Bleomycin-induced lung fibrosis in IL-4-overexpressing and knockout mice

Loss of IGFBP2 mediates alveolar type 2 cell senescence and promotes lung fibrosis

Accumulation of senescent cells contributes to age-related diseases including idiopathic pulmonary fibrosis (IPF). Insulin-like growth factor binding proteins (IGFBPs) regulate many biological processes; however, the functional contributions of IGFBP2 in lung fibrosis remain largely unclear. Here, we report that intranasal delivery of recombinant IGFBP2 protects aged mice from weight loss and demonstrated antifibrotic effects after bleomycin lung injury. Notably, aged human-Igfbp2 transgenic mice reveal reduced senescence and senescent-associated secretory phenotype factors in alveolar epithelial type 2 (AEC2) cells and they ameliorated bleomycin-induced lung fibrosis. Finally, we demonstrate that IGFBP2 expression is significantly suppressed in AEC2 cells isolated from fibrotic lung regions of patients with IPF and/or pulmonary hypertension compared with patients with hypersensitivity pneumonitis and/or chronic obstructive pulmonary disease. Altogether, our study provides insights into how IGFBP2 regulates AEC2-cell-specific senescence and that restoring IGFBP2 levels in fibrotic lungs can prove effective for patients with IPF.

Relaxin in fibrotic ligament diseases: Its regulatory role and mechanism

Fibrotic ligament diseases (FLDs) are diseases caused by the pathological accumulation of periarticular fibrotic tissue, leading to functional disability around joint and poor life quality. Relaxin (RLX) has been reported to be involved in the development of fibrotic lung and liver diseases. Previous studies have shown that RLX can block pro-fibrotic process by reducing the excess extracellular matrix (ECM) formation and accelerating collagen degradation in vitro and in vivo. Recent studies have shown that RLX can attenuate connective tissue fibrosis by suppressing TGF-β/Smads signaling pathways to inhibit the activation of myofibroblasts. However, the specific roles and mechanisms of RLX in FLDs remain unclear. Therefore, in this review, we confirmed the protective effect of RLX in FLDs and summarized its mechanism including cells, key cytokines and signaling pathways involved. In this article, we outline the potential therapeutic role of RLX and look forward to the application of RLX in the clinical translation of FLDs.

The Epithelial-Immune Crosstalk in Pulmonary Fibrosis

Interactions between the lung epithelium and the immune system involve a tight regulation to prevent inappropriate reactions and have been connected to several pulmonary diseases. Although the distal lung epithelium and local immunity have been implicated in the pathogenesis and disease course of idiopathic pulmonary fibrosis (IPF), consequences of their abnormal interplay remain less well known. Recent data suggests a two-way process, as illustrated by the influence of epithelial-derived periplakin on the immune landscape or the effect of macrophage-derived IL-17B on epithelial cells. Additionally, damage associated molecular patterns (DAMPs), released by damaged or dying (epithelial) cells, are augmented in IPF. Next to “sterile inflammation”, pathogen-associated molecular patterns (PAMPs) are increased in IPF and have been linked with lung fibrosis, while outer membrane vesicles from bacteria are able to influence epithelial-macrophage crosstalk. Finally, the advent of high-throughput technologies such as microbiome-sequencing has allowed for the identification of a disease-specific microbial environment. In this review, we propose to discuss how the interplays between the altered distal airway and alveolar epithelium, the lung microbiome and immune cells may shape a pro-fibrotic environment. More specifically, it will highlight DAMPs-PAMPs pathways and the specificities of the IPF lung microbiome while discussing recent elements suggesting abnormal mucosal immunity in pulmonary fibrosis.

Role of interleukins in the pathogenesis of pulmonary fibrosis

Interleukins, a group of cytokines participating in inflammation and immune response, are proved to be involved in the formation and development of pulmonary fibrosis. In this article, we reviewed the relationship between interleukins and pulmonary fibrosis from the clinical, animal, as well as cellular levels, and discussed the underlying mechanisms in vivo and in vitro. Despite the effects of interleukin-targeted treatment on experimental pulmonary fibrosis, clinical applications are lacking and unsatisfactory. We conclude that intervening in one type of interleukins with similar functions in IPF may not be enough to stop the development of fibrosis as it involves a complex network of regulation mechanisms. Intervening interleukins combined with other existing therapy or targeting interleukins affecting multiple cells/with different functions at the same time may be one of the future directions. Furthermore, the intervention time is critical as some interleukins play different roles at different stages. Further elucidation on these aspects would provide new perspectives on both the pathogenesis mechanism, as well as the therapeutic strategy and drug development.

Inhibiting Sialidase-Induced TGF-β1 Activation Attenuates Pulmonary Fibrosis in Mice

The active form of transforming growth factor-β1 (TGF-β1) plays a key role in potentiating fibrosis. TGF-β1 is sequestered in an inactive state by a latency-associated glycopeptide (LAP). Sialidases (also called neuraminidases (NEU)) cleave terminal sialic acids from glycoconjugates. The sialidase NEU3 is upregulated in fibrosis, and mice lacking Neu3 show attenuated bleomycin-induced increases in active TGF-β1 in the lungs and attenuated pulmonary fibrosis. Here we observe that recombinant human NEU3 upregulates active human TGF-β1 by releasing active TGF-β1 from its latent inactive form by desialylating LAP. Based on the proposed mechanism of action of NEU3, we hypothesized that compounds with a ring structure resembling picolinic acid might be transition state analogs and thus possible NEU3 inhibitors. Some compounds in this class showed nanomolar IC₅₀ for recombinant human NEU3 releasing active human TGF-β1 from the latent inactive form. The compounds given as daily 0.1-1-mg/kg injections starting at day 10 strongly attenuated lung inflammation, lung TGF-β1 upregulation, and pulmonary fibrosis at day 21 in a mouse bleomycin model of pulmonary fibrosis. These results suggest that NEU3 participates in fibrosis by desialylating LAP and releasing TGF-β1 and that the new class of NEU3 inhibitors are potential therapeutics for fibrosis. SIGNIFICANCE STATEMENT: The extracellular sialidase NEU3 appears to be a key driver of pulmonary fibrosis. The significance of this report is that 1) we show the mechanism (NEU3 desialylates the latency-associated glycopeptide protein that keeps the profibrotic cytokine transforming growth factor-β1 (TGF-β1) in an inactive state, causing active TGF-β1 release), 2) we then use the predicted NEU3 mechanism to identify nM IC₅₀ NEU3 inhibitors, and 3) these new NEU3 inhibitors are potent therapeutics in a mouse model of pulmonary fibrosis.

Attenuated pulmonary fibrosis in sialidase-3 knockout (Neu3-/-) mice

Pulmonary fibrosis involves the formation of inappropriate scar tissue in the lungs, but what drives fibrosis is unclear. Sialidases (also called neuraminidases) cleave terminal sialic acids from glycoconjugates. In humans and mice, pulmonary fibrosis is associated with desialylation of glycoconjugates and upregulation of sialidases. Of the four mammalian sialidases, we previously detected only NEU3 in the bronchoalveolar lavage fluid from mice with bleomycin-induced pulmonary fibrosis. In this report, we show that NEU3 upregulates extracellular accumulation of the profibrotic cytokines IL-6 and IL-1β, and IL-6 upregulates NEU3 in human peripheral blood mononuclear cells, suggesting that NEU3 may be part of a positive feedback loop potentiating fibrosis. To further elucidate the role of NEU3 in fibrosis, we used bleomycin to induce lung fibrosis in wild-type C57BL/6 and Neu3^-/- mice. At 21 days after bleomycin, compared with male and female C57BL/6 mice, male and female Neu3^-/- mice had significantly less inflammation, less upregulation of other sialidases and the profibrotic cytokine active transforming growth factor β1, and less fibrosis in the lungs. Our results suggest that NEU3 participates in fibrosis and that NEU3 could be a target to develop treatments for fibrosis.

Vaccinia vaccine-based immunotherapy arrests and reverses established pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal disease without any cure. Both human disease and animal models demonstrate dysregulated wound healing and unregulated fibrogenesis in a background of low-grade chronic T lymphocyte infiltration. Tissue-resident memory T cells (Trm) are emerging as important regulators of the immune microenvironment in response to pathogens, and we hypothesized that they might play a role in regulating the unremitting inflammation that promotes lung fibrosis. Herein, we demonstrate that lung-directed immunotherapy, in the form of i.n. vaccination, induces an antifibrotic T cell response capable of arresting and reversing lung fibrosis. In mice with established lung fibrosis, lung-specific T cell responses were able to reverse established pathology - as measured by decreased lung collagen, fibrocytes, and histologic injury - and improve physiologic function. Mechanistically, we demonstrate that this effect is mediated by vaccine-induced lung Trm. These data not only have implications for the development of immunotherapeutic regimens to treat IPF, but also suggest a role for targeting tissue-resident memory T cells to treat other tissue-specific inflammatory/autoimmune disorders.

Chemokines in tissue fibrosis

Fibrosis or scarring of diverse organs and tissues is considered as a pathologic consequence of a chronically altered wound healing response which is tightly linked to inflammation and angiogenesis. The recruitment of immune cells, local proliferation of fibroblasts and the consecutive accumulation of extracellular matrix proteins are common pathophysiological hallmarks of tissue fibrosis, irrespective of the organ involved. Chemokines, a family of chemotactic cytokines, appear to be central mediators of the initiation as well as progression of these biological processes. Traditionally chemokines have only been considered to play a critical role in orchestrating the influx of immune cells to sites of tissue injury. However, within the last years, further aspects of chemokine biology including fibroblast activation and angiogenesis have been deciphered in tissue fibrosis of many different organs. Interestingly, certain chemokines appear to mediate common effects in liver, kidney, lung, and skin of various animal models, while others mediate tissue specific effects. These aspects have to be kept in mind when extrapolating data of animal studies to early human trials. Nevertheless, the further understanding of chemokine effects in tissue fibrosis might be an attractive approach for identifying novel therapeutic targets in chronic organ damage associated with high morbidity and mortality. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Cellular FLICE-like inhibitory protein deviates myofibroblast fas-induced apoptosis toward proliferation during lung fibrosis

A prominent feature of fibrotic tissue in general and of lungs in particular is fibroblast proliferation and accumulation. In patients overcoming fibrosis, apoptosis limits this excessive cell growth. We have previously shown resistance to Fas-induced apoptosis of primary lung fibroblasts from mice with bleomycin-induced lung fibrosis, their escape from immune surveillance, and continued accumulation in spite of overexpression of the Fas death receptor. Cellular FLICE-like inhibitory protein (c-FLIP) is a regulator of cell death receptor-induced apoptosis in many cell types. We aimed to determine c-FLIP levels in myofibroblasts from fibrotic lungs and to directly assess c-FLIP's role in apoptosis and proliferation of primary lung myofibroblasts. c-FLIP levels were determined by apoptosis gene array, flow cytometry, Western blot, and immunofluorescence before and after down-regulation with a specific small interfering RNA. Apoptosis was assessed by caspase cleavage in Western blot and by Annexin V affinity labeling after FACS and tissue immunofluorescence. Proliferation was assessed by BrdU uptake, also using FACS and immunofluorescence. We show that myofibroblasts from lungs of humans with idiopathic pulmonary fibrosis and from bleomycin-treated versus normal saline-treated mice up-regulate c-FLIP levels. Using the animal model, we show that fibrotic lung myofibroblasts divert Fas signaling from apoptosis to proliferation and that this requires signaling by TNF receptor-associated factor (TRAF) and NF-κB. c-FLIP down-regulation reverses the effect of Fas activation, causing increased apoptosis, decreased proliferation, and diminished recruitment of TRAF to the DISC complex. This indicates that c-FLIP is essential for myofibroblast accumulation and may serve as a potential target to manipulate tissue fibrosis.

Pulmonary vaccination as a novel treatment for lung fibrosis

Pulmonary fibrosis is an untreatable, uniformly fatal disease of unclear etiology that is the result of unremitting chronic inflammation. Recent studies have implicated bone marrow derived fibrocytes and M2 macrophages as playing key roles in propagating fibrosis. While the disease process is characterized by the accumulation of lymphocytes in the lung parenchyma and alveolar space, their role remains unclear. In this report we definitively demonstrate the ability of T cells to regulate lung inflammation leading to fibrosis. Specifically we demonstrate the ability of intranasal vaccinia vaccination to inhibit M2 macrophage generation and fibrocyte recruitment and hence the accumulation of collagen and death due to pulmonary failure. Mechanistically, we demonstrate the ability of lung Th1 cells to prevent fibrosis as vaccinia failed to prevent disease in Rag−/− mice or in mice in which the T cells lacked IFN-γ. Furthermore, vaccination 3 months prior to the initiation of fibrosis was able to mitigate the disease. Our findings clearly demonstrate the role of T cells in regulating pulmonary fibrosis as well as suggest that vaccinia-induced immunotherapy in the lung may prove to be a novel treatment approach to this otherwise fatal disease.

Aryl hydrocarbon receptor (AhR) regulates silica-induced inflammation but not fibrosis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is responsible for mediating a variety of pharmacological and toxicological effects caused by halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent evidence has revealed that the AhR also has numerous physiological roles aside from xenobiotic metabolism, including regulation of immune and inflammatory signaling as well as normal development and homeostasis of several organs. To investigate the role of the AhR in crystalline silica (SiO(2))-induced inflammation and fibrosis, C57Bl/6 and AhR(-/)(-) mice were exposed to SiO(2) or vehicle. Similarly, C57Bl/6 mice were exposed to SiO(2) and TCDD either simultaneously or sequentially to assess whether AhR activation alters inflammation and fibrosis. SiO(2)-induced acute lung inflammation was more severe in AhR(-)(/-) mice; however, the fibrotic response of AhR(-)(/-) mice was attenuated compared with C57Bl/6 mice. In a model of chronic SiO(2) exposure, AhR activation by TCDD in C57Bl/6 mice resulted in reduced inflammation; however, the fibrotic response was not affected. Bone marrow-derived macrophages (BMM) from AhR(-)(/-) mice also produced higher levels of cytokines and chemokines in response to SiO(2). Analysis of gene expression revealed that BMM derived from AhR(-)(/-) mice exhibit increased levels of pro-interleukin (IL)-1β, IL-6, and Bcl-2, yet decreased levels of signal transducers and activators of transcription (STAT)2, STAT5a, and serpin B2 (Pai-2) in response to SiO(2).

The effect of class II transactivator mutations on bleomycin-induced lung inflammation and fibrosis

IFN-γ expression increases during the inflammatory response after bleomycin injury in mice. IFN-γ deficiency attenuates lung inflammation and fibrosis. Because IFN-γ stimulates class II transactivator (CIITA) expression, which activates major histocompatibility class (MHC) II and represses collagen expression, it was hypothesized that CIITA mediates IFN-γ action after bleomycin injury. To test this hypothesis, two CIITA mouse lines, one carrying a mutation of the leucine-rich region of CIITA (CIITA C-/-) and one with a deletion extending into the GTP-binding domain (CIITA G-/-), were used. IFN-γ treatment of lung cells isolated from both strains of mice induced mutant CIITA expression, which did not activate MHC II transcription. Collagen expression was similar in both mutant mouse strains and comparable to C57BL/6 (wild-type) mice. When mice were exposed to intratracheal bleomycin, both strains of CIITA mutant mice retained body weight and altered inflammation at 14 days after bleomycin injury compared with bleomycin-treated wild-type mice. However, there was no difference in fibrosis as judged by histology, mRNA, and protein expression of lungs. Bronchoalveolar lavage cells from CIITA C-/- and C57BL/6 lungs were examined at 3, 7, and 14 days after bleomycin injury. CD4 mRNA expression in bronchoalveolar lavage cells was down-regulated, whereas IL-4 and IL-10 expression was up-regulated, in CIITA C-/- mice, indicating a diminished, skewed Th2 response. The expression of IFN-γ was the same in all mice tested. Combined, our data suggest that CIITA mutations altered the immune response without affecting fibrosis.

Polyketal microparticles for therapeutic delivery to the lung

Inflammation in the setting of interstitial lung disease (ILD) occurs in the distal alveolar spaces of the lung, which presents significant challenges for therapeutic delivery. The development of aerosolizable microparticles from non-immunogenic polymers is needed to enable the clinical translation of numerous experimental therapeutics that require localization to the deep lung and repeated delivery for optimal efficacy. Polyketals (PK), a family of polymers, have several unique properties that make them ideal for lung delivery, specifically their hydrolysis into non-acidic, membrane-permeable compounds and their capacity to form microparticles with the aerodynamic properties needed for aerosolization. In this study, we tested the lung biocompatibility of microparticles created from a polyketal polymer, termed PK3, following intratracheal instillation in comparison to commonly used PLGA microparticles. We furthermore tested the initial efficacy of PK3 microparticles to encapsulate and effectively deliver active superoxide dismutase (SOD), a free radical scavenging enzyme, in a model of lung fibrosis. Our findings indicate that PK3 microparticles display no detectable level of alveolar or airway inflammation, whereas PLGA induced a small inflammatory response. Furthermore, SOD-loaded into PK3 microparticles maintained its activity upon release and, when delivered via PK3 microparticles, inhibited the extent of lung fibrosis.

IL-13 as a therapeutic target for respiratory disease

Interleukin-13 (IL-13) is a critical mediator of asthma pathology. On B cells, monocytes, epithelial cells, and smooth muscle cells, IL-13 acts through the IL-13Ralpha1/IL-4Ralpha complex to directly induce activation responses that contribute to atopic disease. In human populations, genetic polymorphisms in IL-13, its receptor components, or the essential signaling element STAT6, have all been associated with increased risk of atopy and asthma. Animal studies using IL-13 deficient mice, IL-13 transgenic animals, and IL-13 neutralization strategies have confirmed an essential role for this cytokine in driving major correlates of asthma pathology, including airway hyperresponsiveness (AHR), lung eosinophilia, mucus generation, and fibrosis. Ongoing studies continue to define both overlapping and distinct roles for IL-13 and the related cytokine, IL-4, in promoting asthmatic changes. Furthermore, new evidence concerning the role of the "decoy" receptor, IL-13Ralpha2, has prompted re-evaluation of the receptor forms that underlie the numerous activities of IL-13. In this review, we summarize the essential role of IL-13 in asthma, compare the relative contributions of IL-13 and IL-4 to key aspects of the asthmatic phenotype, and outline novel therapeutic strategies to target this critical cytokine.

Type 2 immune response associated with silicosis is not instrumental in the development of the disease

It has been proposed that the development of lung fibrosis is associated with a T helper type 2 response, mainly characterized by IL-4 and IL-13 production. We investigated the potential role of type 2 immune polarization in the silicotic process and examined the pulmonary response to silica particles in mice genetically deficient for IL-4. We found that IL-4−/− mice were not protected against the development of silicosis, suggesting that IL-4 is not essential for the development of this fibrotic disease. By evaluating the intensity of silica-induced lung fibrosis in mice deficient for IL-4 receptor α (IL-4Rα), we showed that the establishment of pulmonary fibrosis was independent of both IL-4 and IL-13. Strong impairment of the type 2 immune response (IgG1) in the lungs of IL-4−/− and IL-4Rα−/− mice did not affect the development of the disease. Measurement of IL-13α2 receptor expression and IgG2a, IL-12p70, and IFN-γ levels in silica-treated IL-4−/− and IL-4Rα−/− animals showed that the development of silicosis was not related to an IL-13 signaling pathway or a switch to a type 1 response in deficient animals. Our data clearly indicate that the type 2 immune response associated with silicosis in mice is not required for the development of this inflammatory and fibrotic disease.

Effect of IL-2-Bax, a novel interleukin-2-receptor-targeted chimeric protein, on bleomycin lung injury

The role of lymphocytes in the pathogenesis of lung fibrosis is not clear, but the weight of the evidence supports a pro-fibrotic effect for lymphocytes. The high-affinity interleukin-2 receptor (haIL-2R) is expressed on activated, but not quiescent, T lymphocytes. This selective expression of haIL-2R provides the basis for therapeutic strategies that target IL-2R-expressing cells. We hypothesized that elimination of activated lymphocytes by IL-2R-targeted chimeric proteins might ameliorate lung fibrosis. We investigated the effects of IL-2-Bax, a novel apoptosis-inducing IL-2R-targeted chimeric protein, on bleomycin-induced lung injury in mice. Treatment groups included (i) a single intratracheal instillation of bleomycin and twice-daily intraperitoneal injections of IL-2-Bax; (ii) intratracheal bleomycin and intraperitoneal IL-2-PE66(4Glu), an older-generation chimeric protein; (iii) intratracheal bleomycin/intraperitoneal PBS; (iv) intratracheal saline/intraperitoneal PBS. Lung injury was evaluated 14 days after intratracheal instillation by cell count in bronchoalveolar lavage (BAL) fluid, semi-quantitative and quantitative histomorphological measurements and by biochemical analysis of lung hydroxyproline. Bleomycin induced a BAL lymphocytosis that was significantly attenuated by IL-2-Bax and IL-2-PE66(4Glu). However, morphometric parameters and lung hydroxyproline were unaffected by the chimeric proteins. These results show that IL-2-Bax reduces the lymphocytic infiltration of the lungs in response to bleomycin, but this effect is not accompanied by a decrease in lung fibrosis.

Role of IFN-gamma in regulating T2 immunity and the development of alternatively activated macrophages during allergic bronchopulmonary mycosis

Pulmonary Cryptococcus neoformans infection of C57BL/6 mice is an established model of a chronic pulmonary fungal infection accompanied by an "allergic" response (T2) to the infection, i.e., a model of an allergic bronchopulmonary mycosis. Our objective was to determine whether IFN-gamma plays a role in regulating the pulmonary T2 immune response in C. neoformans-infected C57BL/6 mice. Long-term pulmonary fungistasis was lost in IFN-gamma knockout (KO) mice, resulting in an increased pulmonary burden of fungi at wk 3. IFN-gamma was required for the early influx of leukocytes into the lungs but was not required later in the infection. By wk 3, eosinophil and macrophage numbers were elevated in the absence of IFN-gamma. The inducible NO synthase to arginase ratio was lower in the lungs of IFN-gamma KO mice and the macrophages had increased numbers of intracellular cryptococci and YM1 crystals, indicative of alternatively activated macrophages in these mice. There was evidence of pulmonary fibrosis in both wild-type and IFN-gamma KO mice by 5 wk postinfection. IFN-gamma production was not required for the development of T2 cytokine (IL-4, IL-5, IL-13) producing cells in the lungs and lung-associated lymph nodes or induction of an IgE response. At a number of time points, T2 cytokine production was enhanced in IFN-gamma KO mice. Thus, in the absence of IFN-gamma, C57BL/6 mice develop an augmented allergic response to C. neoformans, including enhanced generation of alternatively activated macrophages, which is accompanied by a switch from a chronic to a progressive pulmonary cryptococcal infection.

Scavenger receptor class A type I/II (CD204) null mice fail to develop fibrosis following silica exposure

Alveolar macrophages express the class A scavenger receptor (CD204) (Babaev VR, Gleaves LA, Carter KJ, Suzuki H, Kodama T, Fazio S, and Linton MF. Arterioscler Thromb Vasc Biol 20: 2593-2599, 2000); yet its role in vivo in lung defense against environmental particles has not been clearly defined. In the current study, CD204 null mice (129Sv background) were used to investigate the link between CD204 and downstream events of inflammation and fibrosis following silica exposure in vivo. CD204-/- macrophages were shown to recognize and uptake silica in vitro, although this response was attenuated compared with 129Sv wild-type mice. The production of tumor necrosis factor-alpha in lavage fluid was significantly enhanced in CD204 null mice compared with wild-type mice following silica exposure. Moreover, after exposure to environmental particles, CD204-/- macrophages exhibited improved cell viability in a dose-dependent manner compared with wild-type macrophages. Finally, histopathology from a murine model of chronic silicosis in 129Sv wild-type mice displayed typical focal lesions, interstitial thickening with increased connective tissue matrix, and cellular infiltrate into air space. In contrast, CD204-/- mice exhibited little to no deposition of collagen, yet they demonstrated enhanced accumulation of inflammatory cells largely composed of neutrophils. Our findings point to an important role of CD204 in mounting an efficient and appropriately regulated immune response against inhaled particles. Furthermore, these results indicate that the functions of CD204 are critical to the development of fibrosis and the resolution of inflammation.

Early response to bleomycin is characterized by different cytokine and cytokine receptor profiles in lungs

The sensitivity to the fibrosis-inducing effect of bleomycin varies considerably from species to species, the reasons for which are unknown. The variability of the response in different strains of mice is well documented. Recent evidence indicates that the upregulated expression of cytokines and cytokine receptors may be involved. We evaluated the expression pattern of some cytokines and their receptors in C57Bl/6J bleomycin-sensitive and Balb/C bleomycin-resistant mice. Animals from both strains received, under ether anesthesia, either saline (50 microl) or bleomycin (0.1 U/50 microl) intratracheally. At various times after the treatment, the lungs were analyzed for cytokines and cytokine receptors by histochemistry and their mRNA by RNase protection assay. A significantly increased expression of TNF-alpha and IL-1beta was observed in both strains. However, an upregulated lung expression for TNF-alpha and IL-1 receptors was observed in C57Bl/6J-sensitive animals only. This profile is evident from 63 h onward. In addition to TNF-alpha, bleomycin administration also resulted in the upregulated expression of TGF-beta in the lungs of both strains at 8 h and in an enhanced expression of TGF-beta receptors I and II in C57Bl/6J mice only. The upregulation of TGF-beta receptor expression was preceded in this strain by an increased expression of IL-4, IL-13, and IL-13 receptor-alpha (at 8 h after bleomycin) and followed by an upregulation of gp130 and IL-6. The difference we observed in the cytokine receptor profile may offer an additional explanation for the different fibrogenic response of the two mouse strains to bleomycin.

Cigarette smoke exposure potentiates bleomycin-induced lung fibrosis in guinea pigs

The role of tobacco smoking in the development and outcome of pulmonary fibrosis is uncertain. To approach the effects of cigarette smoke on bleomycin-induced lung fibrosis, we studied five groups of guinea pigs: 1) controls, 2) instilled with bleomycin (B), 3) exposed to tobacco smoke for 6 wk (TS), 4) bleomycin instillation plus tobacco smoke exposure for 6 wk (B+TS), and 5) tobacco smoke exposure for 6 wk and bleomycin after smoking (TS/B). Guinea pigs receiving bleomycin and tobacco smoke exposure exhibited higher fibrotic lesions including a significant increase in the number of positive alpha-smooth muscle actin cells compared with bleomycin alone (B+TS, 3.4 +/- 1.2%; TS/B, 3.7 +/- 1.5%; B, 2.3 +/- 1.5%; P < 0.01). However, only the TS/B group reached a significant increase in lung collagen compared with the bleomycin group (TS/B, 3.5 +/- 0.7; B +/- TS, 2.9 +/- 0.4; B, 2.4 +/- 0.2 mg hydroxyproline/lung; P < 0.01). Bronchoalveolar lavage (BAL) from TS/B showed an increased number of eosinophils and higher levels of IL-4 and tissue inhibitor of metalloproteinase-2 (P < 0.01 for all comparisons) and induced a significant increase in fibroblast proliferation (P < 0.05). Importantly, smoke exposure alone induced an increase in BAL neutrophils, matrix metalloproteinase-9, and fibroblast proliferation compared with controls, suggesting that tobacco smoke creates a profibrotic milieu that may contribute to the increased bleomycin-induced fibrosis.