In vivo role of platelet-derived growth factor-BB in airway smooth muscle proliferation in mouse lung.

Airway smooth muscle (ASM) hyperplasia in asthma likely contributes considerably to functional changes. Investigating the mechanisms behind proliferation of these cells may lead to therapeutic benefit. Platelet-derived growth factor (PDGF)-BB is a well known ASM mitogen in vitro but has yet to be directly explored using in vivo mouse models in the context of ASM proliferation and airway responsiveness. To determine the in vivo influence of PDGF-BB on gene transcripts encoding contractile proteins, ASM proliferation, and airway physiology, we used an adenovirus overexpression system and a model of chronic allergen exposure. We used adenovirus technology to selectively overexpress PDGF-BB in the airway epithelium of mice. Outcome measurements, including airway physiology, real time RT-PCR measurements, proliferating cell nuclear antigen staining, and airway smooth muscle quantification, were performed 7 days after exposure. The same outcome measurements were performed 24 hours and 4 weeks after a chronic allergen exposure model. PDGF-BB overexpression resulted in airway hyperresponsiveness, decreased lung compliance, increased airway smooth muscle cell numbers, positive proliferating cell nuclear antigen-stained airway smooth muscle cells, and a reduction in genes encoding contractile proteins. Chronic allergen exposure resulted in elevations in lung lavage PDGF-BB, which were observed in conjunction with changes in gene transcript expression encoding contractile proteins and ASM proliferation. We demonstrate for the first time in vivo that PDGF-BB induces ASM hyperplasia and changes in lung mechanics in mice and that, during periods of allergen exposure changes in lung, PDGF-BB are associated with changes in airway structure and function.

Fetal and neonatal exposure to nicotine disrupts postnatal lung development in rats: role of VEGF and its receptors.

Many women are unable to quit smoking during pregnancy and therefore are prescribed drugs, including nicotine (nicotine replacement therapy [NRT]), to aid with smoking cessation. However, the consequences to the offspring of pregnant NRT users have not been well studied. The goals of this study were to determine the consequences of fetal and neonatal exposure to nicotine on lung development and function. Female rats were exposed to nicotine for 2 weeks prior to mating until weaning. Lungs were collected from saline and nicotine-treated rats from birth to adulthood to assess postnatal lung structure and function. Although nicotine exposure altered alveolarization at weaning, an effect that resolved by adulthood, it did not affect lung function at any of the ages investigated. However, nicotine exposure significantly decreased lung vascularization. The current study suggests that perinatal exposure to nicotine alters lung development, an effect which may be mediated via decreased vascular endothelial growth factor (VEGF) signaling.

Influence of airway wall stiffness and parenchymal tethering on the dynamics of bronchoconstriction.

Understanding how tissue remodeling affects airway responsiveness is of key importance, but experimental data bearing on this issue remain scant. We used lung explants to investigate the effects of enzymatic digestion on the rate and magnitude of airway narrowing induced by acetylcholine. To link the observed changes in narrowing dynamics to the degree of alteration in tissue mechanics, we compared our experimental results with predictions made by a computational model of a dynamically contracting elastic airway embedded in elastic parenchyma. We found that treatment of explanted airways with two different proteases (elastase and collagenase) resulted in differential effects on the dynamics of airway narrowing following application of ACh. Histological corroboration of these different effects is manifest in different patterns of elimination of collagen and elastin from within the airway wall and the surrounding parenchyma. Simulations with a computational model of a dynamically contracting airway embedded in elastic parenchyma suggest that elastase exerts its functional effects predominately through a reduction in parenchymal tethering, while the effects of collagenase are more related to a reduction in airway wall stiffness. We conclude that airway and parenchymal remodeling as a result of protease activity can have varied effects on the loads opposing ASM shortening, with corresponding consequences for airway responsiveness.

Comparison of aerosol and intranasal challenge in a mouse model of allergic airway inflammation and hyperresponsiveness.

BACKGROUND: The aim was to optimize antigen challenge for induction of airway hyperresponsiveness (AHR) and inflammation in BALB/c mice sensitized to ovalbumin (OVA). Comparisons were made between mice challenged with OVA either as an aerosol or intranasally. The protocol that induced maximal AHR in BALB/c mice was thereafter tested in C57BL/6 mice. METHOD: Methacholine responsiveness was measured using the flexiVent® system to assess AHR. Inflammatory responses were investigated by histology and cell counts in bronchoalveolar lavage (BAL) fluid. RESULTS: 48 h after challenge with 1 or 6% OVA aerosols, there were similar increments in AHR and BAL cells, predominantly eosinophils. When comparing the effect of 1% OVA aerosol on AHR and cell infiltration at 24 and 48 h after challenge, the responses were similar. At 24 h, intranasal OVA administration (20-200 µg) caused a dose-dependent increase in AHR. BAL cells were increased by all intranasal OVA doses and to a greater extent than after 1% OVA aerosol challenge but without any dose dependency. Histological examination confirmed that there was an increase of eosinophils in lung tissue following either challenge. In C57BL/6 mice, baseline tissue elastance was the only functional outcome that was increased after intranasal OVA challenge. Even though the AHR response was negligible in C57BL/6 mice, a similar infiltration of BAL cells was observed in both strains. CONCLUSION: Intranasal challenge was more effective than aerosol challenge at inducing both AHR and airway inflammation in BALB/c mice. Although intranasal challenge caused airway inflammation in C57BL/6 mice, this strain is not optimal for studying AHR.

Prostaglandin modulation of airway inflammation and hyperresponsiveness in mice sensitized without adjuvant.

As adjuvant during sensitization may cause unspecific immune reactions, the aim of the present study was to define the role of cyclooxygenase (COX) activity on airway inflammation and airway hyperresponsiveness (AHR) in an adjuvant-free allergic mouse model. Administration of diclofenac and indomethacin (non-selective COX inhibitors), FR122047 (COX-1 inhibitor) and lumiracoxib (selective COX-2 inhibitor) enhanced AHR. Only diclofenac and lumiracoxib reduced the inflammatory cell content of bronchoalveolar lavage (BAL). Moreover, levels of prostaglandins in BAL were reduced by indomethacin and FR122047 but were unaffected by lumiracoxib. However, compared with antigen controls, none of the COX inhibitors displayed major effects on the production of cytokines, smooth muscle mass, number of goblet cells and eosinophils, or collagen deposition in the airways. These data in mice sensitized without adjuvant support the fact that COX products have a general bronchoprotective role in allergic airway inflammation. Furthermore, the data suggest that COX-1 activity predominantly generates prostanoids in BAL, whereas COX-2 activity is associated with the accumulation of inflammatory cells in BAL. This study further supports that AHR on the one hand, and the inflammatory response and generation of prostanoids on the other, are dissociated and, at least in part, uncoupled events.

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.

Regional differences in the pattern of airway remodeling following chronic allergen exposure in mice.

BACKGROUND: Airway remodeling present in the large airways in asthma or asthma models has been associated with airway dysfunction in humans and mice. It is not clear if airways distal to the large conducting airways have similar degrees of airway remodeling following chronic allergen exposure in mice. Our objective was to test the hypothesis that airway remodeling is heterogeneous by optimizing a morphometric technique for distal airways and applying this to mice following chronic exposure to allergen or saline. METHODS: In this study, BALB/c mice were chronically exposed to intranasal allergen or saline. Lung sections were stained for smooth muscle, collagen, and fibronectin content. Airway morphometric analysis of small (0-50000 microm2), medium (50000 microm2-175000 microm2) and large (>175000 microm2) airways was based on quantifying the area of positive stain in several defined sub-epithelial regions of interest. Optimization of this technique was based on calculating sample sizes required to detect differences between allergen and saline exposed animals. RESULTS: Following chronic allergen exposure BALB/c mice demonstrate sustained airway hyperresponsiveness. BALB/c mice demonstrate an allergen-induced increase in smooth muscle content throughout all generations of airways, whereas changes in subepithelial collagen and fibronectin content are absent from distal airways. CONCLUSION: We demonstrate for the first time, a systematic objective analysis of allergen induced airway remodeling throughout the tracheobronchial tree in mice. Following chronic allergen exposure, at the time of sustained airway dysfunction, BALB/c mice demonstrate regional differences in the pattern of remodeling. Therefore results obtained from limited regions of lung should not be considered representative of the entire airway tree.

T-cell-mediated inflammation does not contribute to the maintenance of airway dysfunction in mice.

T-cell-mediated airway inflammation is considered to be critical in the pathogenesis of airway hyperresponsiveness (AHR). We have described a mouse model in which chronic allergen exposure results in sustained AHR and aspects of airway remodeling and here sought to determine whether eliminating CD4(+) and CD8(+) cells, at a time when airway remodeling had occurred, would attenuate this sustained AHR. Sensitized BALB/c mice were subjected to either brief or chronic periods of allergen exposure and studied 24 h after brief or 4 wk after chronic allergen exposure. In both models, mice received three treatments with anti-CD4 and -CD8 monoclonal antibodies during the 10 days before outcome measurements. Outcomes included in vivo airway responsiveness to intravenous methacholine, CD4(+) and CD8(+) cell counts of lung and spleen using flow cytometric analysis, and airway morphometry using a computer-based image analysis system. Compared with saline control mice, brief allergen challenge resulted in AHR, which was eliminated by antibody treatment. Chronic allergen challenge resulted in sustained AHR and indexes of airway remodeling. This sustained AHR was not reversed by antibody treatment, even though CD4(+) and CD8(+) cells were absent in lung and spleen. These results indicate that T-cell-mediated inflammation is critical for development of AHR associated with brief allergen exposure, but is not necessary to maintain sustained AHR.

Silk suture used in standard organ bath studies contracts upon exposure to Krebs buffer.

INTRODUCTION: Muscles of all types are routinely excised and studied under isometric conditions using force transducers in standard organ baths. In such studies, the muscle is stretched or "preloaded," as the magnitudes of the contractions evoked by various stimuli can vary markedly depending on this baseline parameter: many such studies refer to an optimal length and/or preload tension. While calibrating our equipment, we were surprised to find that the silk suture, which is commonly used in such studies, can generate considerable tension of its own, completely independent of any muscle tissue. METHODS: We compared two different types of silk suture in muscle baths using the standard organ bath technique, measuring baseline tension upon addition of various solvents/buffers. RESULTS: One type of silk suture was inert in that, upon stretching to a given degree, there was no important change in preload tension upon addition of bathing medium (Krebs buffer). The second type of silk suture, however, which is also widely available commercially, exhibited substantial contractile responses upon exposure to standard Krebs buffer solution, with magnitudes typically exceeding several grams force. This change developed over the first 30-60 min of exposure to Krebs, after which tension was stable. This change was not observed if the suture was presoaked for 60 min before hanging in the muscle bath, but was observed if the suture was allowed to dry again before use. Other solvents such as ethanol and DMSO did not alter tension. DISCUSSION: While this property of silk suture may be well known in the surgical setting, it is less well appreciated by other users of this material. This phenomenon is of major importance to any experimental study of muscle function, as it alters the preload tension under which such studies are carried out.

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.

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.

Increased eosinophil-lineage committed progenitors in the lung of allergen-challenged mice.

BACKGROUND: There is increasing evidence that hemopoietic progenitor cells may traffic from bone marrow to sites of allergen exposure in asthma and undergo in situ differentiation, contributing to ongoing airway inflammation. However, the isolation and detailed phenotyping of true CD34 + progenitors from lung tissue during an allergen-induced airway eosinophilia has not been performed. OBJECTIVE: We attempted to isolate and investigate the in vivo kinetics of hemopoietic progenitor cells and production of eosinophilopoietic mediators in the lung. METHODS: In a mouse model of allergic airway inflammation, cells were extracted from lung tissue by enzymatic digestion. Total (CD34 + 45 + ) and eosinophil lineage committed (CD34 + 45 + IL-5Ralpha + ) progenitors were enumerated by flow cytometry. Outcome measurements were made 2, 6, 12, 24, 48, and 72 hours and 7 and 14 days after allergen challenge. RESULTS: Compared with saline control, CD34 + 45 + progenitors were elevated between 6 and 48 hours ( P < .05), attenuated by 72 hours and subsequently increased by 14 days ( P > .05). CD34 + 45 + IL-5Ralpha + progenitors were transiently elevated at 6 hours ( P < .05) before a return to preallergen levels by 12 hours and a subsequent increase at 14 days ( P < .05). Bronchoalveolar lavage eosinophils were increased at 2 hours, peaking at 72 hours ( P < .00625) and declining by 14 days. Both IL-5 and eotaxin levels were increased by 2 hours, peaking at 12 hours ( P < .05) and 24 hours ( P < .05), respectively. CONCLUSION: We propose that the increase in CD34 + 45 + IL-5Ralpha + cells and the eosinophilopoietic mediators IL-5 and eotaxin in the lung after allergen exposure may promote in situ differentiation of eosinophils that contribute to ongoing allergic airway inflammation.

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.

Morphometric analysis of mouse airways after chronic allergen challenge.

Understanding the mechanisms of airway remodeling in chronic allergic conditions such as asthma is increasingly dependent on the use of animal models. Techniques for quantifying structural changes are required that are reproducible and responsive and that can be applied to different staining techniques in both human and animal airway tissues. Here, we characterize a morphometric technique to quantify changes in extracellular matrix and contractile tissue as two indices of airway remodeling in mice. Specific aims were to establish the optimum projection beneath the epithelium to assess remodeling changes and to determine whether such changes are reproducible within different areas of the lung. Finally, based on the variance within measurements, we calculated sample size requirements for research applications of this technique. BALB/c mice were sensitized to ovalbumin and studied after chronic allergen challenge. Lungs were formalin fixed and sectioned were then assayed for extracellular matrix or contractile tissue using morphometric/colorimetric techniques. In this model, the optimum projected distance to measure changes in extracellular matrix or contractile tissue was 20 micro m beneath the epithelium; projecting beyond this depth resulted in decreased ability to detect allergen-induced changes (signal) because of increased irrelevant staining of surrounding parenchymal tissue (noise). The technique was responsive, because an allergen-induced signal was detected in all airway sections and all lung regions studied (p < 0.05). The power of this analysis was such that allergen-induced changes can be reliably (>80% power) detected using 8 to 10 mice. This morphometric technique provides a valid and objective method to assess structural changes in the airways of mice after chronic allergen exposure.

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.

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.

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.

Type 2 cytokines in the pathogenesis of sustained airway dysfunction and airway remodeling in mice.

The mechanisms underlying airway hyperresponsiveness remain unclear, although airway inflammation and remodeling likely play important roles. We have observed sustained airway hyperreactivity and airway remodeling occurring in mice after chronic allergen exposure and persisting beyond resolution of allergen-induced inflammation. The aim of this study was to delineate mechanisms involved in allergen-induced airway hyperreactivity and airway remodeling and to examine evidence for a causal association between airway remodeling and sustained airway hyperreactivity. Wild-type (WT) and interleukin (IL)-4-, IL-5-, and IL-13-deficient (-/-) mice were sensitized and studied 4 weeks after chronic allergen exposure. By measuring airway responsiveness and airway morphometry, we demonstrated that WT mice developed sustained airway hyperreactivity and aspects of airway remodeling after chronic allergen exposure. Both IL-4(-/-) and IL-13(-/-) mice were protected from developing sustained airway hyperreactivity and aspects of airway remodeling. In contrast, IL-5(-/-) mice developed sustained airway hyperreactivity and aspects of airway remodeling similar to that seen in WT mice. Our results confirm that IL-4 and IL-13, but not IL-5, are critical for the development of sustained airway hyperreactivity and airway remodeling after allergen exposure.

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.

Pathogenesis of murine experimental allergic rhinitis: a study of local and systemic consequences of IL-5 deficiency.

Recent studies have demonstrated an important role for IL-5-dependent bone marrow eosinophil progenitors in allergic inflammation. However, studies using anti-IL-5 mAbs in human asthmatics have failed to suppress lower airway hyperresponsiveness despite suppression of eosinophilia; therefore, it is critical to examine the role of IL-5 and bone marrow responses in the pathogenesis of allergic airway disease. To do this, we studied the effects of IL-5 deficiency (IL-5(-/-)) on bone marrow function as well as clinical and local events, using an established experimental murine model of allergic rhinitis. Age-matched IL-5(+/+) and IL-5(-/-) BALB/c mice were sensitized to OVA followed by 2 wk of daily OVA intranasal challenge. IL-5(-/-) OVA-sensitized mice had significantly higher nasal mucosal CD4(+) cells and basophilic cell counts as well as nasal symptoms and histamine hyperresponsiveness than the nonsensitized group; however, there was no eosinophilia in either nasal mucosa or bone marrow; significantly lower numbers of eosinophil/basophil CFU and maturing CFU eosinophils in the presence of recombinant mouse IL-5 in vitro; and significantly lower expression of IL-5Ralpha on bone marrow CD34(+)CD45(+) progenitor cells in IL-5(-/-) mice. These findings suggest that IL-5 is required for normal bone marrow eosinophilopoiesis, in response to specific Ag sensitization, during the development of experimental allergic rhinitis. However, the results also suggest that suppression of the IL-5-eosinophil pathway in this model of allergic rhinitis may not completely suppress clinical symptoms or nasal histamine hyperresponsiveness, because of the existence of other cytokine-progenitor pathways that may induce and maintain the presence of other inflammatory cell populations.