help button home button
AJRCMB
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Leigh, R.
Right arrow Articles by Inman, M. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Leigh, R.
Right arrow Articles by Inman, M. D.
American Journal of Respiratory Cell and Molecular Biology. Vol. 27, pp. 526-535, 2002
© 2002 American Thoracic Society
DOI: 10.1165/rcmb.2002-0048OC

Dysfunction and Remodeling of the Mouse Airway Persist after Resolution of Acute Allergen-Induced Airway Inflammation

Richard Leigh, Russ Ellis, Jennifer Wattie, David S. Southam, Meta de Hoogh, Jack Gauldie, Paul M. O'Byrne and Mark D. Inman

Firestone Institute for Respiratory Health, Department of Medicine and Center for Gene Therapeutics, Department of Pathology, McMaster University, Hamilton, Ontario, Canada

Address correspondence to: Mark D. Inman, M.D., Ph.D., Firestone Institute for Respiratory Health, St. Joseph's Healthcare, 50 Charlton Avenue East, Hamilton, Ontario L8N 4A6 Canada. E-mail: inmanma{at}mcmaster.ca


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
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.

Abbreviations: airway hyperresponsiveness, AHR • bronchoalveolar lavage, BAL • extracellular matrix, ECM • hematoxylin and eosin, H&E • interleukin, IL • intranasal, IN • intraperitoneal, IP • methacholine, MCh • ovalbumin, OVA • periodic acid Schiff, PAS • total respiratory system resistance, RRS • T helper type 2, Th2 • {alpha}-smooth muscle actin, {alpha}-SMA


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Asthma is characterized by the presence of variable airflow limitation, airway hyperresponsiveness (AHR) and airway inflammation (1). AHR is present in almost all individuals with asthma, and is characterized by exaggerated airway narrowing following exposure to nonspecific stimuli such as methacholine (MCh), histamine, or exercise (2). Airway responsiveness can be quantified as the provocative dose, or concentration, of a stimulus required to produce a given level of bronchoconstriction (typically a 20% fall in forced expiratory volume in 1 s); as much as 500-fold differences exist between asthmatic and normal individuals (3).

The dysfunction underlying AHR includes hypersensitivity (shift to the left of bronchoconstrictor dose–response curves), hyperreactivity (increased slope of these curves), and a greater maximum degree of induced bronchoconstriction. However, the pathophysiologic mechanisms underlying these abnormalities remain unclear. T helper type 2 (Th2) inflammation of the airways is believed to be central in the pathogenesis of asthma (4–6), although the exact contribution of airway inflammation to airway dysfunction remains ill-defined (7). While some studies have shown that the extent of airway eosinophilia in asthmatic subjects was related to the degree of their AHR (4, 8), the observation that profound AHR is sustained in asthma, despite prolonged treatment with anti-inflammatory corticosteroids (9–12), suggests that other mechanisms likely account for a major component of AHR.

Evidence suggests that chronic structural changes in the airway, often termed airway remodeling, may be at least in part responsible for sustained AHR (12–16). These changes include thickening of the airway wall, subepithelial fibrosis, hyperplasia and hypertrophy of smooth muscle cells, and hyperplasia of myofibroblasts and goblet cells (17–22). Mathematical modeling studies postulating that both increased muscle mass and, to a lesser extent, airway wall thickening are determinants of AHR (13, 23–24) are supported by airway biopsy evidence that both the degree of smooth muscle thickness and the extent of subepithelial fibrosis relate to the magnitude of AHR in asthma (17, 25–26).

In an attempt to further elucidate potential mechanisms underlying AHR, considerable attention has been paid to mouse models of allergen-induced airway responses (27–36). These models have greatly increased our understanding of the mechanisms underlying transient responses to inhaled allergen, including the role of interleukin (IL)-5 (31, 33–34) in eosinophilic inflammation, and of IL-13 in transient AHR (32, 35–36). However, despite these and other advances, a limitation of these models is that the airway dysfunction is transient, disappearing 14–21 d after allergen exposure, and appears to be related only to acute increases in inflammatory mediators. This is not equivalent to the sustained AHR present in individuals with asthma, and while these models have provided valuable information, they are unlikely to provide a complete description of the mechanisms underlying AHR. We have therefore attempted to further these advances through the development of a model of induced, sustained airway dysfunction in mice.

Our underlying hypothesis is that repeated episodes of allergic inflammation give rise to some of the remodeling changes associated with asthma, which may in turn be associated with sustained airway dysfunction. In this study we have addressed the specific questions of (i) whether airway physiology differed between mice subjected to either brief or chronic allergen exposure, and (ii) whether these differences were associated with characteristic inflammatory markers and indices of airway remodeling.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals
Female BALB/c mice were purchased from Harlan Sprague Dawley Inc. (Indianapolis, IN). Mice were aged 10 to 12 wk and housed in environmentally controlled, specific pathogen-free conditions for 1 wk prior to study, and for the duration of the experiments. All procedures were reviewed and approved by the Animal Research Ethics Board at McMaster University, and conformed to NIH guidelines for the experimental use of animals (37).

Sensitization
Mice were sensitized with intraperitoneal (IP) ovalbumin (OVA) conjugated to aluminum potassium sulfate injected on Days 1 and 11, and with intranasal (IN) OVA on Day 11. This protocol, including the preparation of OVA, was the same as that used in the past by us (32).

Challenge
Sensitized mice were subjected to either brief or chronic periods of exposure to allergen (Figure 1). Brief exposure involved IN OVA (100-µg in 25-µl saline) challenges on Days 18 and 19. Chronic exposure involved six 2-day periods of IN OVA challenges, each separated by 12 d (a total of 12 challenges over a 10 wk period). Control mice were subjected to the same sensitization protocol but received IN saline challenges. Mice were studied at 24 h and 2, 4, and 8 wk after the final exposure to either allergen or saline in both brief and chronic protocols. Separate groups of 10 mice were studied in each protocol and at each end-point, at which time the following outcome measurements were made: (i) in vivo airway responsiveness to intravenous MCh; (ii) total and differential cell counts in bronchoalveolar lavage (BAL) fluid; (iii) IL-13 levels in BAL supernatant; and (iv) airway morphometry, using a computer-based image analysis system.



View larger version (12K):
[in this window]
[in a new window]
  		Figure 1. Study protocols. Sensitization and challenge protocols used in brief and chronic challenge models. Note that all outcome measurements were made following the final challenge in each protocol.

 
Airway Responsiveness
Airway responsiveness was measured based on the response of total respiratory system resistance (RRS) to saline and increasing (10, 33, 100 and 330 µg) intravenous doses of MCh. RRS was measured using the flow interrupter technique, modified for use in mice, and described by us and others in detail elsewhere (31, 38). Briefly, mice were anesthetized using 2,2,2-tribromoethanol (Avertin, 240 mg/kg intraperitoneally; Aldrich Chemical Co., Milwaukee, WI). When anesthesia was established, the trachea was exposed and cannulated using a blunted 18-gauge needle. The needle was then attached to a ventilator (RV5; Voltek Enterprises Inc., Toronto, ON, Canada) designed to deliver constant inspiratory flow despite the disturbances in the respiratory system impedance that occur during the MCh challenge. Using the same pattern of ventilation as we have described in the past (31), the response of RRS to increasing doses of intravenous MCh was measured. Rather than obtaining a single index of overall airway responsiveness, we analyzed the resulting RRS–MCh dose response curve, obtaining indices of (i) airway reactivity (slope), (ii) airway sensitivity (lowest dose to produce bronchoconstriction), and (iii) maximal degree of bronchoconstriction (Figure 2). The slope of the relationship was calculated by linear regression between the measured RRS and the log10 transformed MCh dose, using data from the 10, 33 and 100 µg doses. The lowest dose of MCh required to produce bronchoconstriction was determined by calculating the dose at which this regression line intercepted with the postsaline RRS (Figure 2).



View larger version (11K):
[in this window]
[in a new window]
  		Figure 2. Airway responsiveness methods. Total respiratory system resistance (RRS) was measured in response to increasing doses of intravenous MCh. Using the resulting RRS–MCh dose response curve, indices of airway reactivity (Slope RRS), airway sensitivity, or the lowest dose to produce bronchoconstriction (Break RRS), and maximal degree of bronchoconstriction (Max RRS) were measured.

 
Bronchoalveolar Lavage
Following airway physiology measurements, BAL was performed as described previously (31). Briefly, two aliquots of 250-µl phosphate buffered saline were injected and withdrawn through the tracheal cannula. Following centrifugation, the supernatant was stored at -20°C for later IL-13 measurement, and cytocentrifuge slides (Cytospin 3; Shandon Scientific, Sewickley, PA) were prepared and stained with Diff-Quik (Dade Behring Inc., Newark, DE). Differential cell counts were performed on 400 cells by one investigator blind to the experimental conditions. Cells were classified, based on morphologic criteria, as macrophages, neutrophils, lymphocytes, or eosinophils. IL-13 levels in BAL fluid were assessed by enzyme-linked immunosorbent assay (Quantikine, R&D Systems, Minneapolis, MN). Measurements below 7.8 pg/mL are considered by the manufacturer to be below the level of detection.

Lung Histology and Morphometry
The heart and lungs were dissected and removed from the thoracic cavity of each mouse. The lungs were then inflated with 10% formalin to a pressure of 20 cm H2O and the trachea tied off; both lungs were fixed in formalin for 24 h after which the left lung was isolated, sectioned in half, and the lower half embedded in paraffin. The left lung was oriented so that transverse sections of the first generation bronchus, with the accompanying artery and vein, were obtained in cross-section (Figure 3). Three-µm thick transverse sections were cut and stained with hematoxylin and eosin for histological assessment using light microscopy. Additional 3 µm sections were stained with Masson's Trichrome to demonstrate the presence of extracellular matrix (ECM), and with periodic acid Schiff (PAS) stain to demonstrate the presence of mucin within goblet cells. Further 3-µm sections were prepared for immunohistochemistry using a monoclonal antibody (Clone 1A4, Dako, Denmark) against {alpha}-smooth muscle actin ({alpha}-SMA) to identify contractile elements.



View larger version (59K):
[in this window]
[in a new window]
  		Figure 3. Airway morphometry methods. (A) Transverse section through the left lung (stained with {alpha}-SMA) of a first-generation airway (aw) with associated artery (a) and vein (v). The rectangle illustrates a section of airway that is not tethered to a neighboring vessel/airway and was thus considered suitable for morphometric analysis (enlarged in B–D). (C) The yellow line immediately beneath the epithelium represents that drawn by the user, while the deeper yellow line is that projected by the computer; the computer then isolates the band of tissue in the 20-µm region defined by the two yellow lines. (D) The computer determines the area in this band that corresponds to positive {alpha}-SMA staining and expresses this as a percentage of the total band area.

 
Morphometric analysis of the lung sections (10 mice per group), stained as indicated above, was performed using a custom prepared computerized image analysis system (Microscope: Olympus BX40; Camera: Sony 3CCD Power HAD Video Camera; Computer: Pentium III, 700 MHz processor, Windows 98 operating system; Software: Northern Eclipse, version 5 [Empix Imaging Inc., Mississauga, ON, Canada]). Morphometric quantification involved calculating the percent of tissue area that was positively stained within regions of interest (one slide per mouse per stain). Sections of the airway wall that were associated with connective tissue attachments to adjacent vessels were not included in the morphometric analysis of the Masson's Trichrome or {alpha}-SMA stain, so as to minimize this area as a potential source of noise. Images of all the remaining first generation airway wall that was identified as being free of intimate contact with the neighboring vessels (Figure 3) were captured into the computer in a blinded fashion by the same operator on each occasion, coded, and stored for later analysis. This process resulted in the analysis of two to three images per slide per mouse.

For sections stained with Masson's Trichrome and {alpha}-SMA, the region of interest was a 20µm band immediately beneath the epithelium (this thickness was chosen because it was considered to include the ECM and contractile elements associated with the airways) (Figure 3). Analysis of each stored image was initiated with the operator drawing a line along the basal border of the airway epithelium using a digital pen mouse and writing tablet. This line did not cover any positively stained tissue associated with or beneath the airway epithelium. Thereafter, the macro software application built into the Northern Eclipse Software projected a second line 20 µm beneath the first line. In the case of sections stained with PAS, the operator added the second line along the inner border of the epithelium using the pen mouse, and the region of interest became the area between the two lines. The software then calculated the area between these lines, and regions within this area that were positively stained were identified based on previously determined settings of hue, saturation, and value, used for Masson's Trichrome and {alpha}-SMA stained sections, or red, blue, green, used for PAS stained sections. These hue, saturation, and value or red, blue, green limits were identified subjectively prior to any analysis as being able to identify most of the positively stained tissue with minimal identification of negatively stained tissue. Where several separate airway bands of airway wall were analyzed from a single mouse for a particular stain, the final score for that mouse was a weighted mean, where each band was weighted in proportion to its total area. Quantification of peribronchial eosinophilia in airway tissue was achieved through counting the numbers of these cells in the 50-µm region beneath the epithelium of the first generation airway in hematoxylin and eosin stained sections. Cells were expressed as number per mm2.

Statistical Analysis
Reported values are expressed as mean and SEM. Comparisons between saline control mice and mice receiving either brief or chronic allergen exposure, with respect to airway reactivity (slope of the RRS log-transformed MCh dose–response curve), maximal bronchoconstriction (maximal MCh–induced RRS), cell counts and BAL IL-13 measurements, and indices of airway remodeling, were made using ANOVA. Post-hoc testing with appropriate corrections for multiple comparisons was performed using Duncan's multiple range test. Similar between-group comparisons were made in mice receiving either brief or chronic allergen exposure. All comparisons were two-tailed, and P values < 0.05 were considered to be significant.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Differences in Responses to MCh Following Brief or Chronic Exposure to Allergen
The underlying contributors to airway responsiveness, namely airway reactivity (rate of increase in RRS for a given increase in MCh dose), airway sensitivity (lowest dose of MCh to produce bronchoconstriction), and also the maximum inducible bronchoconstriction (maximum RRS), were measured following brief or chronic allergen challenge. Following brief exposure to allergen, there was a significant increase in the airway reactivity as measured by the slope of the MCh dose response curve (Figure 4) at 24 h compared with the saline control group (P < 0.01). However, this transient increase in airway reactivity was no longer present at 2 wk or beyond. In contrast, mice exposed to chronic allergen challenge had a significant increase in airway reactivity at 24 h compared with the saline control group (P < 0.01), and this increase was sustained at 2 wk (P = 0.01), 4 wk (P = 0.04), and 8 wk (P = 0.02) postallergen (Figure 4).



View larger version (23K):
[in this window]
[in a new window]
  		Figure 4. Time course of airway function and inflammatory changes following brief or chronic exposure to allergen. Airway function (MCh dose response slope and max RRS) and inflammatory markers (peribronchial eosinophils and BAL IL-13) measured at times following brief or chronic exposure to allergen. * indicates P < 0.05 compared with saline challenged mice.

 
Maximal bronchoconstriction was increased at 24 h (P < 0.01), 2 wk (P = 0.05), and 4 wk (P < 0.01) following brief allergen challenge compared with saline controls (Figure 4). Similarly, maximal bronchoconstriction was also increased at 24 h (P < 0.01), 2 wk (P = 0.01), 4 wk (P < 0.01), and 8 wk (P = 0.02) following chronic exposure to allergen. There was no evidence of brief or chronic allergen-induced changes in airway sensitivity, as indicated by the calculated lowest dose of MCh required to increase RRS compared with saline challenged mice.

Persistent Airway Hyperreactivity Independent of Airway Eosinophilia
Following brief allergen exposure, there was a significant increase in the number of peribronchial eosinophils at 24 h compared with the saline control group (P < 0.01) (Figure 4). Similarly, there was a significant increase in the number eosinophils at 24 h following chronic exposure to allergen compared with the saline control group (P < 0.01). Peribronchial eosinophils had returned to baseline levels 2 wk following either brief or chronic allergen challenge. Responses of BAL eosinophils were similar, increasing from 0 ± 0 (mean ± SEM) in saline-challenged mice to 10.92 ± 1.71 and 1.59 ± 0.30, 24 h after brief or chronic challenge, respectively (P < 0.05). BAL eosinophils remained elevated 2 wk after brief or chronic challenge (1.28 ± 0.24, and 0.21 ± 0.06, respectively) (P < 0.05), but no eosinophils were detected 4 wk after either challenge. As we have observed previously, allergen challenge was associated with transient increases in neutrophils and lymphocytes (31). However, these had returned to baseline levels by 4 wk after brief or chronic challenge (data not shown).

Sustained Airway Hyperreactivity Independent of Airway IL-13
Following brief exposure to allergen, BAL IL-13 levels were significantly increased at 24 h compared with saline control mice (P < 0.01) (Figure 4). However by 2 wk and beyond, IL-13 levels had returned to baseline levels. In mice receiving chronic allergen exposure, BAL IL-13 levels were also significantly increased at 24 h compared with saline control mice (P < 0.01). Similarly, in mice exposed to chronic allergen, IL-13 measurements fell to baseline levels by 2 wk and were not significantly different at 4 wk, despite the presence of sustained airway hyperreactivity at these time points. IL-13 levels 24 h postchallenge were significantly greater in brief compared with chronic OVA groups (P < 0.01) (Figure 4).

Chronic Exposure to Allergen Associated with Increased Airway ECM
There was no significant change in the amount of ECM present in mouse airways 24 h, or 2, 4, or 8 wk after brief exposure to allergen compared with saline exposed mice (Figure 5; Figures 6 A and 6C). In contrast, mice chronically exposed to allergen had significantly greater ECM present at 4 and 8 wk compared with saline control mice (P < 0.01) and compared with mice receiving brief allergen challenge at all time points (P < 0.01) (Figure 5; Figures 6B and 6D). Although changes in ECM were observed in airways beyond the 1st generation, they appeared less pronounced.



View larger version (19K):
[in this window]
[in a new window]
  		Figure 5. Time course of morphometric changes in the airway following brief or chronic exposure to allergen. Staining as assessed using morphometry for ECM (Masson's Trichrome), contractile elements ({alpha}-SMA) in the 20 µm region beneath epithelium, and mucin (PAS) in the epithelial portion of the airway wall, in mice following brief or chronic exposure to allergen. Data are expressed as the percentage of the region of interest that was positively stained. * indicates P < 0.05 compared with saline-challenged mice.

 


View larger version (80K):
[in this window]
[in a new window]
  		Figure 6. Masson's Trichrome-stained sections of airway wall from briefly challenged or chronically challenged mice. Staining for ECM (green) in the airways in saline control mice in the brief (A) or chronic (B) allergen exposure groups, and in mice at 8 wk following brief (C) or chronic (D) exposure to allergen. Bars indicate 100 µm.

 
Brief and Chronic Allergen Exposure Both Associated with Increased Contractile Elements
There were significant increases in the amount of {alpha}-SMA staining present at 24 h, and 2, 4, and 8 wk following brief exposure to allergen, compared with the saline control group (P < 0.05) (Figure 5; Figures 7A and 7C). Similarly, there were significant increases in {alpha}-SMA staining present at 24 h, and 2, 4, and 8 wk after chronic exposure to allergen compared with the saline control group (P < 0.01) (Figure 5; Figures 7B and 7D). Evidence of increased contractile elements was also evident in airways beyond the first generation. Compared with control mice, the average thickness of the airway wall, measured as the distance between the luminal surface of the epithelium and the juncture between the {alpha}-SMA–stained region and lung parenchyma, was significantly increased 4 wks after either brief (28.9 ± 1.7 µm versus 16.2 ± 1.2 µm; P < 0.001) or chronic challenge (33.8 ± 2.2 µm versus 18.9 ± 1.4 µm; P < 0.001).



View larger version (80K):
[in this window]
[in a new window]
  		Figure 7. {alpha}-SMA–stained sections of airway wall from briefly challenged or chronically challenged mice. Staining for contractile elements (red) in the airways in saline control mice in the brief (A) or chronic (B) allergen exposure groups, and in mice at 8 wk following brief (C) or chronic (D) exposure to allergen. Bars indicate 100 µm.

 
Chronic Exposure to Allergen Associated with a Sustained Increase in Airway Epithelium Mucin Content
PAS staining for mucin was significantly increased in the airway epithelium at 24 h and 2 wk after either brief or chronic exposure to allergen compared with saline control mice (P = 0.02 for brief allergen exposure; P < 0.01 for chronic allergen exposure) (Figure 5 and Figures 8C and 8D). By 4 and 8 wk after brief allergen exposure, the amount of mucin present in the airway epithelium returned to levels observed in saline exposed mice (P > 0.05) (Figure 5 and Figure 8E). In contrast, at 4 and 8 wk after chronic allergen exposure, the amount of mucin present in the airway epithelium remained significantly increased compared with saline exposed mice (P < 0.01) (Figure 5 and Figure 8F).



View larger version (119K):
[in this window]
[in a new window]
  		Figure 8. PAS stained sections of airway epithelium from brief or chronically challenged mice. Staining for mucin (magenta) in the airway epithelium in saline control mice in the brief (A) or chronic (B) allergen exposure groups, in mice at 2 wk following brief (C) or chronic (D) exposure to allergen, and in mice at 8 wk following brief (E) or chronic (F) exposure to allergen. Bars indicate 100 µm.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Using mouse models of either brief or chronic exposure to allergen, we observed different aspects of sustained airway dysfunction and airway remodeling, both of which persisted beyond the resolution of acute immune-mediated inflammatory events. By measuring airway responses to MCh we have demonstrated increases in the maximal inducible bronchoconstriction (maximal RRS), which persist for at least 8 wk following either brief or chronic allergen challenge. In both models this was associated with increases in contractile tissue in the airway wall. We also observed increases in airway reactivity (rate of increase in respiratory resistance for a given increase in MCh dose); however, it was only in chronically challenged mice that these changes persisted beyond the resolution of allergen-induced inflammation. As subepithelial fibrosis was only observed in mice chronically challenged with allergen, it is tempting to speculate that this aspect of remodeling was responsible for genesis of the sustained airway hyperreactivity observed in these mice. However, this line of reasoning is weakened by the fact that fibrosis was only evident at 4 wk after chronic allergen exposure, although sustained airway hyperreactivity was present at 2 wk.

Other investigators have developed models in which structural airway changes occurred following chronic exposure to allergen (39–41). In those studies, airway dysfunction was observed, but was only reported for the period immediately following the final exposure to allergen. Our observations are fundamentally different in that using both brief and chronic challenge protocols, we have demonstrated sustained maximal bronchoconstriction that persists for at least 8 wk following the final exposure to allergen. Furthermore, using our chronic exposure model, we have observed that sustained airway hyperreactivity persists for at least 8 wk following final exposure to allergen. This sustained airway dysfunction was not present in control mice following either brief or chronic exposure to saline.

Previous models of brief exposure to allergen have demonstrated that the resulting transient airway hyperreactivity, measured either as the increase in inflation pressure at a given MCh dose (35), the dose of MCh required to double airway resistance (36), or enhanced pause measured over a range of MCh doses (32) was dependent on IL-13. This paradigm has again been supported in our study by the observation that mice receiving brief exposure to allergen developed transient airway hyperreactivity that was associated with increased levels of IL-13. The specific mechanisms underlying this transient airway hyperresponsiveness are not yet fully understood; however, factors such as transient allergen-induced inflammatory edema, likely to be present but not measured in our study, could play an important role.

In contrast, we have shown that sustained airway hyperreactivity persisting for at least 8 wk following chronic allergen challenge was not associated with ongoing Th2 inflammatory markers, such as airway eosinophilia or increased IL-13 levels. We hypothesize that the sustained airway dysfunction was a consequence of airway remodeling rather than ongoing immune-mediated inflammatory events. Clearly, however, earlier immune-mediated events, including cellular inflammation and increased levels of Th2 cytokines, are likely to contribute to the pathogenesis of this sustained dysfunction.

Our observation that sustained airway hyperreactivity persists after resolution of acute airway inflammation may be analogous to human asthma, where AHR typically persists despite optimal anti-inflammatory therapy (11). Moreover, our findings support the notion that complete resolution of airway dysfunction in established asthma is unlikely to occur using therapies that target specific immune mediators; this may explain why anti–IL-5 therapy had limited benefit in a recent clinical trial (42). However, it is plausible that therapeutic interventions that specifically target immune mediators may limit the extent of disease progression in asthma, if they are initiated earlier in the pathogenesis of the disease.

We have also demonstrated that chronic, but not brief, allergen exposure was associated with significantly increased amounts of ECM in the subepithelial region of the airway wall, and with increased mucin content within the airway epithelium at 4 and 8 wk after the last allergen challenge. These observations are in agreement with other models of chronic exposure to allergen, and support the concept that repeated inflammatory events may contribute to airway remodeling in asthma (39, 41). Although subepithelial fibrosis in the chronic allergen model was not detected until 4 wk after the final challenge, it is possible that this structural change contributed to the persistence of airway reactivity. The possibility that collagen deposition beneath the layer of smooth muscle may enhance the reactivity of the airways is consistent with the mathematical model of Wiggs and coworkers (13), in which the same degree of smooth muscle constriction in an airway wall thickened by subepithelial collagen deposition resulted in enhanced airway responses to bronchoconstrictor stimuli. Due to the absence of a clear adventitia in the mouse airway, it was not possible to actually measure the thickness of the airway wall.

Interestingly, we did not observe a significant increase in ECM until 4 wk after chronic allergen challenge, despite the fact that mice examined at 24 h and 2 wk had received the full chronic allergen challenge protocol. A possible explanation for this apparent anomaly is that there was an ongoing cellular inflammation at 24 h and 2 wk, as indicated by tissue and BAL eosinophil numbers. Although it is possible that this cellular inflammation simply interfered with the morphometric quantification of ECM, this seems unlikely given that there was no visible evidence of increased Masson's trichrome staining at these time points. A more intriguing hypothesis is that the ongoing cellular inflammation somehow interfered with the deposition of ECM. This is supported by evidence that inflammatory cells are a rich source of matrix metalloproteases (43–44) and may contribute to ongoing clearance of newly formed ECM. Thus, we hypothesize that excessive deposition of ECM was only able to occur once the inflammatory cell infiltrate had resolved between 2 and 4 wk after final exposure to allergen. Our observations illustrate the potential complexity in the relationship between episodic allergic inflammation and fibrotic airway remodeling. Understanding these mechanisms may be crucial in determining which components of the allergic response should be addressed in the pharmacologic management of asthma.

The increase in maximal bronchocontriction associated with the presence of increased staining for contractile tissue suggests a possible causal relationship between increased contractile tissue mass and maximal bronchoconstriction. This finding is consistent with the hypothesis developed by those using mathematical modeling techniques, that increased contractile cell mass is the major determinant of airway narrowing in asthma (13, 23). We have not distinguished between myofibroblasts and smooth muscle within the {alpha}-SMA–stained contractile tissue, although increases in either of these cells may contribute to increased airway narrowing. Factors other than the amount of contractile tissue may also influence the degree of maximum airway narrowing. Differences in airway wall edema and fibrosis between mice exposed to either brief or chronic allergen challenge would be expected to influence the degree of airway narrowing (41, 45). The fact that there was a fairly constant increase in the maximal narrowing at all time points in both acute and chronically challenged mice suggests that differences between these influences are likely to be small.

In this study we systematically examined cross-sections of the first generation airway of the left lung of each mouse so as to ensure valid comparisons between each study group. The chronic structural changes observed in these airways were also present in smaller airways, suggesting that these changes occurred more peripherally in the bronchial tree.

Levels of BAL and tissue eosinophils and BAL IL-13 measured 24 h after the final allergen challenge in the chronic protocol were markedly reduced compared with the same measurements at this time point in the brief challenge protocol. This likely indicates that some degree of tolerance developed as a result of chronic OVA exposure.

In conclusion, we have demonstrated that both the airway physiology and markers of allergen-induced inflammation and remodeling differ depending on whether mice were subjected to brief or chronic allergen challenge. Sustained airway dysfunction was observed to be present at least 8 wk following the final exposure to allergen, using either brief or chronic challenge protocols. Sustained airway hyperreactivity was only observed in chronically challenged mice. The observations that this airway dysfunction and indices of airway remodeling persist beyond the resolution of acute immune-mediated inflammatory events support the concept that remodeling occurs as a consequence of repeated allergic airway inflammation, and that these structural changes contribute independently to the persistence of AHR.


   Acknowledgments
 
The authors wish to thank Dr Johan Kips for valuable ideas and comments. This work was supported by the Canadian Institutes for Health Research and the St. Joseph Healthcare Foundation. Richard Leigh is a Canadian Institutes for Health Research Fellow, Paul O'Byrne is a Canadian Institutes for Health Research Senior Scientist, and Mark Inman is the Harbinger Scholar in Respiratory Medicine.

Received in original form April 16, 2002

Received in final form May 24, 2002


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Busse, W. W., and R. F. Lemanske, Jr. 2001. Asthma. N. Engl. J. Med. 344:350–362.[Free Full Text]
  2. Cockcroft, D. W. Airway responsiveness. In: Asthma. P. J. Barnes, M. M. Grunstein, A. R. Leff, and A. J. Woolcock, editors. Philadelphia, Lippencourt-Raven Publishers; 1997, p. 1253–1266.
  3. Inman, M. D., A. L. Hamilton, H. A. Kerstjens, R. M. Watson, and P. M. O'Byrne. 1998. The utility of methacholine airway responsiveness measurements in evaluating anti-asthma drugs. J. Allergy Clin. Immunol. 101:342–348.[Medline]
  4. Wardlaw, A. J., S. Dunnette, G. J. Gleich, J. V. Collins, and A. B. Kay. 1988. Eosinophils and mast cells in bronchoalveolar lavage in subjects with mild asthma. Relationship to bronchial hyperreactivity. Am. Rev. Respir. Dis. 137:62–69.[Medline]
  5. Djukanovic, R., W. R. Roche, J. W. Wilson, C. R. Beasley, O. P. Twentyman, R. H. Howarth, and S. T. Holgate. 1990. Mucosal inflammation in asthma. Am. Rev. Respir. Dis. 142:434–457.[Medline]
  6. Bousquet, J., P. Chanez, and J. Y. Lacoste. 1990. Eosinophilic inflammation in asthma. N. Engl. J. Med. 323:1033–1039.[Abstract]
  7. Lotvall, J., M. Inman, and P. O'Byrne. 1998. Measurement of airway hyperresponsiveness: new considerations. Thorax 53:419–424.[Free Full Text]
  8. Brusasco, V., E. Crimi, P. Gianiorio, S. Lantero, and G. A. Rossi. 1990. Allergen-induced increase in airway responsiveness and inflammation in mild asthma. J. Appl. Physiol. 69:2209–2214.[Abstract/Free Full Text]
  9. Djukanovic, R., J. W. Wilson, K. M. Britten, S. J. Wilson, A. F. Walls, W. R. Roche, P. H. Howarth, and S. T. Holgate. 1992. Effect of an inhaled corticosteroid on airway inflammation and symptoms in asthma. Am. Rev. Respir. Dis. 145:669–674.[Medline]
  10. Jeffery, P. K., E. Godfrey, E. Adelroth, F. Nelson, A. Rogers, and S. A. Johansson. 1992. Effects of treatment on airway inflammation and thickening of basement membrane reticular collagen in asthma. Am. Rev. Respir. Dis. 145:890–899.[Medline]
  11. Sont, J. K., L. N. Willems, E. H. Bel, J. H. van Krieken, J. P. Vandenbroucke, and P. J. Sterk. 1999. Clinical control and histopathologic outcome of asthma when using airway hyperresponsiveness as an additional guide to long-term treatment. The AMPUL Study Group. Am. J. Respir. Crit. Care Med. 159:1043–1051.[Abstract/Free Full Text]
  12. Boulet, L. P., H. Turcotte, M. Laviolette, F. Naud, M. C. Bernier, S. Martel, and J. Chakir. 2000. Airway hyperresponsiveness, inflammation, and subepithelial collagen deposition in recently diagnosed versus long-standing mild asthma. Influence of inhaled corticosteroids. Am. J. Respir. Crit. Care Med. 162:1308–1313.[Abstract/Free Full Text]
  13. Wiggs, B. R., C. Bosken, P. D. Pare, A. James, and J. C. Hogg. 1992. A model of airway narrowing in asthma and in chronic obstructive pulmonary disease. Am. Rev. Respir. Dis. 145:1251–1258.[Medline]
  14. Boulet, L. P., J. Chakir, J. Dube, C. Laprise, M. Boutet, and M. Laviolette. 1998. Airway inflammation and structural changes in airway hyperresponsiveness and asthma: an overview. Can. Respir. J. 5:16–21.[Medline]
  15. Laprise, C., M. Laviolette, M. Boutet, and L. P. Boulet. 1999. Asymptomatic airway hyperresponsiveness: relationships with airway inflammation and remodelling. Eur. Respir. J. 14:63–73.[Abstract]
  16. Fish, J. E., and S. P. Peters. 1999. Airway remodeling and persistent airway obstruction in asthma. J. Allergy Clin. Immunol. 104:509–516.[Medline]
  17. Jeffery, P. K., A. J. Wardlaw, F. C. Nelson, J. V. Collins, and A. B. Kay. 1989. Bronchial biopsies in asthma. An ultrastructural, quantitative study and correlation with hyperreactivity. Am. Rev. Respir. Dis. 140:1745–1753.[Medline]
  18. Roche, W. R., R. Beasley, J. H. Williams, and S. T. Holgate. 1989. Subepithelial fibrosis in the bronchi of asthmatics. Lancet 1:520–524.[Medline]
  19. Carroll, N., J. Elliot, A. Morton, and A. James. 1993. The structure of large and small airways in nonfatal and fatal asthma. Am. Rev. Respir. Dis. 147:405–410.[Medline]
  20. Elias, J. A., Z. Zhu, G. Chupp, and R. J. Homer. 1999. Airway remodeling in asthma. J. Clin. Invest. 104:1001–1006.[Medline]
  21. Busse, W., J. Elias, D. Sheppard, and S. Banks-Schlegel. 1999. Airway remodeling and repair. Am. J. Respir. Crit. Care Med. 160:1035–1042.[Free Full Text]
  22. Vignola, A. M., J. Kips, and J. Bousquet. 2000. Tissue remodeling as a feature of persistent asthma. J. Allergy Clin. Immunol. 105:1041–1053.[Medline]
  23. Lambert, R. K., B. R. Wiggs, K. Kuwano, J. C. Hogg, and P. D. Pare. 1993. Functional significance of increased airway smooth muscle in asthma and COPD. J. Appl. Physiol. 74:2771–2781.[Abstract/Free Full Text]
  24. Kuwano, K., C. H. Bosken, P. D. Pare, T. R. Bai, B. R. Wiggs, and J. C. Hogg. 1993. Small airways dimensions in asthma and in chronic obstructive pulmonary disease. Am. Rev. Respir. Dis. 148:1220–1225.[Medline]
  25. Boulet, L. P., M. Laviolette, H. Turcotte, A. Cartier, M. Dugas, J. L. Malo, and M. Boutet. 1997. Bronchial subepithelial fibrosis correlates with airway responsiveness to methacholine. Chest 112:45–52.[Abstract/Free Full Text]
  26. Chetta, A., A. Foresi, M. Del Donno, G. Bertorelli, A. Pesci, and D. Olivieri. 1997. Airways remodeling is a distinctive feature of asthma and is related to severity of disease. Chest 111:852–857.[Abstract/Free Full Text]
  27. Renz, H., H. R. Smith, J. E. Henson, B. S. Ray, C. G. Irvin, and E. W. Gelfand. 1992. Aerosolized antigen exposure without adjuvant causes increased IgE production and increased airway responsiveness in the mouse. J. Allergy Clin. Immunol. 89:1127–1138.[Medline]
  28. Gavett, S. H., D. J. O'Hearn, X. Li, S. K. Huang, F. D. Finkelman, and M. Wills-Karp. 1995. Interleukin 12 inhibits antigen-induced airway hyperresponsiveness, inflammation, and Th2 cytokine expression in mice. J. Exp. Med. 182:1527–1536.[Abstract/Free Full Text]
  29. Corry, D. B., H. G. Folkesson, M. L. Warnock, D. J. Erle, M. A. Matthay, J. P. Wiener-Kronish, and R. M. Locksley. 1996. Interleukin 4, but not interleukin-5 or eosinophils, is required in a murine model of acute airway hyperreactivity. J. Exp. Med. 183:109–117.[Abstract/Free Full Text]
  30. Hogan, S. P., K. I. Matthaei, J. M. Young, A. Koskinen, I. G. Young, and P. S. Foster. 1998. A novel T cell-regulated mechanism modulating allergen-induced airways hyperreactivity in BALB/c mice independently of IL-4 and IL-5. J. Immunol. 161:1501–1509.[Abstract/Free Full Text]
  31. Inman, M. D., R. Ellis, J. Wattie, J. A. Denburg, and P. M. O'Byrne. 1999. Allergen-induced increase in airway responsiveness, airway eosinophilia, and bone-marrow eosinophil progenitors in mice. Am. J. Respir. Cell Mol. Biol. 21:473–479.[Abstract/Free Full Text]
  32. Webb, D. C., A. N. McKenzie, A. M. Koskinen, M. Yang, J. Mattes, and P. S. Foster. 2000. Integrated signals between IL-13, IL-4, and IL-5 regulate airways hyperreactivity. J. Immunol. 165:108–113.[Abstract/Free Full Text]
  33. Wang, J., K. Palmer, J. Lotvall, S. Milan, X. F. Lei, K. I. Matthaei, J. Gauldie, M. D. Inman, M. Jordana, and Z. Xing. 1998. Circulating, but not local lung, IL-5 is required for the development of antigen-induced airways eosinophilia. J. Clin. Invest. 102:1132–1141.[Medline]
  34. Foster, P. S., S. P. Hogan, A. J. Ramsay, K. I. Matthaei, and I. G. Young. 1996. Interleukin 5 deficiency abolishes eosinophilia, airways hyperreactivity, and lung damage in a mouse asthma model. J. Exp. Med. 183:195–201.[Abstract/Free Full Text]
  35. Wills-Karp, M., J. Luyimbazi, X. Xu, B. Schofield, T. Y. Neben, C. L. Karp, and D. D. Donaldson. 1998. Interleukin-13: central mediator of allergic asthma. Science 282:2258–2261.[Abstract/Free Full Text]
  36. Grunig, G., M. Warnock, A. E. Wakil, R. Venkayya, F. Brombacher, D. M. Rennick, D. Sheppard, M. Mohrs, D. D. Donaldson, R. M. Locksley, and D. B. Corry. 1998. Requirement for IL-13 independently of IL-4 in experimental asthma. Science 282:2261–2263.[Abstract/Free Full Text]
  37. Guide for the Care and Use of Laboratory Animals. Washington, DC.: U.S. Government Printing Office: Revised 1985. NIH Publication No. 86–23.
  38. Volgyesi, G. A., L. N. Tremblay, P. Webster, N. Zamel, and A. S. Slutsky. 2000. A new ventilator for monitoring lung mechanics in small animals. J. Appl. Physiol. 89:413–421.[Abstract/Free Full Text]
  39. Temelkovski, J., S. P. Hogan, D. P. Shepherd, P. S. Foster, and R. K. Kumar. 1998. An improved murine model of asthma: selective airway inflammation, epithelial lesions and increased methacholine responsiveness following chronic exposure to aerosolised allergen. Thorax 53:849–856.[Abstract/Free Full Text]
  40. Trifilieff, A., A. El Hashim, and C. Bertrand. 2000. Time course of inflammatory and remodeling events in a murine model of asthma: effect of steroid treatment. Am. J. Physiol. Lung Cell. Mol. Physiol. 279:L1120–L1128.[Abstract/Free Full Text]
  41. Palmans, E., J. C. Kips, and R. A. Pauwels. 2000. Prolonged allergen exposure induces structural airway changes in sensitized rats. Am. J. Respir. Crit. Care Med. 161:627–635.[Abstract/Free Full Text]
  42. Leckie, M. J., A. ten Brinke, J. Khan, Z. Diamant, B. J. O'Connor, C. M. Walls, A. K. Mathur, H. C. Cowley, K. F. Chung, R. Djukanovic, T. T. Hansel, S. T. Holgate, P. J. Sterk, and P. J. Barnes. 2000. Effects of an interleukin-5 blocking monoclonal antibody on eosinophils, airway hyper-responsiveness, and the late asthmatic response. Lancet 356:2144–2148.[Medline]
  43. Shapiro, S. D., and R. M. Senior. 1999. Matrix metalloproteinases. Matrix degradation and more. Am. J. Respir. Cell Mol. Biol. 20:1100–1102.[Free Full Text]
  44. Ohno, I., H. Ohtani, Y. Nitta, J. Suzuki, H. Hoshi, M. Honma, S. Isoyama, Y. Tanno, G. Tamura, K. Yamauchi, H. Nagura, and K. Shirato. 1997. Eosinophils as a source of matrix metalloproteinase-9 in asthmatic airway inflammation. Am. J. Respir. Cell Mol. Biol. 16:212–219.[Abstract]
  45. Brown, R. H., E. A. Zerhouni, and W. Mitzner. 1995. Airway edema potentiates airway reactivity. J. Appl. Physiol. 79:1242–1248.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 Am. J. Respir. Crit. Care Med.Home page
D. C. M. Simoes, G. Xanthou, K. Petrochilou, V. Panoutsakopoulou, C. Roussos, and C. Gratziou
Osteopontin Deficiency Protects against Airway Remodeling and Hyperresponsiveness in Chronic Asthma
Am. J. Respir. Crit. Care Med., May 15, 2009; 179(10): 894 - 902.
[Abstract] [Full Text] [PDF]

Home page
 DMMHome page
F. A. DiGiovanni, R. Ellis, J. Wattie, J. A. Hirota, D. S. Southam, and M. D. Inman
Concurrent dual allergen exposure and its effects on airway hyperresponsiveness, inflammation and remodeling in mice
Dis. Model. Mech., May 1, 2009; 2(5-6): 275 - 282.
[Abstract] [Full Text] [PDF]

Home page
 J. Immunol.Home page
M. Maret, C. Ruffie, S. Letuve, A. Phelep, O. Thibaudeau, J. Marchal, M. Pretolani, and A. Druilhe
A Role for Bid in Eosinophil Apoptosis and in Allergic Airway Reaction
J. Immunol., May 1, 2009; 182(9): 5740 - 5747.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
J. K. Bentley, H. Deng, M. J. Linn, J. Lei, G. A. Dokshin, D. C. Fingar, K. N. Bitar, W. R. Henderson Jr., and M. B. Hershenson
Airway smooth muscle hyperplasia and hypertrophy correlate with glycogen synthase kinase-3{beta} phosphorylation in a mouse model of asthma
Am J Physiol Lung Cell Mol Physiol, February 1, 2009; 296(2): L176 - L184.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
T. A. Doherty, P. Soroosh, D. H. Broide, and M. Croft
CD4+ cells are required for chronic eosinophilic lung inflammation but not airway remodeling
Am J Physiol Lung Cell Mol Physiol, February 1, 2009; 296(2): L229 - L235.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Cell Mol. Bio.Home page
M. Hewitt, A. Creel, K. Estell, I. C. Davis, and L. M. Schwiebert
Acute Exercise Decreases Airway Inflammation, but Not Responsiveness, in an Allergic Asthma Model
Am. J. Respir. Cell Mol. Biol., January 1, 2009; 40(1): 83 - 89.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
D. S. Southam, R. Ellis, J. Wattie, W. Glass, and M. D. Inman
Goblet Cell Rebound and Airway Dysfunction with Corticosteroid Withdrawal in a Mouse Model of Asthma
Am. J. Respir. Crit. Care Med., December 1, 2008; 178(11): 1115 - 1122.
[Abstract] [Full Text] [PDF]

Home page
 DMMHome page
A. T. Nials and S. Uddin
Mouse models of allergic asthma: acute and chronic allergen challenge
Dis. Model. Mech., November 1, 2008; 1(4-5): 213 - 220.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
J. R. Johnson, S. R. Pacitto, J. Wong, E. W. Archer, S. Eirefelt, A. Miller-Larsson, and M. Jordana
Combined budesonide/formoterol therapy in conjunction with allergen avoidance ameliorates house dust mite-induced airway remodeling and dysfunction
Am J Physiol Lung Cell Mol Physiol, November 1, 2008; 295(5): L780 - L788.
[Abstract] [Full Text] [PDF]

Home page
 Eur Respir JHome page
D. S. Southam, R. Ellis, J. Wattie, S. Young, and M. D. Inman
Budesonide prevents but does not reverse sustained airway hyperresponsiveness in mice
Eur. Respir. J., October 1, 2008; 32(4): 970 - 978.
[Abstract] [Full Text] [PDF]

Home page
 Eur Respir JHome page
H. Meurs, R. Gosens, and J. Zaagsma
Airway hyperresponsiveness in asthma: lessons from in vitro model systems and animal models
Eur. Respir. J., August 1, 2008; 32(2): 487 - 502.
[Abstract] [Full Text] [PDF]

Home page
 Toxicol SciHome page
J. Pauluhn
Brown Norway Rat Asthma Model of Diphenylmethane-4,4'-Diisocyanate (MDI): Analysis of the Elicitation Dose-Response Relationship
Toxicol. Sci., August 1, 2008; 104(2): 320 - 331.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
A. Cojocaru, C. G. Irvin, H. C. Haverkamp, and J. H. T. Bates
Computational assessment of airway wall stiffness in vivo in allergically inflamed mouse models of asthma
J Appl Physiol, June 1, 2008; 104(6): 1601 - 1610.
[Abstract] [Full Text] [PDF]

Home page
 J. Biol. Chem.Home page
H. Deng, G. A. Dokshin, J. Lei, A. M. Goldsmith, K. N. Bitar, D. C. Fingar, M. B. Hershenson, and J. K. Bentley
Inhibition of Glycogen Synthase Kinase-3{beta} Is Sufficient for Airway Smooth Muscle Hypertrophy
J. Biol. Chem., April 11, 2008; 283(15): 10198 - 10207.
[Abstract] [Full Text] [PDF]

Home page
 Eur Respir JHome page
A. D. Chew, J. A. Hirota, R. Ellis, J. Wattie, M. D. Inman, and L. J. Janssen
Effects of allergen on airway narrowing dynamics as assessed by lung-slice technique
Eur. Respir. J., March 1, 2008; 31(3): 532 - 538.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
A. G. P. Guedes, J. A. Jude, J. Paulin, H. Kita, F. E. Lund, and M. S. Kannan
Role of CD38 in TNF-{alpha}-induced airway hyperresponsiveness
Am J Physiol Lung Cell Mol Physiol, February 1, 2008; 294(2): L290 - L299.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Cell Mol. Bio.Home page
H. Sugiura, X. Liu, F. Duan, S. Kawasaki, S. Togo, K. Kamio, X. Q. Wang, L. Mao, Y. Ahn, R. F. Ertl, et al.
Cultured Lung Fibroblasts from Ovalbumin-Challenged "Asthmatic" Mice Differ Functionally from Normal
Am. J. Respir. Cell Mol. Biol., October 1, 2007; 37(4): 424 - 430.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
J. R. Johnson, F. K. Swirski, B. U. Gajewska, R. E. Wiley, R. Fattouh, S. R. Pacitto, J. K. Wong, M. R. Stampfli, and M. Jordana
Divergent immune responses to house dust mite lead to distinct structural-functional phenotypes
Am J Physiol Lung Cell Mol Physiol, September 1, 2007; 293(3): L730 - L739.
[Abstract] [Full Text] [PDF]

Home page
 Eur Respir JHome page
C. M. Lloyd and D. S. Robinson
Allergen-induced airway remodelling
Eur. Respir. J., May 1, 2007; 29(5): 1020 - 1032.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Cell Mol. Bio.Home page
N. R. Locke, S. G. Royce, J. S. Wainewright, C. S. Samuel, and M. L. Tang
Comparison of Airway Remodeling in Acute, Subacute, and Chronic Models of Allergic Airways Disease
Am. J. Respir. Cell Mol. Biol., May 1, 2007; 36(5): 625 - 632.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
H. H. Kariyawasam, M. Aizen, J. Barkans, D. S. Robinson, and A. B. Kay
Remodeling and Airway Hyperresponsiveness but Not Cellular Inflammation Persist after Allergen Challenge in Asthma
Am. J. Respir. Crit. Care Med., May 1, 2007; 175(9): 896 - 904.
[Abstract] [Full Text] [PDF]

Home page
 JEMHome page
W. R. Henderson Jr., E. Y. Chi, J. G. Bollinger, Y.-t. Tien, X. Ye, L. Castelli, Y. P. Rubtsov, A. G. Singer, G. K.S. Chiang, T. Nevalainen, et al.
Importance of group X-secreted phospholipase A2 in allergen-induced airway inflammation and remodeling in a mouse asthma model
J. Exp. Med., April 16, 2007; 204(4): 865 - 877.
[Abstract] [Full Text] [PDF]

Home page
 Eur Respir JHome page
E. D. Fixman, A. Stewart, and J. G. Martin
Basic mechanisms of development of airway structural changes in asthma
Eur. Respir. J., February 1, 2007; 29(2): 379 - 389.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
A. G. P. Guedes, J. Paulin, L. Rivero-Nava, H. Kita, F. E. Lund, and M. S. Kannan
CD38-deficient mice have reduced airway hyperresponsiveness following IL-13 challenge
Am J Physiol Lung Cell Mol Physiol, December 1, 2006; 291(6): L1286 - L1293.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
T. Kiwamoto, Y. Ishii, Y. Morishima, K. Yoh, A. Maeda, K. Ishizaki, T. Iizuka, A. E. Hegab, Y. Matsuno, S. Homma, et al.
Transcription Factors T-bet and GATA-3 Regulate Development of Airway Remodeling
Am. J. Respir. Crit. Care Med., July 15, 2006; 174(2): 142 - 151.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
W. R. Henderson Jr., G. K. S. Chiang, Y.-t. Tien, and E. Y. Chi
Reversal of Allergen-induced Airway Remodeling by CysLT1 Receptor Blockade
Am. J. Respir. Crit. Care Med., April 1, 2006; 173(7): 718 - 728.
[Abstract] [Full Text] [PDF]

Home page
 Physiol. Rev.Home page
M. C. Rose and J. A. Voynow
Respiratory Tract Mucin Genes and Mucin Glycoproteins in Health and Disease
Physiol Rev, January 1, 2006; 86(1): 245 - 278.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
T. Koya, T. Kodama, K. Takeda, N. Miyahara, E.-S. Yang, C. Taube, A. Joetham, J.-W. Park, A. Dakhama, and E. W. Gelfand
Importance of Myeloid Dendritic Cells in Persistent Airway Disease after Repeated Allergen Exposure
Am. J. Respir. Crit. Care Med., January 1, 2006; 173(1): 42 - 55.
[Abstract] [Full Text] [PDF]

Home page
 PhysiologyHome page
R. J. Homer and J. A. Elias
Airway Remodeling in Asthma: Therapeutic Implications of Mechanisms
Physiology, February 1, 2005; 20(1): 28 - 35.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Cell Mol. Bio.Home page
M. M. Kelly, R. Leigh, P. Bonniaud, R. Ellis, J. Wattie, M. J. Smith, G. Martin, M. Panju, M. D. Inman, and J. Gauldie
Epithelial Expression of Profibrotic Mediators in a Model of Allergen-Induced Airway Remodeling
Am. J. Respir. Cell Mol. Biol., February 1, 2005; 32(2): 99 - 107.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
M. Lommatzsch, K. Schloetcke, J. Klotz, K. Schuhbaeck, D. Zingler, C. Zingler, O. Schulte-Herbruggen, H. Gill, P. Schuff-Werner, and J. C. Virchow
Brain-derived Neurotrophic Factor in Platelets and Airflow Limitation in Asthma
Am. J. Respir. Crit. Care Med., January 15, 2005; 171(2): 115 - 120.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
R. Leigh, D. S. Southam, R. Ellis, J. N. Wattie, R. Sehmi, Y. Wan, and M. D. Inman
T-cell-mediated inflammation does not contribute to the maintenance of airway dysfunction in mice
J Appl Physiol, December 1, 2004; 97(6): 2258 - 2265.
[Abstract] [Full Text] [PDF]

Home page
 J. Immunol.Home page
E. C. Cates, R. Fattouh, J. Wattie, M. D. Inman, S. Goncharova, A. J. Coyle, J.-C. Gutierrez-Ramos, and M. Jordana
Intranasal Exposure of Mice to House Dust Mite Elicits Allergic Airway Inflammation via a GM-CSF-Mediated Mechanism
J. Immunol., November 15, 2004; 173(10): 6384 - 6392.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
R. Leigh, R. Ellis, J. Wattie, D. D. Donaldson, and M. D. Inman
Is Interleukin-13 Critical in Maintaining Airway Hyperresposiveness in Allergen-challenged Mice?
Am. J. Respir. Crit. Care Med., October 15, 2004; 170(8): 851 - 856.
[Abstract] [Full Text] [PDF]

Home page
 Eur Respir JHome page
P.E. Christie, M. Jonas, C-H. Tsai, E.Y. Chi, and W.R. Henderson Jr
Increase in laminin expression in allergic airway remodelling and decrease by dexamethasone
Eur. Respir. J., July 1, 2004; 24(1): 107 - 115.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
S. Wagers, L. K. A. Lundblad, M. Ekman, C. G. Irvin, and J. H. T. Bates
The allergic mouse model of asthma: normal smooth muscle in an abnormal lung?
J Appl Physiol, June 1, 2004; 96(6): 2019 - 2027.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
R. Leigh, R. Ellis, J. N. Wattie, J. A. Hirota, K. I. Matthaei, P. S. Foster, P. M. O'Byrne, and M. D. Inman
Type 2 Cytokines in the Pathogenesis of Sustained Airway Dysfunction and Airway Remodeling in Mice
Am. J. Respir. Crit. Care Med., April 1, 2004; 169(7): 860 - 867.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
J. R. Johnson, R. E. Wiley, R. Fattouh, F. K. Swirski, B. U. Gajewska, A. J. Coyle, J.-C. Gutierrez-Ramos, R. Ellis, M. D. Inman, and M. Jordana
Continuous Exposure to House Dust Mite Elicits Chronic Airway Inflammation and Structural Remodeling
Am. J. Respir. Crit. Care Med., February 1, 2004; 169(3): 378 - 385.
[Abstract] [Full Text] [PDF]

Home page
 BloodHome page
S. C. Pitchford, Y. Riffo-Vasquez, A. Sousa, S. Momi, P. Gresele, D. Spina, and C. P. Page
Platelets are necessary for airway wall remodeling in a murine model of chronic allergic inflammation
Blood, January 15, 2004; 103(2): 639 - 647.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
R. Leigh, D. Vethanayagam, M. Yoshida, R. M. Watson, T. Rerecich, M. D. Inman, and P. M. O'Byrne
Effects of Montelukast and Budesonide on Airway Responses and Airway Inflammation in Asthma
Am. J. Respir. Crit. Care Med., November 1, 2002; 166(9): 1212 - 1217.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Leigh, R.
Right arrow Articles by Inman, M. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Leigh, R.
Right arrow Articles by Inman, M. D.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Proc. Am. Thorac. Soc. Am. J. Respir. Crit. Care Med.
Copyright © 2002 American Thoracic Society.