Matrix metalloproteinases (MMPs) have been suggested as therapeutic targets in cancer treatment, but broad-spectrum MMP inhibitors have failed in clinical trials. Recent data suggest that several MMPs including MMP-9 exert both pro- and antitumorigenic properties. This is also the case of the natural inhibitors of MMPs, tissue inhibitor of metalloproteinases (TIMPs). The inhibitor of MMP-9 is TIMP-1, and high levels of this enzyme have been associated with decreased survival in breast cancer. Inflammation is one hallmark of cancer progression, and MMPs/TIMPs may be involved in the local immune regulation. We investigated the role of MMP-9/TIMP-1 in regulating innate antitumor immunity in breast cancer. Breast cancers were established in nude mice and treated with intratumoral injections of adenoviruses carrying the human TIMP-1 or MMP-9 gene (AdMMP-9). In vivo microdialysis for sampling of cancer cell–derived (human) and stroma-derived (murine) proteins, immunostainings, as well as cell cultures were performed. We report a dose-dependent decrease of tumor growth and angiogenesis after AdMMP-9 treatment. In addition to increased generation of endostatin, AdMMP-9 promoted an antitumor immune response by inducing massive neutrophil infiltration. Neutrophil depletion prior to gene transfer abolished the therapeutic effects of AdMMP-9. Additionally, AdMMP-9 activated tumor-infiltrating macrophages into a tumor-inhibiting phenotype both in vivo and in vitro. AdMMP-9 also inhibited tumor growth in immune-competent mice bearing breast cancers. Adenoviruses carrying the human TIMP-1 gene had no effect on tumor growth or the immune response. Our novel data identify MMP-9 as a potent player in modulating the innate immune response into antitumor activities.
The growth factor granulocyte/macrophage-colony stimulating factor (GM-CSF) has an important role in pulmonary surfactant metabolism and the regulation of antibacterial activities of lung sentinel cells. However, the potential of intra-alveolar GM-CSF to augment lung protective immunity against inhaled bacterial pathogens has not been defined in preclinical infection models. We hypothesized that transient overexpression of GM-CSF in the lungs of mice by adenoviral gene transfer (Ad-GM-CSF) would protect mice from subsequent lethal pneumococcal pneumonia. Our data show that intra-alveolar delivery of Ad-GM-CSF led to sustained increased pSTAT5 expression and PU.1 protein expression in alveolar macrophages during a 28 day observation period. Pulmonary Ad-GM-CSF delivery two or four weeks prior to infection of mice with S. pneumoniae significantly reduced mortality rates relative to control vector treated mice. This increased survival was accompanied by increased iNOS expression, antibacterial activity and a significant reduction in caspase 3 dependent apoptosis and secondary necrosis of lung sentinel cells. Importantly, therapeutic treatment of mice with recombinant GM-CSF improved lung protective immunity and accelerated bacterial clearance after pneumococcal challenge. We conclude that prophylactic delivery of GM-CSF triggers long-lasting immunostimulatory effects in the lung in vivo and rescues mice from lethal pneumococcal pneumonia by improving antibacterial immunity. These data support use of novel antibiotic-independent immunostimulatory therapies to protect patients against bacterial pneumonias.
GM-CSF; S. pneumoniae; PU.1; pneumonia; therapy; infection
Breast cancer that recurs as metastatic disease many years after primary tumor resection and adjuvant therapy appears to arise from tumor cells that disseminated early in the course of disease but did not develop into clinically apparent lesions. These long-term surviving, disseminated tumor cells maintain a state of dormancy, but may be triggered to proliferate through largely unknown factors. We now demonstrate that the induction of fibrosis, associated with deposition of type I collagen (Col-I) in the in vivo metastatic microenvironment, induces dormant D2.0R cells to form proliferative metastatic lesions through β1-integrin signaling. In vitro studies using a 3D culture system modeling dormancy demonstrated that Col-I induces quiescent D2.0R cells to proliferate through β1-integrin activation of SRC and FAK, leading to ERK-dependent myosin light chain (MLC) phosphorylation by myosin light chain kinase (MLCK) and actin stress fiber formation. Blocking β1-integrin, Src, ERK or MLCK by shRNA or pharmacologic approaches inhibited Col-I-induced activation of this signaling cascade, cytoskeletal reorganization and proliferation. These findings demonstrate that fibrosis with type I collagen enrichment at the metastatic site may be a critical determinant of cytoskeletal reorganization in dormant tumor cells leading to their transition from dormancy to metastatic growth. Thus, inhibiting Col-I production, its interaction with β1-integrin and downstream signaling of β1-integrin may be important strategies for preventing or treating recurrent metastatic disease.
tumor cell dormancy; metastasis; fibrosis; integrin β1 signaling; extracellular matrix
Rationale: Idiopathic pulmonary fibrosis (IPF) is a chronic dysregulated response to alveolar epithelial injury with differentiation of epithelial cells and fibroblasts into matrix-secreting myofibroblasts resulting in lung scaring. The prognosis is poor and there are no effective therapies or reliable biomarkers. Galectin-3 is a β-galactoside binding lectin that is highly expressed in fibrotic tissue of diverse etiologies.
Objectives: To examine the role of galectin-3 in pulmonary fibrosis.
Methods: We used genetic deletion and pharmacologic inhibition in well-characterized murine models of lung fibrosis. Further mechanistic studies were performed in vitro and on samples from patients with IPF.
Measurements and Main Results: Transforming growth factor (TGF)-β and bleomycin-induced lung fibrosis was dramatically reduced in mice deficient in galectin-3, manifest by reduced TGF-β1–induced EMT and myofibroblast activation and collagen production. Galectin-3 reduced phosphorylation and nuclear translocation of β-catenin but had no effect on Smad2/3 phosphorylation. A novel inhibitor of galectin-3, TD139, blocked TGF-β–induced β-catenin activation in vitro and in vivo and attenuated the late-stage progression of lung fibrosis after bleomycin. There was increased expression of galectin-3 in the bronchoalveolar lavage fluid and serum from patients with stable IPF compared with nonspecific interstitial pneumonitis and controls, which rose sharply during an acute exacerbation suggesting that galectin-3 may be a marker of active fibrosis in IPF and that strategies that block galectin-3 may be effective in treating acute fibrotic exacerbations of IPF.
Conclusions: This study identifies galectin-3 as an important regulator of lung fibrosis and provides a proof of principle for galectin-3 inhibition as a potential novel therapeutic strategy for IPF.
fibrosis; epithelial cells; fibroblasts
Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic disease of the lung parenchyma, without curative treatment. Gremlin is a bone morphogenic protein (BMP) antagonist, its expression being increased in IPF lungs. It has been implicated in promoting myofibroblast accumulation, likely through inhibited fibroblast apoptosis and epithelial-to-mesenchymal transition. In the current study, we examined the effects of selective adenovirus-mediated overexpression of Gremlin in rat lungs. We show that transient Gremlin overexpression results in activation of alveolar epithelial cells with proliferation and apoptosis, as well as partly reversible lung fibrosis. We found myofibroblasts arranged in fibroblastic foci. Fibroblast proliferation occurred delayed as compared with epithelial changes. Fibrotic pathology significantly declined after Day 14, the reversal being associated with an increase of the epithelium-protective element, fibroblast growth factor (FGF)–10. Our data indicate that Gremlin-mediated BMP inhibition results in activation of epithelial cells and transient fibrosis, but also induction of epithelium-protective FGF10. A Gremlin–BMP–FGF10 loop may explain these results, and demonstrate that the interactions between different factors are quite complex in fibrotic lung disease. Increased Gremlin expression in human IPF tissue may be an expression of continuing epithelial injury, and Gremlin may be part of activated repair mechanisms.
pulmonary fibrosis; gremlin; bone morphogenic protein; animal model; epithelial cell
The airway is a primary portal of entry for noxious environmental stimuli that can trigger airway remodeling, which contributes significantly to airway obstruction in chronic obstructive pulmonary disease (COPD) and chronic asthma. Important pathologic components of airway remodeling include fibrosis and abnormal innate and adaptive immune responses. The positioning of fibroblasts in interstitial spaces suggests that they could participate in both fibrosis and chemokine regulation of the trafficking of immune cells such as dendritic cells, which are crucial antigen-presenting cells. However, physiological evidence for this dual role for fibroblasts is lacking. Here, in two physiologically relevant models — conditional deletion in mouse fibroblasts of the TGF-β–activating integrin αvβ8 and neutralization of αvβ8 in human COPD fibroblasts — we have elucidated a mechanism whereby lung fibroblast chemokine secretion directs dendritic cell trafficking, in a manner that is critically dependent on αvβ8-mediated activation of TGF-β by fibroblasts. Our data therefore indicate that fibroblasts have a crucial role in regulating both fibrotic and immune responses in the lung.
Micro-computed tomography (micro-CT) is a novel tool for monitoring acute and chronic disease states in small laboratory animals. Its value for assessing progressive lung fibrosis in mice has not been reported so far. Here we examined the importance of in vivo micro-CT as non-invasive tool to assess progression of pulmonary fibrosis in mice over time.
Pulmonary fibrosis was induced in mice by intratracheal delivery of an adenoviral gene vector encoding biologically active TGF-ß1 (AdTGF-ß1). Respiratory gated and ungated micro-CT scans were performed at 1, 2, 3, and 4 weeks post pulmonary adenoviral gene or control vector delivery, and were then correlated with respective histopathology-based Ashcroft scoring of pulmonary fibrosis in mice. Visual assessment of image quality and consolidation was performed by 3 observers and a semi-automated quantification algorithm was applied to quantify aerated pulmonary volume as an inverse surrogate marker for pulmonary fibrosis.
We found a significant correlation between classical Ashcroft scoring and micro-CT assessment using both visual assessment and the semi-automated quantification algorithm. Pulmonary fibrosis could be clearly detected in micro-CT, image quality values were higher for respiratory gated exams, although differences were not significant. For assessment of fibrosis no significant difference between respiratory gated and ungated exams was observed.
Together, we show that micro-CT is a powerful tool to assess pulmonary fibrosis in mice, using both visual assessment and semi-automated quantification algorithms. These data may be important in view of pre-clinical pharmacologic interventions for the treatment of lung fibrosis in small laboratory animals.
Tumor immune responses are first generated and metastases often begin in tumor sentinel lymph nodes (TSLN). Therefore, it is important to promote tumor immunity within this microenvironment. Mifepristone (RU486) treatment can interfere with cortisol signaling that can lead to suppression of tumor immunity. Here, we assessed whether treatment with RU486 in conjunction with an intratumor injection of Ad5IL-12 vector (a recombinant adenovirus expressing IL-12) could impact the TSLN microenvironment and prostate cancer progression.
The human PC3, LNCaP or murine TRAMP-C1 prostate cancer cell lines were used to generate subcutaneous tumors in NOD.scid and C57BL/6 mice, respectively. Adjuvant effects of RU486 were looked for in combination therapy with intratumor injections (IT) of Ad5IL-12 vector in comparison to PBS, DL70-3 vector, DL70-3 + RU486, RU486 and Ad5IL-12 vector treatment controls. Changes in tumor growth, cell cytotoxic activity and populations of CD4+/FoxP3+ T regulatory cells (Treg) in the TSLN were evaluated.
Treatment of human PC3 prostate xenograft or TRAMP-C1 tumors with combination Ad5IL-12 vector and RU486 produced significantly better therapeutic efficacy in comparison to controls. In addition, we found that combination therapy increased the capacity of TSLN lymphocytes to produce Granzyme B in response to tumor cell targets. Finally, combination therapy tended towards decreases of CD4+/FoxP3+ T regulatory cell populations to be found in the TSLN.
Inclusion of RU486 may serve as a useful adjuvant when combined with proinflammatory tumor killing agents by enhancement of the immune response and alteration of the TSLN microenvironment.
Transforming growth factor-beta (TGF-β), a multifunctional cytokine regulating several immunologic processes, is expressed by virtually all cells as a biologically inactive molecule termed latent TGF-β (LTGF-β). We have previously shown that TGF-β activity increases during influenza virus infection in mice and suggested that the neuraminidase (NA) protein mediates this activation. In the current study, we determined the mechanism of activation of LTGF-β by NA from the influenza virus A/Gray Teal/Australia/2/1979 by mobility shift and enzyme inhibition assays. We also investigated whether exogenous TGF-β administered via a replication-deficient adenovirus vector provides protection from H5N1 influenza pathogenesis and whether depletion of TGF-β during virus infection increases morbidity in mice. We found that both the influenza and bacterial NA activate LTGF-β by removing sialic acid motifs from LTGF-β, each NA being specific for the sialic acid linkages cleaved. Further, NA likely activates LTGF-β primarily via its enzymatic activity, but proteases might also play a role in this process. Several influenza A virus subtypes (H1N1, H1N2, H3N2, H5N9, H6N1, and H7N3) except the highly pathogenic H5N1 strains activated LTGF-β in vitro and in vivo. Addition of exogenous TGF-β to H5N1 influenza virus–infected mice delayed mortality and reduced viral titers whereas neutralization of TGF-β during H5N1 and pandemic 2009 H1N1 infection increased morbidity. Together, these data show that microbe-associated NAs can directly activate LTGF-β and that TGF-β plays a pivotal role protecting the host from influenza pathogenesis.
Transforming growth factor-beta (TGF-β) is a multifunctional protein that serves as a global regulator of immunity by controlling the initiation and resolution of inflammatory responses. A pathogen that can regulate TGF-β activation could promote an immune-privileged state for itself within its host. Indeed, multiple parasitic, bacterial, and fungal pathogens successfully evade immune responses by regulating TGF-β. We demonstrate that the neuraminidase proteins from influenza A viruses and Clostridium perfringens convert biologically inactive TGF-β to its active form. Importantly, modulation of TGF-β activity during influenza infection affects viral titers and disease outcome in mice, suggesting that TGF-β plays an important role in influenza pathogenesis, particularly in protecting the host during infection. These studies suggest that neuraminidases from diverse microbes may be able to directly regulate TGF-β, which may in turn play an important role in disease.
It is recognized that functional activities of antigen-presenting cells (APCs) in mucosal tissue sites differ from those of systemic APCs; however, it is unknown whether there are further differences between APC populations residing in different mucosal sites. In this study, we directly compared murine CD11c+ APCs isolated from colon, lung, and spleen and found that APCs isolated from these tissues differ considerably in Toll-like receptor (TLR) expression and responses to in vitro TLR ligand stimulation. We also provide evidence that tissue microenvironments dictate distinct patterns of TLR expression by CD11c+ APCs in different mucosal tissues. Moreover, CD11c+ cells isolated from different tissues have varied capacities to induce the development of T helper 1 (Th1), Th2, or regulatory CD4+ T cells. Thus, unique tissue microenvironments have a significant influence on determining TLR expression by CD11c+ cells that migrate to and reside in each mucosal tissue and are likely to modulate their functional activities.
Smad3, a mediator of TGF-β signaling has been shown to be involved in the epithelial-to-mesenchymal transformation (EMT) of lens epithelial cells in a lens injury model. In this study, the role of Smad3 in anterior subcapsular cataract (ASC) formation was investigated in a transgenic TGF-β/Smad3 knockout mouse model.
TGF-β1 transgenic mice (containing a human TGF-β1 cDNA construct expressed under the αA-crystallin promoter) were bred with mice on a Smad3-null background to generate mice with the following genotypes: TGF-β1/Smad3-/- (null), TGF-β1/Smad3+/-, TGF-β1/Smad3+/+, and nontransgenic/Smad3+/+. Lenses from mice of each genotype were dissected and prepared for histologic or optical analyses.
All transgenic TGF-β1 lenses demonstrated subcapsular plaque formation and EMT as indicated by the expression of α-smooth muscle actin. However, the sizes of the plaques were reduced in the TGF-β1/Smad3-/- lenses, as was the level of type IV collagen deposition when compared with TGF-β1/Smad3+/- and TGF-β1/Smad3+/+ lenses. An increased number of apoptotic figures was also observed in the plaques of the TGF-β1/Smad3-/- lenses compared with TGF-β1/Smad3+/+ littermates.
Lens-specific expression of TGF-β1 induced ASC formation in the absence of the Smad3 signaling mediator, suggests that alternative TGF-β-signaling pathways participate in this ocular fibrotic model.
Idiopathic pulmonary fibrosis (IPF) can lead to the development of secondary pulmonary hypertension (PH) and ultimately death. Despite this known association, the precise mechanism of disease remains unknown. Using a rat model of IPF, we explored the role of the proangiogenic and antiapoptotic growth factor VEGF in the vascular remodeling that underlies PH. In this model, adenoviral delivery of active TGF-β1 induces pulmonary arterial remodeling, loss of the microvasculature in fibrotic areas, and increased pulmonary arterial pressure (PAP). Immunohistochemistry and mRNA analysis revealed decreased levels of VEGF and its receptor, which were inversely correlated with PAP and endothelial cell apoptosis in both the micro- and macrovasculature. Treatment of IPF rats with adenoviral delivery of VEGF resulted in reduced endothelial apoptosis, increased vascularization, and improved PAP due to reduced remodeling but worsened PF. These data show that experimental pulmonary fibrosis (PF) leads to loss of the microvasculature through increased apoptosis and to remodeling of the pulmonary arteries, with both processes resulting in PH. As administration of VEGF ameliorated the PH in this model but concomitantly aggravated the fibrogenic process, VEGF-based therapies should be used with caution.
Tissue repair is a well orchestrated biological process involving numerous soluble mediators, and an imbalance between these factors may result in impaired repair and fibrosis. Transforming growth factor (TGF) β is a key profibrotic element in this process and it is thought that its three isoforms act in a similar way. Here, we report that TGF-β3 administered to rat lungs using transient overexpression initiates profibrotic effects similar to those elicited by TGF-β1, but causes less severe and progressive changes. The data suggest that TGF-β3 does not lead to inhibition of matrix degradation in the same way as TGF-β1, resulting in non-fibrotic tissue repair. Further, TGF-β3 is able to downregulate TGF-β1 induced gene expression, suggesting a regulatory role of TGF-β3. TGF-β3 overexpression results in an upregulation of Smad proteins similar to TGF-β1, but is less efficient in inducing the ALK 5 and TGF-β type II receptor (TβRII). We provide evidence that this difference may contribute to the progressive nature of TGF-β1 induced fibrotic response, in contrast to the limited fibrosis observed following TGF-β3 overexpression. TGF-β3 is important in “normal wound healing”, but is outbalanced by TGF-β1 in “fibrotic wound healing” in the lung.
Different animal models of pulmonary fibrosis have been developed to investigate potential therapies for idiopathic pulmonary fibrosis (IPF). The most common is the bleomycin model in rodents (mouse, rat and hamster). Over the years, numerous agents have been shown to inhibit fibrosis in this model. However, to date none of these compounds are used in the clinical management of IPF and none has shown a comparable antifibrotic effect in humans. We performed a systematic review of publications on drug efficacy studies in the bleomycin model to evaluate the value of this model regarding transferability to clinical use. Between 1980 and 2006 we identified 246 experimental studies describing beneficial antifibrotic compounds in the bleomycin model. In 221 of the studies we found enough details about the timing of drug application to allow inter-study comparison. 211 of those used a preventive regimen (drug given ≤ day 7 after last bleomycin application), only 10 were therapeutic trials (> 7 days after last bleomycin application). It is critical to distinguish between drugs interfering with the inflammatory and early fibrogenic response from those preventing progression of fibrosis, the latter likely much more meaningful for clinical application. All potential antifibrotic compounds should be evaluated in the phase of established fibrosis rather than in the early period of bleomycin-induced inflammation for assessment of its antifibrotic properties. Further care should be taken in extrapolation of drugs successfully tested in the bleomycin model due to partial reversibility of bleomycin induced fibrosis over time. The use of alternative and more robust animal models, which better reflect human IPF, is warranted.
Idiopathic pulmonary fibrosis (IPF) is a treatment resistant disease with poor prognosis. Numerous compounds have been demonstrated to efficiently prevent pulmonary fibrosis (PF) in animal models but only a few were successful when given to animals with established fibrosis. Major concerns of current PF models are spontaneous resolution and high variability of fibrosis, and the lack of assessment methods that can allow to monitor the effect of drugs in individual animals over time. We used a model of experimental PF in rats and compare parameters obtained in living animals with conventional assessment tools that require removal of the lungs.
PF was induced in rats by adenoviral gene transfer of transforming growth factor-beta. Morphological and functional changes were assessed for up to 56 days by micro-CT, lung compliance (measured via a mechanical ventilator) and VO2max and compared to histomorphometry and hydroxyproline content.
Standard histological and collagen assessment confirmed the persistent fibrotic phenotype as described before. The histomorphological scores correlated both to radiological (r2 = 0.29, p < 0.01) and functional changes (r2 = 0.51, p < 0.0001). VO2max did not correlate with fibrosis.
The progression of pulmonary fibrosis can be reliably assessed and followed in living animals over time using invasive, non-terminal compliance measurements and micro-CT. This approach directly translates to the management of patients with IPF and allows to monitor therapeutic effects in drug intervention studies.
The incidence of finding evidence of both emphysema and pulmonary fibrosis in the same patient has received increased attention. Several investigators have found on biopsy the presence of emphysema of the upper zones and diffuse parenchymal disease with fibrosis of the lower zones of the lung, especially associated with current or previous heavy smokers. Believed previously to be two different disease mechanisms, there are now data to implicate some common pathways of cell and molecular activation leading to the different morphologic and physiologic outcomes. According to a current view, emphysema may originate from a protease/antiprotease imbalance, whereas a role for antiproteases has been proposed in the modulation of fibrosis. Overexpression of transforming growth factor β (TGF-β) in experimental rodent models leads to progressive pulmonary fibrosis, accompanied with marked up-regulation of protease inhibitors, such as tissue inhibitor of metalloproteinases (TIMP) and plasminogen activator inhibitor-1 (PAI-1) genes, along with excessive matrix accumulation. It may be that a “matrix degrading” pulmonary microenvironment, one in which metalloproteinase activities prevail, favors the development of emphysema, whereas a “matrix nondegrading” microenvironment, with enhanced presence of TIMPs, would lead to matrix accumulation and fibrosis. Surprisingly, although Smad3 null mice, deficient in TGF-β signal transmission, are resistant to bleomycin- and TGF-β–mediated fibrosis, they develop spontaneous age-related airspace enlargement, consistent with emphysema, with a lack of ability to repair tissue damage appropriately. A common element is tissue damage and repair, with TGF-β and the Smad signaling pathway playing prominent molecular roles. Both changes can be followed in experimental models with noninvasive imaging and physiologic measurements.
chronic obstructive pulmonary disease; emphysema; fibrosis; Smad; transforming growth factor β
To produce a gene-transfer model of rodent anterior subcapsular cataracts (ASC) using a replication-deficient, adenoviral vector containing active TGFβ1. Establishment of this model will be important for further investigations of TGFβ-induced signaling cascades in ASC.
Adenovirus containing the transgene for active TGFβ1 (AdTGFβ1), β-galactosidase (AdLacZ), green fluorescent protein (AdGFP) or no transgene (AdDL) was injected into the anterior chamber of C57Bl/6, Smad3 WT and Smad3 KO mice. Four and 21 days after injection, animals were enucleated and eyes were processed and examined by routine histology. Immunolocalization of markers indicative of epithelial to mesenchymal transition (EMT), fibrosis, proliferation and apoptosis was also carried out.
By day 4, treatment with AdLacZ demonstrated transgene expression in multiple structures of the anterior chamber including the lens epithelium. In contrast to AdDL, treatment with AdTGFβ1 produced αSMA-positive subcapsular plaques in all three groups of mice, which shared features reminiscent of human ASC. At day 21, plaques remained αSMA-positive and extensive extracellular matrix deposition was observed. The AdTGFβ1 model was further employed in Smad3 deficient mice and this resulted in the development of small ASC.
Gene transfer of active TGFβ1 using an adenoviral vector produced cataractous plaques four days postinjection, which were found to develop independent of functional Smad3.
A recent review article suggested that idiopathic pulmonary fibrosis (IPF) is a disease that is associated more with abnormal wound healing than with inflammation. Data derived from transgenic and gene transfer rodent models suggest that lung inflammation may be a necessary but insufficient component of IPF, and that at some point in the natural history of the disease IPF becomes no longer dependent on the inflammatory response for propagation. Altered microenvironment and involvement of epithelial cell/mesenchymal cell interaction are the most likely contributors to the pathogenesis of this chronic progressive disorder.
fibrosis; inflammation; myofibroblast; tissue repair; transforming growth factor (TGF)-β
IL-1β is one of a family of proinflammatory cytokines thought to be involved in many acute and chronic diseases. Although it is considered to participate in wound repair, no major role has been attributed to IL-1β in tissue fibrosis. We used adenoviral gene transfer to transiently overexpress IL-1β in rat lungs after intratracheal administration. The high expression of IL-1β in the first week after injection was accompanied by local increase of the proinflammatory cytokines IL-6 and TNF-α and a vigorous acute inflammatory tissue response with evidence of tissue injury. The profibrotic cytokines PDGF and TGF-β1 were increased in lung fluid samples 1 week after peak expression of IL-1β. Although PDGF returned to baseline in the third week, TGF-β1 showed increased concentrations in bronchoalveolar lavage fluid for up to 60 days. This was associated with severe progressive tissue fibrosis in the lung, as shown by the presence of myofibroblasts, fibroblast foci, and significant extracellular accumulations of collagen and fibronectin. These data directly demonstrate how acute tissue injury in the lung, initiated by a highly proinflammatory cytokine, IL-1β, converts to progressive fibrotic changes. IL-1β should be considered a valid target for therapeutic intervention in diseases associated with fibrosis and tissue remodeling.