Kinetics of the development and recovery of the lung from IgE-mediated inflammation: dissociation of pulmonary eosinophilia, lung injury, and eosinophil-active cytokines

7-Amino acid peptide (7P) decreased airway inflammation and hyperresponsiveness in a murine model of asthma

A 7-amino acid peptide (7P), (Gly-Gln-Thr-Tyr-Thr-Ser-Gly) is one of the synthesized mimic polypeptides, which is the second envelope protein at hypervariable region 1 of chronic hepatitis C virus (HCV HVR1). It contributed to the anti-inflammatory reaction and inhibited lung Th9 responses in asthma through binding to CD81. In this study, we examined the effects of 7P on bronchoconstriction, acute inflammation of the airways, and lung Th2-type responses during allergic lung inflammation. Our results determined that 7P decreased bronchoconstriction and inhibited both acute inflammatory cytokines (TNFα, IL-1β, and IL-6) and Th2 cell cytokine responses (IL-5, IL-4, and IL-13) during allergic lung inflammation. 7P directly inhibited lung Th2 cell differentiation (7P: 5.1% vs. vehicle:12.2% and control 7P:12.2%) and suppressed airway inflammatory cytokine signal transduction to decrease Th2 cell response. Overall, 7P significantly decreased airway hyperresponsiveness (AHR), airway inflammation, and Th2 responses, which may serve as a novel therapeutic candidate during allergic lung inflammation.

Effect of fexofenadine hydrochloride on allergic rhinitis aggravated by air pollutants

In recent decades, seasonal allergic rhinitis (SAR) prevalence has increased and recent studies have shown that air pollutants, such as diesel exhaust particles (DEP), can increase inflammatory and allergic biomarkers. The aim of this study was to investigate the effects of DEP on SAR symptoms induced by ragweed and to evaluate the efficacy and safety of fexofenadine HCl 180 mg versus placebo.

This phase 3, single-centre, sequential, parallel-group, double-blind, randomised study (NCT03664882) was conducted in an environmental exposure unit (EEU) during sequential exposures: Period 1 (ragweed pollen alone), Period 2 (ragweed pollen+DEP), and Period 3 (ragweed pollen+DEP+single-dose fexofenadine HCl 180 mg or placebo). Efficacy and safety were evaluated in Period 3. Primary endpoints were the area under the curve (AUC) of total nasal symptom score (TNSS) from baseline to hour 12 (AUC_0–12) during Period 1 and Period 2; and the AUC of the TNSS from hour 2 to 12 (AUC_2–12) during Period 3.

251 out of 257 evaluable subjects were included in the modified intent-to-treat population. Least squares mean difference (95% CI) for TNSS Log AUC₀₋₁₂ in Period 2 versus Period 1 was 0.13 (0.081–0.182; p<0.0001). Least squares mean difference in TNSS Log AUC₂₋₁₂ for fexofenadine HCl versus placebo during Period 3 was −0.24 (−0.425–−0.047; p=0.0148). One fexofenadine HCl-related adverse event was observed.

SAR symptoms evoked by ragweed were aggravated by DEP. Fexofenadine HCl 180 mg was effective in relieving pollen-induced, air pollution-aggravated allergic rhinitis symptoms.

This is the first randomised, double-blind, large study to demonstrate the beneficial effect of a histamine H1-receptor antagonist by reducing ragweed pollen-induced seasonal allergic rhinitis symptoms aggravated by controlled exposure to air pollutantshttps://bit.ly/3oauMFu

Dibutyl Phthalate Augments Allergen-induced Lung Function Decline and Alters Human Airway Immunology. A Randomized Crossover Study

Rationale: Phthalates are a group of chemicals used in common commercial products. Epidemiological studies suggest that phthalate exposure is associated with development or worsening of allergic diseases such as asthma. However, effects of dibutyl phthalate (DBP) or other phthalates found in high concentrations in indoor air have never been examined in allergic individuals in a controlled exposure setting.Objectives: To investigate the airway effects in humans caused by inhalation of a known concentration of a single phthalate, DBP.Methods: In a randomized crossover study, 16 allergen-sensitized participants were exposed to control air or DBP for 3 hours in an environmental chamber followed immediately by an allergen inhalation challenge. Bronchoalveolar wash and lavage were obtained 24 hours after exposure. Lung function, early allergic response, airway responsiveness, inflammation, immune mediators, and immune cell phenotypes were assessed after DBP exposure.Measurements and Main Results: DBP exposure increased the early allergic response (21.4% decline in FEV₁ area under the curve, P = 0.03). Airway responsiveness was increased by 48.1% after DBP exposure in participants without baseline hyperresponsiveness (P = 0.01). DBP increased the recruitment of BAL total macrophages by 4.6% (P = 0.07), whereas the M2 macrophage phenotype increased by 46.9% (P = 0.04). Airway immune mediator levels were modestly affected by DBP.Conclusions: DBP exposure augmented allergen-induced lung function decline, particularly in those without baseline hyperresponsiveness, and exhibited immunomodulatory effects in the airways of allergic individuals. This is the first controlled human exposure study providing biological evidence for phthalate-induced effects in the airways.Clinical trial registered with www.clinicaltrials.gov (NCT02688478).

Protein Translation and Signaling in Human Eosinophils

We have recently reported that, unlike IL-5 and GM-CSF, IL-3 induces increased translation of a subset of mRNAs. In addition, we have demonstrated that Pin1 controls the activity of mRNA binding proteins, leading to enhanced mRNA stability, GM-CSF protein production and prolonged eosinophil (EOS) survival. In this review, discussion will include an overview of cap-dependent protein translation and its regulation by intracellular signaling pathways. We will address the more general process of mRNA post-transcriptional regulation, especially regarding mRNA binding proteins, which are critical effectors of protein translation. Furthermore, we will focus on (1) the roles of IL-3-driven sustained signaling on enhanced protein translation in EOS, (2) the mechanisms regulating mRNA binding proteins activity in EOS, and (3) the potential targeting of IL-3 signaling and the signaling leading to mRNA binding activity changes to identify therapeutic targets to treat EOS-associated diseases.

Eosinophils contribute to the resolution of lung-allergic responses following repeated allergen challenge

BACKGROUND

Eosinophils accumulate at the site of allergic inflammation and are critical effector cells in allergic diseases. Recent studies have also suggested a role for eosinophils in the resolution of inflammation.

OBJECTIVE

To determine the role of eosinophils in the resolution phase of the response to repeated allergen challenge.

METHODS

Eosinophil-deficient (PHIL) and wild-type (WT) littermates were sensitized and challenged to ovalbumin (OVA) 7 or 11 times. Airway inflammation, airway hyperresponsiveness (AHR) to inhaled methacholine, bronchoalveolar lavage (BAL) cytokine levels, and lung histology were monitored. Intracellular cytokine levels in BAL leukocytes were analyzed by flow cytometry. Groups of OVA-sensitized PHIL mice received bone marrow from WT or IL-10(-/-) donors 30 days before the OVA challenge.

RESULTS

PHIL and WT mice developed similar levels of AHR and numbers of leukocytes and cytokine levels in BAL fluid after OVA sensitization and 7 airway challenges; no eosinophils were detected in the PHIL mice. Unlike WT mice, sensitized PHIL mice maintained AHR, lung inflammation, and increased levels of IL-4, IL-5, and IL-13 in BAL fluid after 11 challenges whereas IL-10 and TGF-β levels were decreased. Restoration of eosinophil numbers after injection of bone marrow from WT but not IL-10-deficient mice restored levels of IL-10 and TGF-β in BAL fluid as well as suppressed AHR and inflammation. Intracellular staining of BAL leukocytes revealed the capacity of eosinophils to produce IL-10.

CONCLUSIONS

After repeated allergen challenge, eosinophils appeared not essential for the development of AHR and lung inflammation but contributed to the resolution of AHR and inflammation by producing IL-10.

Safety of and cellular response to segmental bronchoprovocation in allergic asthma

Rationale

Despite its incorporation into research studies, the safety aspects of segmental allergen bronchoprovocation and differences in cellular response among different allergens have received limited consideration.

Methods

We performed 87 segmental challenges in 77 allergic asthma subjects. Allergen dose was based on each subject’s response to whole lung allergen challenge. Bronchoalveolar lavage was performed at 0 and 48 hours. Safety indicators included spirometry, oxygen saturation, heart rate, and symptoms.

Results

Among subjects challenged with ragweed, cat dander, or house dust mite, there were no differences in safety indicators. Subjects demonstrated a modest oxygen desaturation and tachycardia during the procedure that returned to normal prior to discharge. We observed a modest reduction in forced vital capacity and forced expiratory volume in one second following bronchoscopy. The most common symptoms following the procedure were cough, sore throat and fatigue. Total bronchoalveolar lavage fluid cell numbers increased from 13±4 to 106±108×10⁴ per milliliter and eosinophils increased from 1±2 to 44±20 percent, with no significant differences among the three allergens.

Conclusions

In mild allergic asthma, segmental allergen bronchoprovocation, using individualized doses of aeroallergens, was safe and yielded similar cellular responses.

Are mouse models of asthma appropriate for investigating the pathogenesis of airway hyper-responsiveness?

Whether mouse models of chronic asthma can be used to investigate the relationship between airway inflammation/remodeling and airway hyper-responsiveness (AHR) is a vexed question. It raises issues about the extent to which such models replicate key features of the human disease. Here, we review some of the characteristic pathological features of human asthma and their relationship to AHR and examine some limitations of mouse models that are commonly used to investigate these relationships. We compare these conventional models with our mouse model of chronic asthma involving long-term low-level inhalational challenge and review studies of the relationship between inflammation/remodeling and AHR in this model and its derivatives, including models of an acute exacerbation of chronic asthma and of the induction phase of childhood asthma. We conclude that while extrapolating from studies in mouse models to AHR in humans requires cautious interpretation, such experimental work can provide significant insights into the pathogenesis of airway responsiveness and its molecular and cellular regulation.

Effect of respiratory syncytial virus infection on regulated on activation, normal T-cells expressed and secreted production in a murine model of asthma

PURPOSE

Synthesis of regulated on activation, normal T-cells expressed and secreted (RANTES) in the airway has previously been shown to be elevated after respiratory syncytial virus (RSV) infection. However, since few studies have examined whether RSV-infected asthma patients express a higher level of RANTES than do normal individuals, we used a murine model of asthma to address this question.

METHODS

We prepared Dermatophagoides farinae-sensitized mice as an asthma model, and then infected them with RSV and analyzed the changes in airway responsiveness and the cell populations and cytokine levels of bronchoalveolar lavage fluid.

RESULTS

RANTES synthesis increased in response to RSV infection in both control mice and in asthma model (D. farinae) mice. However, there was no significant difference in the amount of RANTES produced following RSV infection between control and D. farinae mice. RSV infection affected neither interferon-γsynthesis nor airway responsiveness in either control or D. farinae mice.

CONCLUSION

RSV infection did not induce more RANTES in a murine model of asthma than in control mice.

Asthma and gender impact accumulation of T cell subtypes

BACKGROUND

The "Th2 hypothesis for asthma" asserts that an increased ratio of Th2:Th1 cytokine production plays an important pathogenic role in asthma. Although widely embraced, the hypothesis has been challenged by various empirical observations and has been described as overly simplistic. We sought to establish whether CD3+CD28-mediated and antigen-independent accumulation of type 1 and type 2 T cells differs significantly between nonasthmatic and asthmatic populations.

METHODS

An ex vivo system was used to characterize the regulation of IFN-gamma-producing (type 1) and IL-13-producing (type 2) T cell accumulation in response to CD3+CD28 and IL-2 stimulation by flow cytometry.

RESULTS

IL-13-producing T cells increased in greater numbers in response to antigen-independent stimulation in peripheral blood lymphocytes from female atopic asthmatic subjects compared with male asthmatics and both male and female atopic non-asthmatic subjects. IFN-gamma+ T cells increased in greater numbers in response to either antigen-independent or CD3+CD28-mediated stimulation in peripheral blood lymphocytes from atopic asthmatic subjects compared to non-asthmatic subjects, regardless of gender.

CONCLUSIONS

We demonstrate that T cells from asthmatics are programmed for increased accumulation of both type 2 and type 1 T cells. Gender had a profound effect on the regulation of type 2 T cells, thus providing a mechanism for the higher frequency of adult asthma in females.

Asthma in the inner city and the indoor environment

Inner-city residents continue to suffer disproportionate asthma morbidity despite recent progress in reducing asthma morbidity and mortality in other strata of the United States population. Studies over the past decade indicate that the indoor environment is a strong contributor to poor asthma control and asthma-related health care use in inner-city populations. Certain indoor exposures are more common and occur in higher concentrations in inner-city communities than in suburban communities. Identification of "asthmagenic" indoor exposures has paved the way for the development of intervention strategies aimed at reducing asthma morbidity. This article reviews the growing body of evidence that certain indoor environmental exposures contribute to the burden of asthma in the inner city.

Indoor environmental influences on children's asthma

The burden of asthma for children in the United States is substantial and has continued to rise for the past 2 decades. There is growing evidence that the indoor environment may play an important role in the pathogenesis of childhood asthma. This article first reviews the effects of indoor allergen exposure and sensitization on asthma incidence and morbidity, focusing on dust mite, cockroach, pet, and rodent allergens. It then addresses the effects of indoor air pollutants (ozone, particulate matter, nitrogen dioxide, environmental tobacco smoke, sulfur dioxide, and carbon monoxide) on asthma morbidity.

Alterations in vasodilator-stimulated phosphoprotein (VASP) phosphorylation: associations with asthmatic phenotype, airway inflammation and beta2-agonist use

BACKGROUND

Vasodilator-stimulated phosphoprotein (VASP) mediates focal adhesion, actin filament binding and polymerization in a variety of cells, thereby inhibiting cell movement. Phosphorylation of VASP via cAMP and cGMP dependent protein kinases releases this "brake" on cell motility. Thus, phosphorylation of VASP may be necessary for epithelial cell repair of damage from allergen-induced inflammation. Two hypotheses were examined: (1) injury from segmental allergen challenge increases VASP phosphorylation in airway epithelium in asthmatic but not nonasthmatic normal subjects, (2) regular in vivo beta2-agonist use increases VASP phosphorylation in asthmatic epithelium, altering cell adhesion.

METHODS

Bronchial epithelium was obtained from asthmatic and non-asthmatic normal subjects before and after segmental allergen challenge, and after regularly inhaled albuterol, in three separate protocols. VASP phosphorylation was examined in Western blots of epithelial samples. DNA was obtained for beta2-adrenergic receptor haplotype determination.

RESULTS

Although VASP phosphorylation increased, it was not significantly greater after allergen challenge in asthmatics or normals. However, VASP phosphorylation in epithelium of nonasthmatic normal subjects was double that observed in asthmatic subjects, both at baseline and after challenge. Regularly inhaled albuterol significantly increased VASP phosphorylation in asthmatic subjects in both unchallenged and antigen challenged lung segment epithelium. There was also a significant increase in epithelial cells in the bronchoalveolar lavage of the unchallenged lung segment after regular inhalation of albuterol but not of placebo. The haplotypes of the beta2-adrenergic receptor did not appear to associate with increased or decreased phosphorylation of VASP.

CONCLUSION

Decreased VASP phosphorylation was observed in epithelial cells of asthmatics compared to nonasthmatic normals, despite response to beta-agonist. The decreased phosphorylation does not appear to be associated with a particular beta2-adrenergic receptor haplotype. The observed decrease in VASP phosphorylation suggests greater inhibition of actin reorganization which is necessary for altering attachment and migration required during epithelial repair.

IL-5 and granulocyte-macrophage colony-stimulating factor activate STAT3 and STAT5 and promote Pim-1 and cyclin D3 protein expression in human eosinophils

Allergic inflammation is characterized by elevated eosinophil numbers and by the increased production of the cytokines IL-5 and GM-CSF, which control several eosinophil functions, including the suppression of apoptosis. The JAK/STAT pathway is important for several functions in hemopoietic cells, including the suppression of apoptosis. We report in this study that STAT3, STAT5a, and STAT5b are expressed in human eosinophils and that their signaling pathways are active following IL-5 or GM-CSF treatment. However, in airway eosinophils, the phosphorylation of STAT5 by IL-5 is reduced, an event that may be related to the reduced expression of the IL-5Ralpha on airway eosinophils. Furthermore, IL-5 and GM-CSF induced the protein expression of cyclin D3 and the kinase Pim-1, both of which are regulated by STAT-dependent processes in some cell systems. Pim-1 is more abundantly expressed in airway eosinophils than in blood eosinophils. Because Pim-1 reportedly has a role in the modulation of apoptosis, these results suggest that Pim-1 action is linked to the suppression of eosinophil apoptosis by these cytokines. Although cyclin D3 is known to be critical for cell cycle progression, eosinophils are terminally differentiated cells that do not proceed through the cell cycle. Thus, this apparent cytokine regulation of cyclin D3 suggests that there is an alternative role(s) for cyclin D3 in eosinophil biology.

Allergen stimulates bone marrow CD34(+) cells to release IL-5 in vitro; a mechanism involved in eosinophilic inflammation?

The specific mechanisms that alter bone marrow (BM) eosinophilopoiesis in allergen-induced inflammation are poorly understood. The aims of this study were to evaluate (a) whether the number of BM CD34(+) cells is altered due to allergen sensitization and exposure in vivo and (b) whether BM CD34(+) cells produce and release interleukin (IL)-5, IL-3 and granulocyte macrophage-colony stimulating factor (GM-CSF) after stimulation in vitro. A mouse model of ovalbumin (OVA)-induced airway inflammation was used. Bone marrow CD34(+) cells were cultured in vitro and the cytokine release was measured by enzyme-linked immunosorbent assay. The IL-5-production from CD34(+) cells was confirmed by immunocytochemistry. Airway allergen exposure increased the number of BM CD34(+) cells (P = 0.01). Bone marrow CD34(+) cells produced IL-5 when stimulated with the allergen OVA in vitro, but not IL-3 or GM-CSF. Nonspecific stimulus with calcium ionophore and phorbol-myristate-acetate of BM CD34(+) cells caused release of IL-5, IL-3 and GM-CSF. The induced release of IL-5 was increased in alum-injected vs naive mice (P = 0.02), but was not affected by allergen sensitization and exposure. The release of IL-3 and GM-CSF was increased after allergen sensitization and exposure (P < 0.02). In conclusion, allergen can stimulate BM CD34(+) cells to produce IL-5 protein. It is likely that the CD34(+) cells have autocrine functions and thereby regulate the early stages of BM eosinophilopoiesis induced by airway allergen exposure. Alum, a commonly used adjuvant, enhances the release of IL-5 and may thereby enhance eosinophilopoiesis.

Surfactant phospholipid changes after antigen challenge: a role for phosphatidylglycerol in dysfunction

In asthma, inflammation-mediated surfactant dysfunction contributes to increased airway resistance, but the mechanisms for dysfunction are not understood. To test mechanisms that alter surfactant function, atopic asthmatics underwent endobronchial antigen challenge and bronchoalveolar lavage (BAL). BAL fluids were sequentially separated into cells, surfactant, and supernatant, and multiple end points were analyzed. Each end point's unique relationship to surfactant dysfunction was determined. Our results demonstrate that minimum surface tension (gamma(min)) of surfactant after antigen challenge was significantly increased with a spectrum of responses that included dysfunction in 6 of 13 asthmatics. Antigen challenge significantly altered the partitioning of surfactant phospholipid measured as a decreased ratio of large surfactant aggregates (LA) to small surfactant aggregates (SA), LA/SA ratio. Phosphatidylglycerol (PG) was significantly reduced in the LA of the dysfunctional asthmatic BALs. There was a corresponding significant increase in the ratio of phosphatidylcholine to PG, which strongly correlated with both increased gamma(min) and decreased LA/SA. Altered surfactant phospholipid properties correlated with surfactant dysfunction as well or better than either increased eosinophils or protein. Secretory phospholipase activity, measured in vitro, increased after antigen challenge and may explain the decrease in surfactant PG. In summary, alteration of phospholipids, particularly depletion of PG, in the LA of surfactant may be an important mechanism in asthma-associated surfactant dysfunction.

TRAIL in the airways

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) is an important immunomodulatory factor that may play a role in the structural changes observed in the asthmatic airways. In vitro as well as in vivo studies have evidenced a dual role for TRAIL: it can either function as a pro- or anti-inflammatory cytokine on inflammatory cells, participating in the initiation and resolution of inflammatory and immune responses. TRAIL is expressed in the airways by inflammatory cells infiltrated in the bronchial mucosa, as well as by structural cells of the airway wall including fibroblasts, epithelial, endothelial, and smooth muscle cells. By releasing TRAIL, these different cell types may then participate in the increased levels of TRAIL observed in bronchoalveolar lavage fluid from asthmatic patients. Taken together, this suggests that TRAIL may play a role in inflammation in asthma. However, concerning its role is dual in the modulation of inflammation, further studies are needed to elucidate the precise role of TRAIL in the airways.

Bronchoalveolar lavage fluid concentrations of transforming growth factor (TGF)-beta1, TGF-beta2, interleukin (IL)-4 and IL-13 after segmental allergen challenge and their effects on alpha-smooth muscle actin and collagen III synthesis by primary human lung fibroblasts

RATIONALE

Asthmatic airway remodelling is characterized by myofibroblast hyperplasia and subbasement membrane collagen deposition. We hypothesized that cytokines and growth factors implicated in asthmatic airway remodelling are increased in bronchoalveolar lavage (BAL) fluid of asthmatics after segmental allergen challenge (SAC), and that these growth factors and cytokines increase alpha-smooth muscle actin (alpha-SMA) and collagen III synthesis by human lung fibroblasts (HLFs).

METHODS

Transforming growth factor (TGF)-beta1, TGF-beta2, IL-4 and IL-13 levels were measured in BAL fluid from 10 asthmatics and 9 non-asthmatic controls at baseline and then 1 day, 1 week and 2 weeks after SAC. Confluent cultures of HLFs were stimulated by exogenous addition of TGF-beta1, TGF-beta2, IL-4 or IL-13 (concentration range 0.01-10 ng/mL) over 48 h. Collagen III was measured in culture supernates and alpha-SMA in cell lysates by Western blot.

RESULTS

At baseline, there was no difference in BAL fluid concentrations of TGF-beta1, IL-4 and IL-13 between asthmatics and controls; however, non-asthmatics had higher concentrations of total TGF-beta2. In asthmatics, BAL fluid concentrations of all four factors increased significantly 1 day after SAC. TGF-beta1, TGF-beta2 and IL-13 concentrations returned to baseline by 1 week after SAC, but BAL fluid IL-4 concentration remained elevated for at least 2 weeks. TGF-beta1, TGF-beta2 and IL-4 significantly increased alpha-SMA in fibroblasts, but only IL-4 caused corresponding increases in collagen III synthesis. IL-13 had no direct effects on collagen III synthesis and alpha-SMA expression.

CONCLUSIONS

Because IL-4 caused a dose-dependent increase in alpha-SMA and collagen III synthesis, it may be an important cytokine mediating asthmatic airway remodelling. TGF-beta1 and TGF-beta2 may also play a role in airway remodelling by stimulating phenotypic change of fibroblasts to myofibroblasts. Additionally, collagen III synthesis appears to be independent of myofibroblast phenotype and is apparently regulated by different growth factors and cytokines.

Eosinophil cationic protein alters pulmonary surfactant structure and function in asthma

BACKGROUND

Impaired surfactant function has been demonstrated in patients with asthma. Inhibitory proteins originating from plasma or inflammatory mediators are good candidates to contribute to this dysfunction. Eosinophils are potent effector cells in asthma, which, on activation, release inflammatory mediators, especially reactive granula proteins such as eosinophil cationic protein (ECP).

OBJECTIVE

Because the potential role of ECP in the inhibition of surfactant function is not known, we tested the hypothesis of whether ECP levels in bronchoalveolar lavage fluid (BALF) of patients with asthma after segmental allergen provocation correlate to surfactant dysfunction. Furthermore, we tested the effect of purified ECP on surfactant function and structure in vitro.

METHODS

Surfactant isolated from BALF of asthmatic patients was assessed for biophysical function with the Pulsating Bubble Surfactometer and the Capillary Surfactometer and correlated to ECP levels. Purified ECP and plasma proteins at various concentrations were incubated with natural surfactant. Surfactant function was studied with the Capillary Surfactometer, and surfactant structure was determined by electron microscopy.

RESULTS

ECP is elevated in BALF from patients with asthma after allergen challenge compared with baseline. ECP levels after allergen challenge correlate well to surfactant dysfunction. In vitro, ECP induces a concentration-dependent inhibition of surfactant function that can be inhibited by antibodies against ECP. ECP is more potent compared with albumin or fibrinogen. Finally, ECP induces severe ultrastructural changes to surfactant vesicles that are more pronounced than changes induced by either fibrinogen or albumin.

CONCLUSIONS

ECP contributes to surfactant dysfunction in asthma, which in turn could lead to airway obstruction.

Molecular assembly of the ternary granulocyte-macrophage colony-stimulating factor receptor complex

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic cytokine that stimulates the production and functional activity of granulocytes and macrophages, properties that have encouraged its clinical use in bone marrow transplantation and in certain infectious diseases. Despite the importance of GM-CSF in regulating myeloid cell numbers and function, little is known about the exact composition and mechanism of assembly of the GM-CSF receptor complex. We have now produced soluble forms of the GM-CSF receptor alpha chain (sGMRalpha) and beta chain (sbetac) and utilized GM-CSF, the GM-CSF antagonist E21R (Glu21Arg), and the betac-blocking monoclonal antibody BION-1 to define the molecular assembly of the GM-CSF receptor complex. We found that GM-CSF and E21R were able to form low-affinity, binary complexes with sGMRalpha, each having a stoichiometry of 1:1. Importantly, GM-CSF but not E21R formed a ternary complex with sGMRalpha and sbetac, and this complex could be disrupted by E21R. Significantly, size-exclusion chromatography, analytical ultracentrifugation, and radioactive tracer experiments indicated that the ternary complex is composed of one sbetac dimer with a single molecule each of sGMRalpha and of GM-CSF. In addition, a hitherto unrecognized direct interaction between betac and GM-CSF was detected that was absent with E21R and was abolished by BION-1. These results demonstrate a novel mechanism of cytokine receptor assembly likely to apply also to interleukin-3 (IL-3) and IL-5 and have implications for our molecular understanding and potential manipulation of GM-CSF activation of its receptor.

Differential expression of TRAIL and TRAIL receptors in allergic asthmatics following segmental antigen challenge: evidence for a role of TRAIL in eosinophil survival

Asthma is a chronic lung disease exhibiting airway obstruction, hyperresponsiveness, and inflammation, characterized by the infiltration of eosinophils into the airways and the underlying tissue. Prolonged eosinophilic inflammation depends on the balance between the cell's inherent tendency to undergo apoptosis and the local eosinophil-viability enhancing activity. TRAIL, a member of the TNF family, induces apoptosis in most transformed cells; however, its role in health and disease remains unknown. To test the hypothesis that Ag-induced inflammation is associated with TRAIL/TRAIL-R interactions, we used a segmental Ag challenge (SAC) model in ragweed-allergic asthmatics and nonasthmatic patients and analyzed bronchoalveolar lavage (BAL) material for 2 wk. In asthmatic patients, the level of TRAIL in BAL fluid dramatically increased 24 h after SAC, which significantly correlated with BAL eosinophil counts. Immunohistochemical analysis of bronchial biopsies from asthmatic patients demonstrated that TRAIL staining was increased in epithelial, airway smooth muscle, and vascular smooth muscle cells and throughout the interstitial tissue after SAC. This was confirmed by quantitative immunocytochemical image analysis of BAL eosinophils and alveolar macrophages, which demonstrated that expression levels of TRAIL and DcR2 increased, whereas expression levels of the TRAIL-Rs DR4 and DR5 decreased in asthmatic subjects after SAC. We also determined that TRAIL prolongs eosinophil survival ex vivo. These data provide the first in vivo evidence that TRAIL expression is increased in asthmatics following Ag provocation and suggest that modulation of TRAIL and TRAIL-R interactions may play a crucial role in promoting eosinophil survival in asthma.

On the generation of allergic airway diseases: from GM-CSF to Kyoto

The sharp increase in the prevalence of asthma over the past three decades suggests an important contribution of environmental factors in the generation of this disease, and compels a search for molecular pathways by which such factors could facilitate Th2 immune-inflammatory airway responses; granulocyte-macrophage colony-stimulating factor (GM-CSF) might be one such signal. In this review, we appraise the evidence with respect to the presence of GM-CSF in asthma, the roles played by GM-CSF in these immune responses and environmental triggers that can induce GM-CSF expression. Further, we propose a paradigm that unites these divergent observations, and postulate that GM-CSF produced in response to environmental agents can establish an airway microenvironment that promotes the initiation, influences the evolution and supports the maintenance of an aeroallergen-specific adaptive Th2 immune response.

Alterations in airway inflammation and lung function during corticosteroid therapy for atopic asthma

INTRODUCTION

Although corticosteroid therapy for asthma improves lung function and reduces airway inflammation, the relation between these two events is unclear. This article investigates associations between changes in bronchial inflammation and lung function during high-dose inhaled corticosteroid therapy for asthma.

METHODS

Nine subjects with atopic asthma received high-dose inhaled fluticasone propionate (FP), 2,000 microg/d for 8 weeks. Fiberoptic bronchoscopy with endobronchial biopsies, spirometry, and histamine provocation challenge were performed on each subject at baseline, after 2 weeks, and again after 8 weeks of therapy. Spearman rank correlation coefficients between changes in parameters of bronchial inflammation and lung function were computed.

RESULTS

As expected, significant down-regulation of airway inflammation and improvements in lung function were observed after both short-term and long-term therapy with high-dose inhaled FP. During corticosteroid therapy, changes in lymphocyte and macrophage numbers in bronchial biopsy specimens were closely correlated. Changes in EG1+ eosinophils were associated with changes in EG2+ eosinophils after 8 weeks of therapy. Although changes in airway inflammation and changes in lung function were not closely associated after 2 weeks of therapy, changes in eosinophils (EG1) in bronchial biopsy specimens correlated with changes in bronchodilator response (r = 0.77, p = 0.016) after 8 weeks of therapy.

CONCLUSION

In patients with atopic asthma, changes in bronchial eosinophils and lung function during steroid therapy are closely related but do not occur simultaneously.

The role of indoor allergen sensitization and exposure in causing morbidity in women with asthma

Longitudinal evidence that indoor allergen exposure causes morbidity in sensitized individuals with asthma is scarce. We evaluated the association of allergen sensitization and home exposure to short- and long-term morbidity in 140 women with asthma and to asthma prevalence in 458 women from metropolitan Boston. Cockroach (Blattella germanica), dust mite (Dermatophagoides farinae), and cat (Felis domesticus) allergens in home dust samples, and specific immunoglobulin E antibodies were measured at outset, and doctor-diagnosed asthma and markers of asthma morbidity were ascertained by questionnaire during a 4-year follow-up. Cat- and cockroach-sensitive (immunoglobulin E immunocap [Cap] class > or = 1) women with asthma reported greater morbidity in the past year at the start, and during follow-up, if high levels of the relevant allergen were found. Women with asthma sensitized to cat allergen and with concentrations at 8 microg/g or greater were more likely to have used steroid (adjusted odds ratio [95% confidence interval] 2.7 [1.2-6.2]) and wheezed without a cold (odds ratio 6.8 [3.3- 14.0]) during follow-up. Those sensitized and exposed to cockroach (Bla g 1 or 2 > or = 2 U/g) were at least three times more likely to have used steroid and to have attended a hospital emergency room; the size of the effect upon steroid use was maintained, but the precision was reduced and the 95% confidence interval included one (p = 0.07), with adjustment for race and poverty. We conclude that cockroach and cat allergens may contribute to asthma morbidity in sensitized women.

Eotaxin expression by epithelial cells and plasma cells in chronic asthma

Chemoattractants such as eotaxin are believed to play an important role in the recruitment of eosinophils into the airways in asthma. We investigated expression of eotaxin in the airway wall in a model of chronic human asthma, in which systemically sensitized mice were exposed to low mass concentrations of aerosolized antigen for 6 weeks. In these animals, the number of intraepithelial eosinophils in the airways was significantly increased 3 hours after exposure and declined by 24 hours. In parallel, immunoreactivity for eotaxin was strikingly up-regulated in airway epithelial cells and in inflammatory cells in the lamina propria. The latter were identified as plasma cells by double immunofluorescent labeling. Increased expression of eotaxin by epithelial cells and plasma cells was also demonstrated in a case of fatal human asthma. In contrast, sensitized mice that received a single exposure to a high mass concentration of aerosolized antigen exhibited delayed eosinophil recruitment, which did not correlate with eotaxin expression. Furthermore, in sensitized chronically exposed interleukin-13-deficient mice there was virtually no recruitment of eosinophils into the airways, although eotaxin expression was greater than or equal to that in wild-type mice. These results indicate that there are striking differences between acute and chronic exposure models in the time course of eotaxin expression and eosinophil recruitment. Although high eotaxin levels alone are not sufficient to cause recruitment of eosinophils into the airways, recurrent exposure may generate or up-regulate additional signals required for eosinophil chemotaxis.

Asthmatic epithelial cell proliferation and stimulation of collagen production: human asthmatic epithelial cells stimulate collagen type III production by human lung myofibroblasts after segmental allergen challenge

Epithelial injury and subepithelial collagen deposition are characteristic of asthma. We hypothesized that epithelial cell proliferation increases after airway injury in asthmatics, that epithelial cells stimulate lung myofibroblast collagen production, and that both processes are modulated by allergen-recruited inflammatory cells. Epithelial cells obtained at baseline, 1 d, and 1 and 2 wk after endobronchial allergen challenge from asthmatics and nonasthmatics were placed in culture, with and without bronchoalveolar lavage cells obtained from the same segment. Epithelial cell proliferation and collagen synthesis by human lung myofibroblasts stimulated with culture medium from these epithelial cells were determined. Epithelial proliferation increased (108 +/- 50% above baseline, p = 0.01 for d, and p = 0.004 for group x day interaction) 1 wk postchallenge in cells from asthmatics, but not from nonasthmatics, and required bronchoalveolar lavage cell coculture. Culture medium from epithelium harvested from asthmatics, but not from nonasthmatics, at 1 to 2 wk postchallenge stimulated collagen type III production 50% to 70% (p = 0.043 for clinical group, p = 0.012 for day, and p = 0.022 for group x day interaction), but not collagen type I. This effect was independent of an acute eosinophilic response. We conclude that epithelial cells from asthmatics, but not from nonasthmatics, are stimulated to proliferate after allergen challenge, and over 1 to 2 wk postchallenge, stimulate collagen type III synthesis by lung myofibroblasts. Epithelial cell proliferation appears dependent upon infiltrating inflammatory cells, but stimulation of collagen type III does not.

Local lung responses following local lung challenge with recombinant lungworm antigen in systemically sensitized sheep

BACKGROUND

Chronic mast cell-mediated inflammation may contribute significantly towards the extensive tissue remodelling that is a feature of lungworm infection in ruminants. Understanding the factors that control tissue remodelling is a necessary step toward effective management and treatment of conditions that feature such pathology.

OBJECTIVE

We sought to define in a novel ovine model system, the cellular, immune and mast cell phenotypic events that occur following local lung challenge with a recombinant protein antigen, DvA-1, derived from the ruminant lungworm nematode, Dictyocaulus viviparus.

METHODS

Two spatially disparate lung segments in systemically sensitized sheep were challenged on three occasions with DvA-1 (3xDVA) and two further segments were challenged with saline (3xSAL). Two months after the third challenge, one of the two segments previously repeatedly challenged with DvA-1 was challenged again with DvA-1 (3xDVA:DVA) whilst the other was challenged with saline (3xDVA:SAL). A similar protocol was followed with the saline challenged segments (3xSAL:SAL and 3xSAL:DVA). Bronchoalveolar lavage fluid (BALF) (n = 16) and tissue (n = 3) were collected after the last challenge.

RESULTS

Cellular changes 24 h after the fourth challenge were characterized by an increase in the absolute numbers of neutrophils and eosinophils in BALF from 3xDVA:DVA and 3xSAL:DVA segments. Local antibody production was implied through increased levels of antibody in both 3xDVA:DVA and 3xDVA:SAL segments, with the latter being unaffected by inflammation. Levels of active transforming growth factor beta-1 (TGF-beta(1)) were significantly increased in 3xDVA:SAL segments and a trend towards an increase was apparent in 3xDVA:DVA segments. Total TGF-beta1 levels were significantly correlated with eosinophil counts in all except the 3xDVA:SAL segments. Such changes in the bronchoalveolar space were complemented by increased ratios of sheep mast cell proteinase-1 expressing cells and tryptase expressing cells, to toluidine blue positive cells in airways from 3xDVA:DVA segments.

CONCLUSION

Mast cell phenotypic events occurring as a consequence of antigen challenge were limited to segments in which changes in BALF were characterized by neutrophil influx and increased local antibody production.

Increased detection of interleukin-5 in sputum by addition of protease inhibitors

The measurement of interleukin (IL)-5 in sputum is problematic, with interfering factors affecting immunoassay. The authors investigated whether sputum proteases could be acting as interfering factors by studying the effect of protease inhibitors (PI) on sputum IL-5 measurement. Induced sputa from 20 subjects with asthma were divided into aliquots, processed with and without protease inhibitors (in low and high concentrations) and the levels of IL-5 (spiked and endogenous) measured by enzyme immunoassay were compared. The concentration of sputum IL-5 was significantly increased by PI, with median (interquartile range) levels processed with no, low and high PI concentrations being 0 (0), 41.8 (75.6) and 66.1 (124.4) pg x mL(-1), respectively. There was also a significant increase in percentage recovery of spiked IL-5. Although high concentrations of PI reduced cell viability, there was no effect on total or differential cell counts and low concentrations of PI had no effect on cell counts or viability. Levels of endogenous interleukin-5 in sputum of asthmatic subjects can be significantly increased by the addition of protease inhibitors, and samples which would be regarded as negative for interleukin-5 without protease inhibitors may instead have considerable amounts of interleukin-5 detected.

Understanding airway wall remodeling in asthma: a basis for improvements in therapy?

Current strategies for the management of asthma focus on suppressing airway inflammation. Other characteristic features of human asthma, such as airway hyperreactivity and the structural changes collectively referred to as airway remodeling, are largely ignored in existing guidelines for monitoring the effectiveness of treatment. Evidence is accumulating that pharmacologic therapy targeting airway wall remodeling may be valuable in treating asthma. However, development of appropriate therapeutic agents will require a better understanding of the pathogenesis of remodeling, which appears to be regulated by a variety of cytokines and growth factors produced by inflammatory, epithelial, and stromal cells. Furthermore, testing the effectiveness of novel agents that specifically target the process of remodeling will require appropriate experimental models, but most currently available animal models of asthma have major limitations. A recently described murine model of chronic human asthma offers considerable potential for dissection of the mechanisms of airway wall remodeling, as well as for investigation of the therapeutic potential of drugs that can modulate chronic inflammation and remodeling.

New approaches in the treatment of asthma

Asthma is a common and complex inflammatory disease of the airways that remains incurable. Current forms of therapy are long term and may exhibit associated side-effect problems. Major participants in the development of an asthma phenotype include the triggering stimuli such as the allergens themselves, cells such as T cells, epithelial cells and mast cells that produce a variety of cytokines including IL-5, GM-CSF, IL-3, IL-4 and IL-13 and chemokines such as eotaxin. Significantly, the eosinophil, a specialized blood cell type, is invariably associated with this disease. The eosinophil has long been incriminated in the pathology of asthma due to its ability to release preformed and unique toxic substances as well as newly formed pro-inflammatory mediators. The regulation of eosinophil production and function is carried out by soluble peptides or factors. Of these IL-5, GM-CSF and IL-3 are of paramount importance as they control eosinophil functional activity and are the only known eosinophilopoietic factors. In addition they regulate the eosinophil life span by inhibiting apoptosis. While one therapeutic approach in asthma is directed at inhibiting single eosinophil products such as leukotrienes or single eosinophil regulators such as IL-5, we believe that the simultaneous inhibition of more than one component is preferable. This may be particularly important with eosinophil regulators in that not only IL-5, but also GM-CSF has been repeatedly implicated in clinical studies of asthma. The fact that GM-CSF is produced by many cells in the body and in copious amounts by lung epithelial cells highlights this need further. Our approach takes advantage of the fact that the IL-5 and GM-CSF receptors (as well as IL-3 receptors) utilize a shared subunit to bind, with high affinity, to these cytokines and the same common subunit mediates signal transduction culminating in all the biological activities mentioned. By generating the monoclonal antibody BION-1 to the cytokine binding region of the common subunit (betac) we have shown that the approach of inhibiting IL-5, GM-CSF and IL-3 binding and the resulting stimulation of eosinophil production and function with a single agent is feasible. Furthermore we have used BION-1 as a tool to crystallize and define the structure of the cytokine binding domain of betac. This knowledge and this approach may lead to the generation of novel therapeutics for the treatment of asthma.

Granulocyte macrophage-colony-stimulating factor mRNA is stabilized in airway eosinophils and peripheral blood eosinophils activated by TNF-alpha plus fibronectin

Airway eosinophils show prolonged in vitro survival compared with peripheral blood eosinophils (PBEos). Recent studies have shown that autocrine production and release of GM-CSF is responsible for enhanced survival, but the mechanisms controlling cytokine production remain obscure. We compared GM-CSF mRNA decay in eosinophils from bronchoalveolar lavage (BALEos) after allergen challenge or from PBEos. BALEos showed prolonged survival in vitro (60% at 4 days) and expressed GM-CSF mRNA. The enhanced survival of BALEos was 75% inhibited at 6 days by neutralizing anti-GM-CSF Ab. Based on transfection studies, GM-CSF mRNA was 2.5 times more stable in BALEos than in control PBEos. Treatment of PBEos with fibronectin and TNF-alpha increased their in vitro survival, GM-CSF mRNA expression, and GM-CSF mRNA stability to a comparable level as seen in BALEos. These data suggest that TNF-alpha plus fibronectin may increase eosinophil survival in vivo by controlling GM-CSF production at a posttranscriptional level.

Minute quantities of granulocyte-macrophage colony-stimulating factor prolong eosinophil survival

Allergic asthma is characterized by pulmonary infiltration and accumulation of eosinophils, which is enhanced by granulocyte-macrophage colony-stimulating factor (GM-CSF). T cells, fibroblasts, and eosinophils themselves produce GM-CSF, suggesting it functions in the lung microenvironment as a survival factor. However, the amounts and the mechanism by which GM-CSF supports eosinophil survival remain poorly understood. We have previously reported that human peripheral blood eosinophils (PBEo) can be transfected with GM-CSF mRNA using particle-mediated gene transfer (PMGT). Using this technology, GM-CSF mRNA was introduced into resting PBEo, and GM-CSF production and cell survival were assessed. GM-CSF protein was undetectable (< 1 pg/ml) in the supernatant but present intracellularly at very low levels. Unexpectedly, the in vitro survival of transfected PBEo was 4-fold greater than that of controls. Neutralizing anti-GM-CSF but not anti-interleukin-5 (anti-IL-5) antibody added up to 24 h after transfection abolished enhanced survival, demonstrating that the continuous presence of GM-CSF was required. Conditioned medium prepared from transfected PBEo prolonged the survival of naive cells. Comparable survival activity was mimicked by a single dose of 100-500 pg/ml or multiple administrations of 0.1 pg/ml recombinant human GM-CSF (rHuGM-CSF). Survival was completely inhibited by a Jak2 inhibitor, suggesting that GM-CSF-mediated survival involved signaling through the Jak-Stat pathway. Thus, autocrine production of low levels of GM-CSF by a minority of PBEo can block apoptosis of the entire culture by a minute but sustained GM-CSF release.

The role of intervention in established allergy: avoidance of indoor allergens in the treatment of chronic allergic disease

Avoidance of exposure to indoor allergens is an important element in the treatment of allergic disease. The results of several studies provide strong evidence in support of a role for allergen avoidance; however, strategies that optimize allergen reduction in houses have not been determined. Complex issues regarding the efficacy of physical and chemical measures that target house dust mite, pet, and cockroach allergens in the home are discussed. The greatest challenge is to educate allergic patients so that they can play an important role in controlling their own disease.

Kinetics of IL-10 production after segmental antigen challenge of atopic asthmatic subjects

BACKGROUND

IL-10 is an anti-inflammatory cytokine made by lymphocytes, monocytes-macrophages, and eosinophils, and it may have an important role in regulating the asthmatic inflammatory response. IL-10 levels have been reported to be reduced in asthmatic airways, potentially contributing to more intense inflammation.

OBJECTIVE

We sought to determine whether IL-10 levels were deficient in patients with mild asthma compared with controls and to determine whether IL-10 levels were associated with the resolution of eosinophilic inflammation.

METHODS

We quantified IL-10 levels in the bronchoalveolar lavage (BAL) fluid (ELISA), BAL cells (quantitative immunocytochemistry), purified alveolar macrophages-monocytes studied ex vivo (ELISA), before (day 1) and after (24 hours [day 2], 1 week [day 9], and 2 weeks [day 16]) segmental antigen challenge (SAC), and investigated the effect of glucocorticoid treatment on ex vivo macrophage-monocyte IL-10 production.

RESULTS

IL-10 levels were significantly higher in the BAL fluid of mild asthmatic subjects who demonstrated a dual reaction (both early and late) after whole lung ragweed inhalation challenge compared with nonallergic, nonasthmatic control subjects before and 24 hours and 1 week after SAC. Macro-phages-monocytes obtained before and after SAC from asthmatic patients also secreted increased amounts of IL-10 ex vivo than those from controls. Dexamethasone did not significantly change spontaneous IL-10 secretion from macrophages-monocytes in vitro. Quantitative immunocytochemical analysis of BAL cells demonstrated increased IL-10 in macrophages 24 hours after SAC and a similar trend in eosinophils.

CONCLUSION

IL-10 is not deficient in mild asthma. Furthermore, BAL IL-10 levels are significantly higher in asthmatic subjects with a dual response than in control subjects before and after SAC. The increase in IL-10 was coincident with the initial increase in BAL eosinophils, although BAL eosinophilia persisted after IL-10 levels had returned to baseline, suggesting that the increased IL-10 levels could not promptly terminate this localized eosinophilic response.

Induced sputum: validity of fluid-phase IL-5 measurement

BACKGROUND

IL-5 measurement in the fluid phase of induced sputum is considered to be important in the assessment of asthma, but the validity of these measurements is uncertain.

OBJECTIVE

We investigated the validity of sputum IL-5 measurements through a series of spiking experiments and examined the effect of dithiothreitol (DTT) on these measurements.

METHODS

Induced sputum from 26 asthmatic subjects was spiked with IL-5 and processed, and the percentage of recovery was measured by means of immunoassay. In 6 of the 26 samples the effect of adding albumin to the processing fluids was studied. In 3 separate samples radiolabeled IL-5 was added, and the recovery measured by means of gamma counting and immunoassay were compared. In addition, the effect of DTT on the immunoassay was examined.

RESULTS

The mean +/- SD recovery of spiked IL-5 was 26.1% +/- 14.6% measured by means of immunoassay; adding albumin increased the recovery to 47.7% +/- 8.0% (P <.001). The mean recovery measured by means of gamma counting was 84.8% +/- 5.7% (P <.001); adding albumin had no effect on recovery. DTT had no significant effect on IL-5 measurement.

CONCLUSION

The validity of IL-5 measurement by means of current methods is poor. The discrepancy in recovery as measured by gamma counting compared with immunoassay suggests that there is a problem with the recognition of IL-5 epitopes by immunoassay in induced sputum. This cannot be attributed to DTT but may be due to other interfering substances present in sputum, such as sputum proteases, soluble receptors, or autoantibodies.

Structure of the activation domain of the GM-CSF/IL-3/IL-5 receptor common β-chain bound to an antagonist

Heterodimeric cytokine receptors generally consist of a major cytokine-binding subunit and a signaling subunit. The latter can transduce signals by more than 1 cytokine, as exemplified by the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-2 (IL-2), and IL-6 receptor systems. However, often the signaling subunits in isolation are unable to bind cytokines, a fact that has made it more difficult to obtain structural definition of their ligand-binding sites. This report details the crystal structure of the ligand-binding domain of the GM-CSF/IL-3/IL-5 receptor β-chain (βc) signaling subunit in complex with the Fab fragment of the antagonistic monoclonal antibody, BION-1. This is the first single antagonist of all 3 known eosinophil-producing cytokines, and it is therefore capable of regulating eosinophil-related diseases such as asthma. The structure reveals a fibronectin type III domain, and the antagonist-binding site involves major contributions from the loop between the B and C strands and overlaps the cytokine-binding site. Furthermore, tyrosine421 (Tyr421), a key residue involved in receptor activation, lies in the neighboring loop between the F and G strands, although it is not immediately adjacent to the cytokine-binding residues in the B-C loop. Interestingly, functional experiments using receptors mutated across these loops demonstrate that they are cooperatively involved in full receptor activation. The experiments, however, reveal subtle differences between the B-C loop and Tyr421, which is suggestive of distinct functional roles. The elucidation of the structure of the ligand-binding domain of βc also suggests how different cytokines recognize a single receptor subunit, which may have implications for homologous receptor systems.

Structure of the activation domain of the GM-CSF/IL-3/IL-5 receptor common β-chain bound to an antagonist

Heterodimeric cytokine receptors generally consist of a major cytokine-binding subunit and a signaling subunit. The latter can transduce signals by more than 1 cytokine, as exemplified by the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-2 (IL-2), and IL-6 receptor systems. However, often the signaling subunits in isolation are unable to bind cytokines, a fact that has made it more difficult to obtain structural definition of their ligand-binding sites. This report details the crystal structure of the ligand-binding domain of the GM-CSF/IL-3/IL-5 receptor β-chain (βc) signaling subunit in complex with the Fab fragment of the antagonistic monoclonal antibody, BION-1. This is the first single antagonist of all 3 known eosinophil-producing cytokines, and it is therefore capable of regulating eosinophil-related diseases such as asthma. The structure reveals a fibronectin type III domain, and the antagonist-binding site involves major contributions from the loop between the B and C strands and overlaps the cytokine-binding site. Furthermore, tyrosine421 (Tyr421), a key residue involved in receptor activation, lies in the neighboring loop between the F and G strands, although it is not immediately adjacent to the cytokine-binding residues in the B-C loop. Interestingly, functional experiments using receptors mutated across these loops demonstrate that they are cooperatively involved in full receptor activation. The experiments, however, reveal subtle differences between the B-C loop and Tyr421, which is suggestive of distinct functional roles. The elucidation of the structure of the ligand-binding domain of βc also suggests how different cytokines recognize a single receptor subunit, which may have implications for homologous receptor systems.

Simultaneous Antagonism of Interleukin-5, Granulocyte-Macrophage Colony-Stimulating Factor, and Interleukin-3 Stimulation of Human Eosinophils by Targetting the Common Cytokine Binding Site of Their Receptors

Human interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-3 are eosinophilopoietic cytokines implicated in allergy in general and in the inflammation of the airways specifically as seen in asthma. All 3 cytokines function through cell surface receptors that comprise a ligand-specific  chain and a shared subunit (βc). Although binding of IL-5, GM-CSF, and IL-3 to their respective receptor  chains is the first step in receptor activation, it is the recruitment of βc that allows high-affinity binding and signal transduction to proceed. Thus, βc is a valid yet untested target for antiasthma drugs with the added advantage of potentially allowing antagonism of all 3 eosinophil-acting cytokines with a single compound. We show here the first development of such an agent in the form of a monoclonal antibody (MoAb), BION-1, raised against the isolated membrane proximal domain of βc. BION-1 blocked eosinophil production, survival, and activation stimulated by IL-5 as well as by GM-CSF and IL-3. Studies of the mechanism of this antagonism showed that BION-1 prevented the high-affinity binding of125I–IL-5, 125I–GM-CSF, and125I–IL-3 to purified human eosinophils and that it bound to the major cytokine binding site of βc. Interestingly, epitope analysis using several βc mutants showed that BION-1 interacted with residues different from those used by IL-5, GM-CSF, and IL-3. Furthermore, coimmunoprecipitation experiments showed that BION-1 prevented ligand-induced receptor dimerization and phosphorylation of βc, suggesting that ligand contact with βc is a prerequisite for recruitment of βc, receptor dimerization, and consequent activation. These results demonstrate the feasibility of simultaneously inhibiting IL-5, GM-CSF, and IL-3 function with a single agent and that BION-1 represents a new tool and lead compound with which to identify and generate further agents for the treatment of eosinophil-dependent diseases such as asthma.

Simultaneous Antagonism of Interleukin-5, Granulocyte-Macrophage Colony-Stimulating Factor, and Interleukin-3 Stimulation of Human Eosinophils by Targetting the Common Cytokine Binding Site of Their Receptors

Human interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-3 are eosinophilopoietic cytokines implicated in allergy in general and in the inflammation of the airways specifically as seen in asthma. All 3 cytokines function through cell surface receptors that comprise a ligand-specific  chain and a shared subunit (βc). Although binding of IL-5, GM-CSF, and IL-3 to their respective receptor  chains is the first step in receptor activation, it is the recruitment of βc that allows high-affinity binding and signal transduction to proceed. Thus, βc is a valid yet untested target for antiasthma drugs with the added advantage of potentially allowing antagonism of all 3 eosinophil-acting cytokines with a single compound. We show here the first development of such an agent in the form of a monoclonal antibody (MoAb), BION-1, raised against the isolated membrane proximal domain of βc. BION-1 blocked eosinophil production, survival, and activation stimulated by IL-5 as well as by GM-CSF and IL-3. Studies of the mechanism of this antagonism showed that BION-1 prevented the high-affinity binding of125I–IL-5, 125I–GM-CSF, and125I–IL-3 to purified human eosinophils and that it bound to the major cytokine binding site of βc. Interestingly, epitope analysis using several βc mutants showed that BION-1 interacted with residues different from those used by IL-5, GM-CSF, and IL-3. Furthermore, coimmunoprecipitation experiments showed that BION-1 prevented ligand-induced receptor dimerization and phosphorylation of βc, suggesting that ligand contact with βc is a prerequisite for recruitment of βc, receptor dimerization, and consequent activation. These results demonstrate the feasibility of simultaneously inhibiting IL-5, GM-CSF, and IL-3 function with a single agent and that BION-1 represents a new tool and lead compound with which to identify and generate further agents for the treatment of eosinophil-dependent diseases such as asthma.

Airway remodeling and persistent airway obstruction in asthma

There is growing recognition that some patients with long-standing asthma may possess a component of irreversible airflow obstruction despite optimal therapy. This persistent airflow obstruction is thought to be the result of structural changes in the airways that occur as a result of airway remodeling. The structural changes that lead to chronic obstruction are not known, nor are the intricacies of the remodeling process. Hence airway remodeling and its role in the evolution of irreversible airflow obstruction remain conceptual. Much work has been carried out to better define the histopathologic characteristics of asthma, including the characteristic features of airway inflammation. However, attempts to delineate the physiologic consequences of specific histologic findings are at an early stage of development. The thesis that airway remodeling is driven by chronic inflammatory processes has important implications for the way we make treatment decisions, especially in the patient with mild asthma. Abounding interest in airway remodeling has led to a growing literature on the subject, a literature that is largely speculative and perhaps too tautologic in the sense that remodeling is frequently defined by any observed histologic change, irrespective of its physiologic consequences. Careful attempts to link histologic observations with clinical, demographic, and physiologic findings will be necessary to unravel the causes of remodeling and identify who is at risk for development of irreversible airway obstruction.

Kinetics of allergen-induced airway eosinophilic cytokine production and airway inflammation

Airway eosinophilia is the hallmark of asthma exacerbation. Coordination of cytokines such as interleukin (IL)-5, eotaxin and regulated on activation, normal T-cell expressed and secreted (RANTES) seem to be necessary for eosinophil extravasation including adhesion, chemotaxis, and activation. The purpose of this study was to characterize both the kinetics of allergen-induced inflammatory cell recruitment to the airways and cytokines selective for eosinophil chemotaxis, activation, or resolution. Eight atopic asthmatic individuals demonstrating a dual response to inhaled allergen completed a diluent-controlled crossover study. The subjects showed significant allergen-induced early and late airway asthmatic responses (p < 0.001), and an increase in the number of sputum eosinophils and metachromatic cells (p < 0.05). The number of eosinophils immunopositive for IL-5, eotaxin, and RANTES increased 7 h after allergen inhalation (p < 0.05), coincident with the peak number of activated eosinophils. Sputum cells immunopositive for IL-10 decreased significantly following allergen challenge (p = 0. 04), and correlated negatively with sputum eosinophils (r = -0.34, p = 0.02). This study shows that allergen-induced increases in sputum eosinophils are associated with the presence of cytokines specific for the activation and chemotaxis of eosinophils, and suggests that cooperation of eosinophilic cytokines may be important for the accumulation and regulation of activated eosinophils at the site of allergic inflammation.

Role of bronchoscopy in asthma research

Over the past 15 years, much has been learned about the presence of airway inflammation in asthma through the use of investigative bronchoscopy. It has become quite clear that inflammation is present even in mild asthma. In addition to the eosinophils, T-lymphocytes and a variety of cytokines have been identified to play a prominent role in asthmatic inflammation. The concept of delayed asthmatic response after allergen exposure and its relationship to cellular inflammation and airway hyper-reactivity has become more clearly established. Our understanding of asthmatic airway inflammation, however, is incomplete. As interesting as the database has been so far, investigative FB has not defined a unique profile for patients with asthma. Specifically, lavage or endobronchial biopsy has not identified parameters that help in the diagnosis, assessment of disease severity, prognosis, or likelihood to respond to specific therapies. Also, the exact relationship between parameters in lavage compared with mucosal biopsy and how these are related to airway hyper-reactivity and the clinical syndrome of asthma remains poorly understood. In this regard, it must be confessed that currently FB with lavage and biopsy in asthmatics needs to be considered as a research tool for specimen retrieval to help characterize and express inflammation. Although these techniques have contributed immensely to our understanding of asthma pathogenesis, presently these techniques do not have any practical role or clinical usefulness.

Immune dysregulation as a cause for allergic asthma

Allergic asthma is being increasingly understood as a disease caused by Th2-mediated immune responses to inhaled allergens. Most individuals fail to respond to allergens with a Th2 response, and thus, allergic asthma can be considered the result of an abnormally regulated or dysregulated immune response. The prevalence of asthma has risen precipitously in urbanized cultures, as contrasted with third world countries. This observation underlies the heightened efforts in the past few years of basic and applied research efforts to gain a better understanding of both normal and dysregulated immunity to antigens introduced via the airways. This review focuses on recent human studies into the immune dysregulation that results in the asthma phenotype, but also cites selected relevant papers from research with experimental animals.

Kinetics of eotaxin expression and its relationship to eosinophil accumulation and activation in bronchial biopsies and bronchoalveolar lavage (BAL) of asthmatic patients after allergen inhalation

We investigated the kinetics of allergen-induced eotaxin expression and its relationship to eosinophil accumulation and activation in the airways of patients with allergic asthma. Twenty-four patients with allergic asthma and late asthmatic responses to allergen inhalation were randomly allocated into three groups of eight patients each, who received bronchoscopy with bronchial biopsies and BAL at 2, 4 and 24 h, respectively, after the inhalation of the diluent and the allergen. The expression of eotaxin mRNA and protein and eotaxin release were evaluated by in situ hybridization, immunohistochemistry, immunocytochemistry, and radioimmunoassay. Increased transcription from the eotaxin gene preceded the appearance of the late asthmatic response and the influx of activated eosinophils in bronchial tissue and BAL fluid (BALF). This was followed by increased cell expression of eotaxin protein (P<0.001) and increased eotaxin release (P<0.001), which correlated with the numbers of total and activated eosinophils and the level of airflow obstruction at 4 h after allergen exposure (P<0.05 for all correlations). At 24 h after allergen inhalation, enhanced eotaxin expression declined without a similar reduction in the numbers of eosinophils in bronchial biopsies and when there was a further increase in the number of these cells in BALF (P<0.05). These results indicate that eotaxin contributes to the early phase of allergen-induced recruitment of activated eosinophils into the airways of patients with allergic asthma and that other factors are implicated in the persistence of eosinophil infiltration.

Inflammation in asthma: the cornerstone of the disease and target of therapy

Asthma is a chronic disease associated with variable levels of airflow obstruction. Considerable evidence has been obtained to show that airway inflammation is a major factor in the pathogenesis of asthma in associated bronchial hyperresponsiveness, and in the level of disease severity. The inflammatory pattern in asthma is multicellular in nature, with mast cells, neutrophils, eosinophils, T lymphocytes, and epithelial cells participating in the response. Furthermore, it is known that mediators, cytokines, and chemokines from these cells contribute to the orchestration of the inflammatory process. Because airway inflammation appears to be a critical etiologic feature of asthma, it has become the target of therapy. In this review the features of airway inflammation will be examined, and the effect of therapeutic agents on markers of airway injury will be discussed. Establishing, understanding, and finally controlling the features of airway inflammation have given insight to disease pathogenesis and the effectiveness of various treatments. The integral role of inhaled corticosteroids in modifying the complex inflammatory component of asthma will be explored, with special focus on the high degree of efficacy associated with this treatment--vis-á-vis other therapeutic agents--in preventing or blocking specific proinflammatory markers.

Glucocorticoid regulation of GM-CSF: evidence for transcriptional mechanisms in airway epithelial cells

Inflammation plays a central role in the pathogenesis of asthma. Glucocorticoids are first-line anti-inflammatory therapy in the treatment of asthma and are effective inhibitors of inflammatory cytokines. Clinical data demonstrate that granulocyte-macrophage colony-stimulating factor (GM-CSF) production by airway epithelial cells may be an important target of inhaled glucocorticoid therapy. We examined the regulatory mechanisms of GM-CSF expression by interleukin-1beta (IL-1beta) and the synthetic glucocorticoid dexamethasone in the BEAS-2B human bronchial epithelial cell line. IL-1beta stimulation resulted in a 15-fold induction of GM-CSF protein, which was associated with a corresponding 47-fold maximal induction of GM-CSF mRNA levels. Treatment with the transcriptional inhibitor actinomycin D before IL-1beta stimulation completely abolished induction of GM-CSF mRNA, whereas incubation with cycloheximide had no effect. Taken together, these data demonstrate that IL-1beta induction of GM-CSF is mediated through transcriptional mechanisms. Dexamethasone treatment of BEAS-2B cells produced an 80% inhibition of IL-1beta-induced GM-CSF protein and a 51% inhibition of GM-CSF mRNA. GM-CSF mRNA was rapidly degraded in these cells, and dexamethasone treatment did not significantly affect this decay rate. We conclude that, in the BEAS-2B bronchial epithelial cell line, IL-1beta induction and dexamethasone repression of GM-CSF expression are mediated predominantly through transcriptional mechanisms.