Decreased expression of membrane IL-5 receptor alpha on human eosinophils: II. IL-5 down-modulates its receptor via a proteinase-mediated process

Three lysine residues in the common β chain of the interleukin-5 receptor are required for Janus kinase (JAK)-dependent receptor ubiquitination, endocytosis, and signaling

Eosinophils are multifunctional leukocytes implicated in the pathogenesis of numerous inflammatory diseases including allergic asthma and hypereosinophilic syndrome. Eosinophil physiology is critically dependent on IL-5 and the IL-5 receptor (IL-5R), composed of a ligand binding α chain (IL-5Rα), and a common β chain, βc. Previously, we demonstrated that the βc cytoplasmic tail is ubiquitinated and degraded by proteasomes following IL-5 stimulation. However, a complete understanding of the role of βc ubiquitination in IL-5R biology is currently lacking. By using a well established, stably transduced HEK293 cell model system, we show here that in the absence of ubiquitination, βc subcellular localization, IL-5-induced endocytosis, turnover, and IL-5R signaling were significantly impaired. Whereas ubiquitinated IL-5Rs internalized into trafficking endosomes for their degradation, ubiquitination-deficient IL-5Rs accumulated on the cell surface and displayed blunted signaling even after IL-5 stimulation. Importantly, we identified a cluster of three membrane-proximal βc lysine residues (Lys(457), Lys(461), and Lys(467)) whose presence was required for both JAK1/2 binding to βc and receptor ubiquitination. These findings establish that JAK kinase binding to βc requires the presence of three critical βc lysine residues, and this binding event is essential for receptor ubiquitination, endocytosis, and signaling.

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.

Remodeling in asthma

Airway remodeling encompasses the structural alterations in asthmatic compared with normal airways. Airway remodeling in asthmatic patients involves a wide array of pathophysiologic features, including epithelial changes, increased smooth muscle mass, increased numbers of activated fibroblasts/myofibroblasts, subepithelial fibrosis, and vascular changes. Multiple cytokines, chemokines, and growth factors released from both inflammatory and structural cells in the airway tissue create a complex signaling environment that drives these structural changes. However, recent investigations have changed our understanding of asthma from a purely inflammatory disease to a disease in which both inflammatory and structural components are equally involved. Several reports have suggested that asthma primarily develops because of serious defects in the epithelial layer that allow environmental allergens, microorganisms, and toxins greater access to the airway tissue and that can also stimulate the release of mediators from the epithelium, thus contributing to tissue remodeling. Lung-resident fibroblasts and smooth muscle cells have also been implicated in the pathogenesis of airway remodeling. Remodeling is assumed to result in persistent airflow limitation, a decrease in lung function, and airway hyperresponsiveness. Asthmatic subjects experience an accelerated decrease in lung function compared with healthy subjects, which is proportionally related to the duration and severity of their disease.

Increased expression of the chemokine CCL23 in eosinophilic chronic rhinosinusitis with nasal polyps

BACKGROUND

Chronic rhinosinusitis (CRS) is a heterogeneous chronic disease characterized by local inflammation of the sinonasal tissues. The pathogenesis of CRS remains controversial, but it has been associated with the accumulation of various immune and inflammatory cells in sinus tissue.

OBJECTIVES

The objective of this study was to investigate the expression of the chemokine CCL23, which is known to bind to CCR1 and recruit monocytes, macrophages, and dendritic cells, in patients with CRS.

METHODS

We collected nasal tissue from patients with CRS and control subjects. We assayed mRNA for CCL23 by using real-time PCR and measured CCL23 protein by means of ELISA, immunohistochemistry, and immunofluorescence.

RESULTS

CCL23 mRNA levels were significantly increased in nasal polyps (NPs) from patients with CRS with nasal polyps (CRSwNP; P < .05) compared with inferior turbinate and uncinate tissue from patients with CRS or control subjects. CCL23 protein levels were also increased in NPs, although these levels were not statistically significant. Immunohistochemical analysis revealed CCL23 expression in mucosal epithelial cells and inflammatory cells, but accumulation of CCL23(+) inflammatory cells occurred only in NPs. Immunofluorescence data showed CCL23 colocalization with eosinophil cationic protein-positive eosinophils. The concentration of CCL23 in NPs positively correlated with the concentration of eosinophil cationic protein, suggesting that eosinophils are major CCL23-producing cells in NPs. Finally, we found that CCL23 protein levels were significantly increased in NPs from patients with CRSwNP with aspirin sensitivity.

CONCLUSION

Overproduction of CCL23 in NPs might contribute to the pathogenesis of eosinophilic CRSwNP through the recruitment of CCR1(+) inflammatory cells, including monocytes and macrophages, and the amplification of local inflammation.

Pathogenesis of airway inflammation in bronchial asthma

Bronchial asthma is a chronic disorder characterized by airway inflammation, reversible airway obstruction, and airway hyperresponsiveness. Eosinophils are believed to play important roles in the pathogenesis of asthma through the release of inflammatory mediators. In refractory eosinophilic asthma, anti-IL-5 mAb reduces exacerbations and steroid dose, indicating roles of eosinophils and IL-5 in the development of severe eosinophilic asthma. Even in the absence of IL-5, it is likely that the "Th2 network", including a cascade of vascular cell adhesion molecule-1/CC chemokines/GM-CSF, can sufficiently maintain eosinophilic infiltration and degranulation. Cysteinyl leukotrienes can also directly provoke eosinophilic infiltration and activation in the airways of asthma. Therefore, various mechanisms would be involved in the eosinophilic airway inflammation of asthma. In the pathogenesis of severe asthma, not only eosinophils but also mast cells or neutrophils play important roles. Mast cells are much infiltrated to smooth muscle in severe asthma and induce airway remodeling by release of inflammatory mediators such as amphiregulin. Treatment with anti-IgE Ab, which neutralizes circulating IgE and suppresses mast cell functions, reduces asthma exacerbations in severe asthmatic patients. Furthermore, infiltration of neutrophils in the airway is also increased in severe asthma. IL-8 plays an important role in the accumulation of neutrophils and is indeed upregulated in severe asthma. In the absence of chemoattractant for eosinophils, neutrophils stimulated by IL-8 augment the trans-basement membrane migration of eosinophils, suggesting that IL-8-stimulated neutrophils could lead eosinophils to accumulate in the airways of asthma. In view of these mechanisms, an effective strategy for controlling asthma, especially severe asthma, should be considered.

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.

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.

Role of eosinophils and their clinical significance in allergic inflammation

Eosinophils are believed to play roles in the pathophysiology of allergic inflammation, such as bronchial asthma. However, recent studies on anti-interleukin-5 monoclonal antibody treatment of asthmatic patients raised the possibility that eosinophils may play only a limited role. More recent studies established that eosinophils are essentially involved in the development of airway remodeling. Moreover, it is theoretically conceivable that eosinophils are a cellular source of lipid mediators, such as cysteinyl leukotrienes or platelet-activating factor in asthma. Even in the absence of interleukin-5, it is likely that the 'T-helper Type 2 network', including a cascade of vascular cell adhesion molecule-1, intercellular cell adhesion molecule-1, CC chemokines, granulocyte-macrophage colony-stimulating factor, for example, can maintain sufficient eosinophilic infiltration and effector functions, such as superoxide anion generation and degranulation. Long-term studies, wherein tissue eosinophils are eliminated effectively will be required to establish the exact roles of these cells in asthma. Finally, the authors will demonstrate that eosinophils have the potential for not only playing detrimental roles but also beneficial ones.

The signaling mechanism of eosinophil activation

Eosinophils play an important role in certain aspects of asthma pathogenesis. This review focuses on the mechanism of activation of eosinophils by the growth factor interleukin-5 and the CC chemokine receptor-3. Interleukin-5 activates members of the Janus and Src family of kinases. The latter kinases are largely responsible for the generation of initial signaling events. CC chemokine receptor-3, in contrast, signals through heterotrimeric G-proteins. Subsequently, various signaling pathways are activated, which converge on four major pathways - the mitogen-activated protein kinase pathway, the phosphoinositide-3 kinase pathway, the calcium signaling pathway and the Janus-signal transducer and activator of transcription signaling pathway. The biologic consequences of many of these signaling pathways are also discussed.

Cord blood molecular biomarkers of eosinophilopoiesis: kinetic analysis of GATA-1, MBP1 and IL-5R alpha mRNA expression

Eosinophil/basophil (Eo/B) progenitor phenotype and function in cord blood (CB) are associated with atopic risk at birth and infant clinical outcomes. Molecular analyses of eosinophil-basophil differentiation events could identify clinically predictive biomarkers. To determine CB kinetic patterns of Eo/B lineage-associated gene expression (GATA-1, MBP1 and IL-5R alpha) after IL-5 stimulation, CB non-adherent mononuclear cells were isolated from random fresh and frozen samples and incubated in the presence of recombinant human interleukin-5. Some underwent CD34+ positive selection using magnetic cell separation. At various time-points, mRNA expression of GATA-1, MBP1 and IL-5R alpha (total transcripts) was determined utilizing multiplex quantitative polymerase chain reaction (Q-PCR). Relative expression levels of the IL-5R alpha soluble vs. transmembrane isoforms were also analyzed. Stimulation of the non-adherent mononuclear cells with IL-5 resulted in early up-regulation of GATA-1, peaking at 48 h, followed by decreasing expression and down-regulation by 96 h. The CD34+ enriched population demonstrated an equivalent expression pattern (r = 0.963, p = 0.0349). MBP1 mRNA expression [non-adherent mononuclear cells (NAMNCs) and CD34+ alike; r = 0.988, p = 0.012] was slowly up-regulated in response to IL-5, maximal at 96 h. Total IL-5R alpha expression appeared stable over the time-course, mediated by differential expression of the soluble and transmembrane isoforms (i.e., initial increase in the transmembrane contribution followed by a predominance of the soluble isoform by 48-72 h). Multiplex Q-PCR analysis of mRNA from CB demonstrates expression of critical eosinophil-basophil lineage-specific events that are consistent with current understanding of eosinophil differentiation and maturation. The non-adherent mononuclear cell population provides a surrogate signal for the CD34+ progenitor population.

Altered lymphocyte trafficking and diminished airway reactivity in transgenic mice expressing human MMP-9 in a mouse model of asthma

Matrix metalloproteinase-9 (MMP-9) is hypothesized to facilitate leukocyte extravasation and extracellular remodeling in asthmatic airways. Careful descriptive studies have shown that MMP-9 levels are higher in the sputum of asthmatics; however, the consequence of increased MMP-9 activity has not been determined in this disease. We induced asthma in transgenic mice that express human MMP-9 in the murine lung tissue macrophage to determine the direct effect of human MMP-9 expression on airway inflammation. Transgenic (TG) and wild-type (WT) mice were immunized and challenged with ovalbumin. Forty-eight hours after the ovalbumin challenge, airway hyperresponsiveness (AHR) was measured, and inflammatory cell infiltration was evaluated in bronchoalveolar lavage fluid (BALF) and lung tissue. Baseline levels of inflammation were similar in the TG and WT groups of mice, and pulmonary eosinophilia was established in both groups by sensitization and challenge with ovalbumin. There was a significant reduction in AHR in sensitized and challenged trangenics compared with WT controls. Although total BALF cell counts were similar in both groups, the lymphocyte number in the lavage of the TG group was significantly diminished compared with the WT group (0.25 +/- 0.08 vs. 0.89 +/- 0.53; P = 0.0032). In addition, the draining lymphocytes were found to be larger in the TG animals compared with the WT mice. Equal numbers of macrophages, eosinophils, and neutrophils were seen in both groups. IL-13 levels were found to be lower in the sensitized TG compared with the WT mice. These results demonstrate an inverse relationship between human MMP-9 and AHR and suggest that MMP-9 expression alters leukocyte extravasation by reducing lymphocyte accumulation in the walls of asthmatic airways.

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.

Monoclonal antibodies and other biologic agents in the treatment of asthma

Asthma represents a syndrome of airway inflammatory diseases with complex pathology. The immunologic pathogenesis is being increasingly revealed and provides opportunity for targeted biological intervention. Current experience with immunomodulators as targeted therapy in asthma is described in this literature review. Targeted therapies have included strategies to activate dendritic cells through the TLR-9 receptors, to interrupt the action of T(H)2 cytokines with cytokine blockers and monoclonal antibodies, to promote development of T(H)1 responses, to block IgE mediated pathways and to block TNFalpha. Omalizumab is the only biological therapy that has an approved indication in asthma at this time. An improved understanding of the heterogeneity of asthma should allow for specific targeting of different disease phenotypes specific therapies including immunomodulators.

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.

Novel targets of therapy in asthma

PURPOSE OF REVIEW

The use of inhaled corticosteroids, short and long acting beta2-adrenoceptor agonists and inhibitors of leukotrienes provide most asthmatic patients with good disease control. However, none of these therapies are specifically directed to the underlying causal pathways of asthma. In this review the role of selective inhibitors of the inflammatory cascade are presented with a particular emphasis on biologics.

RECENT FINDINGS

Apart from antihuman immunoglobulin E, biologics have had little impact on this disease. However, with the definition of critical pathways in driving ongoing inflammation and airway remodelling, the situation is about to change with several exciting new approaches being on the horizon. Specific cytokines that are considered central to the Th2 inflammatory response as therapeutic targets are discussed along with some entirely new approaches such as restoration of mucosal innate immunity and epithelial barrier function and the application of radiofrequency ablation of airway smooth muscle or thermal bronchoplasty.

SUMMARY

What is becoming clear in filling the pipeline with new asthma therapies that treat the underlying disease causes is the need for closer working between clinical academics and industry to ensure that there is a rapid and sustained transfer of knowledge on novel targets through to their validation, proof of concept studies and clinical trials.

Allergy, asthma, and inflammation: which inflammatory cell type is more important?

: A recent review in Allergy, Asthma, and Clinical Immunology suggested that eosinophils play a minor role, if any, in the inflammatory spectrum of asthma and allergic inflammation. The article that dealt with mast cells suggested that the presence of these important cells within the smooth muscle layer in asthmatic airways renders this cell type primal in asthma and an obvious and important target for therapy. This article proposes that in a complex inflammatory milieu characterizing the complex syndromes we call asthma, no single cell phenotype is responsible for the condition and thus should be a sole target for therapeutic strategies. Our reductionist approach to research in asthma and related conditions has provided us with convincing evidence for multiple roles that immune, inflammatory, and structural cell types can play in complex diseases. The next stage in understanding and ameliorating these complex conditions is to move away from the simplistic notion of one cell type being more important than another. Instead, what is needed is to acquire knowledge of intricate and exquisite biological systems that regulate such conditions in both health and disease involving various cell types, mediators, pharmacologically active products, their multifaceted capacities, and their socio-biological networking.

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.

Matrix metalloproteinase 8 contributes to solubilization of IL-13 receptor alpha2 in vivo

BACKGROUND

IL-13 receptor alpha2 (IL-13R alpha 2) is a high-affinity receptor for IL-13, a central mediator of allergic asthma. It acts predominantly as a decoy receptor but can also contribute to IL-13 responses under certain conditions. IL-13R alpha 2 exists in soluble and membrane forms, which can both bind IL-13 and modulate its activity. Yet the proteolytic processes that contribute to the generation of soluble IL-13R alpha 2 are largely unknown.

OBJECTIVE

We sought to investigate the role of matrix metalloproteinases (MMPs) in the generation of soluble IL-13R alpha 2.

METHODS

Acellular cleavage assays by MMPs were performed by using glutathione-S-transferase fusion proteins of murine or human IL-13R alpha 2. IL-13R alpha 2 stable-transfected cells were used for analysis of surface expression and release of soluble IL-13R alpha 2. Wild-type and MMP-8-deficient mice were used for analysis of allergen-induced airway hyperresponsiveness and solubilization of IL-13R alpha 2.

RESULTS

Among several MMPs tested, only MMP-8 cleaved IL-13R alpha 2. Treatment of transfected human or murine cells expressing high levels of surface IL-13R alpha 2 with MMP-8 resulted in release of soluble IL-13R alpha 2 into the supernatants, with a concomitant decrease in surface IL-13R alpha 2 levels. The IL-13R alpha 2 solubilized by MMP-8 retained IL-13 binding activity. In an asthma model MMP-8-deficient mice displayed increased airway hyperresponsiveness and decreased soluble IL-13R alpha 2 protein levels in bronchoalveolar lavage fluid compared with those seen in wild-type mice after house dust mite challenge.

CONCLUSION

MMP-8 cleaves IL-13R alpha 2 in vitro and contributes to the solubilization of IL-13R alpha 2 in vivo.

Up-regulation and activation of eosinophil integrins in blood and airway after segmental lung antigen challenge

We hypothesized that there are clinically relevant differences in eosinophil integrin expression and activation in patients with asthma. To evaluate this, surface densities and activation states of integrins on eosinophils in blood and bronchoalveolar lavage (BAL) of 19 asthmatic subjects were studied before and 48 h after segmental Ag challenge. At 48 h, there was increased expression of alpha(D) and the N29 epitope of activated beta(1) integrins on blood eosinophils and of alpha(M), beta(2), and the mAb24 epitope of activated beta(2) integrins on airway eosinophils. Changes correlated with the late-phase fall in forced expiratory volume in 1 s (FEV(1)) after whole-lung inhalation of the Ag that was subsequently used in segmental challenge and were greater in subjects defined as dual responders. Increased surface densities of alpha(M) and beta(2) and activation of beta(2) on airway eosinophils correlated with the concentration of IL-5 in BAL fluid. Activation of beta(1) and beta(2) on airway eosinophils correlated with eosinophil percentage in BAL. Thus, eosinophils respond to an allergic stimulus by activation of integrins in a sequence that likely promotes eosinophilic inflammation of the airway. Before challenge, beta(1) and beta(2) integrins of circulating eosinophils are in low-activation conformations and alpha(D)beta(2) surface expression is low. After Ag challenge, circulating eosinophils adopt a phenotype with activated beta(1) integrins and up-regulated alpha(D)beta(2), changes that are predicted to facilitate eosinophil arrest on VCAM-1 in bronchial vessels. Finally, eosinophils present in IL-5-rich airway fluid have a hyperadhesive phenotype associated with increased surface expression of alpha(M)beta(2) and activation of beta(2) integrins.

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.

Evidence of a role for B cell-activating factor of the TNF family in the pathogenesis of chronic rhinosinusitis with nasal polyps

BACKGROUND

The polypoid form of chronic rhinosinusitis (chronic rhinosinusitis with nasal polyps [CRSwNP]) is a highly prevalent disease that often requires surgical intervention for treatment. Nasal polyps contain large quantities of B lymphocytes and immunoglobulin as well as eosinophils.

OBJECTIVES

The objective of this study was to investigate the expression of B cell-activating factor of the TNF family (BAFF), an important regulator of class-switch recombination and immunoglobulin production, in patients with chronic rhinosinusitis (CRS).

METHODS

We collected nasal tissue and nasal lavage fluid from patients with CRS and control subjects. We assayed mRNA for BAFF and B-lymphocyte markers, CD20 and transmembrane activator and calcium-modulator and cyclophilin ligand interactor, by using real-time PCR, and assayed BAFF protein by using ELISA and immunohistochemistry.

RESULTS

BAFF mRNA was significantly increased in nasal polyps from patients with CRSwNP (P < .001) compared with inferior turbinate tissue from patients with CRS or healthy subjects. BAFF protein was also elevated in polypoid tissue and nasal lavage from patients with CRSwNP. Immunohistochemistry showed considerable BAFF staining in mucosal epithelial cells in nasal polyps along with unidentified cells in the lamina propria. Expression of mRNA for BAFF in sinonasal tissue was significantly correlated with CD20 and transmembrane activator and CAML interactor in sinus tissue. IgA, an immunoglobulin isotype known to activate eosinophils, was also significantly elevated in the polypoid tissue.

CONCLUSION

Overproduction of BAFF in nasal polyps may contribute to the pathogenesis of CRSwNP via the local induction of IgA and activation of eosinophils.

Ablation of Matrix Metalloproteinase-9 Increases Severity of Viral Myocarditis in Mice

Background— Coxsackievirus B3 (CVB3) causes human myocarditis, which can result in cardiac damage, maladaptive remodeling, and heart failure. Matrix metalloproteinases (MMP)-8 and -9 have been identified in virus-infected myocardium, but their particular roles and underlying mechanisms of effect are unknown. For the first time, we examine the severity of CVB3-induced myocarditis in MMP-8–and MMP-9–deficient mice.

Methods and Results— CVB3-infected MMP-8 and MMP-9 knockout (KO) mice and corresponding wild-type (WT) mice were euthanized and harvested at 9 days after infection. Expression of MMP-2, -8, -12, and -13 and tissue inhibitors of MMPs was assessed by zymography or immunoblotting on harvested hearts, and in situ hybridization was performed to detect active infection. Infected MMP-9 KO mice had greater myocardial injury and foci of infection than WT mice despite similar pancreatic infection. Increased fibrosis (10.6±2.7% versus 7.1±2.6%, P =0.04), viral titer, as well as decreased cardiac output, were evident in MMP-9 KO compared with WT mice as assessed by picrosirius red staining, plaque assay, and echocardiography, respectively. Immune infiltration was also greatly increased in MMP-9 KO compared with WT mice (15.2±12.6% versus 2.0±3.0%, P <0.002). Myocardial interferon-β1, interferon-γ, interleukin-6, interleukin-10, and macrophage inflammatory protein-1α expression was elevated in MMP-9 KO mice as measured by quantitative real-time polymerase chain reaction and ELISA. In contrast, MMP-8 KO mice had the same degree of cardiac injury, fibrosis, and viral infection as their WT counterparts.

Conclusions— During acute CVB3 infection, MMP-9 appears necessary to halt virus propagation in the heart, promote proper immune infiltration and remodeling, and preserve cardiac output.

The airway epithelium is central to the pathogenesis of asthma

Asthma is an inflammatory disorder principally involving the conducting airways and characterised by infiltration of the airway wall with a range of inflammatory cells driven in large part by activation of Th2-type lymphocytes, mast cells and eosinophils. However a key component of asthma is the structural change that involves all of the elements of the airway wall. Here evidence is presented to suggest that the airway epithelium in asthma is fundamentally abnormal with increased susceptibility to environmental injury and impaired repair associated with activation of the epithelial-mesenchymal trophic unit (EMTU). In addition to adopting an activated phenotype, the barrier function of the epithelium is impaired through defective tight junction formation thereby facilitating penetration of potentially toxic or damaging environmental insults. Activated and repairing epithelial cells generate a range of growth factors that are involved in the early life origins of this disease as well as its progression in the form of mucous metaplasia and airway wall remodeling. By placing the epithelium at the forefront of asthma pathogenesis, different approaches to treatment can be devised focused more on protecting vulnerable airways against environmental injury rather than focusing on suppressing airway inflammation or manipulating the immune response.

Treatment strategies for allergy and asthma

Allergic diseases have reached epidemic proportions worldwide. An understanding of the cellular and soluble mediators that are involved in allergic inflammatory responses not only helps in understanding the mechanisms of current treatments, but is also important for the identification of new targets that are amenable to both small-molecule and biological interventions. There is now considerable optimism with regards to tackling the allergy epidemic in light of improvements in systemic and mucosal allergen-specific immunotherapy, the identification of key cytokines and their receptors that drive T-helper-2-cell polarization, a clearer understanding of the pathways of leukocyte recruitment and the signalling pathways that are involved in cell activation and mediator secretion, and new approaches to vaccine development.

Epithelium dysfunction in asthma

Although asthma is an inflammatory disorder of the conducting airways involving T(H)2-type T cells, there is increasing evidence for an important role played by the epithelium in orchestrating the inflammatory response by interacting with multiple environmental factors to produce a chronic wound scenario involving tissue injury and aberrant repair. Part of this abnormal response is the consequence of impaired barrier function caused by a primary disruption of epithelial tight junctions that allows inhaled substances to pass more easily into the airway wall to interact with immune and inflammatory cells. Aberrant communication between the damaged and stressed epithelium leads to the generation of growth factors that interact with the underlying mesenchyme to promote airway remodeling responses and a more chronic and persistent inflammatory phenotype. Disordered epithelial function with reduced antioxidant defense and impaired capacity to produce primary IFNs may also account for asthmatic susceptibility to air pollution and respiratory virus infection, respectively. Considering asthma as a disease of impaired barrier function opens new opportunities for therapeutic intervention or prevention by agents that could increase the airways resistance to the inhaled environment rather than suppressing the immune or inflammatory response.

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.

Regulation of functional phenotypes of cord blood derived eosinophils by gamma-secretase inhibitor

Eosinophils develop from stem cells in the bone marrow under the influence of hematopoietic cytokines, particularly IL-5. Previously, we have demonstrated that blockage of Notch signaling by a gamma-secretase inhibitor (GSI) promotes the differentiation of umbilical cord blood (UCB)-derived eosinophils. These highly major basic protein (MBP)-positive eosinophils cultured in the presence of the inhibitor lack the migratory response to eotaxin, although their CCR3 levels are similar to those of eosinophils cultured without the inhibitor. We investigated the mechanism underlying the differential responses of differentiating eosinophils and their functionalities in response to eosinophil-active cytokines in the presence and absence of GSI. UCB cells cultured for 4 weeks with hematopoietic cytokines in the presence or absence of GSI were monitored for extracellular signal-regulated kinase (ERK) phosphorylation, MBP expression, and functionality. Eosinophil differentiation from UCB cells was accompanied by activation of the ERK1/2 pathway during the 4-week culture period. In particular, strong ERK1/2 phosphorylation was observed in eosinophils during the final stage of culture when GSI was present. Consistent with this finding, ERK inhibition nullified the effect of GSI on eosinophil differentiation. Eosinophils cultured with GSI resembled airway eosinophils rather than peripheral blood eosinophils based on reduced IL-5Ralpha expression, blunted eosinophil cationic protein (ECP) degranulation, and decreased IL-13 and granulocyte macrophage-colony-stimulating factor production. These results suggest that Notch signaling regulates the terminal differentiation and subsequent effector phenotypes of eosinophils, partly through modulation of the ERK pathway. GSI has therapeutic potential for eosinophilic inflammatory diseases, such as asthma.

Eosinophil apoptosis induced by fungal immunomodulatory peptide-fve via reducing IL-5alpha receptor

BACKGROUND/PURPOSE

Eosinophils are important effector cells in the pathogenesis of allergic bronchial asthma. Enhancement of eosinophil apoptosis has been considered to have therapeutic effect on allergic disease. Fungal immunomodulatory peptide (FIP)-fve has been reported to possess immunoprophylactic activities for allergic diseases. The purpose of this study was to investigate the modulation of FIP-fve on human eosinophil survival derived from allergic asthmatic patients.

METHODS

Eosinophils were obtained from allergic asthmatic patients and purified with the use of density gradients and immunomagnetic beads negative selection. Apoptosis was assessed by annexin V and propidium iodide. The apoptotic signal protein, CD95 and IL-5 receptor expression were assessed by Western blot and flow cytometric analysis.

RESULTS

When the eosinophils were treated with FIP-fve in the presence of IL-5, IL-5-enhanced eosinophil survival diminished. FIP-fve could reduce IL-5-mediated survival of eosinophils and decrease IL-5Ralpha expression. In the presence of FIP-fve, CD95 expression was upregulated and Bcl-xL and pro-caspase 3 expression were downregulated in cultured eosinophils.

CONCLUSION

The results suggest that FIP-fve can inhibit IL-5-mediated survival of eosinophils through the modulation of cytokine receptor expression and apoptotic signal protein production. The modulatory effect of FIP-fve on eosinophil apoptosis in vitro indicates that it may have some therapeutic effect on eosinophil-related allergic inflammation in vivo.

Systemic eosinophil response induced by respiratory syncytial virus

Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract disease (LRTD) in infants. Eosinophils have been suggested to play a role in the disease pathogenesis of LRTD. Inflammation can induce functional and morphological alterations of peripheral blood granulocytes. In patients with RSV LRTD, we aimed to investigate the eosinophil activation status by analysing surface markers. In vitro stimulation of eosinophils with cytokines leads to up-regulation of CD11b and priming markers recognized by the recently developed priming markers A17 and A27, whereas interleukin (IL)-5Ralpha is being down-regulated. In 51 patients and 10 controls we examined the expression of these surface markers on eosinophils in moderate to severe RSV-induced LRTD patients at the time of admission and 6 weeks later during the convalescence phase. RSV-patients were characterized by a higher eosinophil CD11b expression compared to controls. Although basal A17 and A27 expression was not increased, we observed a significantly higher expression of these priming epitopes on N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated cells of RSV patients compared with cells of controls, indicative of prior in vivo priming. Furthermore, IL-5Ralpha expression was down-regulated on peripheral blood eosinophils of these patients. Follow-up blood samples showed normalization of all markers but CD11b, which was persistently increased. Utilizing cellular markers, we observed that peripheral blood eosinophils from infants with RSV LRTD are in a more activated state compared to eosinophils of controls, which normalizes only partially during convalescence.

Dissection of the hyperadhesive phenotype of airway eosinophils in asthma

Asthma is characterized by appearance of eosinophils in the airway. Eosinophils purified from the airway 48 h after segmental antigen challenge are described as exhibiting greater adhesion to albumin-coated surfaces via an unidentified beta2 integrin and increased expression of alphaMbeta2 (CD11b/18) compared with purified blood eosinophils. We have investigated the determinants of this hyperadhesive phenotype. Airway eosinophils exhibited increased reactivity with the CBRM1/5 anti-alphaM activation-sensitive antibody as well as enhanced adhesion to VCAM-1 (CD106) and diverse ligands, including albumin, ICAM-1 (CD54), fibrinogen, and vitronectin. Purified blood eosinophils did not adhere to the latter diverse ligands. Enhanced adhesion of airway eosinophils was blocked by anti-alphaMbeta2. Podosomes, structures implicated in cell movement and proteolysis of matrix proteins, were larger and more common on airway eosinophils adherent to VCAM-1 when compared with blood eosinophils. Incubation of blood eosinophils with IL-5 replicated the phenotype of airway eosinophils. That is, IL-5 enhanced recognition of alphaM by CBRM1/5; stimulated alphaMbeta2-mediated adhesion to VCAM-1, albumin, ICAM-1, fibrinogen, and vitronectin; and increased podosome formation on VCAM-1. Thus, the hyperadhesion of airway eosinophils after antigen challenge is mediated by upregulated and activated alphaMbeta2.

The alpha4bbeta7-integrin is dynamically expressed on murine eosinophils and involved in eosinophil trafficking to the intestine

BACKGROUND

Of the numerous adhesion molecules expressed by eosinophils, the alpha4-integrin has been identified as critically involved in eosinophil trafficking in the lung. Most studies have focused on the role of the alpha4beta1-adhesion complex, but eosinophils also express the alpha4beta7-integrin complex.

OBJECTIVE

To investigate the role of alpha4beta7, by assessing its membrane expression on eosinophils from different compartments using allergen-challenged mice and IL-4/IL-5 bi-transgenic mice. In addition, we aim to determine the impact of beta7-integrin deficiency on eosinophil recruitment to the lungs and intestine in specific experimental allergic models.

RESULTS

Evaluation of alpha4beta7 expression on bronchoalveolar lavage fluid (BALF) and lung tissue eosinophils revealed a down-regulation of this integrin as eosinophils migrate through the lungs. Indeed eosinophils isolated from the BALF and lung of allergic mice had low expression of the alpha4beta7-complex. While expression of the alpha4-chain remained unchanged, a significant decrease in beta7-surface expression was observed. Intestinal eosinophils, isolated from Peyer's patches, also displayed a down-regulation of the alpha4beta7-integrin, albeit only modest. In contrast, circulating eosinophils, isolated from the blood and spleen, expressed high levels of the alpha4beta7-integrin. However, eosinophil trafficking into the lungs of beta7-integrin-deficient mice was not significantly impaired in response to respiratory allergen challenges. In contrast, beta7-deficient mice had impaired eosinophil recruitment to the intestine.

CONCLUSION

Taken together, these results identify differential expression of the alpha4beta7-integrin on eosinophils and its critical role in regulating eosinophil responses in the intestine.

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.

Inhibition of chronic airway inflammation and remodeling by galectin-3 gene therapy in a murine model

We previously demonstrated that treatment of acute asthmatic rats with gene therapy using plasmid-encoding Galectin-3 (Gal-3) resulted in an improvement of cellular and functional respiratory parameters. The next question that we wanted to clarify was if in a chronic situation where the treated animal continues to inhale the Ag, does this procedure prevent the chronicity and the remodeling? Chronic inflammation was induced by intranasal administration of OVA over a period of 12 wk. In the treated group, the Gal-3 gene was introduced by intranasal instillation in 50 mul of plasmid-encoding Gal-3. Noninvasive airway responsiveness to methacholine was tested at different times. Cells were obtained by bronchoalveolar lavage and used for RNA extraction and cytometric studies. Eosinophils were counted in blood and bronchoalveolar lavage fluid. Real-time PCR was used to measure Gal-3 and cytokine mRNA expression in lung. Lungs were paraffined and histologic analyses were performed (H&E, periodic acid-Schiff, and Masson Trichrome stain). Our results showed that 12 wk after the first intranasal Ag instillation in chronically asthmatic mice, treatment with the Gal-3 gene led to an improvement in the eosinophil count and the normalization of hyperresponsiveness to methacholine. Concomitantly, this treatment resulted in an improvement in mucus secretion and subepithelial fibrosis in the chronically asthmatic mice, with a quantitatively measured reduction in lung collagen, a prominent feature of airway remodeling. Plasmid-encoding Gal-3 acts as a novel treatment for chronic asthma in mice producing nearly complete blockade of Ag responses with respect to eosinophil airway accumulation, airway hyperresponsiveness, and remodeling.

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.

Interferon-gamma inhibits in vitro mobilization of eosinophils by interleukin-5

BACKGROUND

Th2 cytokines play pivotal roles in allergic inflammation, including eosinophilia, and their actions are antagonized by Th1 cytokines, conferring them therapeutic potential.

METHODS

In this study, we examined the ability of a number of cytokines to suppress the activation of eosinophils that function as effector cells for allergic airway diseases.

RESULTS

Interleukin (IL)-5, IL-6, and tumor necrosis factor (TNF) induced an eosinophil shape change, whereas interferon (IFN)-gamma significantly inhibited the shape change. Other cytokines, including IL-1beta, IL-4, IL-10 and IL-13, had little or only slightly enhancing or reducing effects on the shape change. We further analyzed the IFN-gamma effect, showing that pretreatment with IFN-gamma strongly suppressed IL-5-induced eosinophil shape change, and cycloheximide (CHX) abrogated the suppression by IFN-gamma, suggesting that new protein synthesis is required for the inhibitory effect by this cytokine. In agreement with these results, IFN-gamma blocked the eosinophil migration and ERK phophorylation induced by IL-5, and the addition of CHX restored eosinophil chemotaxis.

CONCLUSIONS

Collectively, IFN-gamma may attenuate eosinophilic inflammation by directly negating eosinophil mobilization.

Rebound eosinophilia after treatment of hypereosinophilic syndrome and eosinophilic gastroenteritis with monoclonal anti-IL-5 antibody SCH55700

BACKGROUND

Hypereosinophilic syndrome and eosinophilic gastroenteritis with peripheral eosinophilia are characterized by sustained eosinophilia and eosinophil-mediated tissue damage. Although treatment with the humanized monoclonal anti-IL-5 antibody SCH55700 resulted in improvement of eosinophilia and clinical symptoms in 6 of 8 of patients with hypereosinophilic syndrome or eosinophilic gastroenteritis with peripheral eosinophilia for as long as 12 weeks, eosinophil counts subsequently rose above baseline levels, accompanied by an exacerbation of symptoms.

OBJECTIVE

To identify the mechanism underlying this rebound eosinophilia.

METHODS

Purified eosinophils from patients or normal donors were cultured with IL-5, patient serum, and/or anticytokine antibodies, and eosinophil survival was assessed by flow cytometry. Serum and intracellular cytokine levels were measured by multiplex sandwich ELISA and flow cytometry, respectively.

RESULTS

Before treatment with SCH55700, in vitro eosinophil survival in media and in response to recombinant IL-5 was similar in patients and normal donors. At 1 month posttreatment, the eosinophil survival curves were unchanged in 4 of 5 patients in media and in all 5 patients in response to recombinant IL-5. Normal eosinophil survival was prolonged in cultures containing posttreatment but not pretreatment sera (pretreatment vs posttreatment, 10.74% vs 73.02% live cells; P = .01). This posttreatment serum effect on eosinophil survival was reversed by the addition of the monoclonal anti-IL-5 antibody TRFK5. Although increased levels of serum IL-5 were observed at 1 month compared with 2 to 3 days posttreatment in 5 of 6 patients ( P = .04), intracellular cytokine analysis did not reveal increased production of IL-5 by peripheral blood mononuclear cells.

CONCLUSIONS

The rebound eosinophilia after SCH55700 treatment is a result of a serum factor that enhances eosinophil survival. Reversal of this effect by the addition of antibody to IL-5 suggests that this factor may be IL-5 itself.

The rise of the phoenix: the expanding role of the eosinophil in health and disease

We have entered a new phase in the evolution of our understanding of the role of the eosinophil with a greater appreciation of novel potential functions that may be ascribed to this enigmatic cell type. This review not only provides an update to our current understanding of the various immunobiological roles for the eosinophil, but also attracts attention to some novel observations predicting functions beyond its putative effector role. These observations include the intriguing possibility that the eosinophil may possess the capacity to regulate the immune and inflammatory responses in diseases such as asthma.

Localization of receptors in lipid rafts can inhibit signal transduction

Processes of cell survival, division, differentiation, and death are guided by the binding of signal molecules to receptors, which activates intracellular signaling networks and ultimately elicits genetic, biochemical, or biomechanical responses within the cell. While intracellular mechanisms for these processes have been well studied, little attention has been given to the role extracellular ligand transport and binding may play in signal initiation. Recent studies have found that the localization of receptors in lipid rafts is critical for the functions of many signaling pathways. By concentrating membrane components, rafts may promote essential interactions for signaling. Lipid rafts can also have negative effects on signaling, but mechanisms remain elusive. We propose that raft-mediated receptor clustering can reduce signaling by prolonging the diffusion of ligands to their receptors. We quantify this effect using a simple diffusion-limited binding model that accounts for the spatial distribution of lipid rafts and receptors on the cell surface. We find that receptor clustering can reduce the apparent rate of receptor binding by up to 80%, consistent with observed increases in epidermal growth factor (EGF) binding by up to 100% following disruption of lipid rafts (Pike and Casey 2002 Biochemistry 41:10315-10322; Roepstorff et al. 2002 J Biol Chem 277:18954-18960). Failure to account for the effects of receptor clustering on rates of ligand binding can skew the interpretation of current methods of cancer diagnosis and treatment. Finally, we discuss how the activation of particular signaling pathways can change over time, depending, in part, on the overall level and spatial distribution of the receptors.

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.

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.

Chemotaxis inhibitory protein of Staphylococcus aureus, a bacterial antiinflammatory agent

Leukocyte migration is a key event both in host defense against invading pathogens as well as in inflammation. Bacteria generate chemoattractants primarily by excretion (formylated peptides), complement activation (C5a), and subsequently through activation of leukocytes (e.g., leukotriene B4, platelet-activating factor, and interleukin 8). Here we describe a new protein secreted by Staphylococcus aureus that specifically impairs the response of neutrophils and monocytes to formylated peptides and C5a. This chemotaxis inhibitory protein of S. aureus (CHIPS) is a 14.1-kD protein encoded on a bacteriophage and is found in >60% of clinical isolates. CHIPS reduces the neutrophil recruitment toward C5a in a mouse peritonitis model, even though its activity is much more potent on human than on mouse cells. These findings suggest a new immune escape mechanism of S. aureus and put forward CHIPS as a potential new antiinflammatory therapeutic compound.

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.

Matrix metalloproteinase-9 deficiency results in enhanced allergen-induced airway inflammation

Matrix metalloproteinases (MMPs) are a large family of endopeptidases that proteolytically degrade extracellular matrix. Many different cells produce MMP-9, and levels have been shown to be up-regulated in patients with allergic asthma. The aim of this study was to investigate the in vivo role of MMP-9 during allergen-induced airway inflammation. Acute allergic pulmonary eosinophilia was established in MMP-9 knockout (KO) and wild-type (WT) control mice by sensitization and challenge with OVA. Cell recruitment was significantly increased in both bronchoalveolar lavage (BAL) and lung tissue compartments in MMP-9 KO mice compared with WT mice. This heightened cell recruitment was primarily due to increased eosinophils and Th2 cells in the BAL and lung tissue of MMP-9 KO mice in comparison with WT controls. Moreover, levels of the Th2 cytokines, IL-4 and IL-13, and the chemokines eotaxin/CCL11 and macrophage-derived chemokine/CCL22 were substantially increased in MMP-9 KO mice compared with WT after OVA challenge. Resolution of eosinophilia was similar between MMP-9 KO and WT mice, but Th2 cells persisted in BAL and lungs of MMP-9 KO mice for longer than in WT mice. Our results indicate that MMP-9 is critically involved in the recruitment of eosinophils and Th2 cells to the lung following allergen challenge, and suggest that MMP-9 plays a role in the development of Th2 responses to allergen.

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.