Eosinophil hematopoietins antagonize the programmed cell death of eosinophils. Cytokine and glucocorticoid effects on eosinophils maintained by endothelial cell-conditioned medium

Recent advances of eosinophils and its correlated diseases

Eosinophils are differentiated by bone marrow multipotent progenitor cells and are further released into peripheral blood after maturation. Human eosinophils can exhibit unique multi-leaf nuclear morphology, which are filled with cytoplasmic granules that contain cytotoxicity and immune regulatory proteins. In recent years, many studies focused on the origin, differentiation and development process of eosinophils. It has been discovered that the eosinophils have the regulatory functions of innate and adaptive immunity, and can also function in several diseases, including asthma, chronic obstructive pulmonary diseases, acute respiratory distress syndrome, malignant tumors and so on. Hence, the role and effects of eosinophils in various diseases are emphasized. In this review, we comprehensively summarized the development and differentiation process of eosinophils, the research progress of their related cytokines, diseases and current clinical treatment options, and discussed the potential drug target, aiming to provide a theoretical and practical basis for the clinical prevention and treatment of eosinophil-related diseases, especially respiratory diseases. To conclude, the guiding significance of future disease treatment is proposed based on the recent updated understandings into the cell functions of eosinophils.

Eosinophil Development, Disease Involvement, and Therapeutic Suppression

Human eosinophils have characteristic morphologic features, including a bilobed nucleus and cytoplasmic granules filled with cytotoxic and immunoregulatory proteins that are packaged in a specific manner. Eosinophil production in the bone marrow is exquisitely regulated by timely expression of a repertoire of transcription factors that work together via collaborative and hierarchical interactions to direct eosinophil development. In addition, proper granule formation, which occurs in a spatially organized manner, is an intrinsic checkpoint that must be passed for proper eosinophil production to occur. In eosinophil-associated disorders, eosinophils and their progenitors can be recruited in large numbers into tissues where they can induce proinflammatory organ damage in response to local signals. Eosinophils are terminally differentiated and do not proliferate once they leave the bone marrow. The cytokine IL-5 specifically enhances eosinophil production and, along with other mediators, promotes eosinophil activation. Indeed, eosinophil depletion with anti-IL-5 or anti-IL-5Rα is now proven to be clinically beneficial for several eosinophilic disorders, most notably severe asthma, and several therapeutics targeting eosinophil viability and production are now in development. Significant progress has been made in our understanding of eosinophil development and the consequences of tissue eosinophilia. Future research efforts focused on basic eosinophil immunobiology and translational efforts to assist in the diagnosis, treatment selection, and resolution of eosinophil-associated disorders will likely be informative and clinically helpful.

Monoclonal antibody therapy for the treatment of asthma and chronic obstructive pulmonary disease with eosinophilic inflammation

Eosinophils have been linked with asthma for more than a century, but their role has been unclear. This review discusses the roles of eosinophils in asthma and chronic obstructive pulmonary disease (COPD) and describes therapeutic antibodies that affect eosinophilia. The aims of pharmacologic treatments for pulmonary conditions are to reduce symptoms, slow decline or improve lung function, and reduce the frequency and severity of exacerbations. Inhaled corticosteroids (ICS) are important in managing symptoms and exacerbations in asthma and COPD. However, control with these agents is often suboptimal, especially for patients with severe disease. Recently, new biologics that target eosinophilic inflammation, used as adjunctive therapy to corticosteroids, have proven beneficial and support a pivotal role for eosinophils in the pathology of asthma. Nucala® (mepolizumab; anti-interleukin [IL]-5) and Cinquair® (reslizumab; anti-IL-5), the second and third biologics approved, respectively, for the treatment of asthma, exemplifies these new treatment options. Emerging evidence suggests that eosinophils may contribute to exacerbations and possibly to lung function decline for a subset of patients with COPD. Here we describe the pharmacology of therapeutic antibodies inhibiting IL-5 or targeting the IL-5 receptor, as well as other cytokines contributing to eosinophilic inflammation. We discuss their roles as adjuncts to conventional therapeutic approaches, especially ICS therapy, when disease is suboptimally controlled. These agents have achieved a place in the therapeutic armamentarium for asthma and COPD and will deepen our understanding of the pathogenic role of eosinophils.

Anti-interleukin therapy in asthma

Asthma remains one of the most prevalent and costly diseases in the United States. Asthma accounts for a significant amount of direct medical expenditures and indirect cost from days lost at school and work. Modern understanding of its complex pathogenesis has allowed recognition of the heterogeneity of the disease across populations and the various inflammatory pathways that drive airway inflammation in asthma. Interleukins play important roles in both eosinophilic and noneosinophilic asthma, and anti-interleukin therapy will allow for a targeted, personalized approach to asthma management. With the success of anti-interleukin (IL) -4, IL-5, and IL-13 therapy in recent large trials among specific populations of asthmatics, it is likely that targeted anti-interleukin therapy will be approved for use in the near future. It will be important for clinicians and pharmacists to understand their risks, benefits, and proper indications.

Expression profiling of differentiating eosinophils in bone marrow cultures predicts functional links between microRNAs and their target mRNAs

BACKGROUND

MicroRNAs (miRNAs) are small non-coding RNAs that regulate complex transcriptional networks underpin immune responses. However, little is known about the specific miRNA networks that control differentiation of specific leukocyte subsets. In this study, we profiled miRNA expression during differentiation of eosinophils from bone marrow (BM) progenitors (bmEos), and correlated expression with potential mRNA targets involved in crucial regulatory functions. Profiling was performed on whole BM cultures to document the dynamic changes in miRNA expression in the BM microenvironment over the differentiation period. miRNA for network analysis were identified in BM cultures enriched in differentiating eosinophils, and chosen for their potential ability to target mRNA of factors that are known to play critical roles in eosinophil differentiation pathways or cell identify.

METHODOLOGY/PRINCIPAL FINDINGS

We identified 68 miRNAs with expression patterns that were up- or down- regulated 5-fold or more during bmEos differentiation. By employing TargetScan and MeSH databases, we identified 348 transcripts involved in 30 canonical pathways as potentially regulated by these miRNAs. Furthermore, by applying miRanda and Ingenuity Pathways Analysis (IPA), we identified 13 specific miRNAs that are temporally associated with the expression of IL-5Rα and CCR3 and 14 miRNAs associated with the transcription factors GATA-1/2, PU.1 and C/EBPε. We have also identified 17 miRNAs that may regulate the expression of TLRs 4 and 13 during eosinophil differentiation, although we could identify no miRNAs targeting the prominent secretory effector, eosinophil major basic protein.

CONCLUSIONS/SIGNIFICANCE

This is the first study to map changes in miRNA expression in whole BM cultures during the differentiation of eosinophils, and to predict functional links between miRNAs and their target mRNAs for the regulation of eosinophilopoiesis. Our findings provide an important resource that will promote the platform for further understanding of the role of these non-coding RNAs in the regulation of eosinophil differentiation and function.

Targeting eosinophils in allergy, inflammation and beyond

Eosinophils can regulate local immune and inflammatory responses, and their accumulation in the blood and tissue is associated with several inflammatory and infectious diseases. Thus, therapies that target eosinophils may help control diverse diseases, including atopic disorders such as asthma and allergy, as well as diseases that are not primarily associated with eosinophils, such as autoimmunity and malignancy. Eosinophil-targeted therapeutic agents that are aimed at blocking specific steps involved in eosinophil development, migration and activation have recently entered clinical testing and have produced encouraging results and insights into the role of eosinophils. In this Review, we describe recent advances in the development of first-generation eosinophil-targeted therapies and highlight strategies for using personalized medicine to treat eosinophilic disorders.

Th2 cells and cytokine networks in allergic inflammation of the lung

The cytokines released from Th2 and Th2-like cells are likely to be central to the pathophysiolgy of asthma and allergy, contributing to aberrant IgE production, eosinophilia and, perhaps, mucosal susceptibility to viral infection. IL-4 has emerged as a central target, not only for B cell IgE production, but also in the commitment of both CD4+ and CD8+ T cells to cells with Th2 effector function capable of secreting IL-5 resultlng in eosinophilic inflammation. In view of the central role of this cytokine and the evidence that glucocorticoids are unable to modify many IL-4 dependent effects, Th2 inhibitors may prove to be novel therapies for the treatment of bronchial asthma.

Apoptosis and inflammation

During the last few decades it has been recognized that cell death is not the consequence of accidental injury, but is the expression of a cell suicide programme. Kerr et al. (1972) introduced the term apoptosis. This form of cell death is under the influence of hormones, growth factors and cytokines, which depending upon the receptors present on the target cells, may activate a genetically controlled cell elimination process. During apoptosis the cell membrane remains intact and the cell breaks into apoptotic bodies, which are phagocytosed. Apoptosis, in contrast to necrosis, is not harmful to the host and does not induce any inflammatory reaction. The principal event that leads to inflammatory disease is cell damage, induced by chemical/physical injury, anoxia or starvation. Cell damage means leakage of cell contents into the adjacent tissues, resulting in the capillary transmigration of granulocytes to the injured tissue. The accumulation of neutrophils and release of enzymes and oxygen radicals enhances the inflammatory reaction. Until now there has been little research into the factors controlling the accumulation and the tissue load of granulocytes and their histotoxic products in inflammatory processes. Neutrophil apoptosis may represent an important event in the control of intlamtnation. It has been assumed that granulocytes disintegrate to apoptotic bodies before their fragments are removed by local macrophages. Removal of neutrophils from the inflammatory site without release of granule contents is of paramount importance for cessation of inflammation. In conclusion, apoptotic cell death plays an important role in inflammatory processes and in the resolution of inflammatory reactions. The facts known at present should stimulate further research into the role of neutrophil, eosinophil and macrophage apoptosis in inflammatory diseases.

Cysteinyl leukotriene overproduction in aspirin-exacerbated respiratory disease is driven by platelet-adherent leukocytes

Cysteinyl leukotriene (cysLT) overproduction is a hallmark of aspirin-exacerbated respiratory disease (AERD), but its mechanism is poorly understood. Because adherent platelets can convert the leukocyte-derived precursor leukotriene (LT)A(4) to LTC(4), the parent cysLT, through the terminal enzyme LTC(4) synthase, we investigated the contribution of platelet-dependent transcellular cysLT production in AERD. Nasal polyps from subjects with AERD contained many extravascular platelets that colocalized with leukocytes, and the percentages of circulating neutrophils, eosinophils, and monocytes with adherent platelets were markedly higher in the blood of subjects with AERD than in aspirin-tolerant controls. Platelet-adherent subsets of leukocytes had higher expression of several adhesion markers than did platelet nonadherent subsets. Adherent platelets contributed more than half of the total LTC(4) synthase activity of peripheral blood granulocytes, and they accounted for the higher level of LTC(4) generation by activated granulocytes from subjects with AERD compared with aspirin-tolerant controls. Urinary LTE(4) levels, a measure of systemic cysLT production, correlated strongly with percentages of circulating platelet-adherent granulocytes. Because platelet adherence to leukocytes allows for both firm adhesion to endothelial cells and augmented transcellular conversion of leukotrienes, a disturbance in platelet-leukocyte interactions may be partly responsible for the respiratory tissue inflammation and the overproduction of cysLTs that characterize AERD.

The role of nasal corticosteroids in the treatment of rhinitis

Intranasal corticosteroids (INSs) are the first choice for rhinitis pharmacotherapy. This preference is because of their broad range of actions that result in reductions of proinflammatory mediators, cytokines, and cells. Over the past 30 years, INSs have been modified to improve their pharmacodynamic, pharmacokinetic, and delivery system properties, with attention to improving characteristics such as receptor binding affinity, lipophilicity, low systemic bioavailability, and patient preference. Clinically, they have been shown to be the most effective class of nasal medications for treating allergic rhinitis and nonallergic rhinopathy, with no clear evidence that any specific INS is superior to others.

Current strategies in the management of hypereosinophilic syndrome, including mepolizumab

BACKGROUND

Patients with hypereosinophilic syndrome (HES) vary considerably in their clinical presentation with regard to the severity and pattern of end-organ involvement. Clinical manifestations range from nonspecific symptoms to life-threatening, multisystem damage caused by eosinophil infiltration and local release of proinflammatory mediators and toxic granule products from these invading cells. The primary objective of treatment is to reduce blood and tissue eosinophilia and prevent eosinophil-mediated tissue damage as safely as possible. Systemic corticosteroids, such as prednisone, are first-line therapy for the management of patients with symptomatic HES who lack the Fip1-like 1-platelet-derived growth factor receptor-alpha (FIP1L1-PDGFRA) gene fusion mutation. The tyrosine kinase inhibitor, imatinib, is first-line treatment for FIP1L1-PDGFRA-positive patients). Because of the toxicity and serious side-effects that can occur with oral corticosteroids, alternative therapies may need to be introduced to reduce the cumulative corticosteroid exposure while maintaining disease control.

SCOPE

Among corticosteroid-sparing agents are cytotoxic drugs and interferon-alpha; anti-interleukin-5 (IL-5) monoclonal antibodies are also currently under investigation for the treatment of HES. This manuscript reviews the available treatments for HES and the range of side-effects associated with long-term corticosteroid use, and then focuses on the anti-IL-5 monoclonal antibodies, mepolizumab and reslizumab. Of these, only mepolizumab has been studied in a randomized, placebo-controlled trial. Literature search methodology utilized www.pubmed.gov and www.clinicaltrials.gov with search terms including hypereosinophilic syndrome and corticosteroid side-effects coupled with search terms including eosinophils, mepolizumab and reslizumab through March 2010.

FINDINGS

Three case studies are presented that demonstrate the limitations of corticosteroid therapy in terms of tolerability and quality of life, and the subsequent use of mepolizumab as a corticosteroid-sparing agent in these individuals.

CONCLUSION

Targeted eosinophil-directed therapy with an anti-IL-5 neutralizing monoclonal antibody reduced the need for corticosteroids in these three HES patients without disease exacerbations.

The treatment of vasomotor rhinitis with intranasal corticosteroids

Objective

Intranasal steroids (INS) are firmly established as the therapy for choice for allergic rhinitis, but their role in vasomotor rhinitis (VMR) is not fully characterized. This review examines the potential mechanisms of action and reported efficacy of INS in patients with VMR.

Results

INS, through intracellular activation of the glucocorticoid receptor, down-regulate the recruitment and activation of inflammatory cells (T-lymphocytes, eosinophils, mast cells, basophils, neutrophils, macrophages), increase degradation of neuropeptides, and reduce epithelial cell activity, vascular permeability, and chemokine secretion. It is likely that more than vasoconstriction is responsible for the clinical effects of INS.

Eight INS can be prescribed for rhinitis in the US; only 4 have been studied for VMR. Seventy-four percent of patients treated with beclomethasone dipropionate considered themselves symptom-free or greatly improved versus 31% with placebo. Budesonide significantly reduced rhinitis symptoms and methacholine-induced nasal secretions compared with placebo. Fluticasone propionate compared with placebo provided significantly greater relief from nasal obstruction; computed tomographic scans showed significant reductions in the mucosal area of the lower turbinates. Mometasone furoate produced numerically better rhinitis symptom scores and, when discontinued, lower relapse rates than placebo.

Conclusion

Data supports INS as beneficial pharmacotherapy for VMR.

Macrophage migration inhibitory factor is critical to interleukin-5-driven eosinophilopoiesis and tissue eosinophilia triggered by Schistosoma mansoni infection

Macrophage migration inhibitory factor (MIF) participates in the pathogenesis of inflammatory diseases, including asthma, in which it enhances airway hypersensitivity and tissue eosinophilia. Herein, we investigated the role of MIF in eosinophilopoiesis and tissue eosinophilia using Schistosoma mansoni infection. MIF-deficient (Mif(-/-)) mice had similar numbers of adult worms, eggs, and granulomas compared to wild-type mice, but the size of granulomas was strikingly reduced due to smaller numbers of eosinophils. MIF did not affect the acquired response to infection, as Mif(-/-) mice produced normal amounts of Th2 cytokines and IgE. Nevertheless, recombinant MIF (rMIF) behaved as a chemoattractant for eosinophils, what could partially explain the reduced eosinophilia in infected Mif(-/-) mice. Moreover, the percentage of eosinophils was reduced in bone marrows of Mif(-/-) mice chronically infected with S. mansoni compared to wild type. Mif(-/-) had impaired eosinophilopoiesis in response to interleukin (IL)-5 and addition of rMIF to bone marrow cultures from IL-5 transgenic mice enhanced the generation of eosinophils. In the absence of MIF, eosinophil precursors were unable to survive the IL-5-supplemented cell culture, and were ingested by macrophages. Treatment with pancaspase inhibitor z-VAD or rMIF promoted the survival of eosinophil progenitors. Together, these results indicate that MIF participates in IL-5-driven maturation of eosinophils and in tissue eosinophilia associated with S. mansoni infection.

Recombinant surfactant protein-D selectively increases apoptosis in eosinophils of allergic asthmatics and enhances uptake of apoptotic eosinophils by macrophages

Pulmonary surfactant protein-D (SP-D) is a multifunctional, pattern recognition molecule involved in resistance to allergen challenge and pulmonary inflammation. In view of therapeutic effects of exogenous SP-D or recombinant fragment of human surfactant protein-D (rhSP-D) (composed of eight Gly-X-Y collagen repeat sequences, homotrimeric neck and lectin domains) in murine models of lung allergy and hypereosinophilic SP-D gene-deficient mice, we investigated the possibility of a direct interaction of purified rhSP-D with human eosinophils derived from allergic patients and healthy donors. rhSP-D showed a sugar- and calcium-dependent binding to human eosinophils, suggesting involvement of its carbohydrate recognition domain. While eosinophils from allergic patients showed a significant increase in apoptosis, oxidative burst and CD69 expression in presence of rhSP-D, eosinophils from healthy donors showed no significant change. However, these eosinophils from healthy donors when primed with IL-5 exhibited increase in apoptosis on incubation with rhSP-D. Apoptosis mediated by rhSP-D in primed eosinophils was not affected by the antioxidant, N-acetyl-L-cysteine. There was a manifold increase in binding of rhSP-D to apoptotic eosinophils than the normal eosinophils and rhSP-D induced a significant increase in uptake of apoptotic eosinophils by J774A.1 macrophage cells. The study suggests that rhSP-D mediated preferential increase of apoptosis of primed eosinophils while not affecting the normal eosinophils and increased phagocytosis of apoptotic eosinophils may be important mechanisms of rhSP-D and plausibly SP-D-mediated resolution of allergic eosinophilic inflammation in vivo.

Eotaxin-1/CC chemokine ligand 11: a novel eosinophil survival factor secreted by human pulmonary artery endothelial cells

Airway eosinophilia plays a major role in the pathogenesis of asthma with the inhibition of apoptosis by GM-CSF and IL-5 proposed as a mechanism underlying prolonged eosinophil survival. In vivo and ex vivo studies have indicated the capacity of interventions that drive human eosinophil apoptosis to promote the resolution of inflammation. Far less is known about the impact of transendothelial migration on eosinophil survival, in particular, the capacity of endothelial cell-derived factors to contribute toward the apoptosis-resistant phenotype characteristic of airway-resident eosinophils. We examined the effects of conditioned medium from human pulmonary artery endothelial cells (HPAEC-CM) on eosinophil apoptosis in vitro. HPAEC-CM inhibited eosinophil, but not neutrophil apoptosis. This effect was specific to HPAECs and comparable in efficacy to the survival effects of GM-CSF and IL-5. The HPAEC survival factor was shown, on the basis of GM-CSF, IL-5, and IL-3 detection assays, Ab neutralization, and sensitivity to PI3K inhibition, to be clearly discrete from these factors. Gel filtration of HPAEC-CM revealed a peak of eosinophil survival activity at 8-12 kDa, and PCR confirmed the presence of mRNA for CCL5, CCL11, CCL24, CCL26, and CCL27 in the HPAECs. The CCR3 antagonist GW782415 caused a major inhibition of the HPAEC-CM-induced survival effect, and Ab neutralization of individual CCR3 chemokines revealed CCL11 as the major survival factor present in the HPAEC-CM. Furthermore, chemokine Ab arrays demonstrated up-regulation of CCL11 in HPAEC-CM. These data demonstrate the capacity of HPAECs to generate CCR3 agonists and the ability of CCL11 to inhibit human eosinophil apoptosis.

Eosinophils from lineage-ablated Delta dblGATA bone marrow progenitors: the dblGATA enhancer in the promoter of GATA-1 is not essential for differentiation ex vivo

A critical role for eosinophils in remodeling of allergic airways was observed in vivo upon disruption of the dblGATA enhancer that regulates expression of GATA-1, which resulted in an eosinophil-deficient phenotype in the DeltadblGATA mouse. We demonstrate here that bone marrow progenitors isolated from DeltadblGATA mice can differentiate into mature eosinophils when subjected to cytokine stimulation ex vivo. Cultured DeltadblGATA eosinophils contain cytoplasmic granules with immunoreactive major basic protein and they express surface Siglec F and transcripts encoding major basic protein, eosinophil peroxidase, and GATA-1, -2, and -3 to an extent indistinguishable from cultured wild-type eosinophils. Fibroblast coculture and bone marrow cross-transplant experiments indicate that the in vivo eosinophil deficit is an intrinsic progenitor defect, and remains unaffected by interactions with stromal cells. Interestingly, and in contrast to those from the wild type, a majority of the GATA-1 transcripts from cultured DeltadblGATA progenitors express a variant GATA-1 transcript that includes a first exon (1E(B)), located approximately 3700 bp downstream to the previously described first exon found in hemopoietic cells (1E(A)) and approximately 42 bp upstream to another variant first exon, 1E(C). These data suggest that cultured progenitors are able to circumvent the effects of the DeltadblGATA ablation by using a second, more proximal, promoter and use this mechanism to generate quantities of GATA-1 that will support eosinophil growth and differentiation.

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.

Immunological characteristics of subjects with asymptomatic skin sensitization to birch and grass pollen

BACKGROUND

Asymptomatic skin sensitization (AS) has been shown to be a risk factor for respiratory allergic disease.

OBJECTIVE

We investigated allergen and recall antigen-driven T cell proliferation, cytokine production and T cell expression of the chemokine receptor CCR4, in cultures derived from symptomatic atopics (SA), subjects with AS and healthy controls (HC). Numbers of allergen-specific precursor T cells in all three groups were also estimated.

METHODS

Peripheral blood mononuclear cells from the three groups were isolated and stimulated with allergen and tetanus toxoid. Proliferation, cytokine production and CCR4 expression were measured by flow cytometry.

RESULTS

A significantly increased proportion of CD4(+) memory T cells proliferated in response to allergen in SA as compared with subjects with AS (P<0.001) and HC (P<0.001). Only in SA was expansion of CD4(+)CCR4(+) T cells, after allergen stimulation observed. SA had higher frequencies of allergen-specific T cells than subjects with AS and HC (P=0.02, for both). With regard to allergen-induced production of T-helper type 1 (Th1) and Th2 cytokines, subjects with AS and HC resembled each other, while differing significantly from SA.

CONCLUSION

We conclude, that subjects with AS, although clearly IgE sensitized, have significant diminished numbers of allergen-specific T cells as well as decreased allergen-induced CD4(+) memory T cell proliferation as compared with SA. To a large extent, our findings are capable of explaining the immunological characteristics associated with AS. Our findings may serve as better prognostic markers for subsequent allergic progression, than previously described clinical and paraclinical characteristics.

Seasonal dynamics of chemokine receptors and CD62L in subjects with asymptomatic skin sensitization to birch and grass pollen

BACKGROUND

Asymptomatic skin sensitization (AS) has been shown to be a risk factor for respiratory allergic disease. CCR4, CXCR1 and CD62L have all been assigned a role in the immunopathogenesis of allergy. Memory T-cell expression of CCR4, CXCR1 and CD62L has not hitherto been investigated in subjects with AS.

METHODS

We investigated seasonal CD4 memory T-cell expression of the chemokine receptors CCR4, CXCR1 as well as L-selectin (CD62L) in fresh cultures derived from symptomatic atopics (SAs), subjects with AS and healthy controls (HCs). Peripheral blood mononuclear cells from all three groups were isolated during birch and grass pollination as well as in the following winter. CD4 memory T-cell expression of CCR4, CXCR1 and CD62L was determined by flow-cytometry.

RESULTS

During spring and summer, a significantly increased proportion of memory T cells expressed CCR4, CXCR1 and CD62L in SAs when compared with subjects with AS and HCs. Only SAs exhibited seasonal fluctuations in numbers of CCR4, CXCR1 and CD62L positive memory T cells.

CONCLUSION

Although clearly IgE sensitized, subjects with AS have significant diminished numbers of CCR4, CXCR1 and CD62L positive memory T cells, during pollination, when compared with SAs. In contrast to SAs, cultures derived from subjects with AS did not display seasonal variation. Our findings explain the lack of clinical symptoms, during pollination, in subjects with AS.

Prostaglandin E2 and dexamethasone regulate eosinophil differentiation and survival through a nitric oxide- and CD95-dependent pathway

Apoptosis, involving both CD95/CD95L interactions and their modulation by nitric oxide (NO), is central to regulation of mature eosinophil numbers. However, its role in regulating eosinophil production from bone-marrow precursors is unknown. We examined the effects of prostaglandin E2 (PGE2) and dexamethasone on eosinophil differentiation and survival in murine bone-marrow cultures, and their relationship to: NO production as well as CD95/CD95L-dependent apoptosis. Bone-marrow cultures were established with IL-5, alone or in association with PGE2, dexamethasone or both. PGE2 (10(-7)M) inhibited eosinophil differentiation by selectively inducing apoptosis in developing eosinophils. Dexamethasone (10(-7)M) protected developing eosinophils from PGE2-induced apoptosis. Since dexamethasone prevents induction of nitric oxide synthase (NOS), we evaluated the role of NO in the effects of both PGE2 and dexamethasone. NO donors (SNAP and SNP) down-modulated eosinophil precursor responses to IL-5. SNAP induced apoptosis through a dexamethasone-resistant mechanism. The NOS inhibitors, Nomega-nitro-L-arginine and aminoguanidine, blocked the effects of PGE2 on developing eosinophils. PGE2 was ineffective in bone-marrow from knockout mice lacking inducible NOS. PGE2 up-regulated CD95 and CD95L expression in developing eosinophils. Neither PGE2 nor SNAP were effective in cultures from CD95L-deficient gld mice. These data suggest that PGE2 induces apoptosis in developing eosinophils through inducible NOS, leading to NO-dependent activation of the CD95L/CD95 pathway, while dexamethasone antagonizes the effects of PGE2 on the same targets.

Activation of PI3K-Akt pathway mediates antiapoptotic effects of beta-adrenergic agonist in airway eosinophils

beta-Adrenoceptor agonists reportedly decrease spontaneous apoptosis of peripheral blood eosinophils; however, its signaling pathway is unknown. Survival signals can be elicited by the activation of phosphatidylinositol 3-kinase (PI3K) and Akt, both of which are known to be potent regulators of apoptosis, and Akt in turn inactivates Forkhead transcription factors, including FKHR (Forkhead in rhabdomyosarcoma). We have investigated the effect of beta-agonists on apoptosis of local eosinophils isolated from the airways and the involvement of PI3K, Akt, and FKHR in its survival signal. Eosinophils obtained from immunized mice by bronchoalveolar lavage after allergen provocation underwent apoptosis in a time-dependent manner. Incubation of eosinophils with isoproterenol or formoterol dose-dependently inhibited both spontaneous eosinophil apoptosis and apoptosis induced by Fas receptor activation. Incubation with cAMP or forskolin also inhibited eosinophil apoptosis. The PI3K inhibitors wortmannin and LY-294002 and an Akt inhibitor, 1-L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate, but not a mitogen-activated protein kinase kinase inhibitor PD-98059, blocked isoproterenol-mediated eosinophil survival. Wortmannin also inhibited cAMP-mediated eosinophil survival. Isoproterenol rapidly induced phosphorylation of Akt and FKHR in eosinophils in a PI3K-dependent manner. These findings indicate that the PI3K-Akt-FKHR pathway conveys a critical survival signal induced by beta-agonists in airway eosinophils.

Cytokine-regulated accumulation of eosinophils in inflammatory disease

The role of cytokines in the accumulation of eosinophil granulocytes in inflamed tissue has been studied extensively during recent years, and these molecules have been found to participate throughout the whole process of eosinophil recruitment. Haematopoietic cytokines such as IL-3, IL-5 and GM-CSF stimulate the proliferation and differentiation of eosinophils in the bone marrow, and the release of mature eosinophils from the bone marrow into the blood is probably promoted by IL-5. Priming of eosinophils in the blood following, for example, allergen challenge is performed mainly by IL-3, IL-5 and GM-CSF. An important step in the extravasation of eosinophils is their adhesion to the vascular endothelium. Adhesion molecules are upregulated by, e.g. IL-1, IL-4, TNF-alpha and IFN-gamma and the same cytokines may also increase the affinity of adhesion molecules both on eosinophils and endothelial cells. Finally, a number of cytokines have been shown to act as eosinophil chemotactic factors, attracting the cells to the inflammatory focus in the tissue. Some of the most important eosinophil chemoattractant cytokines are IL-5, IL-8, RANTES, eotaxin, eotaxin-2, eotaxin-3, MCP-3, MCP-4 and TNF-alpha. Th2 cells, mast cells and epithelial cells are important sources of proinflammatory cytokines, but in recent years, the eosinophils have also been recognized as cytokine-producing and thereby immunoregulatory cells. The aim of this paper is to review the role of cytokines in the process of eosinophil recruitment in asthma, allergy and ulcerative colitis.

Extremely rapid and intense induction of apoptosis in human eosinophils by anti-CD30 antibody treatment in vitro

Apoptosis is an important cellular mechanism for controlling cell viability and proliferation. With respect to eosinophils, cytokines prolong their survival, whereas corticosteroids reduce their survival in vitro. CD30, a member of the TNFR family, is expressed on the surface of many cell types, including Hodgkin's lymphoma cells. CD30 is capable of inducing apoptosis after Ab treatment in some cell lines. To determine whether this surface structure is involved in apoptosis of human eosinophils, we examined its expression and the effect of anti-CD30 Ab treatment on the viability of eosinophils. Purified human eosinophils expressed low, but consistently detectable, levels of CD30. Immobilized, but not soluble, forms of anti-CD30 Abs (HRS-4 and Ber-H8) or recombinant mouse CD30 ligand exhibited an extremely rapid and intense survival-reducing effect on the eosinophils in the presence of exogenous IL-5; this effect was both concentration and time dependent. Furthermore, high concentrations of IL-5 could not reverse the reduced survival rates. After treatment with anti-CD30 Ab, gel electrophoresis of DNA extracted from the eosinophils demonstrated changes consistent with apoptosis. The immobilized F(ab')(2) of the anti-CD30 Ab failed to induce eosinophil apoptosis. The addition of anti-CD18 Ab also completely abrogated the induction of eosinophil apoptosis. Further examination using specific signal transduction inhibitors suggested the involvement of p38, mitogen-activated protein kinase kinase 1/2, and specific tyrosine kinase, but not NF-kappaB, in the induction of CD30-mediated eosinophil apoptosis. These data demonstrate that CD30 can modify eosinophil survival by causing an extremely rapid and intense induction of apoptosis through a tightly regulated intracellular signaling pathway.

Eosinophils and monocytes produce pulmonary and activation-regulated chemokine, which activates cultured monocytes/macrophages

Pulmonary and activation-regulated chemokine (PARC/CCL18) belongs to the family of CC chemokines and shares 61% sequence identity with monocyte inflammatory protein (MIP)-1alpha. Produced by dendritic cells and macrophages primarily in the lung, PARC is known to be chemotactic for T cells. Because PARC's biological function is largely unknown, we screened various leukocyte populations for PARC expression and for response to PARC, with the idea that the cellular source may link PARC to disease states in which it may be involved. Here we report that eosinophils obtained from individuals with mild eosinophilia express PARC as assessed by RT-PCR on eosinophil RNA. The eosinophil preparations were free of monocytes, a known source of PARC, and no RT-PCR product was obtained from neutrophils. Furthermore, PARC protein was detected by ELISA in the supernatants of eosinophils from seven of nine donors and in higher concentration in the supernatants of monocytes on day 1 of culture. Purified recombinant PARC activated human monocytes/macrophages kept in culture for 3-4 days but not freshly isolated monocytes. The threshold dose for Ca(2+) mobilization as determined fluorometrically in indo 1-AM-labeled monocytes was 5 nM; maximal response was reached with approximately 50 nM PARC. PARC was chemotactic for these cultured monocytes and caused actin polymerization determined by FITC-phalloidin binding and fluorescence-activated cell sorting analysis. In contrast, PARC activated neither neutrophils nor eosinophils. Eosinophil production of PARC, its chemotactic effect on monocytes and lymphocytes, and PARC's previously described localization to the lung suggest that this chemokine might play a role in pulmonary leukocyte trafficking.

Differential effect of dexamethasone on cell death and STAT5 activation during in vitro eosinopoiesis

Glucorticoids reduce eosinophilia through a direct effect on eosinophils or indirectly on cells producing cytokines and chemokines. Conflicting data have been previously reported concerning glucocorticoid effects on eosinopoiesis. To elucidate this point, dexamethasone was added during eosinophil differentiation of CD34+ cells. Dexamethasone enhanced proliferation and differentiation through an early effect on immature cells. Dexamethasone inhibited apoptosis during early differentiation, whereas death of mature cells was increased. Signal transducer and activator of transcription 5 (STAT5) is a transcription factor involved in the proliferation, differentiation and survival of haematopoietic cells, which interacts with glucocorticoid receptor. Activation of STAT5 by interleukin-5 was investigated during eosinophil differentiation. Long isoforms of STAT5 were activated during the entire period in the culture as well as in blood eosinophils, while short isoforms were only activated during early differentiation. Short isoforms were less activated in the presence of dexamethasone. This suggests that dexamethasone could act on proliferation, differentiation and apoptosis during eosinophil differentiation through an association of STAT5 with the glucocorticoid receptor.

Oxidant-mediated mitochondrial injury in eosinophil apoptosis: enhancement by glucocorticoids and inhibition by granulocyte-macrophage colony-stimulating factor

The mainstay of asthma therapy, glucocorticosteroids (GCs) have among their therapeutic effects the inhibition of inflammatory cytokine production and induction of eosinophil apoptosis. In the absence of prosurvival cytokines (e.g., GM-CSF), eosinophils appear to be short-lived, undergoing apoptosis over 96 h in vitro. In a dose-dependent manner, GC further enhances apoptosis, while prosurvival cytokines inhibit apoptosis and antagonize the effect of GC. The mechanisms of eosinophil apoptosis, its enhancement by GC, and antagonism of GC by GM-CSF are not well-understood. As demonstrated in this study, baseline apoptosis of eosinophils resulted from oxidant-mediated mitochondrial injury that was significantly enhanced by GC. Mitochondrial injury was detected by early and progressive loss of mitochondrial membrane potential and the antioxidant protein, Mn superoxide dismutase (SOD). Also observed was the activation/translocation of the proapoptotic protein, Bax, to mitochondria. Underscoring the role of oxidants was the inhibition of mitochondrial changes and apoptosis with culture in hypoxia, or pretreatment with a flavoprotein inhibitor or a SOD mimic. GCs demonstrated early (40 min) and late (16 h) activation of proapoptotic c-Jun NH2-terminal kinase (JNK) and decreased the antiapoptotic protein X-linked inhibitor of apoptosis, a recently demonstrated inhibitor of JNK activation. Similarly, inhibition of JNK prevented GC-enhanced mitochondrial injury and apoptosis. Importantly, GM-CSF prevented GC-induced loss of X-linked inhibitor of apoptosis protein, late activation of JNK, and mitochondrial injury even in the face of unchanged oxidant production, loss of MnSOD, and early JNK activation. These data demonstrate that oxidant-induced mitochondrial injury is pivotal in eosinophil apoptosis, and is enhanced by GC-induced prolonged JNK activation that is in turn inhibited by GM-CSF.

Bcl-2-mediated regulation of CD69-induced apoptosis of human eosinophils: identification and characterization of a novel receptor-induced mechanism and relationship to CD95-transduced signalling

Elimination of the eosinophils from the airways by selective induction of apoptosis represents a therapeutic approach for asthma. Here we report on a possible target molecule, the surface receptor CD69. To simulate an asthmatic response, segmental allergen challenge in mild asthmatics was performed. Eosinophil numbers increased in bronchoalveolar lavage (BAL) at 18 h. In contrast to blood cells, BAL eosinophils expressed the activation marker CD69. Purified blood eosinophils stimulated with granulocyte/macrophage colony-stimulating factor (GM-CSF) or interferon-gamma (IFN-gamma) expressed CD69 and showed prolonged viability. Only IFN-gamma enhanced constitutive CD95 expression. Coincubation with anti-CD69 or anti-CD95 monoclonal antibody (MoAb) induced apoptosis, as revealed by propidium iodide incorporation, membrane blebbing and nuclear fragmentation. Additionally, both anti-CD69 and anti-CD95 MoAb reduced cytokine-enhanced Bcl-2 expression. In conclusion, CD69 transduces a Bcl-2-dependent death signal when ligated by a specific antibody. As, in contrast to the ubiquitous death-inducer CD95, the function of CD69 appears to be restricted to activated eosinophils, it represents an ideal target for therapeutic intervention in asthma.

Interleukin-15 inhibits spontaneous apoptosis in human eosinophils via autocrine production of granulocyte macrophage-colony stimulating factor and nuclear factor-kappaB activation

Prolonged eosinophil survival, i.e., reduced apoptosis, is implicated in the pathogenesis of chronic allergic inflammation. Here we demonstrate that interleukin (IL)-15, in the presence or absence of tumor necrosis factor (TNF)-alpha, reduces spontaneous apoptosis in freshly isolated human eosinophils. The prosurvival effect of IL-15 was abrogated by neutralizing antibody to granulocyte macrophage-colony stimulating factor (GM-CSF), although GM-CSF was not detected in conditioned media by ELISA. Additionally, the effect of IL-15 on spontaneous eosinophil apoptosis appeared to require nuclear factor-kappaB (NF-kappaB) activation based on evidence for NF-kappaB nuclear translocation and abrogation of the effect by the NF-kappaB inhibitor, Bay 11- 7082. Finally, the data demonstrate that IL-15 expression is higher in the submucosa of endobronchial tissues from subjects with moderate to severe asthma when compared with control subjects. Thus, our results suggest that IL-15, either alone or in combination with TNF-alpha, may perpetuate allergic inflammation by reduction of spontaneous eosinophil apoptosis through autocrine production of GM-CSF and NF-kappaB activation.

Interleukin-5 inhibits translocation of Bax to the mitochondria, cytochrome c release, and activation of caspases in human eosinophils

The apoptosis and subsequent clearance of eosinophils without histotoxic mediator release is thought to be crucial in the resolution of airway inflammation in asthma. Interleukin-5 (IL-5) is a potent suppressor of eosinophil apoptosis. The mechanism by which IL-5 inhibits spontaneous eosinophil apoptosis was investigated. Freshly isolated eosinophils constitutively expressed the conformationally active form of Bax in the cytosol and nucleus. During spontaneous and staurosporine-induced apoptosis, Bax underwent a caspase-independent translocation to the mitochondria, which was inhibited by IL-5. Eosinophil apoptosis was associated with the release of cytochrome c from the mitochondria, which was also inhibited by IL-5. IL-5 and the cell-permeable caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-(OMe) fluoromethyl ketone (z-VAD.fmk), prevented phosphatidylserine (PS) externalization, although only IL-5 inhibited loss of mitochondrial membrane potential (DeltaPsim). Peripheral blood eosinophils endogenously expressed "initiator" caspase-8 and -9, and "effector" caspase-3, -6, and -7. Spontaneous eosinophil apoptosis was associated with processing of caspase-3, -6, -7, -8, and -9. IL-5 and z-VAD.fmk prevented caspase activation in spontaneous apoptosis. The results suggest that spontaneous eosinophil apoptosis involves Bax translocation to the mitochondria, cytochrome c release, caspase-independent perturbation of the mitochondrial membrane, and subsequent activation of caspases. IL-5 inhibits spontaneous eosinophil apoptosis at a site upstream of Bax translocation.

Microarray analysis of eosinophils reveals a number of candidate survival and apoptosis genes

The increase in eosinophils at the site of antigen challenge has been used as evidence to suggest that this cell type plays a role in the pathophysiology of asthma. Aberrant production of several different cytokines, particularly interleukin (IL)-5, has been shown to result in eosinophilia. IL-5 influences the development and maturation of eosinophils in a number of different ways. Of note is the ability of IL-5 to act as a survival factor for eosinophils specifically inhibiting apoptosis. The precise mechanism by which IL-5 exerts its effect remains obscure. We used microarray technologies to investigate the changes in the messenger RNA expression profile of eosinophils after treatment with IL-5. Using the Affymetrix Hu6800 chip, a total of 80 genes were observed to be regulated by 2-fold or greater. Many of the genes previously identified as regulated by IL-5 were regulated in our microarray experiments. Of the 73 genes found to be upregulated, many were shown to play a role in adhesion, migration, activation, or survival of eosinophils or hematopoietic cells, whereas the function of others was unknown. To facilitate the identification of genes that govern the apoptosis and survivability of eosinophils, we used an alternative cellular model, TF1.8 cells, whose survival was also dependent on IL-5. Comparison of these models identified four genes, Pim-1, DSP-5 (hVH3, B23), CD24, and SLP-76, whose regulation was similarly coordinated in both systems. Identification of Pim-1 and SLP-76 as regulated by IL-5 led us to suggest a direct role for these proteins in the IL-5 signaling pathway in eosinophils. The tissue distribution of these genes demonstrated that Pim-1 and SLP-76 were relatively restricted to the eosinophil compared with their expression in brain, bone marrow, kidney, liver, and lung. By contrast, DSP-5 and CD24 were confirmed as ubiquitous in their expression by microarray.

Glucocorticoids induce basophil apoptosis

BACKGROUND

Induction of apoptosis represents an important mechanism by which glucocorticoids (GCCs) exert their anti-inflammatory properties. The effects of GCCs on apoptosis have been determined in various immune cells and found to vary among different cell types. On the other hand, the effects of GCCs on apoptosis of basophils, active participants in allergic inflammation, have remained obscure.

OBJECTIVE

The objective of this study was to investigate the effects of GCCs on basophil apoptosis.

METHODS

Basophils were highly purified (purity, >97%) by Percoll density gradient centrifugation followed by negative selection. Cell status was determined by their ability to bind annexin V and exclude propidium iodide. DNA fragmentation was determined by flow cytometry.

RESULTS

Dexamethasone (DEX) significantly accelerated the decrease in live cells and increased the number of apoptotic cells in a time-dependent fashion. Light microscopy as well as DNA fragmentation assay confirmed the induction of apoptosis by DEX. A half-maximal effect was observed in a DEX concentration range from 10(-9) to 10(-8) mol/L. Sex steroids did not induce basophil apoptosis at all. DEX also induced basophil apoptosis in the presence of low doses of IL-3.

CONCLUSION

GCCs exert potent apoptogenic effects on basophils. GCC-mediated apoptogenic effects on basophils might have implications with respect to the mechanism of action of this class of drugs in allergic disorders.

Clonal Th2 cells associated with chronic hypereosinophilia: TARC-induced CCR4 down-regulation in vivo

We analyzed the expression of chemokine receptors on clonal Th2-type CD4(+)CD3(- )lymphocytes isolated from blood of two patients with chronic hypereosinophilia. First, we observed that these Th2 cells express membrane CCR5 and CXCR4 but neither CCR3 nor CCR4 when analyzed immediately after purification. However, CCR4 appeared following culture in human serum-free medium, suggesting that it was down-regulated in vivo. Indeed, patient's serum, but not control human serum, strongly down-regulated CCR4 expression on cultured Th2 cells. As high levels of TARC, a CCR4 ligand, were detected in the serum of four hypereosinophilic patients with CD3(-)CD4(+) clonal Th2 cells, we evaluated the effect of TARC neutralization in this system. Addition of a neutralizing anti-TARC mAb inhibited CCR4 down-regulation by patient's serum, indicating that circulating TARC contributed to CCR4 down-regulation on Th2 cells in vivo. Clonal Th2 cells did not secrete high levels of TARC themselves but induced a sustained production of TARC by monocyte-derived dendritic cells, a phenomenon that was inhibited by addition of blocking mAb against IL-4 receptor. We conclude that high circulating levels of TARC in serum of patients with chronic hypereosinophilia, most likely derived from antigen-presenting cells stimulated by Th2-type cytokines, induce down-regulation of CCR4 on Th2 cells in vivo.

Paediatric issues relating to the pharmacotherapy of allergic rhinitis

The prevalence of allergic rhinitis in children has risen significantly over the last two decades. Important comorbidities like asthma have grown in parallel due to a complex mix of environmental and genetic factors. These conditions have similar allergic inflammatory mechanisms, which raises the possibility of treating both conditions by targeting shared inflammatory mediators pharmacologically. The first line treatment for paediatric allergic rhinitis is a topical nasal corticosteroid or a non-sedating antihistamine. Available intranasal corticosteroids show superior symptom control to second-generation antihistamines. However, most topical steroids and non-sedating antihistamines have equivalent clinical efficacy within their respective classes, so the choice of agent depends on safety and tolerability. Ideally, topical nasal steroids should exhibit high local receptor binding affinity and low systemic bioavailability, allied with a lack of long-term growth suppression in children and adolescents. Regular use of topical steroids is advisable, but intermittent and prophylactic use is also effective. Second-generation antihistamines are effective and some have no adverse cardiac or sedative effects. Non-sedating antihistamine treatment can ameliorate rhinitis-induced decrements in learning. alpha-Adrenergic nasal decongestants provide short-term benefit, but topical agents can cause rebound symptoms. Prophylactic treatment with chromones is safe and effective, but multiple daily dosing is needed. Ipratroprium bromide nasal spray is useful as an intermittent therapy for mild disease or as add-on treatment, but its effect is limited to the control of rhinorrhoea. Children with allergic rhinitis should receive pharmacotherapy if allergen avoidance measures are ineffective, ideally with a topical intranasal steroid or a second-generation antihistamine.

T lymphocytes in asthma: bronchial versus peripheral responses

Recent evidence points to the recruitment of T(H)2 cells, phenotype T lymphocytes, their activation, and the generation of T(H)2 cytokines, particularly IL-4 and IL-5, in both peripheral blood and bronchial mucosa of asthmatic patients, leading to local tissue eosinophilia and IgE-dependent mast-cell activation. Activation of T(H)2 T lymphocytes appears to be specific for asthma (as opposed to airway obstructive disease) and was shown to correlate with asthma severity as evidenced by the inverse correlation between CD25(+)/CD4(+) cells and peak expiratory flow rates. These findings support the fundamental importance of T-lymphocyte responses in bronchial asthma and delineate potential therapeutic strategies, such as broad-based immunosuppression versus a more selective approach targeted against CD4(+) T lymphocytes. The high efficacy of topical treatments (ie, inhalation) supports the notion that changes that are detectable in peripheral blood merely reflect a "spill-over" of local T-lymphocyte responses in the target organ. Conversely, the multiple systemic manifestations of allergy (such as allergic rhinitis and atopic dermatitis in atopic patients) support systemic therapeutic approaches.

Engagement of the CrkL adapter in interleukin-5 signaling in eosinophils

Interleukin-5 (IL-5) drives the terminal differentiation of myeloid progenitors to the eosinophil lineage; blocks eosinophil apoptosis; and primes eosinophils for enhanced functional activities in allergic, parasitic, and other eosinophil-associated diseases. Here we describe a novel signaling pathway activated by the IL-5 receptor in eosinophils involving the CrkL adapter protein. We determined whether IL-5 induces activation of CrkL and STAT5 in eosinophils using both the human eosinophil-differentiated AML14.3D10 cell line and purified peripheral blood eosinophils from normal donors. Stimulation of AML14.3D10 cells or blood eosinophils with IL-5 induced rapid tyrosine phosphorylation of the CrkL adapter and STAT5 and the association of CrkL and STAT5 in vivo as evidenced by the detection of STAT5 in anti-CrkL immunoprecipitates. The resulting CrkL.STAT5 complexes translocated to the nucleus and bound STAT5 consensus DNA-binding sites present in the promoters of IL-5-regulated genes, as shown in gel mobility and antibody supershift assays. IL-5 also induced marked activity of an 8X-GAS (interferon gamma-activated site)-luciferase reporter construct in transient transfections of AML14.3D10 eosinophils, demonstrating that these complexes play a functional role in IL-5 signaling. CrkL was also found to interact, via its N-terminal SH3 domain, with C3G, a guanine exchange factor for the small G-protein Rap1, which was also rapidly activated in an IL-5-dependent manner in these cells, establishing that CrkL mediates downstream activation of at least two signaling cascades in IL-5-stimulated eosinophils. Thus, the CrkL adapter plays an important role in IL-5 signaling in the eosinophil, acting as a nuclear adapter for STAT5 and as an upstream regulator of the C3G-Rap1 signaling pathway.

A method to study apoptosis in eosinophils by flow cytometry

The aim of this study was to develop a simple flow cytometric procedure to study eosinophil apoptosis. Eosinophils were isolated from the peripheral blood of healthy, non-allergic individuals and then cultured in basal culture medium. The cells were examined after 24, 48 and 72 h for forward- and side scatter (FS-SSC) pattern, staining with FDA, PI, and anti-CD95, and light microscopic appearance. After culture for >24 h, two populations with different FS-SSC-patterns appeared, referred to as A and B. Population A consisted of living, FDA-positive eosinophils. The eosinophils in population B showed a lower FS scatter than those in population A and a staining pattern with PI indicating the presence of hypodiploid DNA. Anti-CD95 demonstrated a significant staining of the eosinophils in population B, which increased after 2 days in culture. The cells were sorted using a FACS-Scan cell sorter and by Annexin V-coated magnetic beads to permit separate analyses of PI-staining pattern, DNA electrophoresis, and light microscopic examination of the cells in population B. The present study suggest that it is possible to discriminate between apoptotic and living eosinophils using the FS-SSC pattern and the PI-staining pattern obtained by flow cytometry.

Proliferation and cell death of embryonic primitive erythrocytes

Erythropoietin (EPO) is the principal regulator for the production of adult-type definitive erythrocytes (EryD). EPO not only stimulates both the proliferation and differentiation of EryD progenitors, but also maintains the viability of EryD progenitors. Compared to the abundant knowledge about the function of EPO in EryD production, the roles of EPO in the production of embryonic-type primitive erythrocytes (EryP) are less clear. The effects of EPO on EryP proliferation and differentiation were investigated using EryP purified from developing mouse embryos and the cells obtained from mouse embryonic stem cells using an in vitro differentiation induction. Immature EryP of both in vivo and in vitro origin responded to EPO stimulation and underwent apoptosis with EPO deprivation. In contrast, there were no significant differences between the cultures with and without EPO, when fully mature EryP were examined, that is, EryP lost its dependency on EPO stimulation with maturation. These results show that EPO functions as a survival factor for immature embryonic EryP as well as immature EryD progenitors.

Clonal Th2 lymphocytes in patients with the idiopathic hypereosinophilic syndrome

Idiopathic hypereosinophilic syndrome (HES) and Gleich's syndrome are related disorders characterized by persistent or recurrent hypereosinophilia of unknown origin. Elevated IgE levels and polyclonal hypergammaglobulinaemia are considered as markers of benign outcome in this setting as they are generally associated with predominant cutaneous manifestations and favourable response to glucocorticoid therapy. In a previous study, we identified a clonal population of CD3-CD4+ Th2-like lymphocytes secreting interleukin (IL)-5 and IL-4 in peripheral blood of a patient fulfilling the diagnostic criteria of HES with associated serum hyper-IgE. We now extend this observation by describing identical findings in three additional patients, and we compare their clinical and biological parameters with five other patients with HES. Chromosomal abnormalities were detected in purified CD3-CD4+ Th2 cells from three patients, among whom one developed anaplastic null cell lymphoma. We therefore suggest that a careful search for T-lymphocyte clonality and cytogenetic changes should be included in the work-up of HES for adequate management.

Effect of IL-5, glucocorticoid, and Fas ligation on Bcl-2 homologue expression and caspase activation in circulating human eosinophils

IL-5 is a potent eosinophil viability-enhancing factor that has been strongly implicated in the pathogenesis of IgE-mediated inflammation in vivo. Recently published data have suggested that IL-5 (and related cytokines) may act by altering the expression of the anti-apoptotic regulator Bcl-2 or its homologues, but this is controversial. The behaviour of the recently described pro-apoptotic cysteine proteases (caspases) in eosinophils after IL-5 treatment has not been explored. We examined the effect of IL-5 on the expression of four major Bcl-2 homologues, as well as on the expression/activation of key members of the caspase cell death cascade in cultured circulating human eosinophils. The effect of relevant inducers of eosinophil apoptosis (glucocorticoid and Fas ligation) on these regulatory proteins was also examined. We observed baseline expression of the anti-apoptotic Mcl-1 and pro-apoptotic Bax proteins in immunoblots of eosinophil lysates, but not Bcl-x, Bcl-2. IL-5 treatment had the effect of maintaining this basal level of expression over time without altering the balance of Bcl-2 homologues. The (upstream) caspase 8 and (downstream) caspase 3 proenzymes were detected in eosinophils at baseline, and were processed during spontaneous and stimulated eosinophil death. IL-5 completely blocked caspase processing in spontaneous and dexamethasone-induced cell death, and significantly slowed processing during Fas ligation. Our data do not support the theory that IL-5 acts by altering the balance of anti-apoptotic and pro-apoptotic Bcl-2 homologues, but suggest that it may act by regulating activation of the caspase cell death cascade.

Upregulation by glucocorticoids of responses to eosinopoietic cytokines in bone-marrow from normal and allergic mice

Since the production of eosinopoietic cytokines (GM-CSF, IL-3, IL-5) is inhibited by glucocorticoids, while responsiveness to these cytokines is enhanced in bone-marrow of allergic mice, we studied the ability of glucocorticoids to modulate murine bone-marrow eosinopoiesis. Progenitor (semi-solid) and/or precursor (liquid) cultures were established from bone-marrow of: (a) normal mice; (b) ovalbumin-sensitized and challenged mice or (c) dexamethasone (1-5 mg kg(-1)) injected mice. Cultures were established with GM-CSF (2 ng ml(-1)) or IL-5 (1 ng ml(-1)), respectively, alone or associated with dexamethasone, hydrocortisone or corticosterone. Total myeloid colony numbers, frequency and size of eosinophil colonies, and numbers of eosinophil-peroxidase-positive cells were determined at day 7. In BALB/c mice, dexamethasone (10(-7) M) increased GM-CSF-stimulated myeloid colony formation (P = 0.01), as well as the frequency (P=0.01) and size (P<0.01) of eosinophil colonies. Dexamethasone (10(-7) M) alone had no effect. Dexamethasone (10(-7)-10(-10) M) increased (P<0.002) eosinophil precursor responses to IL-5. Potentiation by dexamethasone was still detectable: (a) on low density, immature, nonadherent BALB/c bone-marrow cells, (b) on bone-marrow from other strains, and (c) on cells from allergic mice. Hydrocortisone and corticosterone had similar effects. Dexamethasone administered in vivo, 24 h before bone-marrow harvest, increased subsequent progenitor responses to GM-CSF (P = 0.001) and precursor responses to IL-5 (P<0.001). These effects were blocked by RU 486 (20 mg kg(-1), orally, 2 h before dexamethasone, or added in vitro at 10 microM, P<0.001). Glucocorticoids, acting in vivo or in vitro, through glucocorticoid receptors, enhance bone-marrow eosinopoiesis in naïve and allergic mice.

IL-18 deficiency selectively enhances allergen-induced eosinophilia in mice

BACKGROUND

T(H2) cytokines are associated with airway inflammation and hyperreactivity in bronchial asthma, and restoration of the T(H1)/T(H2) imbalance is a potential avenue for novel therapies. IL-18 is a cytokine secreted by activated macrophages, and it shares some of its biologic activities with IL-12, a typical T(H1)-type cytokine. Although IL-18 and IL-12 act on T cells synergistically to induce IFN-gamma production, the contribution of IL-18 T(H1)/T(H2) imbalance and to subsequent asthmatic response has not been elucidated in vivo.

OBJECTIVE

We studied a model of allergic asthma in IL-18-deficient mice to investigate the modulatory role of IL-18 on induction and maintenance of T(H2) mucosal immunity. We also have investigated the ability of intraperitoneal instilled IL-18 to reduce T(H2) mucosal immunity in IL-18-deficient mice.

METHODS

IL-18-deficient mice immunized to ovalbumin by means of intraperitoneal injection were challenged 3 times with an aerosol of ovalbumin every second day for 8 days. Recombinant (r)IL-18 was intraperitoneally administered in mice before every first challenge. Mice were analyzed for effects on lung eosinophilia, cytokines, and serum IgE levels.

RESULTS

In IL-18-deficient mice, levels of eosinophilia and lung damage were significantly higher than in wild-type C57/BL6 litter mates. Intraperitoneal administration of rIL-18 in deficient mice reduced these antigen-induced changes to levels seen in wild-type mice in association with a decrease in IL-4 in bronchoalveolar lavage fluid and lung tissue. However, administration of rIL-18 did not affect the IFN-gamma level and somewhat enhanced the production of IL-5. Notably, reconstitution with rIL-18 increased the numbers of cells staining for Fas ligand, as well as apoptotic cells stained by nick end-labeling in bronchial submucosa infiltrates.

CONCLUSION

These findings indicate that in vivo IL-18 not only inhibited antigen-specific T(H2) development but also affected apoptosis through Fas-Fas ligand interactions. These data support a role for IL-18 in the complex pathogenesis of allergic inflammation in which IL-18 limited the development of the local inflammatory response to antigen.

The epidemic of allergy and asthma

Allergic diseases, such as asthma, rhinitis, eczema and food allergies, are reaching epidemic proportions in both the developed and developing world. Key factors driving these rising trends are increased exposure to sensitizing allergens and reduced stimulation of the immune system during critical periods of development. In allergic disease, there is a polarization of T-lymphocyte responses, and enhanced secretion of cytokines involved in regulation of immunoglobulin E, mast cells, basophils and eosinophils, ultimately leading to inflammation and disease. A clear understanding of the cellular and molecular mechanisms of allergic disease and the complex interplay between genetic and environmental factors will undoubtedly create new opportunities for public health and therapeutic interventions.

Resting and Cytokine-Stimulated Human Small Airway Epithelial Cells Recognize and Engulf Apoptotic Eosinophils

Eosinophils, which are prominent cells in asthmatic inflammation, undergo apoptosis and are recognized and engulfed by phagocytic macrophages in vitro. We have examined the ability of human small airway epithelial cells (SAEC) to recognize and ingest apoptotic human eosinophils. Cultured SAEC ingested apoptotic eosinophils but not freshly isolated eosinophils or opsonized erythrocytes. The ability of SAEC to ingest apoptotic eosinophils was enhanced by interleukin-1 (IL-1) or tumor necrosis factor  (TNF) in a time- and concentration-dependent fashion. IL-1 was found to be more potent than TNF and each was optimal at 10−10 mol/L, with a significant (P &lt; .05) effect observed at 1 hour postcytokine incubation that was maximal at 5 hours. IL-1 stimulation not only increased the number of SAEC engulfing apoptotic eosinophils, but also enhanced their capacity for ingestion. The amino sugars glucosamine, n-acetyl glucosamine, and galactosamine significantly inhibited uptake of apoptotic eosinophils by both resting and IL-1–stimulated SAEC, in contrast to the parent sugars glucose, galactose, mannose, and fucose. Incubation of apoptotic eosinophils with the tetrapeptide RGDS, but not RGES, significantly inhibited their uptake by both resting and IL-1–stimulated SAEC, as did monoclonal antibody against vβ3 and CD36. Thus, SAEC recognize apoptotic eosinophils via lectin- and integrin-dependent mechanisms. These data demonstrate a novel function for human bronchial epithelial cells that might represent an important mechanism in the resolution of eosinophil-induced asthmatic inflammation.

Mechanisms of intranasal steroids in the management of upper respiratory allergic diseases

Intranasal steroids have proved to be the most effective class of drugs in reducing the symptoms of allergic rhinitis. This clinical response reflects the broad anti-inflammatory activity that has been demonstrated for corticosteroids. Single doses of topical corticosteroids administered before nasal allergen challenge block the late-phase reaction, whereas repeated dosing with intranasal steroids blocks both the early and the late response, as well as the priming phenomenon. Nasal inflammation is accomplished through a number of effector cells and mechanisms, which in turn are produced by director cells through the release of cytokines and chemokines. The anti-inflammatory action of corticosteroids is largely effected through blocking the synthesis and release of these cytokines/chemokines.