Including, an anti-oxidative effect [4] against silicainduced oxidant stress, a direct anti-inflammatory effect of ApoA1 on silica particles since ApoA1 is known to bind to silica particles leading to repression of the inflammatory cytokine and chemokine responses [31]. However, these findings should be validated in further studies. Lipid mediators participate in the resolution of inflammation and the return to homeostasis in inflamed tissues [32]. LXA4 is a 
potent anti-inflammatory lipid mediator [33]. In the present study, LXA4 levels were increased in the lung and BAL fluid of ApoA1_D15 mice, suggesting that ApoA1 regulates inflammationrelated lipid mediators. The reduction in established silicosis in the lungs of the ApoA1_D7 and D15 mice may be explained in part by the increase in LXA4 activity. Lipoxins are biologically active eicosanoids with anti-inflammatory properties that are produced by lipoxygenases at sites of inflammation [33,34]. LXA4 has been reported to inhibit leukocyte trafficking by attenuating the release of pro-inflammatory cytokines and chemokines such as TNF-a, IL-8, and macrophage inflammatory protein-2 by inflammatory cells [35,36,37]. In addition to its anti-inflammatory activity, LXA4 stimulates neutrophils to phagocytize apoptotic cells without the release of pro-inflammatory cytokines [38,39], thereby leading to the resolution of inflammation. Exogenous resolvin E1 was recently shown to regulate LXA4 in resolving established airway inflammation in an ovalbumin-challenged mouse asthma model [40]. Recently, Borgeson et al. reported that LXA4 have anti-fibrotic effect on renal fibrosis [41]. However, no therapeutic strategies have been proven to attenuate established lung fibrosis to date. To our knowledge, the present study is the first to show a therapeutic effect on established experimental lung fibrosis. The precise mechanisms mediating the beneficial effects of ApoA1 on silica-induced fibrosis remain to be elucidated in future studies. In summary, the findings of the present study indicate that local treatment with human ApoA1 may reduce both early and established lung inflammation and fibrosis by inhibiting the production of TGF-b1, reducing the number of apoptotic cellsand increasing the level of the anti-inflammatory lipid mediator LXA4. ApoA1 appears to be a promising therapeutic agent for the treatment of established lung fibrosis.Supporting InformationFigure S1 Time courses of endogenous ApoA1(A),hApoA1 mRNA expression (B) and secreted hApoA1 (C) levels in the lungs of ApoA1 transgenic mice determined by real-time PCR and ELISA, respectively. ELISA was performed on the first 1-mL fraction of BAL fluid, with a detection limit of 3.13 ng/mL (dashed line). (TIF)Figure S2 Localization of apoptotic cells in the mouse lung detected by double-labeled immunofluororescence. Pro-surfactant C (Pro-SPC) and TUNEL stain and merged image (white arrows, double positive cells; 6100 original magnification). F4/80 and TUNEL stain and merged image (white arrows, double-positive cells; 6100 original magnification). (TIF) Figure S3 Histological analysis and quantification of lung inflammation and fibrosis in silica administered Gracillin intratracheally to UBC-GFP transgenic mice that received doxycycline or distilled water. (A) Hematoxylin and eosin staining of lung sections. Scale bar = 20 mm (B) Differential cell counts from 23115181 BAL fluid. (C) Quantification of the area occupied by AKT inhibitor 2 web silicotic nodules in the lung (n = 6/group). (D).Including, an anti-oxidative effect [4] against silicainduced oxidant stress, a direct anti-inflammatory effect of ApoA1 on silica particles since ApoA1 is known to bind to silica particles leading to repression of the inflammatory cytokine and chemokine responses [31]. However, these findings should be validated in further studies. Lipid mediators participate in the resolution of inflammation and the return to homeostasis in inflamed tissues [32]. LXA4 is a potent anti-inflammatory lipid mediator [33]. In the present study, LXA4 levels were increased in the lung and BAL fluid of ApoA1_D15 mice, suggesting that ApoA1 regulates inflammationrelated lipid mediators. The reduction in established silicosis in the lungs of the ApoA1_D7 and D15 mice may be explained in part by the increase in LXA4 activity. Lipoxins are biologically active eicosanoids with anti-inflammatory properties that are produced by lipoxygenases at sites of inflammation [33,34]. LXA4 has been reported to inhibit leukocyte trafficking by attenuating the release of pro-inflammatory cytokines and chemokines such as TNF-a, IL-8, and macrophage inflammatory protein-2 by inflammatory cells [35,36,37]. In addition to its anti-inflammatory activity, LXA4 stimulates neutrophils to phagocytize apoptotic cells without the release of pro-inflammatory cytokines [38,39], thereby leading to the resolution of inflammation. Exogenous resolvin E1 was recently shown to regulate LXA4 in resolving established airway inflammation in an ovalbumin-challenged mouse asthma model [40]. Recently, Borgeson et al. reported that LXA4 have anti-fibrotic effect on renal fibrosis [41]. However, no therapeutic strategies have been proven to attenuate established lung fibrosis to date. To our knowledge, the present study is the first to show a therapeutic effect on established experimental lung fibrosis. The precise mechanisms mediating the beneficial effects of ApoA1 on silica-induced fibrosis remain to be elucidated in future studies. In summary, the findings of the present study indicate that local treatment with human ApoA1 may reduce both early and established lung inflammation and fibrosis by inhibiting the production of TGF-b1, reducing the number of apoptotic cellsand increasing the level of the anti-inflammatory lipid mediator LXA4. ApoA1 
appears to be a promising therapeutic agent for the treatment of established lung fibrosis.Supporting InformationFigure S1 Time courses of endogenous ApoA1(A),hApoA1 mRNA expression (B) and secreted hApoA1 (C) levels in the lungs of ApoA1 transgenic mice determined by real-time PCR and ELISA, respectively. ELISA was performed on the first 1-mL fraction of BAL fluid, with a detection limit of 3.13 ng/mL (dashed line). (TIF)Figure S2 Localization of apoptotic cells in the mouse lung detected by double-labeled immunofluororescence. Pro-surfactant C (Pro-SPC) and TUNEL stain and merged image (white arrows, double positive cells; 6100 original magnification). F4/80 and TUNEL stain and merged image (white arrows, double-positive cells; 6100 original magnification). (TIF) Figure S3 Histological analysis and quantification of lung inflammation and fibrosis in silica administered intratracheally to UBC-GFP transgenic mice that received doxycycline or distilled water. (A) Hematoxylin and eosin staining of lung sections. Scale bar = 20 mm (B) Differential cell counts from 23115181 BAL fluid. (C) Quantification of the area occupied by silicotic nodules in the lung (n = 6/group). (D).
