution of the eosinophil as a multi-factoral leukocyte with diverse functions in asthma.

BCG-infected adherent mononuclear cells release cytokines that regulate group 1 CD1 molecule expression

Increasing evidence is now available showing that CD1-restricted T cell responses against non-peptide mycobacterial antigens could play a role in the immune resistance against tuberculosis. BCG, widely used in anti-tubercular vaccination, shares various constituents with Mycobacterium tuberculosis, but does not provide full protection. In the present study we have investigated the pattern of group 1 CD1 molecule expression in adherent mononuclear cells (AMNC) of human peripheral blood, infected in vitro with BCG. Shortly after exposure to BCG, both BCG-positive and BCG-negative AMNC showed a moderate CD1 expression elicited by BCG-induced release of GM-CSF presumably acting through an autocrine and a paracrine mechanism. This was demonstrated using two-color flow cytometry with green fluorescent BCG and anti-CD1 PE-labeled antibodies. However, high CD1 expression induced by exogenously added GM-CSF in AMNC was reduced if target cells were cocultivated with BCG. Monoclonal antibodies against IL-10 partially restored CD1 expression, thus showing that IL-10, released from infected AMNC, is involved, at least in part, in CD1 negative modulation. Therefore, through a complex cytokine network, including not yet identified factor(s), BCG triggers but does not allow full expression of CD1 on AMNC. It cannot be excluded that this mechanism could play a role in the limited efficiency of BCG vaccination.

CD48 is an allergen and IL-3-induced activation molecule on eosinophils

Eosinophils are involved in a variety of allergic, parasitic, malignant, and idiopathic disorders by releasing a variety of factors including specific granule proteins, lipid mediators, and proinflammatory and immunoregulatory cytokines and chemokines. In addition, they interact with various cell types in the inflamed tissue. Yet, the mechanism of eosinophil activation is still poorly understood. Recently, we described the expression and function of the CD2-subfamily of receptors and especially 2B4 on human eosinophils. In this study we focus on CD48, the high-affinity ligand of 2B4. CD48 is a GPI-anchored protein involved in cellular activation, costimulation, and adhesion, but has not been studied on eosinophils. We demonstrate that human eosinophils from atopic asthmatics display enhanced levels of CD48 expression and that IL-3 up-regulates CD48 expression. Furthermore, cross-linking CD48 on human eosinophils triggers release of eosinophil granule proteins. Assessment of CD48 expression in a murine model of experimental asthma revealed that CD48 is induced by allergen challenge and partially regulated by IL-3. Additionally, anti-IL-3 reduces CD48 expression and the degree of airway inflammation. Thus, CD48 is an IL-3-induced activating receptor on eosinophils, likely involved in promoting allergic inflammation.

Substituted 2-phenyl-benzimidazole derivatives: novel compounds that suppress key markers of allergy

The pharmacotherapy of allergy and asthma has traditionally focused on the effecter molecules of the allergic cascade, while neglecting targets that play an early role in their development. Reasoning that IgE is central to the expansion of atopic diseases, we identified and extended a novel family of 2-(substituted phenyl)-benzimidazole inhibitors of IgE response. Pharmacological activity depends on an intact phenylbenzimidazole-bis-amide backbone, and is optimized by the presence of lipophilic terminal groups composed of either bis cycloalkyl or combinations of aliphatic and halogen-substituted aromatic groups. These compounds also inhibit IL-4 and IL-5 responses in T cells and CD23 expression on B cells, with potencies that parallel their inhibition of IgE. The broad profile of these compounds thus underscores their potential for treating the multifarious pathology of asthma.

Anti-Interleukin-5 Antibody Therapy in Eosinophilic Diseases

Eosinophilia in atopic diseases and hypereosinophilic syndrome is often associated with a high expression of interleukin-5 (IL-5). IL-5 plays an important role in regulating the production, differentiation, recruitment, activation, and survival of eosinophils. Therefore, neutralizing IL-5 with an antibody is a promising therapeutic strategy in eosinophilic diseases. In patients with hypereosinophilic syndrome and eosinophilic esophagitis, anti-IL-5 antibody therapy resulted in an improvement of symptoms. In patients with bronchial asthma, no effect on the late phase reaction and on airway hyperresponsiveness has been observed. Moreover, patients with atopic dermatitis demonstrated only a moderate improvement of their skin lesions and pruritus. Anti-IL-5 therapy was followed by a rapid and sustained decrease of peripheral blood eosinophil numbers. The decrease of tissue eosinophils was, however, less dramatic. Investigating the effects of anti-IL-5 therapy will improve our understanding of the pathogenic roles of both IL-5 and eosinophils in eosinophilic inflammatory responses.

The role of interleukin-3 in classical Hodgkin's disease

Classical Hodgkin's disease (HD) is a peculiar form of lymphoma characterized by a low frequency of tumor cells, the so-called Hodgkin (H) and Reed/Sternberg (RS) cells, embedded in a background of non-neoplastic (reactive) cells believed to be recruited and activated by H-RS cell-derived cytokines/chemokines. How these tumor cells can survive in such a seemingly hostile environment has confused researchers. We have previously identified interleukin (IL)-3 receptor (R) expression as a common feature of classical HD and unveiled the potential role of IL-3 as a growth and anti-apoptotic factor for H-RS cells. More then 90% of malignant cells of classical HD usually express the alpha chain of the IL-3R (IL-3R(alpha)), as evidenced by immunostaining of frozen sections and cell suspensions from neoplastic lymph nodes. Consistently, HD-derived cell lines (L428, KMH2, HDLM2 and L1236) express the alpha and beta chains that form IL-3R, both at the mRNA and protein level, with a molecular size of IL-3R(alpha) identical (70 kDa) to that expressed by human myeloid cells. Exogenous IL-3 promotes the growth of cultured H-RS cells, such an effect being potentiated by IL-9 and stem cell factor (SCF) co-stimulation, and is able to partially rescue tumor cells from apoptosis induced by serum deprivation. Finally, cultured H-RS cells are able to increase the production of IL-3 by pre-activated T cells, suggesting an involvement of IL-3/IL-3R interactions in the cellular growth of HD through paracrine mechanisms. This review will outline the biological activity of IL-3 and summarize the evidence indicating IL-3 as a growth and anti-apoptotic factor for H-RS cells in classical HD.

Much atopy about the skin: genome-wide molecular analysis of atopic eczema

BACKGROUND

Atopic eczema (AE) is a chronic inflammatory skin disorder with an increasing prevalence in industrialized countries.

METHODS

Genox Research Incorporation was founded in 1996 to identify new genes involved in allergic diseases in collaboration with the National Children's Hospital in Tokyo. In the AE project, they have discovered several hundred new genes and partial DNA sequences by mainly using microarrays. Here, I review the results obtained using transcriptome analysis, performed by Genox and other investigators.

RESULTS

Transcriptome analysis using skin lesion, CD4+ T cells, monocytes and eosinophils derived from AE patients identified some differentially expressed genes which became biologically relevant in the following studies. Missing linkages between these genes have been found due to the recent development of genomics.

CONCLUSION

Many AE-related genes found in the genome-wide studies still remain to be determined regarding their functions and to be systemically organized. After the comprehensive characterization of these genes by further studies, we will identify the precise molecular mechanisms involved in AE and other diseases.

Spred-1 negatively regulates allergen-induced airway eosinophilia and hyperresponsiveness

T helper 2 cytokines, including interleukin (IL)-4, IL-5, and IL-13, play a critical role in allergic asthma. These cytokines transmit signals through the Janus kinase/signal transducer and activator of transcription (STAT) and the Ras–extracellular signal-regulated kinase (ERK) signaling pathways. Although the suppressor of cytokine signaling (SOCS) family proteins have been shown to regulate the STAT pathway, the mechanism regulating the ERK pathway has not been clarified. The Sprouty-related Ena/VASP homology 1–domain-containing protein (Spred)-1 has recently been identified as a negative regulator of growth factor–mediated, Ras-dependent ERK activation. Here, using Spred-1–deficient mice, we demonstrated that Spred-1 negatively regulates allergen-induced airway eosinophilia and hyperresponsiveness, without affecting helper T cell differentiation. Biochemical assays indicate that Spred-1 suppresses IL-5–dependent cell proliferation and ERK activation. These data indicate that Spred-1 negatively controls eosinophil numbers and functions by modulating IL-5 signaling in allergic asthma.

Heterogeneity of expression of IgA receptors by human, mouse, and rat eosinophils

IgA is the most abundant class of Abs at mucosal surfaces where eosinophils carry out many of their effector functions. Most of the known IgA-mediated functions require interactions with IgA receptors, six of which have been identified in humans. These include the IgA FcR FcalphaRI/CD89 and the receptor for the secretory component, already identified on human eosinophils, the polymeric IgR, the Fcalpha/muR, asialoglycoprotein (ASGP)-R, and transferrin (Tf)R/CD71. In rodents, the existence of IgA receptors on mouse and rat eosinophils remains unclear. We have compared the expression and function of IgA receptors by human, rat, and mouse eosinophils. Our results show that human eosinophils express functional polymeric IgR, ASGP-R, and TfR, in addition to CD89 and the receptor for the secretory component, and that IgA receptors are expressed by rodent eosinophils. Indeed, mouse eosinophils expressed only TfR, whereas rat eosinophils expressed ASGP-R and CD89 mRNA. These results provide a molecular basis for the differences observed between human, rat, and mouse regarding IgA-mediated immunity.

Anti-interleukin-5 therapy for asthma and hypereosinophilic syndrome

Interleukin 5 (IL-5) is a key cytokine in the regulation of eosinophilia and eosinophil activation in humans. Monoclonal antibodies to anti-IL-5 have become available for use in clinical studies in humans. This article discusses the rationale for the use of anti-IL-5 therapy in asthma and hypereosinophilic syndrome and summarizes the available clinical data on the use of anti-IL-5 to treat these disorders.

Interleukin-5 receptors on human lung eosinophils after segmental allergen challenge

BACKGROUND

IL-5 is a specific cytokine for eosinophil accumulation, activation and prolongation of survival and can be recovered in elevated concentrations from the bronchoalveolar compartment in atopic asthma following allergen challenge.

OBJECTIVE

The action of IL-5 is mediated via the specific IL-5 receptor-alpha (IL-5Ralpha). Although in vitro data suggest that IL-5R expression is regulated by cytokines such as IL-3, IL-5 and GM-CSF, IL-5R regulation in vivo and its kinetics following allergen provocation are incompletely understood.

METHODS

We investigated IL-5R regulation in vivo following segmental allergen provocation (SAP) with an individually standardized dose of allergen in 12 patients with atopic asthma. Lavage was performed 10 min and 18 h (eight patients) and 10 min and 42 h (eight patients) after allergen challenge. In addition to differential cell counts, IL-5Ralpha was measured by flow cytometry and IL-5 concentrations in bronchoalveolar lavage (BAL) fluid were determined by ELISA.

RESULTS

IL-5Ralpha expression decreased significantly on peripheral blood and on BAL eosinophils 18 and 42 h after SAP. In contrast, IL-5 concentrations increased significantly in BAL fluid 18 and 42 h after SAP. In four and two patients, respectively, there were detectable IL-5 concentrations in serum 18 or 42 h after allergen exposure.

CONCLUSIONS

Although there was no correlation between IL-5 concentrations and IL-5Ralpha expression on eosinophils in BAL, our data support previous in vitro and in vivo findings of a negative feedback mechanism between IL-5 concentrations and IL-5Ralpha expression on eosinophils.

A role for eosinophils in airway remodelling in asthma

Over the years, the role of the eosinophil in asthma and allergic processes has been disputed. Recent human experiments using a humanised monoclonal antibody to interleukin-5 (IL-5), and animal studies involving specific IL-5 gene deletion, indicates that eosinophils might control downstream repair and remodelling processes. Eosinophils are a rich source of fibrogenic factors, particularly transforming growth factor-beta (TGF-beta), the latent form of which is activated by epithelial-cell expression of the intergin alpha(v)beta(6). The emerging role for the eosinophil in airway remodelling might be important in future anti-asthma strategies. However, more effective eosinophil-depleting agents than anti-IL-5 are required before the definitive role of this cell type in asthma airway pathophysiology can be established.

Biochemical assessment of intracellular signal transduction pathways in eosinophils: implications for pharmacotherapy

Allergic asthma and allergic rhinitis are inflammatory diseases of the airway. Cytokines and chemokines produced by T helper (Th) type 2 cells (GM-CSF, IL-4, IL-5, IL-6, IL-9, IL-10 and IL-13), eotaxin, transforming growth factor-beta, and IL-11 orchestrate most pathophysiological processes of the late-phase allergic reaction, including the recruitment, activation, and delayed apoptosis of eosinophils, as well as eosinophilic degranulation to release eosinophilic cationic protein, major basic protein, and eosinophil-derived neurotoxin. These processes are regulated through an extensive network of interactive intracellular signal transduction pathways that have been intensively investigated recently. Our present review updates the cytokine and chemokine-mediated signal transduction mechanisms including the RAS-RAF-mitogen-activated protein kinases, Janus kinases (signal transducers and activators of transcription), phosphatidylinositol 3-kinase, nuclear factor-kappa B, activator protein-1, GATA, and cyclic AMP-dependent pathways, and describes the roles of different signaling pathways in the regulation of eosinophil differentiation, recruitment, degranulation, and expression of adhesion molecules. We shall also discuss different biochemical methods for the assessment of various intracellular signal transduction molecules, and various antagonists of receptors, modulators, and inhibitors of intracellular signaling molecules, many of which are potential therapeutic agents for treating allergic diseases.

Expression of interleukin-13 receptor alpha 1-subunit on peripheral blood eosinophils is regulated by cytokines

Interleukin-13 (IL-13) is critical for the development of allergic asthma and is involved in the activation of eosinophils within the airways. IL-13 exerts its activity on target cells via the dimeric IL-13 receptor (IL-13R), which comprises the IL-13 receptor alpha1-chain (IL-13Ralpha1) as a specific component. The aim of this study was to investigate the expression of the IL-13Ralpha1-chain on primary human eosinophilic granulocytes. Furthermore, it addresses the regulatory influence of cytokines on the level of surface abundance of this receptor subunit. Expression of IL-13- and IL-4-receptor subunits in purified primary human eosinophils was monitored at the messenger RNA level by reverse transcription polymerase chain reaction and at the protein level by flow cytometry. For the analysis of IL-13Ralpha1 surface expression, a new monoclonal antibody, which was generated using genetic immunization, was employed. Different cytokines with established activity on eosinophils were studied with regard to their influence on IL-13Ralpha1 in vitro by flow cytometry. Whereas IL-13 and IL-4 had inhibitory effects on IL-13Ralpha1 expression on eosinophils, interferon-gamma, tumour necrosis factor-alpha, and, to the largest extent, transforming growth factor-beta, enhanced the expression of this receptor subunit. A positive regulatory response evoked by transforming growth factor-beta and interferon-gamma does not prevent inhibitory effects caused by IL-13. These findings suggest a regulatory cytokine network influencing the reactivity of eosinophils to IL-13.

Asthma: mechanisms of disease persistence and progression

When asthma is diagnosed, eosinophilic inflammation and airway remodeling are established in the bronchial airways and can no longer be separated as cause and effect because both processes contribute to persistence and progression of disease, despite anti-inflammatory therapy. Th2 cells are continually active in the airways, even when disease is quiescent. IL-13 is the key effector cytokine in asthma and stimulates airway fibrosis through the action of matrix metalloproteinases on TGF-beta and promotes epithelial damage, mucus production, and eosinophilia. The production of IL-13 and other Th2 cytokines by non-T cells augments the inflammatory response. Inflammation is amplified by local responses of the epithelium, smooth muscle, and fibroblasts through the production of chemokines, cytokines, and proteases. Injured cells produce adenosine that enhances IL-13 production. We review human and animal data detailing the cellular and molecular interactions in established allergic asthma that promote persistent disease, amplify inflammation, and, in turn, cause disease progression.

Intravenous anti-IL-5 monoclonal antibody reduces eosinophils and tenascin deposition in allergen-challenged human atopic skin

Anti-IL-5 monoclonal antibody (mepolizumab) reduces baseline bronchial mucosal eosinophils and deposition of extracellular matrix proteins in the reticular basement membrane in mild asthma. Here we report the effect of anti-IL-5, in the same patients, on allergen-induced eosinophil accumulation, tenascin deposition (as a marker of repair and remodelling) and the magnitude of the late-phase allergic cutaneous reaction. Skin biopsies were performed in 24 atopic subjects at allergen- and diluent-injected sites before 6 and 48 h after, three infusions of a humanized, monoclonal antibody against IL-5 (mepolizumab) using a randomized double-blind, placebo-controlled design. Anti-IL-5 significantly inhibited eosinophil infiltration in 6 h and 48 h skin biopsies as well as the numbers of tenascin immunoreactive cells at 48 h. In contrast, anti-IL-5 had no significant effect on the size of the 6 or 48 h late-phase cutaneous allergic reaction. This study (a) suggests that eosinophils are unlikely to cause the redness, swelling, and induration characteristic of the peak (6 h) late-phase cutaneous allergic reaction and (b) shows that decreases in tenascin positive cells at 48 h correlates with reduction of eosinophils, so providing further evidence of involvement in remodelling processes associated with allergic inflammation.

Anti-IL-5 treatment reduces deposition of ECM proteins in the bronchial subepithelial basement membrane of mild atopic asthmatics

Eosinophil-derived TGF-beta has been implicated in remodeling events in asthma. We hypothesized that reduction of bronchial mucosal eosinophils with anti-IL-5 would reduce markers of airway remodeling. Bronchial biopsies were obtained before and after three infusions of a humanized, anti-IL-5 monoclonal antibody (mepolizumab) in 24 atopic asthmatics in a randomized, double-blind, placebo-controlled study. The thickness and density of tenascin, lumican, and procollagen III in the reticular basement membrane (RBM) were quantified immunohistochemically by confocal microscopy. Expression of TGF-beta1 mRNA by airway eosinophils was assessed by in situ hybridization, and TGF-beta1 protein was measured in bronchoalveolar lavage (BAL) fluid by ELISA. At baseline, airway eosinophil infiltration and ECM protein deposition was increased in the RBM of asthmatics compared with nonasthmatic controls. Treating asthmatics with anti-IL-5 antibody, which specifically decreased airway eosinophil numbers, significantly reduced the expression of tenascin, lumican, and procollagen III in the bronchial mucosal RBM when compared with placebo. In addition, anti-IL-5 treatment was associated with a significant reduction in the numbers and percentage of airway eosinophils expressing mRNA for TGF-beta1 and the concentration of TGF-beta1 in BAL fluid. Therefore eosinophils may contribute to tissue remodeling processes in asthma by regulating the deposition of ECM proteins.

Changing expression of IL-3 and IL-5 receptors in cultured human eosinophils

IL-3, IL-5, and GM-CSF exert overlapping functions in eosinophils via a shared receptor beta-chain, and IL-3Ralpha transcript expression is the weakest in blood eosinophils. We investigated the long-term regulation of surface expression of IL-3Ralpha. IL-3 was the most potent inducer of CD69 expression after 24-h stimulation, but not after 1-h stimulation. Expression of IL-5Ralpha and GM-CSFRalpha was significantly downregulated by culturing with their respective ligands, while IL-3Ralpha expression was not. IL-3 at 30pM significantly increased IL-3Ralpha expression and IL-3Ralpha expression was also upregulated by both IL-5 and GM-CSF. In parallel with the surface protein expression, IL-3Ralpha mRNA was also upregulated by IL-3, IL-5, and GM-CSF. These results demonstrated that long-term culturing of eosinophils with CSFs induced a change in the potency order of CSFs, with IL-3 coming to exert the strongest effect. They thus suggest that IL-3 plays more important roles in local eosinophil activation than previously recognized.