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Lungs are exposed to the outside environment and therefore to toxic and infectious agents or allergens. This may lead to permanent activation of innate immune response elements. A Disintegrin And Metalloproteinases (ADAMs) and ADAMs with Thrombospondin motifs (ADAMTS) are proteinases closely related to Matrix Metalloproteinases (MMPs). These multifaceted molecules bear metalloproteinase and disintegrin domains endowing them with features of both proteinases and adhesion molecules. Proteinases of the ADAM family are associated to various physiological and pathological processes and display a wide spectrum of biological effects encompassing cell fusion, cell adhesion, "shedding process", cleavage of various substrates from the extracellular matrix, growth factors or cytokines... This review will focus on the putative roles of ADAM/ADAMTS proteinases in airway diseases such as asthma and COPD. [ABSTRACT FROM AUTHOR]

IL-13 is a prototypic T helper type 2 cytokine and a central mediator of the complex cascade of events leading to asthmatic phenotype. Indeed, IL-13 plays key roles in IgE synthesis, bronchial hyperresponsiveness, mucus hypersecretion, subepithelial fibrosis, and eosinophil infiltration. We assessed the potential efficacy of inhaled anti-IL-13 monoclonal antibody Fab' fragment on allergen-induced airway inflammation, hyperresponsiveness, and remodeling in an experimental model of allergic asthma. Anti-IL-13 Fab' was administered to mice as a liquid aerosol generated by inExpose inhalation system in a tower allowing a nose-only exposure. BALB/c mice were treated by PBS, anti-IL-13 Fab', or A33 Fab' fragment and subjected to ovalbumin exposure for 1 and 5 weeks (short-term and long-term protocols). Our data demonstrate a significant antiasthma effect after nebulization of anti-IL-13 Fab' in a model of asthma driven by allergen exposure as compared with saline and nonimmune Fab fragments. In short- and long-term protocols, administration of the anti-IL-13 Fab' by inhalation significantly decreased bronchial responsiveness to methacholine, bronchoalveolar lavage fluid eosinophilia, inflammatory cell infiltration in lung tissue, and many features of airway remodeling. Levels of proinflammatory mediators and matrix metalloprotease were significantly lower in lung parenchyma of mice treated with anti-IL-13 Fab'. These data demonstrate that an inhaled anti-IL-13 Fab' significantly reduces airway inflammation, hyperresponsiveness, and remodeling. Specific neutralization of IL-13 in the lungs using an inhaled anti-IL-13 Fab' could represent a novel and effective therapy for the treatment of asthma.

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) constitute a family of endopeptidases related to matrix metalloproteinases. These proteinases have been largely implicated in tissue remodeling associated with pathological processes. Among them, ADAMTS12 was identified as an asthma-associated gene in a human genome screening program. However, its functional implication in asthma is not yet documented. The present study aims at investigating potential ADAMTS-12 functions in experimental models of allergic airways disease. Two different in vivo protocols of allergen-induced airways disease were applied to the recently generated Adamts12-deficient mice and corresponding wild-type mice. In this study, we provide evidence for a protective effect of ADAMTS-12 against bronchial inflammation and hyperresponsiveness. In the absence of Adamts12, challenge with different allergens (OVA and house dust mite) led to exacerbated eosinophilic inflammation in the bronchoalveolar lavage fluid and in lung tissue, along with airway dysfunction assessed by increased airway responsiveness following methacholine exposure. Furthermore, mast cell counts and ST2 receptor and IL-33 levels were higher in the lungs of allergen-challenged Adamts12-deficient mice. The present study provides, to our knowledge, the first experimental evidence for a contribution of ADAMTS-12 as a key mediator in airways disease, interfering with immunological processes leading to inflammation and airway hyperresponsiveness.

Asthma is a complex disease linked to various pathophysiological events including the activity of proteinases. The multifunctional A disintegrin and metalloproteinases (ADAMs) displaying the ability to cleave membrane-bound mediators or cytokines appear to be key mediators in various inflammatory processes. In the present study, we investigated ADAM-8 expression and production in a mouse model of allergen-induced airway inflammation. In allergen-exposed animals, increased expression of ADAM-8 was found in the lung parenchyma and in DC purified from the lungs. The potential role of ADAM-8 in the development of allergen-induced airway inflammation was further investigated by the use of an anti-ADAM-8 antibody and ADAM-8 knockout animals. We observed a decrease in allergen-induced acute inflammation both in BALF and the peribronchial area in anti-ADAM-8 antibody-treated mice and in ADAM-8-deficient mice (ADAM-8(-/-) ) after allergen exposure. ADAM-8 depletion led to a significant decrease of the CD11c(+) lung DC. We also report lower levels of CCL11 and CCL22 production in antibody-treated mice and ADAM-8- deficient mice that might be explained by decreased eosinophilic inflammation and lower numbers of DC, respectively. In conclusion, ADAM-8 appears to favour allergen-induced acute airway inflammation by promoting DC recruitment and CCL11 and CCL22 production., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Matrix metalloproteinases (MMPs) recently appeared as key regulators of inflammation, allowing the recruitment and clearance of inflammatory cells and modifying the biological activity of many peptide mediators by cleavage. MMP-19 is newly described, and it preferentially cleaves matrix proteins such as collagens and tenascin-C. The role of MMP-19 in asthma has not been described to date. The present study sought to assess the expression of MMP-19 in a murine asthma model, and to address the biological effects of MMP-19 deficiency in mice. Allergen-exposed, wild-type mice displayed increased expression of MMP-19 mRNA and an increased number of MMP-19-positive cells in the lungs, as detected by immunohistochemistry. After an allergen challenge of MMP-19 knockout (MMP-19(-/-)) mice, exacerbated eosinophilic inflammation was detected in bronchoalveolar lavage fluid and bronchial tissue, along with increased airway responsiveness to methacholine. A shift toward increased T helper-2 lymphocyte (Th2)-driven inflammation in MMP-19(-/-) mice was demonstrated by (1) increased numbers of cells expressing the IL-33 receptor T(1)/ST(2) in lung parenchyma, (2) increased IgG(1) levels in serum, and (3) higher levels of IL-13 and eotaxin-1 in lung extracts. Tenascin-C was found to accumulate in peribronchial areas of MMP-19(-/-) after allergen challenges, as assessed by Western blot and immunohistochemistry analyses. We conclude that MMP-19 is a new mediator in asthma, preventing tenascin-C accumulation and directly or indirectly controlling Th2-driven airway eosinophilia and airway hyperreactivity. Our data suggest that MMP-19 may act on Th2 inflammation homeostasis by preventing the accumulation of tenascin protein.

Air pollutant exposure has been linked to a rise in wheezing illnesses. Clinical data highlight that exposure to mainstream tobacco smoke (MS) and environmental tobacco smoke (ETS) as well as exposure to diesel exhaust particles (DEP) could promote allergic sensitization or aggravate symptoms of asthma, suggesting a role for these inhaled pollutants in the pathogenesis of asthma. Mouse models are a valuable tool to study the potential effects of these pollutants in the pathogenesis of asthma, with the opportunity to investigate their impact during processes leading to sensitization, acute inflammation and chronic disease. Mice allow us to perform mechanistic studies and to evaluate the importance of specific cell types in asthma pathogenesis. In this review, the major clinical effects of tobacco smoke and diesel exhaust exposure regarding to asthma development and progression are described. Clinical data are compared with findings from murine models of asthma and inhalable pollutant exposure. Moreover, the potential mechanisms by which both pollutants could aggravate asthma are discussed.

Objective: Animal models of asthma mimic major features of human disease. Since the genetic background of experimental animals might affect hyperresponsiveness and inflammation, we studied its potential influence and the mechanisms leading to differences in strains., Methods: We applied a mouse model of allergic asthma to BALB/c and C57BL/6 mice., Results: BALB/c mice displayed greater levels of airway reactivity to methacholine than C57BL/6 mice. Moreover, BALB/c mice exhibited higher numbers of mast cells in lung tissue when compared to C57BL/6. On the contrary, eosinophil and neutrophil counts in bronchoalveolar lavage fluid (BALF) as well as peribronchial eosinophilia were greater in C57BL/6. IL (Interleukin)-4, IL-5, IL-13, and CCL11 levels measured in whole-lung extracts were higher in BALB/c, while, in sharp contrast, CCL11 and CCL5 levels were higher in BALF of C57BL/6 mice., Conclusions: We observed phenotypic differences between C57BL/6 and BALB/c mice in an asthma model with different distributions of pro-inflammatory cytokines and inflammatory cells.

Background: The interactions between airway responsiveness, structural remodelling and inflammation in allergic asthma remain poorly understood. Prolonged challenge with inhaled allergen is necessary to replicate many of the features of airway wall remodelling in mice. In both mice and humans, genetic differences can have a profound influence on allergy, inflammation, airway responsiveness and structural changes., Methods: The aim of this study was to provide a comparative analysis of allergen-induced airway changes in sensitized BALB/c and C57BL/6 mice that were exposed to inhaled allergen for 2 ('acute'), 6 or 9 weeks ('chronic'). Inflammation, remodelling and responsiveness were analyzed., Results: Both strains developed a Th-2-driven airway inflammation with allergen-specific IgE, airway eosinophilia and goblet cell hyperplasia upon 2 weeks of allergen inhalation. This was accompanied by a significant increase in airway smooth muscle mass and hyperresponsiveness in BALB/c but not in C57BL/6 mice. However, airway eosinophilia was more pronounced in the C57BL/6 strain. Chronic allergen exposure (6 or 9 weeks) resulted in an increase in airway smooth muscle mass as well as subepithelial collagen and fibronectin deposition in both strains. The emergence of these structural changes paralleled the disappearance of inflammation in both C57BL/6 and BALB/c mice and loss of hyperresponsiveness in the BALB/c strain. TGF-beta(1 )was accordingly elevated in both strains., Conclusion: Airway inflammation, remodelling and hyperresponsiveness are closely intertwined processes. Genetic background influences several aspects of the acute allergic phenotype. Chronic allergen exposure induces a marked airway remodelling that parallels a decreased inflammation, which was largely comparable between the two strains.

Objectives: The ADAMs (a disintegrin and metalloproteinase) enzymes compose a family of membrane-bound proteins characterized by their multi-domain structure and ADAM-12 expression is elevated in human non-small cell lung cancers. The aim of this study was to investigate the roles played by ADAM-12 in critical steps of bronchial cell transformation during carcinogenesis., Materials and Methods: To assess the role of ADAM-12 in tumorigenicity, BEAS-2B cells were transfected with a plasmid encoding human full-length ADAM-12 cDNA, and then the effects of ADAM-12 overexpression on cell behaviour were explored. Treatment of clones with heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) neutralizing antibodies as well as an EGFR inhibitor allowed the dissection of mechanisms regulating cell proliferation and apoptosis., Results: Overexpression of ADAM-12 in BEAS-2B cells promoted cell proliferation. ADAM-12 overexpressing clones produced higher quantities of HB-EGF in their culture medium which may rely on membrane-bound HB-EGF shedding by ADAM-12. Targeting HB-EGF activity with a neutralizing antibody abrogated enhanced cell proliferation in the ADAM-12 overexpressing clones. In sharp contrast, targeting of amphiregulin, EGF or transforming growth factor-alpha failed to influence cell proliferation; moreover, ADAM-12 transfectants were resistant to etoposide-induced apoptosis and the use of a neutralizing antibody against HB-EGF activity restored rates of apoptosis to be similar to controls., Conclusions: ADAM-12 contributes to enhancing HB-EGF shedding from plasma membranes leading to increased cell proliferation and reduced apoptosis in this bronchial epithelial cell line.

ADAMTS-1 (a disintegrin and metalloproteinase with thrombospondin motifs), the first described member of the ADAMTS family, is differentially expressed in various tumors. However, its exact role in tumor development and progression is still unclear. The aim of this study was to investigate the effects of ADAMTS-1 transfection in a bronchial epithelial tumor cell line (BZR) and its potential to modulate tumor development. ADAMTS-1 overexpression did not affect in vitro cell properties such as (a) proliferation in two-dimensional culture, (b) proliferation in three-dimensional culture, (c) anchorage-independent growth in soft agar, (d) cell migration and invasion in modified Boyden chamber assay, (e) angiogenesis in the aortic ring assay, and (f) cell apoptosis. In contrast, ADAMTS-1 stable transfection in BZR cells accelerated the in vivo tumor growth after s.c. injection into severe combined immunodeficient mice. It also promoted a stromal reaction characterized by myofibroblast infiltration and excessive matrix deposition. These features are, however, not observed in tumors derived from cells overexpressing a catalytically inactive mutant of ADAMTS-1. Conditioned media from ADAMTS-1-overexpressing cells display a potent chemotactic activity toward fibroblasts. ADAMTS-1 overexpression in tumors was associated with increased production of matrix metalloproteinase-13, fibronectin, transforming growth factor beta (TGF-beta), and interleukin-1beta (IL-1beta). Neutralizing antibodies against TGF-beta and IL-1beta blocked the chemotactic effect of medium conditioned by ADAMTS-1-expressing cells on fibroblasts, showing the contribution of these factors in ADAMTS-1-induced stromal reaction. In conclusion, we propose a new paradigm for catalytically active ADAMTS-1 contribution to tumor development, which consists of the recruitment of fibroblasts involved in tumor growth and tumor-associated stroma remodeling.

Background: In this study, we assess the effectiveness of inhaled doxycycline, a tetracycline antibiotic displaying matrix metalloproteinases (MMP) inhibitory effects to prevent allergen-induced inflammation, hyperresponsiveness and remodeling. MMPs play key roles in the complex cascade of events leading to asthmatic phenotype., Methods: Doxycycline was administered by aerosols by the mean of a novel formulation as a complex with hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) used as an excipient. BALB/c mice (n=16-24 in each group) were sensitized and exposed to aerosolized ovalbumin (OVA) from day 21 to 27 (short-term exposure protocol) or 5 days/odd weeks from day 22 to 96 (long-term exposure protocol)., Results: In the short-term exposure model, inhaled doxycycline decreased allergen-induced eosinophilic inflammation in bronchoalveolar lavage (BAL) and in peribronchial areas, as well as airway hyperresponsiveness. In lung tissue, exposure to doxycycline via inhaled route induced a fourfold increase in IL-10 levels, a twofold decrease in IL-5, IL-13 levels and diminished MMP-related proteolysis and the proportion of activated MMP-9 as compared to placebo. In the long-term exposure model, inhaled doxycycline significantly decreased the extent of glandular hyperplasia, airway wall thickening, smooth muscle hyperplasia and subepithelial collagen deposition which are well recognized features of airway remodeling., Conclusion: Doxycycline administered by aerosols decreases the allergen-induced airway inflammation and hyperresponsiveness and inhibits the development of bronchial remodeling in a mouse model of asthma by modulation of cytokines production and MMP activity.

ADAMs (a disintegrin and metalloprotease) constitute a family of cell surface proteins containing disintegrin and metalloprotease domains which associate features of adhesion molecules and proteases. ADAMTSs (a disintegrin and metalloprotease with thrombospondin motifs) bear thrombospondin type I motifs in C-terminal extremity, and most of them are secreted proteins. Because genetic studies have shown that ADAM-33 gene polymorphisms are associated with asthma, we designed this study to assess mRNA expression profile of several ADAM and ADAMTS proteases in sputum from patients with asthma and to investigate the relationship between expression of these proteases and asthma-associated inflammation and airway obstruction. mRNA expression profile of selected ADAM and ADAMTS proteinases (ADAM-8, -9, -10, -12, -15, -17, and -33; ADAMTS-1, -2, -15, -16, -17, -18, and -19), their physiological inhibitors TIMP-1 and TIMP-3, and RECK, a membrane-anchored MMP activity regulator, was obtained by RT-PCR analysis performed on cells collected by sputum induction from 21 patients with mild to moderate asthma and 17 healthy individuals. mRNA levels of ADAM-8, ADAM-9, ADAM-12, TIMP-1, and TIMP-3 were significantly increased, whereas mRNA levels coding for ADAMTS-1, ADAMTS-15, and RECK were significantly decreased in patients with asthma compared with control patients. ADAM-8 expression was negatively correlated with the forced expiratory volume at the first second (FEV(1)) (r = -0.57, P < 0.01), whereas ADAMTS-1 and RECK expressions were positively correlated to FEV(1) (r = 0.45, P < 0.05, and r = 0.55, P = 0.01, respectively). We conclude that expression of ADAMs and ADAMTSs and their inhibitors is modulated in airways from patients with asthma and that these molecules may play a role in the pathogenesis of asthma.

In healthy lung, Matrix Metalloproteinases (MMPs) and their physiological inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs), are produced in the respiratory tract by a panel of different structural cells. These activities are mandatory for many physiological processes including development, wound healing and cell trafficking. Deregulation of proteolytic-antiproteolytic network and inappropriate secretion of various MMPs by stimulated structural or inflammatory cells is thought to take part to pathophysiology of numerous lung diseases including asthma, chronic obstructive pulmonary disease (COPD), lung fibrosis and lung cancer. Cytokines and growth factors are involved in these inflammatory processes and some of those mediators interact directly with MMPs and TIMPs leading either to a regulation of their expression or changes in their biological activities by proteolytic cleavage. In turn, cytokines and growth factors modulate secretion of MMPs establishing a complex network of reciprocal interactions. Every MMP seem to play a rather specific role and some variations of their expression are observed in different lung diseases. The precise role of these enzymes and their inhibitors is now studied in depth as they could represent relevant therapeutic targets for many diseases. Indeed, MMP inhibition can lead either to a decrease of the intensity of a pathological process or, in the contrary for some of them, to an increase of disease severity. In this review, we focus on the role played by MMPs and TIMPs in asthma and we provide an overview of their potential roles in COPD, lung fibrosis and lung cancer, with a special emphasis on loops including MMPs and cytokines and growth factors relevant in these diseases.

Matrix metalloproteinases (MMPs) are involved in inflammatory reaction, including asthma-related airway inflammation. MMP-8, mainly produced by neutrophils, has recently been reported to be increased in the bronchoalveolar lavage fluid (BALF) from asthmatic patients. To evaluate the role of MMP-8 in asthma, we measured MMP-8 expression in lung tissue in an OVA-sensitized mouse model of asthma and addressed the effect of MMP-8 deletion on allergen-induced bronchial inflammation. MMP-8 production was increased in lungs from C57BL/6 mice exposed to allergens. After allergen exposure, MMP-8(-/-) mice developed an airway inflammation characterized by an increased neutrophilic inflammation in BALF and an increased neutrophilic and eosinophilic infiltration in the airway walls. MMP-8 deficiency was associated with increased levels of IL-4 and anti-OVA IgE and IgG1 in BALF and serum, respectively. Although allergen exposure induced an enhancement of LPS-induced CXC chemokine, KC, and MIP-2 levels in BALF and lung parenchyma, no difference was observed between the two genotypes. Inflammatory cell apoptosis was reduced in the lungs from MMP-8(-/-) mice. For the first time, our study evidences an important role of MMP-8 in the control of neutrophilic and eosinophilic infiltration during allergen-induced lung inflammation, and demonstrates that the anti-inflammatory effect of MMP-8 is partly due to a regulation of inflammatory cell apoptosis.

Asthma is a chronic inflammatory disease characterized by profound extracellular matrix changes referred to as bronchial remodelling. In this study, we evaluated matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) mRNA expression in bronchial secretions of asthmatics and correlated MMPs modulations with the lung function as a reflection of the bronchial extracellular matrix remodelling. Quantitative RT-PCR was performed on cell pellets obtained from induced sputum in order to detect the mRNAs for MMP-1, -2, -3, -8, -9, -12, -13 TIMP-1, -2, while semiquantitative RT-PCR was performed to assess the expression of MMP-7, monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor-beta(1) (TGF-beta(1)). The mRNA transcripts for MMP-1, TIMP-1 and monocyte chemoattractant protein-1 (MCP-1) were increased in cell pellets of induced sputum from asthmatics when compared to controls (P<0.05), and the intensity of MMP-1 mRNA expression inversely correlated with the FEV(1) in asthmatics (r=-0.49, P<0.05). The MMP-1 mRNA/TIMP-1 mRNA ratio correlated with the levels of MCP-1 mRNA in asthmatics (r=0.47, P<0.05). There were no differences between the groups with respect to mRNA coding for MMP-2, -3, -7, -8, -9, -12, -13, -14, TIMP-2 and TGF-beta(1). We conclude that cells contained in the bronchial secretions from asthmatics express higher amounts of mRNA for MMP-1 and TIMP-1, perhaps related to an increased expression of MCP-1, which might contribute to the extracellular matrix changes observed during airway remodelling.

Matrix metalloproteinases (MMPs) are an at least 23 member family of calcium and zinc dependent enzymes implicated in many physiological and pathological processes. Asthma, chronic obstructive pulmonary disease (COPD) and emphysema are diseases associated with an inflammation of the airways and lung parenchyma. In this review, we focus on the role played by MMPs in the pathogenesis of inflammation, airway remodelling and alveolar destruction, depicting the observational studies in humans and the experimental studies in animal models. During the course of asthma, MMP-2,-8,-9 and TIMP-1 are expressed at baseline and the allergen exposure or exacerbations of the disease lead to an increase of MMP-9 secretion being at this time much higher than that of TIMP-1, allowing temporarily a matrix damage, possibly followed by abnormal repair. Animal models suggest a predominant role for MMP-9 and MMP-12 in the pathogenesis of pulmonary inflammation and link an absence of MMP-2 to an increased parenchymal inflammation. In COPD and emphysema, human studies indicate an over-secretion of MMP-2,-8,-9 and animal models pointout MMP-1 and MMP-12 as being key players in the pathogenesis of emphysema. Taken together, these data identify specific MMP inhibition as appropriate target for therapeutic intervention in asthma or COPD/emphysema They also strongly argue against the widespread use of large spectrum non specific inhibitors that could be detrimental.

Objective: The aim of the study was to determine whether allergen inhalation modulates the levels of matrix metalloproteinase (MMP)-9 and tissue inhibitor of matrix metalloproteinase (TIMP)-1 in the induced sputum recovered from patients during a late-phase reaction., Method: Eight allergic asthma patients and five healthy control subjects inhaled a dose of Dermatophagoides pteronyssinus extract corresponding to the provocative concentration of the allergen causing a 20% fall in FEV(1) and saline solution. Lung function was carefully monitored for 6 h, and an induced sputum test was performed at 6 h after sham challenge or allergen challenge. The total and differential cell counts were analyzed, and the levels of MMP-9 (by enzyme-linked immunosorbent assay [ELISA] and zymography), TIMP-1 (by ELISA), and albumin (by rocket immunoelectrophoresis) were measured., Results: The sputum eosinophil counts (p < 0.01) and MMP-9 levels (p < 0.05) increased significantly in atopic asthma patients after undergoing the allergen challenge but did not in the control subjects. By contrast, TIMP-1 and albumin levels were not significantly increased in any group. MMP-9 levels, measured after the allergen challenge in asthmatic patients, were significantly correlated with FEV(1) variations after allergen inhalation (r = 0.51; p < 0.05) and with the sputum neutrophil percentage (r = 0.71; p < 0.01)., Conclusion: The levels of MMP-9, but not TIMP-1, increase after inhaled allergen challenge in the sputum of allergic asthmatic patients. This protease increase may lead to a transient imbalance between MMP-9 and TIMP-1 favoring proteolytic extracellular matrix degradation.

We investigated the specific role of matrix metalloproteinase (MMP)-9 in allergic asthma using a murine model of allergen-induced airway inflammation and airway hyperresponsiveness in MMP-9(-/-) mice and their corresponding wild-type (WT) littermates. After a single intraperitoneal sensitization to ovalbumin, the mice were exposed daily either to ovalbumin (1%) or phosphate-buffered saline aerosols from days 14 to 21. Significantly less peribronchial mononuclear cell infiltration of the airways and less lymphocytes in the bronchoalveolar lavage fluid were detected in challenged MMP-9(-/-) as compared to WT mice. In contrast, comparable numbers of bronchoalveolar lavage fluid eosinophils were observed in both genotypes. After allergen exposure, the WT mice developed a significant airway hyperresponsiveness to carbachol whereas the MMP-9(-/-) mice failed to do so. Allergen exposure induced an increase of MMP-9-related gelatinolytic activity in WT lung extracts. Quantitative reverse transcriptase-polymerase chain reaction showed increased mRNA levels of MMP-12, MMP-14, and urokinase-type plasminogen activator after allergen exposure in the lung extracts of WT mice but not in MMP-9-deficient mice. In contrast, the expression of tissue inhibitor of metalloproteinases-1 was enhanced after allergen exposure in both groups. We conclude that MMP-9 plays a key role in the development of airway inflammation after allergen exposure.