Mast cells are essential for the full development of silica-induced pulmonary inflammation: a study with mast cell-deficient mice

FcεRI deficiency alleviates silica-induced pulmonary inflammation and fibrosis

Silicosis is one of the most important occupational diseases worldwide, caused by inhalation of silica particles or free crystalline silicon dioxide. As a disease with high mortality, it has no effective treatment and new therapeutic targets are urgently needed. Recent studies have identified FCER1A, encoding α-subunit of the immunoglobulin E (IgE) receptor FcεRI, as a candidate gene involved in the biological pathways leading to respiratory symptoms. FcεRI is known to be important in allergic asthma, but its role in silicosis remains unclear. In this study, serum IgE concentrations and FcεRI expression were assessed in pneumoconiosis patients and silica-exposed mice. The role of FcεRI was explored in a silica-induced mouse model using wild-type and FcεRI-deficient mice. The results showed that serum IgE concentrations were significantly elevated in both pneumoconiosis patients and mice exposed to silica compared with controls. The mRNA and protein expression of FcεRI were also significantly increased in the lung tissue of patients and silica-exposed mice. FcεRI deficiency significantly attenuated the changes in lung function caused by silica exposure. Silica-induced elevations of IL-1β, IL-6, and TNF-α were significantly attenuated in the lung tissue and bronchoalveolar lavage fluid (BALF) of FcεRI-deficient mice compared with wild-type controls. Additionally, FcεRI-deficient mice showed a significantly lower score of pulmonary fibrosis than wild-type mice following exposure to silica, with significantly lower hydroxyproline content and expression of fibrotic genes Col1a1 and Fn1. Immunofluorescent staining suggested FcεRI mainly on mast cells. Mast cell degranulation took place after silica exposure, as shown by increased serum histamine levels and β-hexosaminidase activity, which were significantly reduced in FcεRI-deficient mice compared with wild-type controls. Together, these data showed that FcεRI deficiency had a significant protective effect against silica-induced pulmonary inflammation and fibrosis. Our findings provide new insights into the pathophysiological mechanisms of silica-induced pulmonary fibrosis and a potential target for the treatment of silicosis.

Proteomic profiling change during the early development of silicosis disease

BACKGROUND

Silicosis is one of several severe occupational diseases for which effective diagnostic tools during early development are currently unavailable. In this study we focused on proteomic profiling during the early stages of silicosis to investigate the pathophysiology and identify the proteins involved.

METHODS

Two-dimensional (2D) gel electrophoresis and MALDI-TOF-MS were used to assess the proteomic differences between healthy individuals (HI), dust-exposed workers without silicosis (DEW) and silicosis patients (SP). Proteins abundances that differed by a factor of two-fold or greater were subjected to more detailed analysis, and enzyme linked to immunosorbent assay (ELISA) was employed to correlate with protein expression data.

RESULTS

Compared with HI, 42 proteins were more abundant and 8 were less abundant in DEW, and these were also differentially accumulated in SP. Closer inspection revealed that serine protease granzyme A, alpha-1-B-glycoprotein (A1BG) and the T4 surface glycoprotein precursor (TSGP) were among the up-regulated proteins in DEW and SP. Significant changes in serine proteases, glycoproteins and proto-oncogenes may be associated with the response to cytotoxicity and infectious pathogens by activation of T cells, positive regulation of extracellular matrix structural constituents and immune response, and fibroblast proliferation. Up-regulation of cytokines included TNFs, interferon beta precursor, interleukin 6, atypical chemokine receptor 2, TNFR13BV, and mutant IL-17F may be involved in the increased and persistent immune response and fibrosis that occurred during silicosis development.

CONCLUSIONS

Granzymes, glycoproteins, cytokines and immune factors were dramatically involved in the immune response, metabolism, signal regulation and fibrosis during the early development of silicosis. Proteomic profiling has expanded our understanding of the pathogenesis of silicosis, and identified a number of targets that may be potential biomarkers for early diagnosis of this debilitating disease.

Mast cell accumulation precedes tissue fibrosis induced by intravenously administered amorphous silica nanoparticles

Despite the increasing use of amorphous silica nanoparticles (SNPs) in biomedical applications, their toxicity after intravenous administration remains a major concern. We investigated the effects of single 7 mg/kg intravenous infusions of 13 nm SNPs on hemodynamic parameters in rats. Hematological and biochemical parameters were assessed at 7, 30, and 60 d post treatment. Silicon content in the liver, lungs, heart, and kidney was analyzed, as well as tissue histology with special emphasis on mast cell (MC) content. SNP infusion had no effect on hemodynamics, nor did it alter hematological or biochemical parameters. SNP retention in the liver was conspicuous for up to 60 d. Among the other organs analyzed, silicon content was significantly increased only in the lung at 1-h post infusion. Despite the relatively low dose, SNP administration caused extensive liver remodeling, including the formation of multiple foreign body-type granulomas starting 7 d post treatment, and subsequent development of fibrosis. Histopathological changes in the liver were not preceded by hepatocyte necrosis. We found increased MC abundance in the liver, lungs, and heart starting on day 30 post treatment. MC recruitment in the liver preceded fibrosis, suggesting that MCs are involved in liver tissue remodeling elicited by intravenously administered SNPs.

Crystalline silica-induced leukotriene B4-dependent inflammation promotes lung tumour growth

Chronic exposure to crystalline silica (CS) causes silicosis, an irreversible lung inflammatory disease that may eventually lead to lung cancer. In this study, we demonstrate that in K-ras(LA1) mice, CS exposure markedly enhances the lung tumour burden and genetic deletion of leukotriene B4 receptor-1 (BLT1(-/-)) attenuates this increase. Pulmonary neutrophilic inflammation induced by CS is significantly reduced in BLT1(-/-)K-ras(LA1) mice. CS exposure induces LTB4 production by mast cells and macrophages independent of inflammasome activation. In an air-pouch model, CS-induced neutrophil recruitment is dependent on LTB4 production by mast cells and BLT1 expression on neutrophils. In an implantable lung tumour model, CS exposure results in rapid tumour growth and decreased survival that is attenuated in the absence of BLT1. These results suggest that the LTB4/BLT1 axis sets the pace of CS-induced sterile inflammation that promotes lung cancer progression. This knowledge may facilitate development of immunotherapeutic strategies to fight silicosis and lung cancer.

Tryptase is involved in the development of early ventilator-induced pulmonary fibrosis in sepsis-induced lung injury

Introduction

Most patients with sepsis and acute lung injury require mechanical ventilation to improve oxygenation and facilitate organ repair. Mast cells are important in response to infection and resolution of tissue injury. Since tryptase secreted from mast cells has been associated with tissue fibrosis, we hypothesized that tryptase would be involved in the early development of ventilator-induced pulmonary fibrosis in a clinically relevant model of sepsis-induced lung injury.

Methods

Prospective, randomized, controlled animal study using Sprague-Dawley rats. Sepsis was induced by cecal ligation and perforation. Animals were randomized to spontaneous breathing or two ventilatory strategies for 4 h: protective ventilation with tidal volume (VT) = 6 ml/kg plus 10 cmH₂O positive end-expiratory pressure (PEEP) or injurious ventilation with VT = 20 ml/kg plus 2 cmH₂O PEEP. Healthy, non-ventilated animals served as non-septic controls. We studied the following end points: histology, serum cytokine levels, hydroxyproline content, tryptase and proteinase-activated receptor-2 (PAR-2) protein level in lung homogenates, and tryptase and PAR-2 immunohistochemical localization in the lungs.

Results

All septic animals developed acute lung injury. Animals ventilated with high VT had a significant increase of pulmonary fibrosis, hydroxyproline content, tryptase and PAR-2 protein levels compared to septic controls (P <0.0001). However, protective ventilation attenuated sepsis-induced lung injury and decreased lung tryptase and PAR-2 protein levels. Immunohistochemical staining confirmed the presence of tryptase and PAR-2 in the lungs.

Conclusions

Mechanical ventilation modified tryptase and PAR-2 in injured lungs. Increased levels of these proteins were associated with development of sepsis and ventilator-induced pulmonary fibrosis early in the course of sepsis-induced lung injury.

Activated MCTC mast cells infiltrate diseased lung areas in cystic fibrosis and idiopathic pulmonary fibrosis

Background

Although mast cells are regarded as important regulators of inflammation and tissue remodelling, their role in cystic fibrosis (CF) and idiopathic pulmonary fibrosis (IPF) has remained less studied. This study investigates the densities and phenotypes of mast cell populations in multiple lung compartments from patients with CF, IPF and never smoking controls.

Methods

Small airways, pulmonary vessels, and lung parenchyma were subjected to detailed immunohistochemical analyses using lungs from patients with CF (20 lung regions; 5 patients), IPF (21 regions; 7 patients) and controls (16 regions; 8 subjects). In each compartment the densities and distribution of MC_T and MC_TC mast cell populations were studied as well as the mast cell expression of IL-6 and TGF-β.

Results

In the alveolar parenchyma in lungs from patients with CF, MC_TC numbers increased in areas showing cellular inflammation or fibrosis compared to controls. Apart from an altered balance between MC_TC and MC_T cells, mast cell in CF lungs showed elevated expression of IL-6. In CF, a decrease in total mast cell numbers was observed in small airways and pulmonary vessels. In patients with IPF, a significantly elevated MC_TC density was present in fibrotic areas of the alveolar parenchyma with increased mast cell expression of TGF-β. The total mast cell density was unchanged in small airways and decreased in pulmonary vessels in IPF. Both the density, as well as the percentage, of MC_TC correlated positively with the degree of fibrosis. The increased density of MC_TC, as well as MC_TC expression of TGF-β, correlated negatively with patient lung function.

Conclusions

The present study reveals that altered mast cell populations, with increased numbers of MC_TC in diseased alveolar parenchyma, represents a significant component of the histopathology in CF and IPF. The mast cell alterations correlated to the degree of tissue remodelling and to lung function parameters. Further investigations of mast cells in these diseases may open for new therapeutic strategies.

Mast cells in lung inflammation

Mast cells play an important role in the lung in both health and disease. Their primary role is to initiate an appropriate program of inflammation and repair in response to tissue damage initiated by a variety of diverse stimuli. They are important for host immunity against bacterial infection and potentially in the host immune response to non small cell lung cancer. In situations of ongoing tissue damage, the sustained release of numerous pro-inflammatory mediators, proteases and cytokines, contributes to the pathophysiology of lung diseases such as asthma and interstitial lung disease. A key goal is the development of treatments which attenuate adverse mast cell function when administered chronically to humans in vivo. Such therapies may offer a novel approach to the treatment of many life-threatening diseases.

The specific chymase inhibitor TY-51469 suppresses the accumulation of neutrophils in the lung and reduces silica-induced pulmonary fibrosis in mice

Chymase is a chymotrypsin-like serine protease that is present in mast cells. Its activities include various effects associated with inflammatory responses. But little is known about the effects of chymase in pulmonary fibrosis. The mouse silicosis model was induced by intratracheal injection of 10 mg silica. The Ashcroft pathological score and the hydroxyproline content of lungs were measured to evaluate the effect of a chymase inhibitor, 2-[4-(5-fluoro-3-methylbenzo[b]thiophen-2-yl)sulfonamido-3-methanesulfonylphenyl] thiazole-4-carboxylic acid (TY-51469). The cellular composition and cytokine levels in bronchoalveolar lavage fluid (BALF) were also examined. Following TY-51469 treatment, the lung fibrosis score and hydroxyproline level were significantly reduced, and the number of neutrophils and the levels of macrophage inflammatory protein-2, monocyte chemoattractant protein-1, and transforming growth factor-β₁ in BALF were reduced on day 21. The administration of TY-51469 at an early stage showed a greater reduction of fibrosis compared to administration at a later stage. The neutrophil number in BALF in mice treated with TY-51469 both at an early stage and late stage was significantly reduced. The level of mouse mast cell proteinase-4 mRNA increased with time in silica-induced fibrosing lung tissue. These results show that the chymase inhibitor TY51469 suppresses the migration of neutrophils, which results in the suppression of lung fibrosis.

Mast cells in the promotion and limitation of chronic inflammation

Observations of increased numbers of mast cells at sites of chronic inflammation have been reported for over a hundred years. Light and electron microscopic evidence of mast cell activation at such sites, taken together with the known functions of the diverse mediators, cytokines, and growth factors that can be secreted by appropriately activated mast cells, have suggested a wide range of possible functions for mast cells in promoting (or suppressing) many features of chronic inflammation. Similarly, these and other lines of evidence have implicated mast cells in a variety of adaptive or pathological responses that are associated with persistent inflammation at the affected sites. Definitively characterizing the importance of mast cells in chronic inflammation in humans is difficult. However, mice that genetically lack mast cells, especially those which can undergo engraftment with wildtype or genetically altered mast cells, provide a means to investigate the importance of mast cells and specific mast cell functions or products in diverse models of chronic inflammation. Such work has confirmed that mast cells can significantly influence multiple features of chronic inflammatory responses, through diverse effects that can either promote or, perhaps more surprisingly, suppress aspects of these responses.

Apoptosis and extracellular matrix remodelling in human silicosis

AIMS

Silicosis is a chronic occupational disease caused by the inhalation of free crystalline silica particles which produce inflammation and tissue destruction followed by remodelling of the extracellular matrix. Apoptosis has been implicated in the development of the initial inflammation that triggers the remodelling process. Our aim was to elucidate the importance of Fas-ligand (Fas-L) in this disorder and to study the relationship between Fas-L and several other inflammatory and fibrotic remodelling markers.

METHODS AND RESULTS

We analysed 23 lung biopsies from silicotic patients and five controls, quantifying Fas-L and Bcl-2 expression by inflammatory cells as well as mast cells and collagen and elastic fibres. We used immunohistochemistry and morphometry to evaluate the amount of Fas-L and Bcl-2. Our analysis revealed that the silicotic lung stage was significantly related to Fas-L, mast cell and extracellular matrix remodelling. Fas-L expression was inversely associated with mast cells, collagen/elastic deposition and the silicotic lung.

CONCLUSION

Fas-L, mast cell staining and collagen/elastic fibre quantities in silicotic lungs are strongly related to silicosis progression.

Silica-directed mast cell activation is enhanced by scavenger receptors

Inhalation of crystalline silica results in pulmonary fibrosis and silicosis. It has been suggested that mast cells play a role in these conditions. How mast cells would influence pathology is unknown. We thus explored mast cell interactions with silica in vitro and in B6.Cg-kit(W-sh) mast cell-deficient mice. B6.Cg-kit(W-sh) mice did not develop inflammation or significant collagen deposition after instillation of silica, while C57Bl/6 wild-type mice did have these findings. Given this supporting evidence of a role for mast cells in the development of silicosis, we examined the ability of silica to activate mouse bone marrow-derived mast cells (BMMC), including degranulation (beta-hexosaminidase release); production of reactive oxygen species (ROS) and inflammatory mediators; and the effects of silica on Fc epsilon RI-dependent activation. Silica did not induce mast cell degranulation. However, TNF-alpha, IL-13, monocyte chemotactic protein-1, protease activity, and production of ROS were dose-dependently increased after silica exposure, and production was enhanced after Fc epsilon RI stimulation. This mast cell activation was inhibited by anti-inflammatory compounds. As silica mediates some effects in macrophages through scavenger receptors (SRs), we first determined that mast cells express scavenger receptors; then explored the involvement of SR-A and macrophage receptor with colleagenous structure (MARCO). Silica-induced ROS formation, apoptosis, and TNF-alpha production were reduced in BMMC obtained from SR-A, MARCO, and SR-A/MARCO knockout mice. These findings demonstrate that silica directs mast cell production of inflammatory mediators, in part through SRs, providing insight into critical events in the pathogenesis and potential therapeutic targets in silicosis.

Transcriptional regulation of plasminogen activator inhibitor-1 by transforming growth factor-β, activin A and microphthalmia-associated transcription factor

Plasminogen activator inhibitor-1 (PAI-1) is a key molecule that regulates turnover of the extracellular matrix. In the present study, we characterized PAI-1 gene expression in mast cells and melanocytes. In bone marrow-derived cultured mast cells, up-regulation of the PAI-1 gene was observed upon treatment with TGF-beta1, and was regulated at the transcriptional level. Microphthalmia-associated transcription factor (MITF), a member of the basic helix-loop-helix leucine zipper family of tissue-specific transcription factors predominantly expressed in mast cells, melanocytes and osteoclasts, also stimulated PAI-1 gene transcription, and TGF-beta1 did not increase PAI-1 mRNA levels in mast cells from mi/mi mice expressing dominant-negative MITF. MITF isoforms regulated TGF-beta1-induced transcription of PAI-1 differently; MITF-E-mediated transcription was further increased by TGF-beta1, whereas transcriptional activation by TGF-beta1 was blocked by MITF-M or MITF-mc expression. In contrast, activin A, another member of the TGF-beta family, enhanced transcription induced by MITF-M, as well as by MITF-E, although MITF-mc blocked activin A-induced transcription of PAI-1. Different regulation of PAI-1 gene expression upon TGF-beta1 and activin A treatment was also detected in B16 melanocytes; TGF-beta1 transiently increased the PAI-1 mRNA level, whereas activin A had prolonged effects on up-regulation of PAI-1. Our results on the control of PAI-1 gene expression by MITF isoforms, TGF-beta1 and activin A suggest that discrete regulation of the plasminogen activator system occurs in a cell type-specific manner.

Regulation of activin A expression in mast cells and asthma: its effect on the proliferation of human airway smooth muscle cells

Activin A, a homodimeric protein (betaAbetaA) and a member of the TGF-beta superfamily, is involved in the inflammatory repair process. Using cDNA microarray analysis, we discovered strong induction of the activin betaA gene in human mast cells (MC) on stimulation with PMA and calcium ionophore (A23187). Activin betaA mRNA was also highly induced in primary cultured murine bone marrow MC (BMMC) after stimulation by IgE receptor cross-linking. Secretion of activin A was evident in human mast cell-1 line cells 3 h after stimulation and progressively increased over time. Activin A was present in the cytoplasm of activated but not unstimulated murine bone marrow MC as demonstrated by immunofluorescence studies, suggesting that secretion of activin A by MC was due to de novo synthesis rather than secretion of preformed protein. Activin A also colocalized with human lung MC from patients with asthma by double-immunofluorescence staining. Furthermore, secretion of activin A was significantly increased in the airway of wild-type mice after OVA sensitization followed by intranasal challenge. Secretion of activin A, however, was greatly reduced in MC-deficient WBB6F(1)-W/W(v) mice as compared with wild-type mice, indicating that MC are an important contributor of activin A in the airways of a murine asthma model. Additionally, activin A promoted the proliferation of human airway smooth muscle cells. Taken together, these data suggest that MC-derived activin A may play an important role in the process of airway remodeling by promoting the proliferation of airway smooth muscle.

Role of interferon-gamma in the development of murine bronchus-associated lymphoid tissues induced by silica in vivo

Exposure to silica is associated with the development of chronic airflow obstruction as well as pulmonary fibrosis, probably mediated in part by silica-induced small airway disease. To elucidate the mechanism of mucosal immune responses in the small airways, we analyzed the roles of interferon-gamma (IFN-gamma) using mice deficient of this cytokine in silicotic lung. IFN-gamma knockout mice (-/-) and wild-type C57BL/6 mice were treated with either a single fibrogenic dose of silica or an equivalent volume of saline and euthanized 21 days after intratracheal instillation. Total cell counts in bronchoalveolar lavage fluids increased in silica-instilled mice compared to saline-instilled mice, but there were no significant differences between IFN-gamma knockout mice and wild-type mice treated with silica. Morphometric estimation for fibrotic lesions within the lung did not show any differences between these mice. However, bronchus-associated lymphoid tissues (BALT), which are known to be involved in the mucosal immune responses, were significantly larger in the lungs of IFN-gamma knockout mice than in those of wild-type mice treated with silica. In addition, we evaluated the development of BALT in interleukin 4 (IL-4) knockout mice in order to clarify the effect of Th2 cytokine. Morphometric estimation for BALT did not show any differences between IL-4 knockout mice and wild-type mice in silicotic lung. These results suggest that IFN-gamma has an inhibitory effect on the development of BALT and may be involved in small airway disease in silicotic lung.

Basic fibroblast growth factor and its receptors in idiopathic pulmonary fibrosis and lymphangioleiomyomatosis

Basic fibroblast growth factor (bFGF) is a potent mitogenic factor for smooth muscle cells, myofibroblasts, and fibroblasts, proliferation of which is a hallmark of idiopathic pulmonary fibrosis (IPF) and lymphangioleiomyomatosis (LAM). Mast cells produce bFGF and have been associated with pulmonary fibrosis. We hypothesize that smooth muscle cell/myofibroblast-like cells will be spatially associated with bFGF-containing mast cells and that bFGF receptors will be expressed on the effector cells in IPF and LAM. We performed quantitative immunohistochemistry for bFGF, mast cell tryptase, smooth muscle actin for smooth muscle cell/myofibroblast-like cells, and fibroblast growth factor receptors (Flg, Bek) and measured collagen and elastic fiber in lung sections from IPF (n = 14), LAM (n = 9), and control lung (n = 10). IPF and LAM lung contained more smooth muscle cell/myofibroblast-like cells than did control lung. bFGF-containing mast cells were abundant both in IPF and LAM and were associated with collagen, elastic fibers, and smooth muscle cell/myofibroblast-like cells in IPF. Flg was expressed on epithelial cells, endothelial cells, smooth muscle cell/myofibroblast-like cells, and macrophages in IPF. In LAM, Flg was expressed on epithelial cells adjacent to smooth muscle cell/myofibroblast-like cell aggregates. Bek was expressed dominantly on smooth muscle cell/myofibroblast-like cells in LAM and on smooth muscle cell/myofibroblast-like cells as well as neutrophils in IPF. These data suggest that mast cell-derived bFGF might exert fibrogenic, proliferative effects on smooth muscle cell/myofibroblast-like cells through its receptors.

Lung tissue mechanics and extracellular matrix composition in a murine model of silicosis

The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung.

Airway responses to chronic ozone exposure are partially mediated through mast cells

Airways inflammation and epithelial injury induced by chronic ozone (O(3)) in genetically mast cell-deficient mice (Kit(W)/Kit(W-v)) were compared with those in mast cell-sufficient mice (+/+) and Kit(W)/Kit(W-v) mice repleted of mast cells (Kit(W)/Kit(W-v)-BMT). Mice were exposed to 0.26 ppm O(3) 8 h/day, 5 days/wk, for 1-90 days. Background was 0.06 ppm O(3). Age-matched mice were exposed to filtered air for O(3) controls. Reversibility of lesions was evaluated 35 days after exposure. Compared with Kit(W)/Kit(W-v), O(3) caused greater increases in lavageable macrophages, epithelial cells, and polymorphonuclear leukocytes in +/+ and Kit(W)/Kit(W-v)-BMT mice. O(3) also caused lung hyperpermeability, but the genotypic groups were not different. Cells and permeability returned to air control levels after O(3). O(3) induced lung cell proliferation only in +/+ and Kit(W)/Kit(W-v)-BMT mice; proliferation remained elevated or increased in +/+ and Kit(W)/Kit(W-v)-BMT mice after O(3). Greater O(3)-induced cell proliferation was found in nasal epithelium of +/+ and Kit(W)/Kit(W-v)-BMT mice compared with Kit(W)/Kit(W-v) mice. Results are consistent with the hypothesis that mast cells affect airway responses induced by chronic O(3) exposure.

Determination of the platelet activating factor in silicotic patients and its effect on fibroblasts

Platelet-activation factor (PAF), one of the potent proinflammatory mediators, is produced from a large range of cells, including polymorphonuclear neutrophils, monocytes, and natural killer cells. To study the role of PAF in the pathogenesis of silicosis, we determined the PAF in silicotic patients and in healthy persons. The results showed that the concentration of PAF in the plasma of silicotic patients was significantly higher than that of healthy persons. Ourin vitro experimental results showed that the total numbers of fibroblasts were markedly raised with added PAF from 0 to 1 μ g/ml. Adding 1 μ g/ml PAF significantly increased the total numbers of fibroblasts after culture for 48, 72, 96 hrs. Therefore, we suggest that PAF be possibly involved in the pathogenesis of silicosis. However, the mechanism remains to be further elucidated.

Nuclear factor-kappa b activation in silica-induced interleukin 8 production by human bronchial epithelial cells

Recent studies indicate that interleukin 8 (IL-8) plays an important role in interstitial lung diseases including silica-induced lung inflammation. To investigate the regulation of IL-8 expression and production in human bronchial epithelial cells, we examined the effects of silica on NF-kappaB activation. Human bronchial epithelial cell line BET-1A was cultured with hormonally defined Ham's F12 medium. The administration of silica induced IL-8 production in BET-1A dose-dependently and time-dependently. Northern blot analysis demonstrated that silica upregulated IL-8 expression in BET-1A. Moreover, electrophoretic mobility shift assays revealed that NF-kappaB activation occurred in the presence of silica, which was inhibited by antioxidants such as N-acetylcysteine (NAC). These data suggest that reactive oxygen species may be involved in the activation of NF-kappaB induced by silica.

Mast cell basic fibroblast growth factor in silicosis

To investigate the role of mast cells (MC) and their fibrogenic growth factors in silicosis, we performed quantitative immunohistochemistry for MC tryptase and for basic fibroblast growth factor (bFGF) in lung tissue from silicotic and control subjects. Anti-bFGF antibody was bound to lung MC, basement membrane, endothelial cells, and smooth-muscle cells. Morphometric analysis revealed that the volume density (V(v)) of MC was increased in silicotic lung and that the V(v) of bFGF-positive (bFGF(+)) cells was significantly higher than normal in silicotic lung. Most MC contained bFGF (rho = 0.88, p < 0.001). The V(v) of collagen/reticulin fibers was increased in silicosis and correlated with the V(v) of bFGF(+) cells (rho = 0.81, p < 0.001). Immature silicotic nodules contained bFGF(+) MC throughout the loose array of collagen/reticulin fibers. In large, mature nodules, the density of collagen/reticulin fibers was higher, and bFGF(+) MC were found only in the nodule periphery. Because of this circumferential MC alignment in silicotic nodules, we observed a negative correlation between the V(v) of bFGF(+) MC and the density of collagen/reticulin fibers in silicotic nodules (rho = -0.80, p < 0.001) and between the V(v) of all other nodule-associated cells and the density of collagen/reticulin fibers in the hypocellular nodule centers (rho = -0.84, p < 0.001). We conclude that MC that produce bFGF may play an important role in the development of silicosis.

Interferon-gamma production by specific lung lymphocyte phenotypes in silicosis in mice

We recently described overproduction of interferon (IFN)-gamma by lung lymphocytes in mice with silicosis (11% of cells in air-control versus 19% of cells from silica-exposed mice; Davis and colleagues, Am. J. Respir. Cell Mol. Biol. 1999;20:813-824). We hypothesized that the increased IFN-gamma production might be due to selective enrichment of one lymphocyte phenotype. To test this hypothesis, small mononuclear cells from lung digest preparations of mice exposed 4 mo previously to cristobalite silica (70 mg/m(3), 12 d, 5 h/d) or to sham-air were stained for intracellular cytokines and surface antigen phenotypes, and examined by flow cytometry. Air-sham mouse lung digests included CD4(+) (16%) and CD8(+) (6%) T cells, gammadelta T-cell antigen receptor (TCR)(+) CD4(-)CD8(-) T cells (3%), natural killer (NK) cells (15%), B cells (6%), and macrophages (12%). The total number of lung lymphocytes was increased 1.7-fold in silicosis, but the phenotype frequencies did not change significantly. In the control lungs IFN-gamma was produced by three major phenotypes of lymphocytes: 5% of CD4(+) T cells, 5% of gammadelta-TCR(+) CD4(-)CD8(-) T cells, and 2% of NK cells. The percentage of each type producing IFN-gamma was increased 2- to 3-fold in silicosis. When multiplied by cell number, the increased percentages yielded a 3- to 5-fold increase in the total number of each IFN- gamma-producing phenotype in the lung. Our results demonstrate no selective phenotype enrichment but upregulated IFN-gamma production by at least three lymphocyte phenotypes. IFN-gamma may be an important signal driving lymphocyte differentiation and macrophage activation in silicosis.

An essential role of mast cells in the development of airway hyperresponsiveness in a murine asthma model

Immunization of BALB/c mice with alum-adsorbed OVA, followed by three bronchoprovocations with aerosolized OVA, resulted in the development of airway hyperresponsiveness (AHR) and allergic inflammation in the lung accompanied by severe infiltration of eosinophils into airways. In this murine asthma model, administration of monoclonal anti-IL-5 Ab before each Ag challenge markedly inhibited airway eosinophilia, but the treatment did not affect the development of AHR. Immunization and aerosol challenges with OVA following the same protocol failed to induce AHR in the mast cell-deficient W/Wv mice, but induced AHR in their congenic littermates, i.e., WBB6F1 (+/+) mice. No significant difference was found between the W/Wv mice and +/+ mice with respect to the IgE and IgG1 anti-OVA Ab responses and to the airway eosinophilia after Ag provocations. It was also found that reconstitution of W/Wv mice with bone marrow-derived mast cells cultured from normal littermates restored the capacity of developing Ag-induced AHR, indicating that lack of mast cells was responsible for the failure of W/Wv mice to develop Ag-induced AHR under the experimental conditions. However, the OVA-immunized W/Wv mice developed AHR by increasing the frequency and Ag dose of bronchoprovocations. The results suggested that AHR could be developed by two distinct cellular mechanisms. One would go through mast cell activation and the other is IgE/mast cell independent but an eosinophil/IL-5-dependent mechanism.

Cellular and molecular mechanisms of asbestos-induced fibrosis

Pleural and pulmonary fibrosis (asbestosis) are ramifications of occupational exposures to asbestos fibers, a diverse family of ubiquitous, naturally-occurring minerals. The pathogenesis of asbestos-associated fibrosis involves the participation of a number of cell types and is characterized by an early and persistent inflammatory response that involves the generation of oxidants, growth factors, chemokines, and cytokines. These mediators may also contribute directly to cell injury, proliferation, and fibrogenesis. After interaction with cells, asbestos fibers trigger a number of signaling cascades involving mitogen-activated protein kinases (MAPK) and nuclear factor kappa-B (NF-kappaB). Activation of transcription factors such as NF-kappaB and activator protein-1 (AP-1) may be linked to increases in early response genes (e.g., c-jun and c-fos) which govern proliferation, apoptosis, and inflammatory changes in the cells of the lung. The goal of this article is to review the cellular and molecular mechanisms of asbestos-induced fibrosis that may be critical to the development of effective treatment regimens.

Lung fibrosis induced by silica particles in NMRI mice is associated with an upregulation of the p40 subunit of interleukin-12 and Th-2 manifestations

Interleukin (IL)-12 is a cytokine produced principally by activated macrophages which is involved in control of the T-helper 1/T-helper 2 cell (Th1/Th2) polarization of immune responses. To examine its potential involvement in the development of lung fibrosis, we examined the expression (protein, messenger RNA [mRNA]) of IL-12 (p70) and of its subunits (p40 and p35) in lung homogenates, bronchoalveolar lavage fluid (BALF), and bronchoalveolar lavage (BAL) cell cultures in mouse models of resolutive alveolitis (RA) and fibrosing alveolitis (FA) induced by inorganic particles (manganese dioxide [MnO2] and crystalline silica, respectively). The administration of tungsten carbide (WC), which behaved as an innocuous dust for the lung, served as a negative control condition. The FA was specifically accompanied by a Th2-like polarization characterized by high levels of immunoglobulin (Ig)G1 in BALF and by a protracted overproduction of both p40 protein and mRNA, but not by the biologically active form of IL-12 (p70). In the RA model, the p40 response was only transient, and a Th1-like response was reflected by increased levels of interferon (IFN)-gamma and dominant levels of IgG2a in BALF. Taken together, these findings suggest that production of the p40 subunit of IL-12 and Th2 polarization play important roles in lung inflammatory and fibrotic responses to inhaled inorganic particles.

Fibroproliferation and mast cells in the acute respiratory distress syndrome

BACKGROUND

Mast cells (MCs), which are a major source of cytokines and growth factors, have been implicated in various fibrotic disorders. To clarify the contribution of MCs to fibrogenesis, lung tissue from patients with the acute respiratory distress syndrome (ARDS) was examined during exudative through to fibroproliferative stages.

METHODS

Lung tissue was obtained from 17 patients with ARDS who had pathological features of the early exudative stage (n = 6) or the later reparative stages (n = 11), from four patients with idiopathic pulmonary fibrosis, and from three patients with normal lung tissue. Immunohistochemical localisation of tryptase (found in all human MCs), chymase (found in a subset of human MCs), alpha-smooth muscle actin (identifies myofibroblasts), and procollagen type I was performed.

RESULTS

Normal lung tissue exhibited myofibroblast and procollagen type I immunolocalisation scores each of < 5 and MC scores of 1. Increased scores were defined as myofibroblast and procollagen type I scores of > 10 and MC scores of > or = 2. Eighty percent of lung tissue samples from the early exudative stage of ARDS exhibited increased numbers of myofibroblasts, 50% had increased numbers of procollagen type I producing cells, while only 17% had increased numbers of MCs compared with control samples. All samples from the later reparative stages of ARDS had increased numbers of myofibroblasts and procollagen type I producing cells. Increased numbers of MCs were seen in 55% of samples from the reparative stages. There was no significant shift in MC phenotype in the ARDS samples.

CONCLUSIONS

Increased numbers of myofibroblasts and procollagen type I producing cells were frequently found early in the course of ARDS. MC hyperplasia was unusual during this stage, but was often a feature of the later reparative stages. MCs do not appear to initiate fibroproliferation in ARDS.

T lymphocytes and silica-induced pulmonary inflammation and fibrosis in mice

BACKGROUND

Silica-induced pulmonary inflammation and fibrosis in animals provides a good model for chronic pulmonary inflammation and fibrosis. Although lymphocytes are implicated in the pathogenesis of pulmonary fibrosis, experimental models using silica-treated athymic nude mice have not been successful in showing the fibrogenic mechanism regulated by T cells. The aim of this study was to re-evaluate the role of T lymphocytes in the development of silicosis by comparing the response to silica administration of nude athymic mutants with that of euthymic animals.

METHODS

Suspensions of silica particles were transnasally administered to nude athymic mice (Balb/c nu/nu) as well as to their euthymic littermates (Balb/c nu/+). The degree of pulmonary inflammation and fibrosis was assessed on days 14, 28, and 56 based upon histological observation, analysis of collagen deposition in the lungs, and analysis of the cellular constituent, protein, and phospholipid content in the bronchoalveolar lavage fluid.

RESULTS

Histologically, athymic mice developed less severe interstitial pneumonitis than euthymic mice. In euthymic mice the lung hydroxyproline content increased with time after silica administration from 6.48 (0.38) micrograms hydroxyproline/mg dry lung weight on day 0 to 8.87 (0.41) micrograms/mg on day 56. A gradual increase in lung hydroxyproline content was also observed in athymic mice but the increase was significantly smaller than in euthymic mice (6.63 (0.43) micrograms/mg on day 0, 7.90 (0.19) micrograms/mg on day 56). Administration of silica resulted in an increase in the number of macrophages and neutrophils and in the total protein and phospholipid content of the bronchoalveolar lavage (BAL) fluid in both mouse strains. No significant difference was detected between athymic and euthymic mice in the numbers of macrophages, but the increase in neutrophils in the BAL fluid of athymic mice was significantly smaller than in euthymic mice on days 14 and 56. The total protein and phospholipid content of the BAL fluid from athymic mice was lower than that from euthymic mice.

CONCLUSIONS

T lymphocytes appear to be involved in the pathogenesis of silica-induced pneumonitis. Since pulmonary fibrosis develops even in nude athymic mice, T cells do not seem to play a primary part in fibrogenic response but they regulate, at least to some extent, the response of inflammatory cells and fibrogenesis of the lung.

Mast cell modulation of neutrophil influx and bacterial clearance at sites of infection through TNF-alpha

Although mast cells have been implicated in a variety of inflammatory conditions including immediate hypersensitivity and interstitial cystitis, their physiological role in the body is unknown. We investigated the role of mast cells in host defence against bacterial infections using a well characterized mast-cell-deficiency mouse model. We report here that mast cells, which are selectively located at portals of bacterial entry, are important to host defence. Mast-cell-deficient WBB6F1-W/Wv mice (W/Wv) were up to 20-fold less efficient in clearing enterobacteria than control WBB6F1 +/+ (+/+) mice or mast-cell-reconstituted W/Wv (W/Wv+MC) mice. With higher bacteria inocula, only W/Wv mice died (80%). The limited bacterial clearance in W/Wv mice directly correlated with impaired neutrophil influx. The mast-cell chemoattractant TNF-alpha was implicated in the neutrophil response because TNF-alpha was locally released only in +/+ and W/Wv+MC mice, TNF-alpha-specific antibodies blocked over 70% of the neutrophil influx, and purified mast cells released TNF-alpha upon incubation with bacteria. Additionally, the type-1 fimbrial subunit, FimH, was the necessary enterobacterial component for mast-cell activation and neutrophil influx because an isogenic FimH- mutant evoked a limited neutrophil response in +/+ mice compared to wild-type bacteria.

Messages and handshakes: cellular interactions in pulmonary fibrosis

A better understanding of early cellular events following pulmonary injury may permit the identification of those patterns of response which are destined to progress to fibrosis. Interactions between inflammatory, fibroblastic and epithelial cells appear to play crucial roles in fibrogenesis. Intercellular communication may be via "messages" delivered by soluble mediators or "handshakes" at sites of cell-to-cell contact. In this review, we question the validity of some prevailing concepts about the importance of growth factor secretion by alveolar macrophages; examine the possible role of activated T-lymphocytes in regulating macrophage production of mediators; and hypothesise that whereas fibroblast proliferation may primarily be stimulated by macrophage-derived cytokines, accumulation of collagen may be regulated by growth factors expressed by injured alveolar epithelial cells.