Neuromedin-U Mediates Rapid Activation of Airway Group 2 Innate Lymphoid Cells in Mild Asthma

RATIONALE

In asthma, sputum group 2 innate lymphoid cells (ILC2) are activated within 7h after allergen challenge. Neuroimmune interactions mediate rapid host responses at mucosal interfaces. In murine models of asthma, lung ILC2 co-localize to sensory neuronal termini expressing the neuropeptide, neuromedin U (NMU) and NMU stimulates type 2 cytokines secretion by ILC2 with additive effects to alarmins, in vitro.

OBJECTIVES

Investigate effect of NMU/NMUR1 axis on early activation of ILC2 in asthma.

METHODS

M ild asthmatics (n=8) were enrolled in a diluent-controlled, allergen-inhalation challenge study. Sputum ILC2 expression of NMU receptor 1 (NMUR1) and T2 cytokines were enumerated by flow cytometry and airway NMU levels were assessed by ELISA. This was compared to samples from moderate-severe asthmatics (n=9). Flow sort-purified and ex-vivo expanded ILC2 were used for functional assays and transcriptomic analyses.

RESULTS

Significant increases in sputum ILC2 expressing NMUR1 were detected 7h post- allergen versus diluent challenge where the majority of NMUR1+ILC2 expressed IL-5/IL-13. Sputum NMUR1+ILC2 were significantly greater in mild versus moderate-severe asthmatics and NMUR1+ILC2 correlated inversely with the dose of inhaled corticosteroid in the latter group. Co-culturing with alarmins upregulated NMUR1 in ILC2, which was attenuated by dexamethasone. NMU stimulated T2 cytokine expression by ILC2, maximal at 6h was abrogated by dexamethasone or specific signaling inhibitors for mitogen-activated protein kinase ½, phospho-inositol 3 kinase but not IL-33 signaling moiety MyD88, in vitro.

CONCLUSIONS

The NMU/NMUR1 axis stimulates rapid effects on ILC2, and maybe an important early activator of these cells in eosinophilic inflammatory responses in asthma.

Evaluation of the reproducibility of responses to nasal allergen challenge and effects of inhaled nasal corticosteroids

BACKGROUND

Similar immune responses in the nasal and bronchial mucosa implies that nasal allergen challenge (NAC) is a suitable early phase experimental model for drug development targeting allergic rhinitis (AR) and asthma. We assessed NAC reproducibility and the effects of intranasal corticosteroids (INCS) on symptoms, physiology, and inflammatory mediators.

METHODS

20 participants with mild atopic asthma and AR underwent three single blinded nasal challenges each separated by three weeks (NCT03431961). Cohort A (n = 10) underwent a control saline challenge, followed by two allergen challenges. Cohort B (n = 10) underwent a NAC with no treatment intervention, followed by NAC with 14 days pre-treatment with saline nasal spray (placebo), then NAC with 14 days pre-treatment with INCS (220 μg triamcinolone acetonide twice daily). Nasosorption, nasal lavage, blood samples, forced expiratory volume 1 (FEV1), total nasal symptom score (TNSS), peak nasal inspiratory flow (PNIF) were collected up to 24 h after NAC. Total and active tryptase were measured as early-phase allergy biomarkers (≤30 min) and IL-13 and eosinophil cell counts as late-phase allergy biomarkers (3-7 h) in serum and nasal samples. Period-period reproducibility was assessed by intraclass correlation coefficients (ICC), and sample size estimates were performed using effect sizes measured after INCS.

RESULTS

NAC significantly induced acute increases in nasosorption tryptase and TNSS and reduced PNIF, and induced late increases in nasosorption IL-13 with sustained reductions in PNIF. Reproducibility across NACs varied for symptoms and biomarkers, with total tryptase 5 min post NAC having the highest reproducibility (ICC = 0.91). Treatment with INCS inhibited NAC-induced IL-13 while blunting changes in TNSS and PNIF. For a similar crossover study, 7 participants per treatment arm are needed to detect treatment effects comparable to INCS for TNSS.

CONCLUSION

NAC-induced biomarkers and symptoms are reproducible and responsive to INCS. NAC is suitable for assessing pharmacodynamic activity and proof of mechanism for drugs targeting allergic inflammation.

Gene Polymorphisms of Epithelial Cell-Derived Alarmins and Their Effects on Protein Levels and Disease Severity in Patients with COVID-19

BACKGROUND

The immune response in COVID-19 is characterized by the release of alarmin cytokines, which play crucial roles in immune activation and inflammation. The interplay between these cytokines and genetic variations may influence disease severity and outcomes, while sex differences might further contribute to variations in the immune response.

METHODS

We measured the levels of alarmin cytokines in a cohort of COVID-19 and non-COVID-19 patients using a sensitive Meso Scale Discovery system. Additionally, we conducted an SNP analysis to identify genetic variations within the IL-33 and TSLP genes. The association between these genetic variations, cytokine production, and COVID-19 severity was examined.

RESULTS

Our findings revealed elevated levels of IL-33 and IL-25 in COVID-19-positive patients compared to COVID-19-negative patients (p < 0.05), indicating their potential as therapeutic targets for disease modulation. Moreover, a minor allele within the IL-33 gene (rs3939286) was found to be associated with a protective effect against severe COVID-19 (p < 0.05), and minor alleles of the TSLP gene (rs2289276 and rs13806933) were found to significantly reduce TSLP protein levels in serum (p < 0.05). Sex-specific effects of TSLP and IL-33 SNPs were observed, suggesting a potential influence of sex hormones and genetic variations on the regulation of cytokine production.

CONCLUSION

The present study highlights the importance of alarmin cytokines and genetic variations in COVID-19 severity, providing valuable insights into personalized treatment approaches. Our results suggest that targeting alarmin cytokines may offer potential therapeutic benefits in managing COVID-19. Furthermore, the sex-specific effects of genetic variations emphasize the need to consider individual genetic profiles and sex differences when designing targeted interventions.

Limosilactobacillus reuteri DSM-17938 for preventing cough in adults with mild allergic asthma: A double-blind randomized placebo-controlled cross-over study

BACKGROUND

Cough is a common troublesome symptom in asthma which is neuronally mediated. Limosilactobacillus reuteri DSM-17938 (L. reuteri DSM-17938) is a probiotic shown to be effective in pre-clinical models at suppressing neuronal responses to capsaicin, a transient receptor potential vanilloid agonist (TRPV1).

OBJECTIVE

Investigate the effects of DSM-17938 versus matched placebo on capsaicin-evoked coughs in mild allergic asthmatics.

METHODS

We performed a 4-visit, randomized, double-blind, placebo-controlled, two-way cross-over study comparing full dose cough responses with inhaled capsaicin in mild allergic asthmatics after 1 month of treatment with DSM-17938 compared with matched placebo. Randomization and allocation to trial group were carried out by a central computer system. Histamine skin prick testing, airway hyper-responsiveness and inflammatory cells in induced sputum were measured at every visit. Blood was collected to extract PBMCs and stimulated with CD3/CD28 to ascertain the effects of DSM-17938 /placebo on T-cell cytokine responses.

RESULTS

Seventeen subjects were recruited and 15 completed the study (8 females, mean age 27.3 years). There was no difference in the change in maximum capsaicin-evoked coughs (Emax) after treatment with L. reuteri DSM-17938 compared with placebo [mean difference 2.07 coughs (95% CI -2.77 to 6.91, p = .38) or relative changes in geometric mean ratios for the dose evoking at least half the Emax (ED50) [1.05 (95% CI 0.31-3.58, p = .94)], concentration evoking 2 coughs (C2) [0.63 (0.26-1.53), p = .28] and 5 coughs (C5) [0.79 (0.25-2.50), p = .67]. There was no effect on histamine skin prick wheal size, intensity of itch sensation, methacholine PC20, airway inflammation or T-cell responses after stimulation with CD3/CD28. There were no serious adverse events. One subject developed a mild upper respiratory tract infection and another mild transient nausea whilst on DSM-17938.

CONCLUSION

In this small study in adults with mild allergic asthma, we found no evidence that L. reuteri DSM-17938 has any systemic effects on airway nerves, smooth muscle, sputum inflammatory cells, skin responses or T-cell responses after oral consumption.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT03603522.

Induction of bystander tolerance and immune deviation after Fel d 1 peptide immunotherapy

BACKGROUND

Treatment of patients with cat allergy with peptides derived from Fel d 1 (the major cat allergen) ameliorated symptoms of cat allergy in phase 2 clinical trials.

OBJECTIVE

We sought to demonstrate that the tolerance induced by Fel d 1 peptide immunotherapy can be exploited to reduce allergic responses to a second allergen, ovalbumin (OVA), in mice sensitized dually to OVA and Fel d 1.

METHODS

Induction of tolerance to OVA was achieved through simultaneous exposure to both allergens after peptide treatment. Functional tolerance to each allergen was assessed in a model of allergic airways disease in which treated mice were protected from eosinophilia, goblet cell hyperplasia, and T_H2 cell infiltration.

RESULTS

Suppression of allergic responses to cat allergen challenge was associated with significant increases in numbers of CD4⁺CD25⁺Foxp3⁺ T cells, IL-10⁺ cells, and CD19⁺IL-10⁺ B cells, whereas the response to OVA was associated with a marked reduction in numbers of T_H2 cytokine-secreting T cells and less prominent changes in outcomes associated with immune regulation.

CONCLUSIONS

These observations suggest that immune tolerance induced by peptide immunotherapy can be used experimentally to treat an allergic response to another allergen and that the molecular mechanisms underlying induction of tolerance to a treatment-specific allergen and a bystander allergen might be different.

Effects of furosemide on allergic asthmatic responses in mice

BACKGROUND

The syndrome of allergic asthma features reversible bronchoconstriction, airway inflammation and hyperresponsiveness as well as airway remodelling, including goblet cell hyperplasia. Managing severe asthma is still a clinical challenge. Numerous studies report that furosemide, an inhibitor of Na(+)-K(+)-Cl(-) cotransporter (NKCC) reduces airway hyperresponsiveness (AHR) in asthmatic patients. However, the mechanism by which furosemide exerts anti-asthmatic action remains unclear.

OBJECTIVE

This study sought to investigate the cellular profile of NKCC1 expression in the lung and examine the effects of furosemide on several outcome measurements in a mouse model of allergic asthma.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA). Before challenge, the OVA-sensitized mice were treated with furosemide (4.0 mg/kg/day, via daily intraperitoneal injection for 5 days). Outcome measurements in naïve, OVA-exposure, furosemide-treated naïve and furosemide-treated OVA-exposed mice included the slope of the relationship between inhaled methacholine (MCh) concentration and respiratory system resistance (Slope·R(RS)), bronchoalveolar lavage (BAL) cell counts and immunohistochemical and immunoblotting assays of lung tissues.

RESULTS

NKCC1 immunoreactivity was observed in airway epithelial cells (AECs) and alveolar type II (ATII) cells of the control mice. OVA exposure enhanced the expression of NKCC1 in AECs and ATII cells, and increased the infiltration of NKCC1-expressing T lymphocytes in the lung. NKCC1 immunoreactivity was not detected in the airway smooth muscle (ASM) cells. Furosemide treatment reduced the Slope·R(RS) in both naïve and OVA-exposed mice by about 50%. Furosemide treatment also increased T lymphocyte infiltration to the lung in OVA-exposed mice by approximately 53%, but had no effect on pulmonary goblet cell hyperplasia.

CONCLUSIONS AND CLINICAL RELEVANCE

Furosemide decreases basal airway responsiveness, thereby reducing the extent of allergen-induced AHR. However, the same treatment also increases T lymphocytes infiltration in the course of allergic asthma. Further studies are necessary to address the usefulness of furosemide in the clinical treatment of asthma.

Concurrent dual allergen exposure and its effects on airway hyperresponsiveness, inflammation and remodeling in mice

Experimental mouse models of asthma have broadened our understanding of the mechanisms behind allergen-induced asthma. Typically, mouse models of allergic asthma explore responses to a single allergen; however, patients with asthma are frequently exposed to, and tend to be allergic to, more than one allergen. The aim of the current study was to develop a new and more relevant mouse model of asthma by measuring the functional, inflammatory and structural consequences of chronic exposure to a combination of two different allergens, ovalbumin (OVA) and house dust mite (HDM), in comparison with either allergen alone. BALB/c mice were sensitized and exposed to OVA, HDM or the combination of HDM and OVA for a period of 10 weeks. Following allergen exposure, airway responsiveness was measured using the flexiVent small animal ventilator, and mice were assessed for indices of airway inflammation and remodeling at both 24 hours and 4 weeks after the final allergen exposure. Mice exposed to the HDM-OVA combination exhibited increased numbers of inflammatory cells in the bronchoalveolar lavage (BAL) when compared with mice exposed to a single allergen. Mice exposed to HDM-OVA also exhibited an elevated level of lung tissue mast cells compared with mice exposed to a single allergen. Following the resolution of inflammatory events, mice exposed to the allergen combination displayed an elevation in the maximal degree of total respiratory resistance (Max R(RS)) compared with mice exposed to a single allergen. Furthermore, trends for increases in indices of airway remodeling were observed in mice exposed to the allergen combination compared with a single allergen. Although concurrent exposure to HDM and OVA resulted in increased aspects of airway hyperresponsiveness, airway inflammation and airway remodeling when compared with exposure to each allergen alone, concurrent exposure did not result in a substantially more robust mouse model of allergic asthma than exposure to either allergen alone.

Role of STAT6 and SMAD2 in a model of chronic allergen exposure: a mouse strain comparison study

BACKGROUND

Asthma is a disease characterized by variable and reversible airway obstruction and is associated with airway inflammation, airway remodelling (including goblet cell hyperplasia, increased collagen deposition and increased smooth muscle mass) and increased airway responsiveness. It is believed that airway inflammation plays a critical role in the development of airway remodelling, with IL-13 and TGF-beta1 pathways being strongly associated with the disease progression. Mouse models of asthma are capable of recapitulating some components of asthma and have been used to look at both IL-13 and TGF-beta1 pathways, which use STAT6 and SMAD2 signalling molecules, respectively.

OBJECTIVES

Using brief and chronic models of allergen exposure, we utilized BALB/c and C57Bl/6 to explore the hypothesis that observed differences in responses to allergen between these mouse strains will involve fundamental differences in IL-13 and TGF-beta1 responses.

METHODS

The following outcome measurements were performed: airway physiology, bronchoalveolar lavage cell counts/cytokine analysis, histology, immunoblots and gene expression assays.

RESULTS

We demonstrate in BALB/c mice an IL-13-dependent phosphorylation of STAT6, nuclear localized in inflammatory cells, which is associated with indices of airway remodelling and development of airway dysfunction. In BALB/c mice, phosphorylation of SMAD2 is delayed relative to STAT6 activation and also involves an IL-13-dependent mechanism. In contrast, despite an allergen-induced increase in IL-4, IL-13 and eosinophils, C57Bl/6 demonstrates a reduced and distinct pattern of phosphorylated STAT6, no SMAD2 phosphorylation changes and fail to develop indices of remodelling or changes in airway function.

CONCLUSION

The activation of signalling pathways and nuclear translocation of signalling molecules downstream of IL-13 and TGF-beta1 further support the central role of these molecules in the pathology and dysfunction in animal models of asthma. Activation of signalling pathways downstream from IL-13 and TGF-beta1 may be more relevant in disease progression than elevations in airway inflammation alone.

Goblet cell rebound and airway dysfunction with corticosteroid withdrawal in a mouse model of asthma

RATIONALE

Although corticosteroids are highly effective at preventing allergen-induced increases in goblet cell numbers, we observed in unpublished experiments a rebound increase in goblet cell numbers in mice after the simultaneous withdrawal of corticosteroid and cessation of exposure to allergen that reached levels greater than those observed in mice exposed to allergen alone, without corticosteroid treatment.

OBJECTIVES

To formally explore the goblet cell hyperplasia rebound observed after corticosteroid withdrawal in allergen-exposed mice to determine the mechanism responsible for this previously undescribed pathology.

METHODS

Mice airways were assessed for mucin-containing goblet cells after exposure to varying durations of allergen and corticosteroid.

MEASUREMENTS AND MAIN RESULTS

We confirmed that the simultaneous withdrawal of corticosteroid and cessation of exposure to allergen resulted in a goblet cell hyperplasia rebound that reached levels greater than those observed in allergen-exposed corticosteroid naive mice. Importantly, the goblet cell rebound was associated with a significant airway dysfunction greater than that observed in allergen-exposed corticosteroid naive mice. The goblet cell hyperplasia rebound is independent of the type of corticosteroid or allergen and was associated with an increased level of bronchoalveolar lavage IL-13. Inhibition of IL-13, but not CD4+ T cells, completely inhibited the goblet cell hyperplasia rebound and, critically, the associated airway dysfunction.

CONCLUSIONS

These findings suggest that certain corticosteroid treatment regimes may actually potentiate airway remodeling and dysfunction in patients with asthma and lead to increased exacerbations and worsening of asthma symptoms.

Budesonide prevents but does not reverse sustained airway hyperresponsiveness in mice

Despite the effectiveness of corticosteroids at resolving airway inflammation, they are only moderately effective at attenuating airway hyperresponsiveness (AHR). The extent to which corticosteroids are able to reverse or inhibit the development of sustained AHR is not known. The present study aimed to determine whether budesonide can resolve and or prevent the development of sustained AHR in mice. Mice were chronically exposed to allergen and treated with budesonide either: 1) briefly during the final weeks of exposure to allergen; 2) prolonged concurrently throughout exposure to allergen; or 3) delayed following final exposure to allergen. AHR was assessed 24 h (brief treatment) or 4 weeks (prolonged concurrent and delayed treatments) following final exposure to allergen. Brief budesonide intervention significantly attenuated the inflammation-associated AHR assessed immediately following final exposure to allergen. Similarly, prolonged concurrent budesonide treatment prevented the development of sustained AHR. Delayed budesonide intervention, however, did not resolve sustained AHR. In conclusion, the early introduction and, importantly, the persistence of corticosteroid treatment prevented the development of sustained airway hyperresponsiveness; however, the inability of corticosteroids to reverse established airway dysfunction indicates a limitation in their use for the complete, long-term management of airway hyperresponsiveness.

Effects of allergen on airway narrowing dynamics as assessed by lung-slice technique

Asthma is characterised by an excessive airway narrowing in response to a variety of stimuli, called airway hyperresponsiveness (AHR). Previous comparisons between mouse strains have shown that increased velocity of airway narrowing correlates with baseline airway responsiveness. These data prompted the investigation into models of induced AHR to see whether airway narrowing dynamics correlated with in vivo responsiveness. In an attempt to reproduce some of the features of asthma, BALB/c mice were sensitised and subjected to either brief or chronic periods of allergen exposure. Brief exposure involved two challenges with intranasal chicken egg ovalbumin (OVA(in)). Chronic exposure involved six 2-day periods of OVA(in) challenges, each separated by 12 days. Control mice received intranasal saline challenges. Outcomes included videomicrometry of lung slices (magnitude and velocity of airway narrowing), in vivo respiratory physiology measurements and histological staining with morphometric analysis. Neither brief nor chronic allergen exposure resulted in greater airway narrowing and increased velocity compared with saline controls. Structural changes in the airway, such as goblet cell hyperplasia, subepithelial fibrosis and increased contractile tissue, were detected in mice chronically challenged with allergen. In conclusion, increased responsiveness to methacholine following allergen challenge may not be due to an intrinsic change to the smooth muscle per se, but rather to other changes in the lung, which ultimately manifest as an increase in respiratory resistance.

Components of airway hyperresponsiveness and their associations with inflammation and remodeling in mice

BACKGROUND

Pathologic changes, including inflammation and remodeling, occur in the asthmatic airway. However, their relative contribution to the components of airway hyperresponsiveness (AHR) remains unclear.

OBJECTIVE

Attempting to delineate AHR into discrete immune-mediated and structural remodeling components, we performed a detailed time course of the development, progression, and persistence of maximal respiratory system resistance, airway reactivity, and airway sensitivity.

METHODS

Mice exposed to increasing durations of persistent allergen were assessed for airway function, morphometry, and inflammation.

RESULTS

Allergen exposure resulted in increases for all indices of AHR that persisted for at least 4 weeks after chronic allergen exposure (P < .01 for all values). Early increases in AHR were associated with increases in immune-mediated events, including airway eosinophils (P < .01), whereas sustained AHR was associated with structural remodeling events. Increased maximal respiratory system resistance, evident by 6 weeks postallergen and persisting for at least 4 weeks after 8 weeks of chronic exposure, was associated with an increase in collagen deposition (P < .01). Increased airway reactivity and sensitivity, each evident by 1 week after allergen and persisting for at least 4 weeks after 8 weeks of chronic exposure, were associated with an increase in airway smooth muscle area (P < .01).

CONCLUSION

Our novel observation of distinct temporal relationships in the development, progression, and persistence of the individual indices of AHR supports our hypothesis that multiple underlying factors contribute to airway dysfunction.

CLINICAL IMPLICATIONS

These findings illustrate the importance of clearly addressing specific components of airway dysfunction to provide greater insight into specific pathophysiologic mechanisms in airway disease.

Epithelial expression of profibrotic mediators in a model of allergen-induced airway remodeling

Airway remodeling, including subepithelial fibrosis, is a characteristic feature of asthma and likely contributes to the pathogenesis of airway hyperresponsiveness. We examined expression of genes related to airway wall fibrosis in a model of chronic allergen-induced airway dysfunction using laser capture microdissection and quantitative real-time PCR. BALB/c mice were sensitized and subjected to chronic ovalbumin exposure over a 12-wk period, after which they were rested and then harvested 2 and 8 wk after the last exposure. Chronic allergen-exposed mice had significantly increased indices of airway remodeling and airway hyperreactivity at all time points, although no difference in expression of fibrosis-related genes was found when mRNA extracted from whole lung was examined. In contrast, fibrosis-related gene expression was significantly upregulated in mRNA obtained from microdissected bronchial wall at 2 wk after chronic allergen exposure. In addition, when bronchial wall epithelium and smooth muscle were separately microdissected, gene expression of transforming growth factor-beta1 and plasminogen activating inhibitor-1 were significantly upregulated only in the airway epithelium. These data suggest that transforming growth factor-beta1 and other profibrotic mediators produced by airway wall, and specifically, airway epithelium, play an important role in the pathophysiology of airway remodeling.

Intranasal Exposure of Mice to House Dust Mite Elicits Allergic Airway Inflammation via a GM-CSF-Mediated Mechanism

It is now well established that passive exposure to inhaled OVA leads to a state of immunological tolerance. Therefore, to elicit allergic sensitization, researchers have been compelled to devise alternative strategies, such as the systemic delivery of OVA in the context of powerful adjuvants, which are alien to the way humans are exposed and sensitized to allergens. The objectives of these studies were to investigate immune-inflammatory responses to intranasal delivery of a purified house dust mite (HDM) extract and to evaluate the role of GM-CSF in this process. HDM was delivered to BALB/c mice daily for 10 days. After the last exposure, mice were killed, bronchoalveolar lavage was performed, and samples were obtained. Expression/production of Th2-associated molecules in the lymph nodes, lung, and spleen were evaluated by real-time quantitative PCR and ELISA, respectively. Using this exposure protocol, exposure to HDM alone generated Th2 sensitization based on the expression/production of Th2 effector molecules and airway eosinophilic inflammation. Flow cytometric analysis demonstrated expansion and activation of APCs in the lung and an influx of activated Th2 effector cells. Moreover, this inflammation was accompanied by airways hyper-responsiveness and a robust memory-driven immune response. Finally, administration of anti-GM-CSF-neutralizing Abs markedly reduced immune-inflammatory responses in both lung and spleen. Thus, intranasal delivery of HDM results in Th2 sensitization and airway eosinophilic inflammation that appear to be mediated, at least in part, by endogenous GM-CSF production.

Is interleukin-13 critical in maintaining airway hyperresponsiveness in allergen-challenged mice?

Interleukin (IL)-13 is regarded as being a central effector in the pathophysiology of airway hyperresponsiveness. We have described a mouse model in which chronic allergen exposure results in sustained airway hyperresponsiveness and aspects of airway remodeling, and here sought to demonstrate that this component of airway hyperresponsiveness is independent of biologically active IL-13. Sensitized mice were subjected to either brief or chronic periods of allergen exposure and studied 24 hours after brief or 4 weeks after chronic allergen inhalation. A soluble murine anti-IL-13 receptor fusion protein that specifically binds to and neutralizes IL-13 was given daily during the 4 days before the day of outcome measurements in both protocols. Outcome measurements included airway responses to intravenous methacholine, bronchoalveolar lavage fluid cell counts, and airway morphometry. Compared with the saline control, brief allergen challenge resulted in airway hyperresponsiveness, which was prevented by anti-IL-13 treatment. Chronic allergen challenge resulted in sustained airway hyperresponsiveness and indices of airway remodeling; IL-13 blockade failed to reverse this sustained airway hyperresponsiveness. These results confirm that IL-13 is critical for the development of airway hyperresponsiveness associated with brief allergen exposure, but is not necessary to maintain the sustained airway hyperresponsiveness associated with airway remodeling.

Electrophysiological effects of erythromycin, but lack of mechanical effects, in airway smooth muscle

The antibiotic erythromycin has been shown to modulate a variety of electrophysiological and mechanical responses in many cell types. We investigated whether it did so in airway smooth muscle using standard patch clamp, fura-2 fluorimetric and organ bath techniques. Erythromycin (10(-4) M) evoked a small transient inward current with reversal potential and time-course similar to that of the Ca2+-dependent Cl- currents seen in these cells. Unlike its effects in other cell types, however, it did not alter basal [Ca2+]i, voltage-dependent Ca2+ currents, nor mechanical tone at rest, nor the corresponding responses to cholinergic stimulation (membrane currents; release of internally sequestered Ca2+, nor contractions evoked by neural stimulation or exogenously added cholinergic agonist). In conclusion, erythromycin does exert interesting electrophysiological actions in airway smooth muscle, but does not alter mechanical activity as it has been shown to do elsewhere.

Dysfunction and remodeling of the mouse airway persist after resolution of acute allergen-induced airway inflammation

The mechanisms underlying airway hyperresponsiveness remain unclear, although airway inflammation and remodeling are likely important contributing factors. We hypothesized that airway physiology would differ between mice subjected to brief or chronic allergen exposure, and that these differences would be associated with characteristic inflammatory markers and indices of airway remodeling. BALB/c mice were sensitized to ovalbumin and studied at several time points following brief or chronic allergen challenge protocols. By measuring airway responses to methacholine, we demonstrated increases in maximal inducible bronchoconstriction that persisted for 8 wk following either brief or chronic allergen challenge; we also observed increases in airway reactivity, although it was only in chronically challenged mice that these changes persisted beyond the resolution of allergen-induced inflammation. Using airway morphometry, we further demonstrated that increases in maximal bronchoconstriction were associated with increases in airway contractile tissue in both models, and that chronic, but not brief, allergen challenge resulted in subepithelial fibrosis. Our observations that different aspects of sustained airway dysfunction and remodeling persist beyond the resolution of acute inflammatory events support the concept that remodeling occurs as a consequence of allergic airway inflammation, and that these structural changes contribute independently to the persistence of airway hyperresponsiveness.

Effect of interferon-gamma on allergic airway responses in interferon-gamma-deficient mice

Interferon (IFN)-gamma reduces airway responses after allergen challenge in mice. The mechanisms of this effect are not clear. These studies investigate whether IFN-gamma can reverse prolonged airway responses after allergen challenge in IFN-gamma-deficient (IFN-gammaKO) mice. Sensitized mice (IFN-gammaKO and wild-type [WT]) were challenged with ovalbumin. Airway responsiveness, eosinophils in bronchoalveolar lavage fluid, and lung lymphocyte subsets (CD4(+) and CD8(+)) were measured 24 hours and 8 weeks after challenge. In further experiments, we treated IFN-gammaKO mice with recombinant IFN-gamma starting 4 weeks after the challenge for 1 week or 4 weeks. Airway responsiveness, bronchoalveolar lavage eosinophils, and lung CD4(+) cells were increased 8 weeks after challenge in IFN-gammaKO but not WT mice. IFN-gamma treatment returned lung CD4(+) cell numbers to values obtained in unchallenged mice. One week of IFN-gamma treatment also returned airway responsiveness to baseline levels; however, 4-week treatment with IFN-gamma failed to decrease airway responsiveness below levels observed in untreated animals. This suggests that IFN-gamma plays an essential role in reversing allergen-induced airway inflammation and hyperresponsiveness and that it may have dual actions on the latter. Observations that IFN-gamma reverses airway responses, even when administered after challenge, suggests that IFN-gamma treatment could control allergic disease, including asthma.

The effects of intranasal budesonide on allergen-induced production of interleukin-5 and eotaxin, airways, blood, and bone marrow eosinophilia, and eosinophil progenitor expansion in sensitized mice

We have previously demonstrated that allergen inhalation induces expansion of bone marrow eosinophil progenitors in sensitized mice and subjects with asthma and that the inhaled corticosteroid, budesonide, reduced baseline but not allergen-induced increase in bone marrow eosinophil/basophil progenitors (EoB-CFU) in subjects with asthma. Here, we evaluated the effects of intranasal budesonide on allergen-induced increases in interleukin (IL)-5 and eotaxin in the airway and peripheral blood, expansion of bone marrow Eo-CFU and eosinophilia in bone marrow, peripheral blood and airway, as well as airway hyperresponsiveness, in ovalbumin (OVA)-sensitized mice. Budesonide treatment attenuated allergen-induced eosinophilia in bone marrow, peripheral blood, and airways as well as allergen-induced increases in bone marrow eosinophil progenitors but not allergen-induced increases in IL-5 or eotaxin 12 h following the second of two daily exposures to allergen; at later time points treatment was associated with attenuation of IL-5, eosinophilia, Eo-CFU, and airway hyperresponsiveness. These results suggest that a component of the mechanism by which corticosteroid treatment attenuates allergen-induced airway inflammation is through suppression of bone marrow eosinophilopoiesis, and that this is likely not mediated simply through the blocking of IL-5 production at the airway.

Allergen-induced murine upper airway inflammation: local and systemic changes in murine experimental allergic rhinitis

The role of inflammatory effector cells in the pathogenesis of airway allergy has been the subject of much investigation. However, whether systemic factors are involved in the development of local responses in both upper and lower airways has not been fully clarified. The present study was performed to investigate aspects of the pathogenesis of isolated allergic rhinitis in a murine model sensitized to ovalbumin (OVA). Both upper- and lower-airway physiological responsiveness and inflammatory changes were assessed, as well as bone marrow progenitor responses, by culture and immunohistological methods. Significant nasal symptoms and hyper-responsiveness appeared after intranasal OVA challenge (P < 0.0001 and P < 0.01, respectively), accompanied with significant nasal mucosal changes in CD4+ cells (P < 0.001), interleukin (IL)-4+ cells (P < 0.01), IL-5+ cells (P < 0.01), basophilic cells (P < 0.02) and eosinophils (P < 0.001), in the complete absence of hyper-responsiveness or inflammatory changes in the lower airway. In the bone marrow, there were significant increases in CD34+ cells, as well as in eosinophils and basophilic cells. In the presence in vitro of mouse recombinant IL-5, IL-3 or granulocyte-macrophage colony-stimulating factor (GM-CSF), the level of bone marrow eosinophil/basophil (Eo/Baso) colony-forming cells increased significantly in the OVA-sensitized group. We conclude that, in this murine model of allergic rhinitis, haemopoietic progenitors are upregulated, which is consistent with the involvement of bone marrow in the pathogenesis of nasal mucosal inflammation. Both local and systemic events, initiated in response to allergen provocation, may be required for the pathogenesis of allergic rhinitis. Understanding these events and their regulation could provide new therapeutic targets for rhinitis and asthma.

Muscarinic excitation-contraction coupling mechanisms in tracheal and bronchial smooth muscles

We investigated the mechanisms underlying muscarinic excitation-contraction coupling in canine airway smooth muscle using organ bath, fura 2 fluorimetric, and patch-clamp techniques. Cyclopiazonic acid (CPA) augmented the responses to submaximal muscarinic stimulation in both tracheal (TSM) and bronchial smooth muscles (BSM), consistent with disruption of the barrier function of the sarcoplasmic reticulum. During maximal stimulation, however, CPA evoked substantial relaxation in TSM but not BSM. CPA reversal of carbachol tone persisted in the presence of tetraethylammoium or high KCl, suggesting that hyperpolarization is not involved; CPA relaxations were absent in tissues preconstricted with KCl alone or by permeabilization with beta-escin, ruling out a nonspecific effect on the contractile apparatus. Peak contractions were sensitive to inhibitors of tyrosine kinase (genistein) or Rho kinase (Y-27632). Sustained responses were dependent on Ca(2+) influx in TSM but not BSM; this influx was sensitive to Ni(2+) but not La(3+). In conclusion, there are several mechanisms underlying excitation-contraction coupling in airway smooth muscle, the relative importance of which varies depending on tissue and degree of stimulation.

In vitro airway responsiveness of Flinders sensitive and resistant line rats

Recently, we reported that freely moving Flinders sensitive line rats (FSL, selectively bred for their cholinergic hyperresponsiveness) are more susceptible to allergen-induced airway hyperresponsiveness than their control counterparts-Flinders resistant line (FRL) rats. In this study the two Flinders lines were compared for responsiveness of excised tracheal and primary bronchial smooth muscle in vitro. FSL tissues were slightly but significantly more sensitive to cholinergic stimulation than FRL tissues (slightly lower EC(50) value for carbachol) but the FRL tissues were more responsive, exhibiting larger amplitude of response. Surprisingly, previous exposure to allergen challenge was accompanied by reduced in vitro responses to spasmogens in both rat lines. We conclude that FSL and FRL airways do not differ greatly with respect to sensitivity to cholinergic stimulation in vitro and that inflamed airways show reduced in vitro responses to spasmogens. The discrepancy between the in vivo and in vitro findings suggests that responsiveness of airway smooth muscle involves regulation from both proximal and distal sites.

Allergen-induced increase in airway responsiveness, airway eosinophilia, and bone-marrow eosinophil progenitors in mice

Increases in bone-marrow (BM) inflammatory cell progenitors are associated with allergen-induced airway hyperresponsiveness and inflammation in asthmatics and dogs. Here, for the first time, we compare the time course of airway hyperresponsiveness, inflammation, and marrow progenitor responses in a mouse model of airway allergen challenge. Sensitized BALB/c mice were studied at 2, 12, 24, 48, and 72 h after intranasal ovalbumin or saline challenges. Outcome measurements included airway responsiveness, airway inflammation as assessed via bronchoalveolar lavage (BAL) and lung tissue sections, and BM eosinophil colony-forming units (Eo-CFU) as enumerated using a semisolid culture assay with optimal concentrations of interleukin-5. We observed significant increases in BAL fluid eosinophils, neutrophils, lymphocytes, and macrophages by 2 h after the second of two intranasal allergen challenges (P < 0.05). Significant increases in airway responsiveness or BM Eo-CFU were observed at 24 h and persisted until 48 h after the second challenge (P < 0.05). Airway inflammation, including eosinophils, persisted until at least 72 h (P < 0.05). We observed that allergen-induced airway eosinophilia is accompanied by increases in BM eosinophil progenitors, indicating that in this model, increased eosinophil production involves an expansion of the relevant stem-cell population. These findings support the use of this model to explore the mechanisms of increased eosinopoiesis observed in human asthma.

Effects of cromolyn and nedocromil on ion currents in canine tracheal smooth muscle

Cromolyn and nedocromil are often used in the treatment of asthma. Recently, these agents have been shown to block Cl- currents and/or Ca2+ currents in a variety of cell preparations. Ca2+ and Cl- currents play central roles in excitation-contraction coupling in airway smooth muscle. This study therefore aimed to investigate the effects of these agents on membrane currents, elevations of [Ca2+] and contractions evoked by depolarization and/or acetylcholine in airway smooth muscle. Patch-clamp, fura-2 fluorimetric and muscle-bath techniques were used to monitor ion currents, [Ca2+] and contractions, respectively, in canine tracheal smooth muscle in the presence and absence of the chromones. Cromolyn and nedocromil eliminated voltage-dependent Ca2+ currents, leading to a reduction in depolarization-evoked K+ currents. Both chromones had little or no effect on either acetylcholine-evoked release of internal Ca2+ or the subsequent contraction; however, cromolyn (but not nedocromil) at high concentrations suppressed Ca2+-dependent Cl- currents triggered by acetylcholine. In conclusion, cromolyn and nedocromil abolished voltage-dependent Ca2+ currents and cromolyn also suppressed Ca2+-dependent Cl- currents in airway smooth muscle; neither chromone greatly altered either the release of internally sequestered Ca2+ or the resultant contractions. Further investigation is needed to determine whether the local concentrations obtained by inhaled chromones within the airway wall allow these cellular effects to occur in patients in vivo.

Release of epithelium-derived PGE2 from canine trachea after antigen inhalation

To investigate the role of prostaglandin (PG) E2 in allergen-induced hyperresponsiveness, dogs inhaled either the allergen Ascaris suum or vehicle (Sham). Twenty-four hours after inhalation, some animals exposed to allergen demonstrated an increased responsiveness to acetylcholine challenge in vivo (Hyp-Resp), whereas others did not (Non-Resp). Strips of tracheal smooth muscle, either epithelium intact or epithelium denuded, were suspended on stimulating electrodes, and a concentration-response curve to carbachol (10(-9) to 10(-5) M) was generated. Tissues received electrical field stimulation, and organ bath fluid was collected to determine PGE2 content. With the epithelium present, all three groups contracted similarly to 10(-5) M carbachol, whereas epithelium-denuded tissues from animals that inhaled allergen contracted more than tissues from Sham dogs. In response to electrical field stimulation, Hyp-Resp tissues contracted less than Sham tissues in the presence of epithelium and more than Sham tissues in the absence of epithelium. PGE2 release in the muscle bath was greater in Non-Resp tissues than in Sham or Hyp-Resp tissues when the epithelium was present. Removal of the epithelium greatly inhibited PGE2 release. We conclude that tracheal smooth muscle is hyperresponsive in vitro after in vivo allergen exposure only when the modulatory effect of the epithelium, largely through PGE2 release, is removed.

Myogenic and neurogenic mechanisms and arachidonate metabolites in bronchial muscle response to allergen

We investigated allergen-induced airway hyperresponsiveness (AH) in bronchial tissues obtained from dogs that inhaled Ascaris suum leading to AH (RESP) in vivo or that exhibited no change (NON-RESP) as well as from dogs that inhaled saline (SHAM). RESP tissues were not hyperresponsive to KCl or to carbachol, whereas contractions to electrical field stimulation (EFS) were reduced. This reduction was reversed partially by indomethacin and completely by replacement of the bathing fluid. Radioimmunoassay revealed marked elevation of prostaglandin (PG) E2 generation in RESP tissues compared with SHAM and NON-RESP tissues. EFS-evoked contractions were often followed by a slowly developing secondary contraction in RESP tissues but not in SHAM or NON-RESP tissues. However, indomethacin unmasked such secondary contractions in many SHAM and NON-RESP tissues and markedly enhanced those in RESP tissues, whereas L-655,240 (thromboxane A2/PGD2 receptor antagonist) abolished such contractions in all groups. We were unable to detect thromboxane using radioimmunoassay. We conclude that allergen-induced AH involves altered generation of cyclooxygenase metabolites of arachidonic acid (particularly PGE2) as well as of a nonprostanoid inhibitory factor; as such, the responsiveness of the tissue in vitro is dependent on the relative levels of inhibitory and excitatory metabolites.

Regulation of [Ca2+]i in canine airway smooth muscle by Ca(2+)-ATPase and Na+/Ca2+ exchange mechanisms

We investigated Ca2+ handling in airway smooth muscle (SM) using fura 2 fluorescence, ion currents, and contractions as indexes of intracellular Ca2+ concentration ([Ca2+]i). Carbachol evoked a transient elevation of [Ca2+]i, the magnitude of which was smaller and the rate of decay faster at 37 degrees C, indicating that some temperature-sensitive mechanism contributed to recovery. Removal of external Na+ had no effect on agonist-evoked Ca2+ transients or contractions or on spontaneous Ca(2+)-dependent K+ currents. Cyclopiazonic acid, a selective inhibitor of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase, evoked a transient elevation of [Ca2+]i and contraction, markedly slowed recovery of the cholinergic Ca2+ transient, and depleted the SR. Sodium vanadate evoked a sustained elevation of [Ca2+]i and markedly slowed the decay of the cholinergic Ca2+ transient. We conclude that, in canine airway SM, 1) Na+/Ca2+ exchange makes at best only a minor contribution to Ca2+ homeostasis, 2) the SR Ca(2+)-ATPase compensates for spontaneous and agonist-triggered release of Ca2+, and 3) [Ca2+]i homeostasis involves some other extrusion pathway, likely the plasmalemmal Ca(2+)-ATPase.

Non-neurogenic electrically evoked relaxation in canine airway muscle involves action of free radicals on K+ channels

Cyclopiazonic acid (selective blocker of the internal Ca+2 pump) evoked tonic contraction in canine bronchial smooth muscle (BSM) and tracheal smooth muscle. This contraction was biphasic, including an initial component that was relatively insensitive to blockade of Ca+2 influx (e.g., removal of external Ca+2; nifedipine; hyperpolarization using lemakalim) followed by a component that was sensitive to all such interventions. In BSM, but not in tracheal smooth muscle, electrical field stimulation (EFS) evoked relaxations that were not affected by interventions designed to prevent release of autacoids from nerve endings or the epithelium, Na+/Ca+2 exchange or Ca(+2)-ATPase activities (internal or plasmalemmal). EFS evoked little or no relaxant response in carbachol-precontracted BSM in the presence of propranolol. After Ca+2 was replaced with Sr+2, however, carbachol evoked comparable contraction after which EFS evoked non-neurogenic relaxations. We found that the EFS-evoked relaxations were abolished by TEA or high KCI, were reduced significantly by charydotoxin or quinine, were reduced partially by ouabain and were unaffected by removal of external K+, by apamin or by glybenclamide. In addition, the relaxations were reduced significantly by the free radical scavenger N-acetylcysteine, were mimicked by H2O2 but were unaffected by superoxide dismutase or catalase. These observations suggest that the cyclopiazonic acid-evoked contraction involves pharmacomechanical coupling mechanisms (i.e., Ca(+2)-release) initially, followed by electromechanical coupling (i.e., voltage-dependent Ca+2 influx). After depletion of the internal Ca+2 store (e.g., by cyclopiazonic acid or Sr+2), EFS is able to evoke in BSM (but not in tracheal smooth muscle) relaxations that seem to involve opening of K+ channels (including those of the large-conductance Ca(+2)-dependent type) by EFS-liberated free radicals.

Effect of a leukotriene B4 receptor antagonist SC-53228 on ozone-induced airway hyperresponsiveness and inflammation in dogs

The importance of the potent neutrophil chemoattractant leukotriene (LT)B4 in causing ozone-induced bronchoconstriction, airway inflammation, and airway hyperresponsiveness in dogs was studied using the LTB4-receptor antagonist SC-53228. Seven dogs from random sources were studied three times, at least 2 wk apart. On each occasion, acetylcholine (Ach) airway responsiveness was measured before and 1 h after ozone (3 ppm, 30 min) or dry air inhalation, followed by a bronchoalveolar lavage (BAL). On the first day, dogs were treated with SC-53228 (0.4 mg/kg intravenously) followed by a continuous intravenous infusion of 1.2 mg/kg/h before ozone inhalation. On the other two days, diluent was infused followed by ozone or dry air inhalation. Cell counts were measured in BAL and cell activation was measured by spontaneous and by phorbol myristate acetate-stimulated (PMA) (2.4 mumol/L) oxygen radical release, measured from washed BAL cells (4 x 10(6) cells) by lucigenin-enhanced chemiluminescence. Ozone inhalation caused bronchoconstriction and airway hyperresponsiveness. SC-53228 inhibited the ozone-induced airway hyperresponsiveness (p = 0.006), but not the bronchoconstriction. Spontaneous (p = 0.004) and PMA-stimulated (p = 0.04) lucigenin-enhanced chemiluminescence were increased after ozone inhalation. The ozone-induced increases in PMA-stimulated chemiluminescence were significantly attenuated by treatment with SC-53228 (p = 0.04). These results suggest that LTB4 is involved in the pathogenesis of ozone-induced airway hyperresponsiveness, possibly through activation of airway inflammatory cell.

The effects of an inhaled corticosteroid on oxygen radical production by bronchoalveolar cells after allergen or ozone in dogs

Both ozone and allergen inhalation increase the capacity to produce oxygen radicals by bronchoalveolar lavage cells in dogs. The purpose of these studies was to determine whether inhaled corticosteroids inhibits these increases in oxygen radical production from bronchoalveolar lavage cells. Six random source dogs were studied after dry air or ozone inhalation (3 ppm, 30 min). Seven random source dogs were studied after diluent or allergen inhalation. The dogs inhaled budesonide (2.74 mg/day) or lactose powder, twice daily for 7 days before ozone and allergen. 90 min after ozone or dry air, and 24 h after Ascaris suum or diluent a bronchoalveolar lavage was carried out. Spontaneous luminol-enhanced chemiluminescence was measured from bronchoalveolar lavage cells (4 x 10(6) cells) for 10 min, followed by a measurement of phorbol myristate acetate (PMA 2.4 micromol/l) stimulated chemiluminescence for 10 min. Both ozone and allergen inhalation caused an increase in PMA stimulated chemiluminescence (P<0.05). Budesonide pretreatment inhibited ozone-induced (P<0.008), but not allergen-induced PMA stimulated chemiluminescence (P>0.90). Both ozone and allergen inhalation caused an increase in the bronchoalveolar lavage neutrophils. Budesonide pretreatment significantly inhibited the ozone-induced (P=0.007), but not the ascaris-induced neutrophil influx (P=0.93). These results demonstrate that ozone, but not allergen, stimulated oxygen radical release and neutrophil influx are attenuated by inhaled corticosteroids. This suggests that luminol-enhanced chemiluminescence from bronchoalveolar lavage cells measures oxygen radicals derived from neutrophils, and that ozone-and allergen-induced bronchoalveolar lavage neutrophilia are caused by different mechanisms.

Allergen-induced oxygen radical release from bronchoalveolar lavage cells and airway hyperresponsiveness in dogs

Allergen inhalation causes airway hyperresponsiveness and airway inflammation in dogs. The purpose of this study was to determine whether allergen-induced airway hyperresponsiveness is associated with increases in oxygen radical production from bronchoalveolar lavage (BAL) cells. A group of 10 random-source dogs were studied twice, 4 wk apart. On each occasion, acetylcholine (ACh) airway responsiveness was measured before and 24 h after inhalation of Ascaris suum or its diluent, followed by BAL. The response to ACh was expressed as the concentration causing an increase in lung resistance of 5 cm H2/O/L/s above baseline. Spontaneous and phorbol myristate acetate (PMA)-stimulated (2.4 mumol/L) oxygen radical release were measured, for 10 min each, from washed BAL cells (4 x 10(6) cells/ml) by luminol-enhanced chemiluminescence in a luminometer at 37 degrees C. Superoxide anion production was measured using a cytochrome c assay. Allergen inhalation caused bronchoconstriction, airway inflammation, and airway hyperresponsiveness. The acetylcholine provocative concentration fell from 7.47 mg/ml (% SEM 1.61) before to 1.23 mg/ml (% SEM 1.62) after allergen (p < 0.0001). Allergen inhalation significantly increased absolute neutrophil (p = 0.03) and eosinophil (p = 0.02) counts in BAL. Spontaneous (p < 0.0003) and PMA-stimulated (p < 0.0005) chemiluminescence and superoxide anion production (p = 0.039) were increased after allergen inhalation. The allergen-induced increases in chemiluminescence were significantly correlated with the increases in ACh airway hyperresponsiveness (r = 0.75, p < 0.012). These results indicate that inhaled allergen increases oxygen radical release from bronchoalveolar lavage cells and supports the hypothesis that oxygen radicals are important in causing allergen-induced airway hyperresponsiveness.

Effect of inhaled budesonide on ozone-induced airway hyperresponsiveness and bronchoalveolar lavage cells in dogs

Inhaled corticosteroids are known to reduce components of the airway inflammation characteristic of asthma and improve airway hyperresponsiveness. However, the effect of inhaled corticosteroids on ozone-induced airway responses is unknown. Eight dogs inhaled budesonide [2.74 +/- 0.25 (SE) mg/day] or lactose powder twice daily for 7 days before inhaling ozone (3 ppm for 30 min) or dry air. Acetylcholine airway responsiveness was measured before and 1 h after ozone, followed by a bronchoalveolar lavage (BAL). The response to acetylcholine was expressed as the concentration causing an increase in lung resistance of 5 cmH2O.l-1.s above baseline (acetylcholine provocation concentration). Budesonide pretreatment significantly attenuated the ozone-induced increase in pulmonary resistance (P = 0.003) and neutrophil influx into BAL (P = 0.001) and significantly reduced BAL eosinophils (P = 0.026). However, budesonide pretreatment had no significant effect on ozone-induced airway hyperresponsiveness. After budesonide, the acetylcholine provocative concentration fell from 5.96 mg/ml (%SE 1.46) before to 1.11 mg/ml (%SE 1.63) after ozone (P = 0.006). After lactose, the acetylcholine provocative concentration fell from 5.34 mg/ml (%SE 1.40) before to 0.50 mg/ml (%SE 1.85) after ozone (P = 0.001). Dry air inhalation did not cause airway hyperresponsiveness (P = 0.68). These results suggest that ozone-induced airway hyperresponsiveness is steroid resistant and that airway neutrophils or eosinophils are not important in its pathogenesis.

Effect of an inhaled corticosteroid on airway eosinophils and allergen-induced airway hyperresponsiveness in dogs

The presence of airway eosinophils before allergen inhalation may contribute to the development of allergen-induced airway responses. We examined whether a reduction in airway eosinophil numbers before allergen inhalation as a result of inhalation of the corticosteroid budesonide would prevent allergen-induced airway hyperresponsiveness in seven dogs. Acetylcholine airway responsiveness was measured before and 24 h after inhalation of Ascaris suum allergen (10(-6)-10(-2) wt/vol) or its diluent on 4 test days separated by > or = 4 wk. Dogs were pretreated for 7 days before and on the morning of each test day with inhaled budesonide (2.69 mg/day) or a placebo (lactose). Airway eosinophil numbers were assessed by bronchoalveolar lavage. Inhaled budesonide significantly reduced the number of airway eosinophils before allergen inhalation from 3.6 +/- 2.38 x 10(4) (SE) cells/ml after inhaled lactose to 0.3 +/- 0.21 x 10(4) cells/ml after inhaled budesonide (P = 0.028). The decrease in eosinophil number was associated with a significant reduction in allergen-induced airway hyperresponsiveness (P = 0.005). These results support the hypothesis that the number of eosinophils in the airways before allergen inhalation is an important determinant in the development of allergen-induced airway hyperresponsiveness in dogs.