Bilirubin ameliorates bleomycin-induced pulmonary fibrosis in rats

Many possible treatments for pulmonary fibrosis have been investigated, but except for some current clinical trials, none have succeeded in clinical trials. On the basis of the antioxidant action of bilirubin (BIL), we examined the effects of hyperbilirubinemia on the development of bleomycin (BLM)-induced pulmonary fibrosis in rats. The animals' plasma BIL level was kept within 3 and 10 mg/dl by repeated intravenous infusion of a high dose of BIL. We studied the inhibitory effects of hyperbilirubinemia on BLM-induced pulmonary fibrosis through histopathologic and biochemical analyses. Mortality of rats with BLM-induced pulmonary fibrosis was significantly lower in the three groups with hyperbilirubinemia. The ameliorating effect of hyperbilirubinemia on pulmonary fibrosis was shown by lung histology, as well as by a decreased lung content of hydroxyproline and reduced bronchoalveolar lavage fluid (BALF) concentration of transforming growth factor (TGF)-beta(1). The number of polymorphonuclear leukocytes and lymphocytes in BALF was also decreased in the groups with hyperbilirubinemia. Furthermore, oxidative metabolites of BIL in urine were present at significantly higher levels in BLM-treated rats with hyperbilirubinemia than in those without hyperbilirubinemia. These data suggest that the antioxidative action of BIL can attenuate BLM-induced pulmonary fibrosis, partly by inhibiting lung inflammation and production of TGF-beta1.     

Administration of alpha 1-proteinase inhibitor ameliorates bleomycin-induced pulmonary fibrosis in hamsters.

The effect of alpha 1-proteinase inhibitor (alpha 1Pi) administration on the acute lung injury and subsequent fibrosis induced by bleomycin (BLM) was examined in hamsters. Pulmonary lesions were quantitatively reduced in alpha 1Pi-administered BLM-treated (BLM-alpha 1Pi) animals compared with animals treated by BLM alone (BLM-control) at both 7 days (acute stage) and 30 days (fibrotic stage) after BLM treatment. Analysis of intraalveolar cells from bronchoalveolar lavage (BAL) fluid revealed that neutrophils and lymphocytes were significantly decreased in the BLM-alpha 1Pi animals at 7 days after BLM treatment and that 30 days after BLM treatment macrophages as well as neutrophils and lymphocytes were remarkably decreased in the BLM-alpha 1Pi animals. The elastase activity in supernatants of BAL fluid during 7 days following BLM treatment was detected, but there was no difference between the two groups. In vitro studies on neutrophil responsiveness to stimulation of BAL fluid at 3 days after BLM treatment revealed noticeable chemotaxis and generation of superoxide anion of isolated neutrophils, but alpha 1Pi did not show any inhibitory effects on neutrophil responsiveness. We suggest that alpha 1Pi administration ameliorates pulmonary fibrosis preceded by acute lung injury induced by BLM treatment in hamsters and that the inhibitory effects of alpha 1Pi on lung injury may not be brought about by altered elastase activity, chemotaxis, or superoxide generation in neutrophils. Alternative mechanisms are discussed.     

Imatinib as a novel antifibrotic agent in bleomycin-induced pulmonary fibrosis in mice

Imatinib mesylate is a potent and specific tyrosine kinase inhibitor against c-ABL, BCR-ABL, and c-KIT, and has been demonstrated to be highly active in chronic myeloid leukemia and gastrointestinal stromal tumors. We examined the antifibrotic effects of imatinib using a bleomycin-induced lung fibrosis model in mice because imatinib also inhibits tyrosine kinase of platelet-derived growth factor receptors (PDGFRs). Imatinib inhibited the growth of primary murine lung fibroblasts and the autophosphorylation of PDGFR-beta induced by PDGF. Administration of imatinib significantly prevented bleomycin-induced pulmonary fibrosis in mice, partly by reducing the number of mesenchymal cells incorporating bromodeoxyuridine. Analysis of bronchoalveolar lavage cells demonstrated that imatinib did not suppress early inflammation on Days 7 and 14 caused by bleomycin. These results suggest that imatinib has the potential to prevent pulmonary fibrosis by inhibiting the proliferation of mesenchymal cells, and that imatinib might be useful for the treatment of pulmonary fibrosis in humans.     

A novel single-chain-Fv antibody against connective tissue growth factor attenuates bleomycin-induced pulmonary fibrosis in mice

Background and objective: Connective tissue growth factor (CTGF) has been identified as playing critical roles in fibrosis and is a promising therapeutic target. In a previous study, we used a phage display library to develop a humanized single‐chain variable fragment antibody (scFv) against CTGF. In the present study, the protective effect of anti‐CTGF scFv against bleomycin (BL)‐induced pulmonary fibrosis was investigated in mice. Methods: The expression of α‐smooth muscle actin in human embryonic lung fibroblast (HELF) cells was analysed by western blotting. A mouse model of pulmonary fibrosis was established by tracheal injection of BL (5 mg/kg). Mice received anti‐CTGF scFv (4 mg/kg, three times a week) by i.v. injection. The effects of anti‐CTGF scFv were evaluated by leukocyte counts in BAL fluid, hydroxyproline measurements in lung tissue and pathological examination. Results: α‐Smooth muscle actin expression was decreased in HELF cells treated with anti‐CTGF scFv. Anti‐CTGF scFv significantly reduced the numbers of inflammatory leukocytes (total and differential count) in BAL fluid, as well as the hydroxyproline content of lung tissue. The severity of alveolitis and fibrosis in the mouse model was markedly attenuated by treatment with anti‐CTGF scFv. Conclusions: Anti‐CTGF scFv may potentially be developed as a useful inhibitor of pulmonary fibrosis.     

Cyclosporin A upmodulates bleomycin-induced pulmonary fibrosis in BALB/c mice

BACKGROUND: Intratracheal instillation of bleomycin (Bleo) into rodents serves as a model for human lung fibrosis. Various mouse strains respond differently to Bleo, and BALB/c mice are relatively resistant. OBJECTIVE: Since T lymphocytes have been shown to play a major role in this model, the effect of the immunomodulator cyclosporin A (CyA) on lung fibrosis was studied in Bleo-'resistant' BALB/c mice. METHODS: Pulmonary fibrosis was induced by a single intratracheal (IT) instillation of Bleo. One of the four following treatments was given to one of four groups of female BALB/c mice: (1) Bleo-CyA: IT Bleo and daily intraperitoneal (IP) injections of CyA 100 mg/day starting 1 day before IT instillation of Bleo; (2) Bleo-Sal: IT Bleo and IP injections of saline; (3) Sal-CyA: IT saline and IP CyA 100 mg/kg; (4) Sal-Sal: IT and IP saline. The animals were killed on day 14. Fibrosis was evaluated by analysis of hydroxyproline and by quantitative image analysis of the fibrosis fraction. Ex vivo IFN-gamma, IL-4, IL-13 and IL-5 secretion by peribronchial lymphatic tissue lymphocytes was measured. RESULTS: Pretreatment with CyA upmodulated Bleo-induced lung fibrosis in the Bleo-'resistant' BALB/c mice; hydroxyproline was higher in Bleo-CyA compared to Bleo-Sal animals and both hydroxyproline and fibrosis fraction measurements were higher in Bleo-CyA compared to Sal-Sal. Cytokine secretion by lymphocytes demonstrated increased IFN-gamma/IL-4 and IFN-gamma/IL-13 mean secretion ratios in the Bleo-CyA animals compared to the Bleo-Sal animals. CONCLUSIONS: These results indicate that CyA upmodulates Bleo-induced lung fibrosis in Bleo-'resistant' BALB/c mice by allowing the emergence of a Th1 inflammatory response.     

白三烯抑制剂对博莱霉素所致大鼠肺纤维化的干预作用

目的 观察白三烯抑制剂(LT-S)齐留通对博莱霉素(BLM)所致大鼠肺纤维化模型肺纤维化形成过程的影响.方法 54只SD雄性大鼠随机分为正常组(C组)、模型对照组(M组)和LT-S组(S组)3组,每组18只.S组于气管内滴注BLM(5 mg/kg)诱导肺纤维化,于造模当天开始每日给予齐留通100 mg/kg灌胃;M组以生理盐水代替齐留通灌胃;C组均用生理盐水代替BLM和齐留通.各组动物均于制模后的第7天、第14天和第28天分别随机处死6只动物,分取肺组织行病理切片苏木精-伊红染色和Masson染色观察肺泡炎和肺纤维化程度、碱水解法检测肺组织羟脯氨酸(Hyp)浓度、免疫组织化学技术检测肺组织α平滑肌肌动蛋白(α-SMA)和转化生长因子β1(TGF-β1)水平.结果 S组肺泡炎和肺纤维化程度及肺组织Hyp含量均显著低于M组,其TGF-β1和α-SMA在肺组织中的表达水平亦均显著低于M组.结论 LT-S可减轻BLM诱导的大鼠肺纤维化,并可能通过抑制TGF-β1蛋白表达而实现对成纤维原细胞增殖的抑制.     

Effect of the beige mutation on bleomycin-induced pulmonary fibrosis in mice

A single endotracheal administration of bleomycin causes pulmonary fibrosis in several animal species. In view of the functional deficits in neutrophil function as a result of the beige mouse (bg/bg) mutation, its effect on bleomycin-induced pulmonary fibrosis was examined to evaluate the role of the neutrophil in such a response. Neutrophils from beige mice showed a selective defect in the ability to degranulate in response to cytochalasin B and formyl-methionyl-leucyl-phenylalanine, without impairing their ability to produce superoxide anion and H2O2 in response to the same stimuli as well as phorbol myristate acetate. Despite this functional deficit, beige mice responded more intensely to bleomycin than did their heterozygote controls at both 2 wk and 1 month after drug instillation, as assessed by both lung collagen and deposition. This suggests that the inability to mobilize hydrolytic enzymes has no effect on the ability to mount a fibrogenic response, and it would even be detrimental by enhancing such a response caused by decreased connective tissue catabolism as a consequence of the inability to release the granule enzymes to the extracellular space.     

Polyinosinic-polycytidylic acid, an interferon inducer, ameliorates bleomycin-induced lung fibrosis in mice.

The inhibitory effect of polyinosinic-polycytidylic acid (Poly IC), an inducer of interferons, on bleomycin-induced lung collagen accumulation was investigated in mice. Poly IC (10 mg/kg, intraperitoneally) or saline was given for 2 days and immediately prior to intratracheal instillation of bleomycin (0.125 units/mouse) or an equivalent volume of saline and thereafter daily for 13 days. Lung hydroxyproline levels in saline-saline (control), Poly IC-saline (Poly IC), bleomycin-saline and bleomycin-Poly IC groups averaged 279, 287, 459, and 358 micrograms/lung, respectively. The bleomycin + Poly IC mice had significantly less lung hydroxyproline than bleomycin mice, but significantly more hydroxyproline than control or Poly IC mice. Similarly, bleomycin + Poly IC mice had significantly less protein in bronchoalveolar lavage fluid (BALF) supernatant than bleomycin mice, but significantly more protein than control or Poly IC mice. Total cell counts for cells recovered from BALF showed significant increases of 174 and 167% in bleomycin and bleomycin + Poly IC as compared to controls, while the Poly IC group showed a significant decrease of 47% which was primarily due to a decrease in alveolar macrophages. The bleomycin group had significantly more neutrophils, monocytes, macrophages, and lymphocytes than control mice, while bleomycin + Poly IC mice lacked the significant increase in lymphocytes. Bleomycin + Poly IC mice had significantly more monocytes than the bleomycin group. All bleomycin-treated mice had lung lesions, but no lesions were observed in control or Poly IC mice. Bleomycin + Poly IC mice had significantly more (58%) lesions than bleomycin. In contrast, the volume of interstitial lesion in bleomycin + Poly IC mice showed significantly less extracellular fibers (decreased by 62%) and no difference in fibroblasts as compared to bleomycin mice. Fibrotic lesions in bleomycin mice were multifocal and varied from large areas of organized connective tissue to thickened septa lined by cuboidal epithelial cells. Interstitial lesions in bleomycin + Poly IC had a significantly greater volume of mononuclear phagocytes and lymphocytes, but less organized connective tissue than the bleomycin group. Poly IC treatment ameliorated bleomycin-induced lung collagen accumulation.     

静脉注射不同剂量博莱霉素诱导小鼠肺纤维化的比较研究

目的寻求建立小鼠肺纤维化模型的改良方案。方法雄性C57BL/6小鼠随机分为单次和多次注射模型组。单次注射模型组分为博莱霉素100、150、200 mg/kg组及对照组1;多次注射模型组分为博莱霉素50 mg/kg组及对照组2。取小鼠肺组织行病理检查,免疫组化检测肺Ⅰ型胶原蛋白、TGF-β1和α-SMA的表达。结果在单次注射模型组中,100、150、200 mg/kg组的肺泡炎均于第2周达峰(P0.01);肺纤维化分别在第2、4、4周达峰(P0.01)。在多次注射模型组中,50 mg/kg组肺泡炎和肺纤维化均在第10周达峰(P0.05)。TGF-β1和α-SMA在肺泡炎和纤维化部位表达明显增加。结论尾静脉单次注射博莱霉素200mg/kg可有效诱导肺纤维化,复制一个相对稳定的肺纤维化模型。     

Angiotensin II antagonism fails to ameliorate bleomycin-induced pulmonary fibrosis in mice.

Based on current evidence, transforming growth factor (TGF)-beta plays a central pathogenic role in the development of pulmonary fibrosis. There is growing evidence that angiotensin II can serve as a stimulus for TGF-beta-mediated lung fibrosis. However, the role of angiotensin II in the pathobiology of pulmonary fibrosis in vivo remains unclear and the therapeutic potential for targeting angiotensin II in a bleomycin-induced pulmonary fibrosis model is not well known. Therefore, the aim of this study was to test whether the angiotensin II antagonist, losartan, attenuated the development of bleomycin-induced pulmonary fibrosis in two distinct murine strains, C57/BL6 and Sv129. This was determined by histopathology and quantification of collagen content by hydroxyproline assay. Despite demonstrable angiotensin II antagonism in vivo and a reduction in measures of acute lung injury, losartan therapy, at a dose shown to reduce renal and cardiac fibrosis in mice, failed to significantly ameliorate bleomycin-induced pulmonary fibrosis. In conclusion, these data suggest that the pulmonary fibrotic disease process in vivo is not solely dependent on angiotensin II activity and the potential for angiotensin II receptor blockers as a therapeutic strategy in patients with pulmonary fibrosis may be limited.     

N-乙酰半胱氨酸与IL-27对博莱霉素诱导的小鼠肺纤维化的影响

目的探讨研究IL-27与N-乙酰半光氨酸(NAC)对博来霉素诱导的小鼠肺纤维化模型影响; 方法经小鼠支气管内注入博来霉素建立模型后,分为正常组(A组)、博莱霉素模型(BLM)组(B组)、BLM+IL-27组(C组)、BLM+NAC组(D组),各组分别于7、14、28 d处死小鼠5只,取肺组织行HE染色及Masson染色,行肺组织肺泡炎、肺纤维化评分、羟脯氨酸含量测定并对比; 结果7 d肺泡炎评分：A组(1.00±0.00),B组(3.47±0.23),C组(2.17±0.13),D组(2.89±0.29);14 d肺泡炎评分：A组(1.00±0.00),B组(2.94±0.31),C组(1.92±0.16),D组(2.48±0.19);28 d肺泡炎评分：A组(1.00±0.00),B组(1.97±0.19),C组(1.38±0.18),D组(1.65±0.17)。7 d肺纤维化评分：A组(1.00±0.00),B组(1.82±0.22),C组(1.21±0.13),D组(1.51±0.26);14 d肺纤维化评分：A组(1.00±0.00),B组(2.64±0.32),C组(1.95±0.15),D组(2.13±0.16);28 d肺纤维化评分：A组(1.00±0.00),B组(3.48±0.14),C组(2.17±0.17),D组(2.96±0.18);7 d肺组织羟脯胺酸含量：A组(143.19±4.09),B组(281.83±8.31),C组(207.81±5.29),D组(231.49±3.97);14 d肺组织羟脯胺酸含量：A组(147.81±8.91),B组(317.63±6.30),C组(253.86±4.91),D组(289.73±5.09);14 d肺组织羟脯胺酸含量：A组(141.82±7.28),B组(381.97±5.49),C组(303.81±4.92),D组(358.29±7.38);各组差异具有统计学意义。 结论NAC、IL-27均有抑制博来霉素诱导的小鼠肺纤维化进程的作用,但IL-27干预组小鼠肺泡炎评分、肺肺纤维化评分、羟脯胺酸含量均低于NAC干预组。故IL-27抑制肺纤维化进程的疗效优于NAC。     

Losartan attenuates bleomycin-induced pulmonary fibrosis in rats

BACKGROUND: In addition to regulating blood pressure and body fluid homeostasis, the renin-angiotensin system is also involved in lung fibrogenesis. OBJECTIVE: To study the effect of losartan, an angiotensin II antagonist, on bleomycin-induced pulmonary fibrosis in rats and its possible mechanism. METHODS: Pulmonary fibrosis was induced in SD rats by intratracheal instillation of bleomycin (5 mg x kg(-1)). Subsequently, the rats received daily losartan (3, 9 and 27 mg x kg(-1)) or prednisone (20 mg x kg(-1)) orally. Six rats in each group were sacrificed 14 and 21 days after intratracheal instillation. Hydroxyproline, superoxide dismutase (SOD), and malondialdehyde (MDA) levels in lung tissues were determined by spectroscopy. The levels of TGF-beta1 in serum were measured by ELISA. Histological changes in the lungs were evaluated by hematoxylin-eosin stain, and scored. RESULTS: Rat body weight evidently decreased while the indices of lung and hydroxyproline contents in lung tissue were significantly increased 14 and 21 days after intratracheal bleomycin instillation. Inflammatory cell infiltration and fibrotic scores were more prominent in the model group compared to the sham group. Losartan (3, 9 and 27 mg.kg(-1), i.g.) apparently attenuated the degree of pulmonary fibrosis. Further study showed that losartan significantly increased SOD levels while it decreased MDA contents in lung homogenates. Serum TGF-beta1 levels of pulmonary fibrosis rats were also decreased by losartan. CONCLUSIONS: Losartan had an inhibitory effect on bleomycin-induced pulmonary fibrosis, and its effect may be associated with its anti-free radicals and the reduction in TGF-beta1.     

Gefitinib prevents bleomycin-induced lung fibrosis in mice

RATIONALE: Transforming growth factor-alpha and epidermal growth factor (EGF), the ligands for EGF receptor (EGFR), stimulate fibroblast proliferation and play an important role in the pathogenesis of pulmonary fibrosis. Therefore, inhibition of the EGFR signal by an EGFR tyrosine kinase inhibitor (EGFR-TKI) may prevent pulmonary fibrosis. However, there is a possibility that blocking the EGFR signal may inhibit epithelial cell repair, thereby exaggerating lung fibrosis. OBJECTIVE: To investigate the effect of EGFR-TK inhibition on lung fibrosis. METHODS: We looked at the effects of the EGFR-TKIs gefitinib (20, 90, 200 mg/kg) and AG1478 (12 mg/kg) on a bleomycin-induced lung fibrosis model in mice. MEASUREMENTS AND MAIN RESULTS: Gefitinib prevented lung fibrosis at all three doses. Furthermore, in those mice that did not receive bleomycin treatment, gefitinib at 200 mg/kg did not induce lung fibrosis. Immunohistochemistry revealed that phosphorylation of EGFR in lung mesenchymal cells induced by bleomycin was inhibited by gefitinib. AG1478 also attenuated the lung fibrosis. In vitro studies further demonstrated that the addition of gefitinib or AG1478 suppressed the EGFR ligand-induced proliferation of lung fibroblasts. CONCLUSIONS: These findings suggest that, in the preclinical setting, EGFR-TKIs may have a protective effect on lung fibrosis induced by bleomycin. Because these molecular targeted drugs may have differing effects depending on species and individuals, a cautious interpretation is warranted.     

Lung cytokine production in bleomycin-induced pulmonary fibrosis.

In bleomycin-induced pulmonary fibrosis, lung injury is accompanied with inflammation and subsequent fibrosis. In this study, lung mRNA for several cytokines was measured in bleomycin-treated mice to evaluate their roles in lung fibrosis. Significant increases in tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) mRNA were found in lungs of bleomycin-treated responder CBA mice but not in nonresponder BALB/c mice. Increases in responder animals peaked on day 7 after bleomycin administration, and subsequently returned toward control levels. This time course paralleled that for the increase in beta-actin mRNA, but preceded the peak increase in mRNA for collagens I and III. When lung macrophages were analyzed for cytokine secretion, differences were observed between alveolar macrophages and interstitial cells, and between cells from bleomycin-responsive CBA and nonresponsive BALB/c mice. Only alveolar macrophages from CBA mice secreted increased amounts of IL-1. TNF-alpha activity was increased in conditioned media of alveolar and interstitial cells of CBA mice, while only alveolar macrophages of nonresponder BALB/c mice secreted any activity. The kinetics of the increased secretion of TNF-alpha was dissimilar for these different cells. These results are consistent with the conclusion that increased production of TNF-alpha and TGF-beta is an important component of the fibrotic process.     

Alveolar wall basement membranes in bleomycin-induced pulmonary fibrosis

The ultrastructural characteristics of alveolar wall basement membranes (BM) were defined in an experimental model of pulmonary fibrosis. Lungs of adult hamsters were examined 2 to 60 days after a single intratracheal instillation of 0.5 units of bleomycin sulfate. Sections of lung fixed with tannic acid and glutaraldehyde were analyzed for epithelial basement membrane (EPI-BM) thickness and duplication, and tissue incubated in ruthenium red prior to fixation was evaluated for distribution of EPI-BM anionic sites. There were no major alterations in capillary EPI-BM. Six days after bleomycin, during acute inflammation, there was focal injury to alveolar epithelial cells and resultant denudation of EPI-BM. Denuded EPI-BM was folded with the lamina densa 60% thicker than in control animals, suggesting its active or passive retraction. Despite type 2 cell hyperplasia and repopulation of the epithelium, there was no duplication of EPI-BM. Thirty and 60 days after bleomycin, the epithelium was intact, inflammation had subsided, and widespread but focal fibrosis was present. This stage was characterized by thickening and duplication of the EPI-BM; 10% of EPI-BM on the thin side of the alveolar wall were duplicated at 30 days and 30% at 60 days. Duplication and thickening, although worse in fibrotic areas, also occurred in normal-appearing areas of lung, showing that EPI-BM changes may be the only residuum of previous damage. Duplication of EPI-BM in this model of pulmonary fibrosis is a late rather than an early feature of disease.(ABSTRACT TRUNCATED AT 250 WORDS)     

beta-Aminopropionitrile prevents bleomycin-induced pulmonary fibrosis in the hamster

beta-Aminopropionitrile (beta APN), an agent that prevents collagen accumulation in tissues, was evaluated for its ability to prevent excess collagen formation in bleomycin-induced pulmonary fibrosis in the hamster. Two groups of animals received a single endotracheal dose of bleomycin; one of these was injected with beta APN twice daily for 30 days. A third group received endotracheal saline and a fourth group received saline and beta APN. After 30 days, we measured pressure-volume curves of saline-filled lungs, collagen content, and degree of fibrosis. Endotracheal bleomycin increased collagen content, decreased lung volume, and produced fibrosis and a mortality rate of 51%. The administration of beta APN to bleomycin-treated animals prevented excess collagen accumulation and diminished total protein, reversed volume diminution, produced less fibrosis, and improved the mortality rate to 24%; beta APN alone had no effect on lung mechanics or collagen content. The biochemical, functional, and structural features of bleomycin-induced lung fibrosis are amenable to control with beta APN.     

Attenuation of bleomycin-induced pulmonary fibrosis by follistatin

RATIONALE: Activins are members of the transforming growth factor-beta superfamily thought to be involved in repair processes after tissue injury. OBJECTIVES: The aim of this study was to clarify whether activin and its antagonist, follistatin, played a significant role in lung injury and fibrosis. METHODS AND RESULTS: In bleomycin (BLM)-treated rat lung, mRNA for the beta(A) subunit of activin was upregulated on Days 3 and 7 and decreased gradually thereafter. Immunoreactive activin A was abundantly expressed in macrophages infiltrated in the lung, and was detected in fibroblasts accumulated in the fibrotic area on Day 28. We then administered follistatin, an activin antagonist, to BLM-treated rats. Follistatin significantly reduced the number of macrophages and neutrophils in bronchoalveolar lavage and reduced the protein content. Histologically, follistatin markedly reduced the number of infiltrating cells, ameliorated the destruction of lung architecture on Day 7, and attenuated lung fibrosis on Day 28. The hydroxyproline content was significantly lower in follistatin-treated rats. In cultured lung fibroblasts, production of activin A was augmented by transforming growth factor-beta, and activin antagonist follistatin significantly inhibited transforming growth factor-beta-induced fibroblast activation. These results suggest that activin A was produced in the lung after BLM treatment and promoted acute inflammation and subsequent fibrosis. CONCLUSIONS: Follistatin is effective in treating acute lung injury and BLM-induced fibrosis by blocking the actions of activin and transforming growth factor-beta.