Eosinophil Apoptosis Research Articles

Effects of steroid treatment on lung CC chemokines, apoptosis and transepithelial cell clearance during development and resolution of allergic airway inflammation

Steroid treatment of allergic eosinophilic airway diseases is considered to attenuate cell recruitment by inhibiting several chemokines and to cause eosinophil clearance through inducement of apoptosis of these cells. However, roles of these mechanisms in the actions of steroids in vivo have not been fully established. Also, as regards clearance of tissue eosinophils other mechanisms than apoptosis may operate in vivo. This study explores anti-inflammatory effects of steroids instituted during either development or resolution of airway allergic inflammation. Immunized mice were subjected to week-long daily allergen challenges (ovalbumin). Steroid treatment was instituted either amidst the challenges or exclusively post-allergen challenge. CC chemokines, goblet cell hyperplasia, occurrence of eosinophil apoptosis, and airway tissue as well as lumen eosinophilia were examined at different time-points. Daily steroids instituted amid the allergen challenges non-selectively attenuated a range of chemokines, permitted egression of tissue eosinophils into airway lumen to increase, and reduced development of lung tissue eosinophilia. Steroid treatment instituted post-challenge selectively inhibited the CC-chemokine regulation upon activation, normal T cell expressed and secrted (RANTES), permitted continued egression of eosinophils into airway lumen, and resolved the tissue eosinophilia. Eosinophil apoptosis rarely occurred at development and resolution of the allergic eosinophilic inflammation whether the animals were steroid treated or not. However, anti-Fas monoclonal antibodies given to mice with established eosinophilia post-challenge produced apoptosis of the tissue eosinophils indicating that apoptotic eosinophils, if they occur, are well detectible in vivo. Airway tissue eosinophils are likely eliminated through egression into airway lumen with little involvement of apoptosis and phagocytosis. Our data further suggest that therapeutic steroids may resolve airway inflammation by permitting clearance of tissue eosinophils through egression and inhibiting RANTES-dependent cell recruitment to lung tissues.

Antagonistic effects of nobiletin, a polymethoxyflavonoid, on eosinophilic airway inflammation of asthmatic rats and relevant mechanisms

Eosinophils are known to be the important effector cells in asthmatic airway inflammation. The purpose of this study was to investigate the effects of nobiletin, a polymethoxyflavonoid, on eosinophilic airway inflammation of asthmatic rats, and explore its possible mechanisms. Animals were actively sensitized by subcutaneous injection of ovalbumin (OVA). The inflammation in lung tissues of asthmatic rats was observed by hematoxylin and eosin (HE) staining. The eosinophils in blood and BALF were separated by Percoll density gradient centrifugation and counted under microscope. The level of Eotaxin was detected by enzyme-linked immunosorbent assay (ELISA). In addition, the apoptosis of eosinophils was labeled by TdT-mediated dUTP nick end labeling (TUNEL) technique, the semi-quantitative detection for Fas mRNA expression of eosinophils was performed by reverse transcription-polymerase chain reaction (RT-PCR). The airway inflammation of asthmatic rats pretreated with nobiletin was obviously alleviated. Nobiletin (1.5 and 5.0 mg/kg given intraperitoneally) significantly reduced OVA-induced increases in eosinophils, remarkably lowered the level of Eotaxin in blood and broncho-alveolar lavage fluid (BALF) of asthmatic rats. On the other hand, semi-quantitative RT-PCR analysis for Fas of eosinophils from OVA aerosol-challenged sensitized rats showed that Fas mRNA expression of eosinophils was obviously enhanced by nobiletin. Meanwhile, the apoptosis index of cultured eosinophils was significantly elevated after treatment with different doses of nobiletin. These results indicated that nobiletin could inhibit the eosinophilic airway inflammation. Lowering the levels of Eotaxin, relieving airway infiltration of eosinophils and promoting apoptosis of eosinophils by enhancing expression of Fas mRNA may be important mechanisms for nobiletin to antagonize eosinophilic airway inflammation of asthmatic rats.

Effects of low doses of inhaled fluticasone propionate on inflammation and remodelling in persistent‐mild asthma

In asthma a dysregulation of eosinophil apoptosis and an imbalance of metalloproteinase-9 (MMP-9) and tissue inhibitor metalloproteinase-1 (TIMP-1) play an important role in airway inflammation and remodelling. We evaluated the effects of a low dose of inhaled fluticasone proprionate (FP) (100 microg bid by Diskus) for 4 weeks in 24 steroid naive patients with mild persistent asthma, symptomatic and with a sputum eosinophilia >or=3% on clinical outcomes and inflammatory markers such as the induced sputum eosinophils, the induced sputum apoptotic eosinophils, the levels of MMP-9 and TIMP-1 and their molar ratio in the induced sputum supernatants. After FP treatment forced expiratory volume (FEV1) and FEV1/forced vital capacity values, PEF (L/min), sputum apoptotic eosinophils, and MMP-9/TIMP-1 molar ratio in sputum supernatants of asthmatic subjects were significantly increased in comparison with baseline, while sputum eosinophils significantly decreased. Change (Delta) in FEV1 after treatment with FP negatively correlated with the Delta in sputum eosinophils, while the Delta in MMP-9 values positively correlated with Delta in TIMP-1 values. This study shows that the clinical improvement achieved by the use of low doses of FP in asthmatics is related, at least in part, to the resolution of eosinophilic inflammation and the downregulation of remodelling markers.

Leptin is an eosinophil survival factor

Leptin regulates food intake, as well as metabolic, endocrine, and immune functions. It exerts proliferative and antiapoptotic activities in a variety of cell types, including T cells. Leptin also stimulates macrophages and neutrophils, and its production is increased during inflammation. We sought to examine the expression of leptin receptors on eosinophils and the effect of recombinant leptin on proapoptotic pathways in these cells. The presence of leptin receptor was examined by means of RT-PCR and immunofluorescence analysis in freshly isolated blood eosinophils and tissue eosinophils. The effect of recombinant leptin on apoptotic pathways in eosinophils was studied by using flow cytometric, immunoblotting, and immunofluorescence techniques. Human eosinophils express leptin surface receptors under in vitro and in vivo conditions, and leptin delays apoptosis of mature eosinophils in vitro. The antiapoptotic effects of leptin were concentration dependent and blocked by an anti-leptin receptor mAb. The efficacy of leptin to block eosinophil apoptosis was similar to that of GM-CSF. Leptin delayed the cleavage of Bax, as well as the mitochondrial release of cytochrome c and second mitochondria-derived activator of caspase, suggesting that it blocks proapoptotic pathways proximal to mitochondria in eosinophils. Using pharmacological inhibitors, we obtained evidence that leptin initiates a signaling cascade involving phosphatidylinositol-3-OH kinase and mitogen-activated protein kinase-dependent pathways in eosinophils. Leptin is a survival cytokine for human eosinophils, a finding with potential pathologic relevance in allergic and parasitic diseases.

Mechanism of Siglec-8-induced human eosinophil apoptosis: Role of caspases and mitochondrial injury

Sialic acid binding immunoglobulin like lectin (Siglec)-8 crosslinking with specific antibodies causes human eosinophil apoptosis. Mechanisms by which Siglec-8 crosslinking induces apoptosis are not known. Peripheral blood eosinophils were examined for caspase, mitochondria and reactive oxygen species (ROS) involvement after incubating the cells with anti-Siglec-8 crosslinking Abs or control Abs, in the presence or absence of selective inhibitors. Siglec-8 crosslinking induced rapid cleavage of caspase-3, caspase-8, and caspase-9 in eosinophils. Selective caspase-8 and/or caspase-9 inhibitors inhibited this apoptosis. Siglec-8 crosslinking on eosinophils increased dissipation of mitochondrial membrane potential upstream of caspase activation. Rotenone and antimycin, inhibitors of mitochondrial respiratory chain components, completely inhibited apoptosis. Additional experiments with an inhibitor of ROS, diphenyleneiodonium, demonstrated that ROS was also essential for Siglec-8-mediated apoptosis and preceded Siglec-8-mediated mitochondrial dissipation. These experiments show that Siglec-8-induced apoptosis occurs through the sequential production of ROS, followed by induction of mitochondrial injury and caspase cleavage.

Anti-Fas mAb-induced apoptosis and cytolysis of airway tissue eosinophils aggravates rather than resolves established inflammation

BackgroundFas receptor-mediated eosinophil apoptosis is currently forwarded as a mechanism resolving asthma-like inflammation. This view is based on observations in vitro and in airway lumen with unknown translatability to airway tissues in vivo. In fact, apoptotic eosinophils have not been detected in human diseased airway tissues whereas cytolytic eosinophils abound and constitute a major mode of degranulation of these cells. Also, Fas receptor stimulation may bypass the apoptotic pathway and directly evoke cytolysis of non-apoptotic cells. We thus hypothesized that effects of anti-Fas mAb in vivo may include both apoptosis and cytolysis of eosinophils and, hence, that established eosinophilic inflammation may not resolve by this treatment.MethodsWeeklong daily allergen challenges of sensitized mice were followed by airway administration of anti-Fas mAb. BAL was performed and airway-pulmonary tissues were examined using light and electron microscopy. Lung tissue analysis for CC-chemokines, apoptosis, mucus production and plasma exudation (fibrinogen) were performed.ResultsAnti-Fas mAb evoked apoptosis of 28% and cytolysis of 4% of eosinophils present in allergen-challenged airway tissues. Furthermore, a majority of the apoptotic eosinophils remained unengulfed and eventually exhibited secondary necrosis. A striking histopathology far beyond the allergic inflammation developed and included degranulated eosinophils, neutrophilia, epithelial derangement, plasma exudation, mucus-plasma plugs, and inducement of 6 CC-chemokines. In animals without eosinophilia anti-Fas evoked no inflammatory response.ConclusionAn efficient inducer of eosinophil apoptosis in airway tissues in vivo, anti-Fas mAb evoked unprecedented asthma-like inflammation in mouse allergic airways. This outcome may partly reflect the ability of anti-Fas to evoke direct cytolysis of non-apoptotic eosinophils in airway tissues. Additionally, since most apoptotic tissue eosinophils progressed into the pro-inflammatory cellular fate of secondary necrosis this may also explain the aggravated inflammation. Our data indicate that Fas receptor mediated eosinophil apoptosis in airway tissues in vivo may cause severe disease exacerbation due to direct cytolysis and secondary necrosis of eosinophils.

Pharmacological Regulation of Human Eosinophil Apoptosis

Eosinophilic inflammation of the airways is a key characteristic of asthma. The balance between eosinophil recruitment into the lung and their removal from the lungs determines the number of eosinophils in the airways. Apoptosis or programmed cell death is of importance in the removal of eosinophils from the lungs. In asthma, eosinophil apoptosis is delayed. Glucocorticoids enhance eosinophil apoptosis, whereas beta(2)-agonists may delay apoptosis in eosinophils. Detailed knowledge on the mechanisms that regulate this process gives an opportunity to develop specific asthma therapies targeting the eosinophil. This review aims to focus on the signalling leading to or preventing apoptosis in human eosinophils as well as reviews the current evidence on the regulation of eosinophil apoptosis and/or survival in allergic diseases.

Ketotifen Induces Primary Necrosis of Human Eosinophils

Eosinophils are considered essential in the pathogenesis of allergy. Reduced eosinophil apoptosis is considered to be a key element in the formation of eosinophilia in allergic conditions. Antihistamines are widely used in the treatment of allergic disorders, but their effects on eosinophil apoptosis are poorly understood. The histamine H1-receptor antagonist, ketotifen, is available orally and as eye drops for the treatment of allergic symptoms. The aim of our study was to investigate the possible effect of ketotifen on constitutive eosinophil apoptosis and on interleukin (IL)-5-mediated eosinophil survival. Isolated peripheral blood eosinophils were cultured with or without the survival-prolonging cytokine IL-5 and ketotifen. Apoptosis was assessed by measuring the relative DNA content and by morphological analysis. Ketotifen was found to reverse eosinophil survival induced by interleukin-5. However, the flow cytometry histogram of DNA in propidium iodide-stained cells was not typical to apoptosis. Morphological analysis of the eosinophils by bright-field microscopy suggested that the effect of ketotifen was due to the induction of primary necrosis rather than apoptosis. Histological assessment of eosinophil ultrastructure by transmission electron microscopy confirmed signs of advanced necrosis. In summary, our results suggest that at clinically relevant drug concentrations, ketotifen induces primary necrosis in IL-5-treated human eosinophils.

Anti-Inflammatory Mechanisms of Glucocorticoids Targeting Granulocytes

Asthmatic inflammation involves the recruitment and activation of inflammatory cells, and changes in the structural cells of the lung and asthma are characterized by an increased expression of components of the inflammatory cascade including cytokines, chemokines, growth factors, enzymes, receptors and adhesion molecules. The increased expression of these proteins seen in asthma is generally the result of enhanced gene transcription, since many of the genes are not expressed in normal cells but are induced in a cell-specific manner during the inflammatory process. There is clear evidence that neutrophils, long thought of as being transcriptionally inert, can respond to stimuli to induce inflammatory genes. Glucocorticoids are very effective in controlling the inflammation seen in asthmatic airways. Beyond their recognized actions on eosinophil and neutrophil apoptosis, glucocorticoids have profound effects on the chemotaxis, activation and release of mediators from granulocytes (eosinophils, neutrophils and basophils). Few mechanistic studies are available in these cells, but it appears that in granulocytes, glucocorticoids target the same signaling pathways, such as nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1), that are important in other cells. We summarize these known mechanisms at the end of this review.

Viscum album agglutinin‐I induces apoptosis and degradation of cytoskeletal proteins via caspases in human leukaemia eosinophil AML14.3D10 cells: differences with purified human eosinophils

Although there are several agents that induce neutrophil apoptosis, few are known as inducers of eosinophil apoptosis. As eosinophils are potent effector cells contributing to allergic inflammation and asthma, we investigated whether the pro-apoptotic agent Viscum album agglutinin-I (VAA-I) could induce eosinophil apoptosis. VAA-I was found to induce apoptosis in eosinophilic AML14.3D10 (3D10) cells and that these cells expressed caspases-1, -2, -3, -4, -7, -8, -9 and -10. VAA-I-induced gelsolin degradation was reversed by the pan-caspase inhibitor N-benzyloxycarbonyl-V-A-D-O-methylfluoromethyl ketone (z-VAD). Also, paxillin, vimentin and lamin B1 were cleaved by caspases in VAA-I-induced 3D10 cells. VAA-I activated caspase-3 and -8 in 3D10 cells but, unlike z-VAD, treatment with a caspase-8 inhibitor slightly reversed apoptosis. Treatment of purified human eosinophils with VAA-I was found to induce apoptosis, degradation of gelsolin and lamin B1, but unlike 3D10 cells, cleavage of lamin B1 and cell apoptosis was not reversed by z-VAD. We conclude that VAA-I is a potent inducer of eosinophil apoptosis and that proteases other than those inhibited by z-VAD in 3D10 cells are involved in VAA-I-induced peripheral blood eosinophil apoptosis and lamin B1 cleavage. Thus, VAA-I represents a potential candidate for the reduction of the number of eosinophils in diseases where they play important roles.

The effect of natural pollen exposure on eosinophil apoptosis and its relationship to bronchial hyperresponsiveness in patients with seasonal allergic rhinitis

Limited data suggest that there is increased eosinophilic inflammation in the airways of patients with seasonal allergic rhinitis (SAR) during pollen season even if they do not have asthma. To investigate the effect of natural pollen exposure on inflammatory cells and apoptosis of eosinophils and its association with bronchial hyperresponsiveness (BHR) during and out of pollen season in SAR patients sensitized to only grass pollens. Forty SAR patients and 10 patients with nonallergic rhinitis (NAR) from Ankara, Turkey, were recruited to participate in the study. Two induced sputum samples were taken from SAR patients during pollen season (May-June) and out of pollen season (November-January), but only 1 induced sputum sample was taken from NAR patients. Slides of induced sputum were evaluated by 2 cytologists with the use of light microscopy after cytocentrifuged and dyed with May-Grünwald-Giemsa stain. Induced sputum samples were sufficient for differential cell counts in 14 SAR and 7 NAR patients. Eosinophil counts in SAR patients were statistically higher in pollen season (19.4% +/- 16.2%) compared with out of season (4.6% +/- 6.9%, P = .003) and with NAR patients (4.7% +/- 9.5%, P = .01). The apoptotic eosinophil counts in SAR patients were statistically higher out of pollen season (3.0% +/- 4.5%) than in pollen season (0.38% +/- 0.80%, P = .02) and higher than those of NAR patients (0.14% +/- 0.26%, P = .005). The apoptotic ratio was statistically higher after pollen season compared with pollen season (0.720% +/- 0.394% vs 0.044% +/- 0.116%, P = .002). Blood eosinophil counts of SAR patients were increased during the pollen season (364 +/- 187/mm3) compared with out of season (278 +/- 219/mm3, P = .04) and with NAR patients (85 +/- 54/mm3, P = .001). The number of SAR patients who had BHR during the pollen season (7/14) was higher than the number who had BHR out of season (2/14, chi2 = 4.2, P = .04). Our data indicate that changes in eosinophil counts and eosinophil apoptosis may be related to the changes of natural pollen exposure and seasonal changes of BHR in SAR patients.

Die molekulare Regulation der Apoptose eosinophiler Granulozyten

Apoptosis is the most common form of physiologic cell death and a necessary process to maintain cell numbers in multicellular organisms. Eosinophils are constantly produced in the bone marrow and the same numbers die, under normal circumstances, within a relatively short time period. In many eosinophilic inflammatory diseases, reduced eosinophil apoptosis has been described. This mechanism may contribute to increased eosinophil numbers, a phenomenon called eosinophilia. Overexpression ofIL-5 appears to be crucial for delaying eosinophil apoptosis in many allergic disorders. Survival factor withdrawal leads to the induction of apoptosis. Besides survival cytokines, eosinophil apoptosis is also regulated by death factors. Recent observations suggest a role for mitochondria in conducting eosinophil apoptosis, although the mechanisms that trigger mitochondria to release proapoptotic factors remain less clear. Drugs that specifically induce eosinophil apoptosis might be useful for triggering the resolution of unwanted eosinophilic inflammatory responses.

NR4A Orphan Nuclear Receptor Family in Peripheral Blood Eosinophils from Patients with Atopic Dermatitis and Apoptotic Eosinophils in vitro

To identify novel genes related to the clinical signs of atopic dermatitis (AD), differentially expressed genes were sought in peripheral blood eosinophils from both AD patients and healthy volunteers. RNA was prepared from eosinophils, expression of various genes was monitored using the Affymetrix GeneChip, and expression was quantified by real-time RT-PCR. Two genes, Nur77 and NOR1, members of NR4A orphan nuclear receptor family, were expressed at a significantly higher level in AD patients than in healthy volunteers. Expression of another gene in the NR4A receptor family, Nurr1, was also higher in AD patients than in healthy volunteers. When peripheral blood leukocytes from healthy volunteers were fractionated, NOR1 expression was highest in eosinophils, but expression of Nur77 and Nurr1 genes was not eosinophil-specific. Extremely intense apoptosis was induced in both eosinophils and an eosinophil cell line, AML14.3D10, by treatment with antibody (Ab) to both CD30 and Fas. Rapid expression of the genes for the NR4A receptor family was observed with anti-CD30 Ab treatment but not with anti-Fas Ab. The NR4A orphan nuclear receptor family gene expression and the subsequent eosinophil apoptosis were downregulated by the MAPK inhibitor, U0126. These results suggest that the expression of the NR4A receptor family genes through CD30 signaling may regulate eosinophil apoptosis in allergic conditions such as AD.

Brain-derived neurotrophic factor is increased in atopic dermatitis and modulates eosinophil functions compared with that seen in nonatopic subjects

Recently, the pivotal role of brain-derived neurotrophic factor (BDNF) has been described in allergic asthma. However, the role of this neurotrophin in atopic dermatitis (AD) still remains unknown. The aim of this study was to investigate the functional role of BDNF on eosinophils and to assess BDNF levels in patients with AD and nonatopic control subjects. Methods p75 Neurotrophin receptor and tyrosine kinase B receptor expression was demonstrated by using FACS analysis and immunohistochemistry. BDNF levels were assessed with ELISA and FACS analysis. Chemotactic activity (modified Boyden chamber assay), eosinophil cationic protein release (fluoroenzyme immunoassay), respiratory burst (lucigenin-dependent chemiluminescence), and apoptosis (Nicoletti protocol and Annexin-V method) assays were used to assess BDNF functional activity. BDNF levels were increased in serum, plasma, eosinophils, and supernatants of stimulated eosinophils from patients with AD compared with levels seen in nonatopic control subjects ( P < .05-.001). In addition, p75 neurotrophin receptor and tyrosine kinase B expression was higher on eosinophils from patients with AD compared with that seen on eosinophils from nonatopic control subjects ( P < .05-.001). Eosinophil apoptosis was inhibited by BDNF ( P < .05-.01) and chemotactic index was increased ( P < .001) in BDNF-stimulated eosinophils from patients with AD, whereas this effect was not shown in eosinophils from nonatopic control subjects. However, no response of BDNF through the release of eosinophil cationic protein or reactive oxygen species was found. This study provides the first evidence for a functional role of BDNF on eosinophils from patients with AD, probably mediated by an increased expression of BDNF receptors compared with that seen in nonatopic control subjects. In addition, higher intracellular, serum, and plasma BDNF levels, as well as the release of BDNF by eosinophils, underline the particular importance of BDNF in patients with AD, pointing to new pathophysiologic aspects of this chronic inflammatory skin disease.

Rottlerin induces apoptosis of human blood eosinophils: A possible role for PKC-δ in mediating eosinophil survival

Rottlerin induces apoptosis of human blood eosinophils: A possible role for PKC-δ in mediating eosinophil survival

Rhinophototherapy: A new therapeutic tool for the management of allergic rhinitis

Phototherapy has a profound immunosuppressive effect and is able to inhibit hypersensibility reactions in the skin. We evaluated whether phototherapy using a combination of UV-B (5%), UV-A (25%), and visible light (70%), referred to as mUV/VIS, is effective in treating allergic rhinitis. We conducted a randomized, double-blind study, in 49 patients with hay fever. The study was performed during the ragweed season. Each intranasal cavity was illuminated 3 times a week for 3 weeks with mUV/VIS or with low-intensity visible light. Symptom scores, inflammatory cells, and their mediators were assessed in nasal lavages. In vitro effects of mUV/VIS irradiation on T-cell and eosinophil apoptosis and its inhibitory effect on mediator release from basophils were examined. Rhinophototherapy was tolerated well and resulted in a significant improvement of clinical symptoms for sneezing (P < .016), rhinorrhea (P < .007), nasal itching (P < .014), and total nasal score (P < .004). None of the scores improved significantly in the control group. Scores for nasal obstruction slightly improved after mUV/VIS treatment and significantly increased in the control group (P < .017). In the nasal lavage, phototherapy significantly reduced the number of eosinophils and the level of eosinophil cationic protein and IL-5. In vitro irradiation of T cells and eosinophils with mUV/VIS light dose-dependently induced apoptosis. Furthermore, mUV/VIS irradiation inhibited the mediator release from RBL-2H3 basophils. These results suggest that phototherapy is an effective modality to treat allergic rhinitis and offer new options for the treatment of immune-mediated mucosal diseases.

The effect of montelukast on eosinophil apoptosis: induced sputum findings of patients with mild persistent asthma

Background Apoptosis may be important in limiting airway eosinophilia. Treatment with leukotriene antagonists decreases the number of eosinophils in both peripheral blood and sputum. Aim To assess the effect of montelukast on eosinophil apoptosis in a group of patients with mild persistent asthma (MPA) and to compare this effect with the apoptotic effect of fluticasone propionate (FP). Methods Randomly selected patients with MPA (n = 22) who had not taken anti-inflammatory therapy within the preceding 12 months were included in the study. The sputum induction procedure was performed and the patients were divided into two groups: group 1 (n = 10) received FP 250 μg/day and group 2 (n = 22) received montelukast 10 mg/day orally for 4 weeks. Sputum induction was repeated after the treatment period. The resulting cytospin slides were stained by Wright's stain and morphologic changes in apoptotic eosinophils were assessed by the use of light microscopy by two blinded expert pathologists. Serum soluble Fas ligand (sFasL) concentrations were measured by an ELISA method at baseline and after treatment in both groups, as well as in a group of healthy subjects. Results In within-group comparisons, the apoptotic ratio (AR) increased at the end of the study period in group 1 (p = 0.05). In the group treated with FP the ratio of sputum eosinophils significantly decreased (p = 0.02), and the AR significantly increased (p < 0.005). No differences were found in the two study groups in serum sFasL levels at the end of the treatment period compared with baseline values (p > 0.05). Conclusion Our findings demonstrate that 4 weeks’ treatment with a CysLT receptor antagonist (montelukast) resulted in an increase in eosinophil apoptosis comparable to that produced by FP, suggesting that induction of apoptosis may be a potential mechanism for the mode of action of CysLT receptor antagonists in asthma.

Eosinophils from Asthmatics Release IL-5 in an Autocrine Fashion to Prevent Apoptosis Through Upregulation of Bcl-2 Expression

Interleukin (IL)-5 plays an important role in maintaining the survival of eosinophils via the specific α-subunit of its receptor. Apoptosis, a form of programmed cell death, is thought to represent a mechanism that promotes the resolution of eosinophilic inflammation in asthma. The aim of our present study is to investigate whether IL-5 acts in an autocrine fashion on eosinophil apoptosis in asthmatics. Immunoreactivities of intracellular IL-5 and IL-5 receptor α-subunit (Rα) were detected uniquely on the eosinophils. The magnitude of IL-5 and IL-5 Rα expression on eosinophils was significantly higher in asthmatics than that of normal subjects (p < 0.05) determined by flow cytometry. Apoptosis of eosinophils was measured by the propidium iodide staining method and DNA ladder. The percent of apoptotic eosinophils from asthmatics was significantly increased by coincubation with anti-hIL-5 Rα Ab (0.1, 0.5, and 2.5 µg/mL) for 1, 2, or 16 hours than was those of corresponding controls (p < 0.05, n = 8). However, there was no significant effect of anti-hIL-5 Rα Ab on eosinophil apoptosis in normal subjects. Furthermore, the expression of B-cell lymphoma-2 (Bcl-2) proteins was significantly inhibited by the anti-hIL-5 Rα Ab or antisense IL-5 oligonucleotides in asthmatics (p < 0.05, n = 8), but there was no significant change in eosinophils from normal subjects. This study demonstrates that eosinophils from asthmatics release IL-5 in an autocrine fashion to act on their own IL-5 receptors in prevention of apoptosis through the upregulation of Bcl-2 expression.

Activation of PI3K-Akt pathway mediates antiapoptotic effects of β-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.

Inhibition of NF-κB by a cell permeable form of IκBα induces apoptosis in eosinophils

An 11 amino acid HIV-TAT peptide can deliver target proteins into a variety of cells in a receptor-independent manner. To generate a highly specific inhibitor of the transcription factor NF-κB, we have fused the TAT-peptide to a version of IκBα that is resistant to signal-induced degradation. TAT-IκBα(S32A, S36A) inhibited NF-κB-dependent transcription in HeLa and A549 cells by retaining NF-κB p65 in the cytoplasm. Introduction of TAT-IκBα(S32A, S36A) into human eosinophils inhibited the nuclear translocation of NF-κB and induced apoptosis. Thus, continuous NF-κB-dependent transcription is important for eosinophil survival. While eosinophils are normally refractive to standard methods of gene delivery, the ability of TAT fusion proteins to be taken up by these cells should enable a detailed molecular analysis of survival pathways in these cells.