Macrophage production of transforming growth factor beta and fibroblast collagen synthesis in chronic pulmonary inflammation

Spontaneous increase of transforming growth factor beta production by bronchoalveolar mononuclear cells of patients with systemic autoimmune diseases affecting the lung

The spontaneous increase in the transcription of the transforming growth factor beta (TGF beta) gene in bronchoalveolar mononuclear cells of patients with autoimmune diseases affecting the lung has been shown by northern blot assay and a nuclear run on transcription assay. Transcription of the TGF beta gene in bronchoalveolar mononuclear cells of patients with autoimmune diseases affecting the lung was increased 10 times compared with normal healthy subjects or patients with bronchial asthma as controls. This observation, confirmed by protein data, suggests that TGF beta, a potent mitogen for fibroblasts, may be produced in bronchoalveolar mononuclear cells during an active immune response in such patients and may be involved in autoimmune related changes of the pathophysiology of cytokine networks when the lung is affected, such as in lung fibrosis.

Bleomycin Regulation of Transforming Growth Factor-βmRNA in Rat Lung Fibroblasts

Pulmonary fibrosis is a well-known toxic response to bleomycin treatment. Here we demonstrate the direct effects of bleomycin on lung fibroblasts that resulted in a marked increase of collagen synthesis as compared with total noncollagen protein synthesis. Bleomycin treatment of rat lung fibroblast cultures resulted in an increase of total cellular transforming growth factor-beta (TGF-beta) mRNA and increased secretion of TGF-beta protein into the conditioned media. beta 2-Microglobulin was measured as an mRNA that did not increase with bleomycin treatment. The bleomycin-induced increase of TGF-beta mRNA was decreased by cells cultured in the presence of either cycloheximide, an inhibitor of protein synthesis, or 2-mercapto-1-(beta-4-pyridethyl) benzimidazole, an inhibitor of RNA synthesis. To assess the mechanism underlying increased steady-state mRNA levels, the nuclear fraction was isolated from bleomycin-treated cells and the TGF-beta transcripts were determined. Transcription of TGF-beta mRNA was increased 12 h after bleomycin treatment, whereas the transcription of type I procollagen, type III procollagen, and beta-actin mRNAs were increased after 48 h of bleomycin treatment. beta 2-Microglobulin mRNA synthesis was not increased within this time frame. These results suggest bleomycin regulation of TGF-beta at both the mRNA and protein levels. Rats lung fibroblasts were separated by cell sorting into two subpopulations. One population of fibroblasts demonstrated increased procollagen type I mRNAs, whereas fibroblasts in the other population had increased procollagen type III mRNA. Following bleomycin treatment, TGF-beta mRNA was shown to be located more prominently in those fibroblasts that contain primarily collagen type I mRNAs.

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.

Decreased level of transforming growth factor-beta in blood lymphocytes of patients with aplastic anemia

Levels of transforming growth factor-beta (TGF-beta) activity in the conditioned medium of blood lymphocytes of twelve patients with aplastic anemia (AA), nine patients with myelodysplastic syndromes (MDS) and five normal volunteers were investigated. We were able to observe growth inhibitory activity on porcine endothelial cells only after acidification of the materials. The growth inhibitory activity is neutralized by anti-TGF-beta antibody. It indicates that TGF-beta exists as a latent form in the conditioned medium. On the basis of growth inhibition assay, the mean level of TGF-beta production of MDS patients was estimated to be 188 +/- 199 pg/1 x 10(7) cells and that of normal volunteers was 668 +/- 314 pg/1 x 10(7) cells. In contrast, the lymphocytes of almost all of the AA patients failed to produce detectable amounts of TGF-beta. No correlation between TGF-beta levels and peripheral blood parameters could be detected. Stimulation of lymphocytes by phytohemagglutinin is known to increase the production of TGF-beta. Induction of TGF-beta production was also observed in AA (45% of normal controls). Possible roles of the decreased production of TGF-beta in the pathogenesis of AA were discussed.

Expression of transforming growth factor-beta 1, -beta 2, and -beta 3 mRNA and protein in the murine lung

Evidence has accumulated suggesting that the various isoforms of beta-type transforming growth factors (TGF-beta s) regulate important functions in the lung; however, the cellular source of these proteins is not well defined. Northern blot analysis of murine lung tissue demonstrates that mRNA transcripts for all three TGF-beta isoforms are found from birth through adulthood. Although the level of expression for each TGF-beta is variable during the first 2 wk post partum, all three isoforms are equal in the adult lung. Using in situ hybridization and immunohistochemical analysis, we have localized both mRNA and protein expression for all three isoforms of TGF-beta in the adult murine lung. At low magnification, immunohistochemical localization of TGF-beta proteins appears coincident in their pattern of expression with TGF-beta mRNAs in the large proximal conducting airways of the lung. However, on closer analysis, protein expression of all three TGF-beta isoforms is confined to the bronchiolar epithelium, while TGF-beta mRNA transcripts for each of the TGF-beta genes are found in smooth muscle cells and connective tissue fibroblasts lying subjacent to the epithelium. Although the levels of both TGF-beta mRNA and protein expression are high in the proximal bronchiolar tree, their signal intensities completely disappear as the terminal bronchioles progress to respiratory bronchioles. Additionally, in the lung vasculature, there is very high expression of all three TGF-beta mRNA transcripts in the smooth muscle cells of the large vessels. TGF-beta2 and TGF-beta but not TGF-beta1 proteins are expressed in these same smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous activation of transforming growth factor-beta gene transcription in broncho-alveolar mononuclear cells of individuals with systemic autoimmune diseases with lung involvement

The spontaneous elevation of the transcription of the transforming growth factor-beta (TGF-beta) gene in broncho-alveolar mononuclear cells (BMC) of individuals with autoimmune diseases with lung involvement, by nuclear run-on transcription assay, is shown in this study. In quantification analysis of TGF-beta gene transcription, we found more than 10 times the enhanced transcription of the TGF-beta gene in BMC of individuals with autoimmune diseases with lung involvement, in comparison to normal healthy subjects or patients with bronchial asthma used as controls. Our observation suggests that TGF-beta, a potent mitogen for fibroblasts, may be produced in BMC during an active immune response in individuals with systemic autoimmune diseases with lung involvement, and may be involved in autoimmune-related pathophysiological changes of cytokine networks in lung involvement such as lung fibrosis.

Possible mechanism of the preventive effect of BCG against diabetes mellitus in NOD mouse. I. Generation of suppressor macrophages in spleen cells of BCG-vaccinated mice

With the aim of clarifying the mechanism of the suppressive action of BCG against insulitis and overt diabetes in NOD mice, we studied the effects of BCG on spleen cell populations and on the in vitro immune responses of spleen cells. The spleen cells of BCG-vaccinated mice showed much lower responsiveness to various mitogens such as Con A, PHA, PWM, and LPS than those of saline-treated mice. Low responsiveness to alloantigens was also observed. Flow cytometric analysis of the spleen cells revealed that Mac-1+ and Mac-2+ cells had increased while T and B cells had decreased in the BCG-vaccinated mice compared with the saline-treated mice at the time when the maximum level of inhibition of mitogen responses of BCG-vaccinated mice was observed. This suggests that the decreased in vitro immune response was due to the increase in macrophages which suppress lymphocyte functions. Support for this interpretation comes from the following two findings: (1) the restoration of mitogen responses of spleen cells when macrophages were eliminated by plastic adhesion or FACS sorting and (2) resuppression of PHA and Con A responses of plastic-nonadherent spleen cells by addition of adherent cells or flow cytometrically sorted Mac-1+ cells obtained from BCG-vaccinated mice. These results indicate the generation of suppressor macrophages after BCG vaccination and suggest that these macrophages prevent the autoimmune pathogenesis leading to diabetes in NOD mice.

Transforming growth factor beta 1 is present at sites of extracellular matrix gene expression in human pulmonary fibrosis

Idiopathic pulmonary fibrosis is an inexorably fatal disorder characterized by connective tissue deposition within the terminal air spaces resulting in loss of lung function and eventual respiratory failure. Previously, we demonstrated that foci of activated fibroblasts expressing high levels of fibronectin, procollagen, and smooth muscle actin and thus resembling those found in healing wounds are responsible for the connective tissue deposition and scarring in idiopathic pulmonary fibrosis. Using in situ hybridization and immunohistochemistry, we now demonstrate the presence of transforming growth factor beta 1 (TGF-beta 1), a potent profibrotic cytokine, in the foci containing these activated fibroblasts. These results suggest that matrix-associated TGF-beta 1 may serve as a stimulus for the persistent expression of connective tissue genes. One potential source of the TGF-beta 1 is the alveolar macrophage, and we demonstrate the expression of abundant TGF-beta 1 mRNA in alveolar macrophages in lung tissue from patients with idiopathic pulmonary fibrosis.

Increased production and immunohistochemical localization of transforming growth factor-beta in idiopathic pulmonary fibrosis

Transforming growth factor-beta (TGF-beta) can regulate cell growth and differentiation as well as production of extracellular matrix proteins. Elevated production of TGF-beta has been associated with human and rodent chronic inflammatory and fibrotic diseases. Using immunohistochemical staining, we have examined lung sections of patients with advanced idiopathic pulmonary fibrosis (IPF), a disease characterized by chronic inflammation and fibrosis and demonstrated a marked and consistent increase in TGF-beta production in epithelial cells and macrophages when compared to patients with nonspecific inflammation and those with no inflammation or fibrosis. In patients with advanced IPF, intracellular staining with anti-LC (1-30) TGF-beta antibody was seen prominently in bronchiolar epithelial cells. In addition, epithelial cells of honeycomb cysts and hyperplastic type II pneumocytes stained intensely. Anti-CC (1-30) TGF-beta antibody, which reacts with extracellular TGF-beta, was localized in the lamina propria of bronchioles and in subepithelial regions of honeycomb cysts in areas of dense fibroconnective tissue deposition. The close association of subepithelial TGF-beta to the intracellular form in advanced IPF suggests that TGF-beta was produced and secreted primarily by epithelial cells. Because of the well-known effects of TGF-beta on extracellular matrix formation and on epithelial cell differentiation, the increased production of TGF-beta in advanced IPF may be pathogenic to the pulmonary fibrotic and regenerative responses seen in this disease.

The roles of the myofibroblast in idiopathic pulmonary fibrosis. Ultrastructural and immunohistochemical features of sites of active extracellular matrix synthesis

The synthesis of collagen and EIIIA-containing cellular fibronectin in certain forms of pulmonary fibrosis occurs in discrete locations: in the Masson bodies in bronchiolitis obliterans with organizing pneumonia and in focal clusters of fibroblasts (fibroblastic foci) within airspaces in usual interstitial pneumonia. These sites were examined by electron microscopy and immunohistochemistry using antibodies against cytoskeletal markers and extracellular matrix components in biopsies from three patients with bronchiolitis obliterans with organizing pneumonia and four patients with usual interstitial pneumonia. Fibroblasts of both Masson bodies and fibroblastic foci expressed vimentin and alpha smooth muscle actin but not desmin, distinguishing them from true smooth muscle. In both structures fibroblasts with well-formed actin filament bundles were aligned parallel to one another, enmeshed in a matrix of fibronectin-containing fibrils (microtendons) that linked cells and collagen bundles. Similar features characterize the phase of contraction during the healing of skin wounds. This suggests that active contractions of fibroblasts plays a role in the remodeling of the lung in pulmonary fibrosis.

Receptors for transforming growth factor-beta (TGF-beta) on rat lung fibroblasts have higher affinity for TGF-beta 1 than for TGF-beta 2

Most cell types have receptors for transforming growth factor-beta (TGF-beta) and respond similarly to TGF-beta 1 and TGF-beta 2. We have demonstrated the presence of a single class of high-affinity receptors (approximately 10,000 sites/cell) for TGF-beta 1 (Kd = 23 pM) and TGF-beta 2 (Kd = 41 pM) on early-passage rat lung fibroblasts (RLF). Incubation with unlabeled TGF-beta 1 and TGF-beta 2 resulted in concentration-dependent inhibition of binding of 15 pM [125I]TGF-beta 1 (ED50, 20 and 28 pM, respectively) and [125I]TGF-beta 2 (ED50, 36 and 56 pM, respectively). TGF-beta receptors affinity-cross-linked with 100 pM [125I]TGF-beta 1 or [125I]TGF-beta 2 were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and exhibited labeled protein bands of 68, 88, and 286 kD. Densitometric analysis of the resulting autoradiograms showed that the different molecular weight TGF-beta binding proteins exhibited separate affinities for the two forms of TGF-beta. Both TGF-beta 1 and TGF-beta 2 altered the morphology and cytoskeleton of RLF in a similar manner, but TGF-beta 1 was more potent than TGF-beta 2 in the inhibition of RLF growth and colony formation, with 50% inhibition by 0.12 pM TGF-beta 1 and 4.4 pM TGF-beta 2. Different affinities for the TGF-beta s may indicate selectivity among the receptor subtypes with regard to the biologic responsiveness of RLF to TGF-beta s. We believe this to be the first demonstration of biologically responsive TGF-beta receptors with different affinities for TGF-beta 1 and TGF-beta 2 on cells derived from normal, nonimmortal RLF. In establishing the basic mechanisms of pulmonary fibrosis, it will be essential to understand the biology and biochemistry of the receptors that may control cell division and production of extracellular matrix components by fibroblasts.

Mechanisms of bleomycin-induced lung damage

Bleomycins are a family of compounds produced by Streptomyces verticillis. They have potent tumour killing properties which have given them an important place in cancer chemotherapy. They cause little marrow suppression, but pulmonary toxicity is a major adverse effect. The mechanisms of cell toxicity are well described based on in vitro experiments on DNA. The bleomycin molecule has two main structural components: a bithiazole component which partially intercalates into the DNA helix, parting the strands, as well as pyrimidine and imidazole structures, which bind iron and oxygen forming an activated complex capable of releasing damaging oxidants in close proximity to the polynucleotide chains of DNA. This may lead to chain scission or structural modifications leading to release of free bases or their propenal derivatives. The mechanisms are well described based on in vitro experiments on DNA, but how they relate to intact cells in whole animals is more tenuous. Bleomycin is able to cause cell damage independent from its effect on DNA by induction lipid peroxidation. This may be particularly important in the lung and in part account for its ability to cause alveolar cell damage and subsequent pulmonary inflammation. The lung injury seen following bleomycin comprises an interstitial oedema with an influx of inflammatory and immune cells. This may lead to the development of pulmonary fibrosis, characterized by enhanced production and deposition of collagen and other matrix components. Several polypeptide mediators capable of stimulating fibroblasts replication or excessive collagen deposition have been implicated in this, but the precise role of these in bleomycin-induced fibrosis is yet to be demonstrated. Current therapy for bleomycin-induced lung damage is inadequate, with corticosteroids most often used. Given the mechanism of action described above, antioxidants and iron chelators might be beneficial. Although, studies to date are equivocal and there is insufficient evidence to promote their use clinically. Novel drugs are currently being developed and it is hoped these may be more useful.

Suppression of splenic macrophage interleukin-1 secretion following intracerebroventricular injection of interleukin-1 beta: evidence for pituitary-adrenal and sympathetic control

Intracerebroventricular (ICV) injections of interleukin-1 beta (IL-1 beta) produced a dose-dependent increase in plasma corticosterone and adrenocorticotropic hormone (ACTH) within 2 hr of injection and then declined over the next 24 hr. Using a potent steroidogenic dose of IL-1 beta (5 ng), ICV injection resulted in suppression of splenic macrophage IL-1 secretion following stimulation by LPS in vitro. Macrophage TGF-beta secretion was not affected, indicating a differential action of ICV IL-1 beta on macrophage cytokine production. Following adrenalectomy (ADX), the suppressive effect of ICV IL-1 beta was reversed and resulted in stimulation of macrophage IL-1 secretion, indicating that the suppression was mediated by adrenocorticol activation. However, surgical interruption of the splenic nerve to eliminate autonomic innervation of the spleen also prevented the macrophage suppressive signal in rats given ICV IL-1 beta. Furthermore, the combination of ADX and splenic nerve section resulted in a potent stimulatory effect of ICV IL-1 beta on splenic macrophage IL-1 secretion which was greater than either ADX or splenic nerve section alone. These results support the concept of a negative feedback on macrophage IL-1 secretion by the central action of IL-1 beta and indicate that both the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system mediate this effect.

Transforming growth factor-beta production in anti-glomerular basement membrane disease in the rabbit

The purpose of this study was to assay for the presence of collagen synthesis stimulatory activity in the kidney during immune-induced renal injury that results in severe fibrosis in both glomerular and interstitial compartments. A model of antiglomerular basement (anti-GBM) disease in the rabbit was induced on day 0 by the injection of anti-GBM antibody and renal cortex tissues were then sampled at various time points. Only conditioned media prepared from diseased renal cortical samples showed collagen synthesis stimulatory activity when tested on rabbit mesangial cells. The activity had an estimated molecular weight range of 16 to 25 kd and was neutralized by antibody to transforming growth factor-beta (TGF-beta). A standard assay for TGF-beta using a mink lung epithelial cell line confirmed the increase in TGF-beta activity in conditioned media of diseased cortex from day 7 and day 14 animals, which was not significantly activated by previous acidification. This suggests that most of the TGF-beta present in renal conditioned media was in the active form. The increase in renal cortical secretion of active TGF-beta was accompanied by increases in renal cortical TGF-beta mRNA content on days 4 and 7 after induction, with subsequent return to control levels. A similar increase in TGF-beta activity was present in nonacidified conditioned media of purified glomeruli from diseased days 7 and 14 animals, which was also accompanied by significant increases in TGF-beta mRNA. However with acidification no significant differences were noted between control and diseased samples, suggesting the presence of substantial latent TGF-beta activity in control glomerular conditioned media. These same control-conditioned media contained inhibitor activity for added exogenous TGF-beta. These results support the conclusion that the association between increased TGF-beta secretion and increased renal cortical collagen synthesis in this model is consistent with a role for this cytokine in directing fibrogenesis in the kidney.

Fibrogenic cytokines: the role of immune mediators in the development of scar tissue

A variety of diseases that are characterized by fibrosis share common features including the proliferation of fibroblasts and the deposition of extracellular matrix. Fibrosis often begins as an inflammatory reaction with leukocyte infiltration followed by the elaboration of cytokines. Here, Elizabeth J. Kovacs argues that the aberrant production of these mediators sustains the connective tissue accumulation that results in permanent alteration in tissue structure and function.

Stimulation of rat endothelial cell transforming growth factor-beta production by bleomycin

This study examines the hypothesis that mediators from lung endothelial cells could promote lung collagen synthesis in pulmonary fibrosis. Since bleomycin induces pulmonary fibrosis in humans and animals, the effects of this drug on endothelial cells were examined. Endothelial cell conditioned media were prepared in the presence of various doses of bleomycin, and tested for their ability to stimulate lung fibroblast collagen synthesis. The results show a dose-dependent stimulation of endothelial cell secretion of collagen synthesis stimulatory activity by bleomycin, which peaked at a dose greater than or equal to 100 ng/ml. Stimulation was selective for collagenous protein synthesis. Gel filtration analysis showed most of the activity to reside in fractions with an estimated molecular mass range of 10-27 kD. The activity was inhibited by anti-transforming growth factor-beta (TGF-beta)antibody, but not by nonimmune control IgG. The presence of TGF-beta was confirmed using the mink lung epithelial cell assay. Northern blotting revealed significant increases in TGF-beta mRNA in bleomycin-stimulated endothelial cells. Thus in vitro stimulation of endothelial cells by bleomycin upregulates TGF-beta production, presumably by increased transcription. In view of the chemotactic and matrix synthesis stimulatory properties of this cytokine, such an increase in TGF-beta production may play an important role in bleomycin-induced pulmonary fibrosis.

Inflammatory macrophages in the dog contain high amounts of intravesicular ferritin and are associated with pouches of connective tissue fibers

We have studied the subcellular distribution of ferritin in inflammatory macrophages present in regional lymph nodes from dogs subjected to a pulmonary inflammatory reaction. The inflammatory reaction was induced by intrabronchial instillation of calcium tungstate (CaWO4), a water-insoluble powder. Ferritin was identified by electron microscopy, and its electron density was enhanced by the use of a modified Perls method. From day 14 on after the CaWO4 deposition, tungsten-positive lymph node macrophages showed a massive accumulation of ferritin. Most of the ferritin was stored in membrane-bounded vesicles that showed heterogeneous concentrations of the protein. A significant complement of ferritin was also detected in the cytoplasmic ground substance of phagocytes. The cell surface of the ferritin-rich, tungsten-positive macrophages showed deep infoldings that encompassed small pockets of connective tissue fibers. These features were not observed in control samples or in lymph nodes from dogs subjected to CaWO4-induced inflammation for periods shorter than 1 week. Our data indicate that inflammatory macrophages greatly increase their content of ferritin macrophages greatly increased their content of ferritin and that ferritin is stored predominantly by a membrane-bounded vesicular compartment. This is in contrast with suggestions that the inflammation-induced increase in macrophage iron is restricted to the labile pool of iron and it does not involve the iron bound to ferritin molecules. Our observation of nodules of connective-tissue fibers in intimate topographical association with ferritin-rich macrophages may indicate that the increase in intracellular ferritin in the macrophage is in some way related to the secretion of factors by the phagocyte that will stimulate fibrillogenesis by neighboring fibroblats.

Rat alveolar macrophage-derived platelet-derived growth factor is chemotactic for rat lung fibroblasts

Alveolar macrophages and their products are thought to be important mediators of the inflammatory lesions and consequent interstitial fibrosis caused by inhalation of inorganic particles. Identification of a homolog of platelet-derived growth factor (PDGF) produced by rat alveolar macrophages that were stimulated with carbonyl iron particles and asbestos fibers motivated our studies on the biologic activity of this potent cytokine. Macrophage-derived PDGF (MD-PDGF) competes for specific membrane receptors on rat lung fibroblasts, initiating DNA synthesis and cell replication. The present report demonstrates that purified human PDGF and the MD-PDGF are chemotactic for early passage rat lung fibroblasts, but not for lung macrophages. Rat lung fibroblasts exhibit a typical bell-shaped, dose-related curve and respond optimally between 2 and 4 ng/ml PDGF. We found that alveolar macrophage-conditioned medium (AMCM), fractionated by gel filtration in 1 M acetic acid, induced a clear chemotactic response in the same fractions (20 to 22 ml) where PDGF was identified by enzyme immunoassay. In contrast, AMCM fractionated by gel filtration in phosphate-buffered saline did not induce any chemotactic activity unless the fractions were treated further with 1 M acetic acid. In this case, chemotactic activity was observed in those fractions with molecular weights of 150 and greater than 200 kD. All chemotactic activity observed with fractionated AMCM was blocked greater than 90% by an anti-PDGF antibody. These observations demonstrate that MD-PDGF is chemotactic for rat lung fibroblasts if it first is released from its binding protein, alpha-macroglobulin (alpha-M), which is secreted into the medium along with PDGF.(ABSTRACT TRUNCATED AT 250 WORDS)

Requirement of tumour necrosis factor for development of silica-induced pulmonary fibrosis

The deposition of silica particles in the lung of man or experimental animals leads to silicosis, a disease of progressive respiratory failure caused by a fibrotic reaction. It has long been suspected that the phagocytosis of silica by pulmonary macrophages induces the secretion of fibrogenic factors. Several potentially fibrogenic cytokines released by macrophages have been identified, including interleukin-1 (IL-1), tumour necrosis factor-alpha (TNF), platelet-derived growth factor, basic fibroblast growth factor and transforming growth factor-beta (TGF-beta). Here we show that TNF plays an important part in silica-induced pulmonary fibrosis in mice in that (1) a single instillation of silica leads to a marked increase in the level of lung TNF messenger RNA which lasts for greater than 70 days, while there are no obvious changes in the amounts of IL-1 alpha or TGF-beta mRNAs; and (2) silica-induced collagen deposition is almost completely prevented by anti-TNF antibody, but is significantly increased by continuous infusion of mouse recombinant TNF.

Aberrant TGF-beta production and regulation in metastatic malignancy

We have examined the possible role of transforming growth factor-beta (TGF-beta) in metastatic malignancy by analyzing the production and activation of TGF-beta 1 and -beta 2 and the regulation of TGF-beta-responsive genes in oncogene-transformed metastatic fibrosarcomas. All transformed lines derived from either 10T1/2 or NIH 3T3 by either H-ras or protein-kinase encoding oncogenes produced more TGF-beta than parental cells. However, only highly metastatic fibrosarcomas secreted activated TGF-beta at rates that were greater than parental fibroblasts. Immunohistochemical staining for TGF-beta 1 showed widespread intra- and extracellular distribution in metastatic lung nodules and adjacent tissue. Cells isolated from tumors successfully metastasizing to the lung had TGF-beta 1 mRNA levels which were increased 19-fold over in vitro controls. Despite the greatly enhanced rate of secretion of activated TGF-beta, metastatic cells exhibited markedly altered responses of TGF-beta 1 and TGF-beta 2, being unable to either increase collagen secretion or enhance collagen alpha 2(1) or TGF-beta 1 mRNA levels. This lack of response was not due to either altered TGF-beta receptor affinity or numbers. Metastatic progression was, therefore, associated with an increase in the secretion of activated TGF-beta 1 and a loss of the ability to deregulate TGF-beta-responsive genes.

Bleomycin: a pharmacologic tool in the study of the pathogenesis of interstitial pulmonary fibrosis

Bleomycin is a unique DNA-interactive antitumor agent that has become a popular tool in studies of the pathogenesis of interstitial pulmonary fibrosis. The biochemical and morphological changes seen in the lungs of many species after bleomycin simulate those seen in humans. The availability of these animal models of interstitial pulmonary fibrosis also provides the opportunity to investigate novel pharmacological approaches to preventing this disease.

In situ expression of transforming growth factor beta in streptococcal cell wall-induced granulomatous inflammation and hepatic fibrosis

The expression of transforming growth factor beta (TGF-beta) was examined during the evolution of streptococcal cell wall (SCW)-induced hepatic granulomas in rats to evaluate the role of TGF-beta in chronic inflammation progressing to fibrosis. As determined by immunocytochemistry, Kupffer cells rapidly expressed TGF-beta 1 following intraperitoneal (i.p.) injection of SCW, and TGF-beta was expressed by mononuclear phagocytes in the earliest cell aggregates as well as by mononuclear phagocytes within the capsule of mature lesions. Interestingly, apparent extracellular TGF-beta was observed in mature lesions at the interface of the capsule and the cellular core, a region of active fibrogenesis. Granulomas isolated 3, 6, and 12 weeks post-SCW injection elaborated nanogram (ng) quantities of latent and active TGF-beta into culture supernatants, and expressed high levels of 2.4 and 1.9 kb TGF-beta 1 transcripts. Expression of procollagen type I and III mRNAs were observed in parallel with the expression of the TGF-beta 1 transcripts. Thus, TGF-beta is expressed throughout SCW-granuloma development, and, based on known bioactivities, it appears that TGF-beta mediates, in part, the recruitment and activation of monocytes and fibroblasts and deposition of collagen in SCW-granulomas and likely other chronic inflammatory lesions progressing to fibrosis.