Lung mesothelial cell and fibroblast responses to pleural and alveolar macrophage supernatants and to lavage fluids from crocidolite-exposed rats

Our plain-English summary of Lung mesothelial cell and fibroblast responses to pleural and alveolar macrophage supernatants and to lavage fluids from crocidolite-exposed rats, by I.Y. Adamson, H. Prieditis, L. Young (American Journal of Respiratory Cell and Molecular Biology, 1997).

The study

• Authors: I.Y. Adamson, H. Prieditis, L. Young
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 1997;16(6):650-6
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

An early phase of proliferation by mesothelial cells and fibroblasts occurs in the lung after asbestos deposition, but the source and identity of the cytokine(s) involved is not clear. In the present study, rats received crocidolite asbestos intratracheally and were killed at 1 and 6 wk later, animals received tritiated thymidine 1 h before death. An increase in inflammatory cells was found in bronchoalveolar and pleural lavage fluids at both times, and after 6 wk the lungs showed fibrosis which was confirmed biochemically. Asbestos fibers were found in alveolar and interstitial macrophages but not in pleural macrophages. In autoradiographs, both mesothelial cells and fibroblasts showed increased DNA synthesis at 1 wk, but only fibroblast labeling was increased at 6 wk. Lavaged macrophages from the lung (alveolar macrophages; AM) and the pleura (pleural macrophages; PLM) were cultured and supernatants tested on rat lung mesothelial cells and fibroblasts in vitro; concentrated lavaged fluids were also tested. At 1 wk, macrophages secreted growth factors for both cell types but the effect was more pronounced using lavage fluids, particularly from the pleura. The increase in fibroblast growth was reduced by an antibody to platelet-derived growth factor, but this had no effect on mesothelial cells. The growth stimulation of these cells was blocked by an antibody to keratinocyte growth factor (KGF). Using cell supernatants and lavage fluids from rats 6 wk after asbestos, growth stimulation was only observed in fibroblasts. The results suggest at least 2 cytokine effects in the lung and pleural space after asbestos exposure; one responsible for fibroblast stimulation is seen up to 6 wk later, while the other, probably involving KGF, stimulates mesothelial cell proliferation in the early response phase after a single exposure to crocidolite.

In plain English

This was an animal experiment. The authors put 1 mg of crocidolite asbestos into the windpipes of 12 male rats and examined them 1 and 6 weeks later. Control rats received water only. At 1 week, increased DNA synthesis, a sign of cell division, was seen in mesothelial (lining) cells on the lung surface and in fibroblasts inside the lung. At 6 weeks it was still raised only in fibroblasts. Fibrosis, measured by a collagen marker, was found at 6 weeks. Fibers were seen in lung macrophages but never in pleural macrophages. In lab cultures, fluids and macrophage secretions from the pleural space collected at 1 week stimulated mesothelial cell growth. Samples collected at 6 weeks did not. Cultured fibroblasts were also stimulated, and the increase in their DNA synthesis caused by lavage fluids was mostly blocked by an antibody to platelet-derived growth factor. An antibody to keratinocyte growth factor (KGF) blocked the growth-promoting effect of pleural lavage fluid on mesothelial cells. The authors concluded that at least 2 cytokine effects occur after asbestos exposure, and that the early mesothelial response probably involves KGF.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment (rats given asbestos into the windpipe), combined with lab-culture (in vitro) tests of lavage fluids and macrophage secretions on rat lung mesothelial cells and fibroblasts
• Who was studied: 12 male Sprague-Dawley rats weighing about 160 g, killed in groups of 6 at 1 and 6 weeks; controls received water only; 4 extra asbestos-exposed rats were used for electron microscopy; Department of Pathology, University of Manitoba, Winnipeg, Canada
• Exposure: A single dose of 1 mg crocidolite asbestos (UICC reference sample) in 1 ml sterile water, instilled into the trachea. 28% of fibers were under 5 micrometers long, less than 1% were over 20 micrometers, and 82% were under 0.5 micrometers in diameter.
• Main results:
  • In exposed rats, alveolar macrophage numbers in lung lavage were twice control values at 1 week and only slightly lower at 6 weeks
  • In exposed rats, pleural macrophage numbers tripled at 1 week and stayed at that level up to 6 weeks
  • In exposed rats, 58% of alveolar macrophages contained particles at 1 week and 28% contained fibers at 6 weeks. Fibers were never seen in pleural macrophages or pleural PMN at either time.
  • Hydroxyproline (a collagen marker) in exposed rats was unchanged at 1 week but significantly increased at 6 weeks compared with controls (1264 +/- 84 per right lung lobe at 6 weeks versus 837 +/- 7 in controls)
  • Labeling (a measure of DNA synthesis) of mesothelial cells on the lung surface was below 0.3% in controls. In exposed rats it rose to 2.0% at 1 week and was back to control level by 6 weeks.
  • Labeling of fibroblasts in the lung interstitial tissue of exposed rats rose to 1.5% at 1 week and to 3% at 6 weeks
  • In culture, pleural macrophage secretions and pleural lavage fluid from rats 1 week after exposure caused a larger, significant increase in mesothelial cell DNA synthesis. Samples from 6 weeks had no effect on mesothelial cells.
  • Samples from rats 6 weeks after exposure produced greater fibroblast growth stimulation in culture
  • The increase in fibroblast DNA synthesis caused by lavage fluids could mostly be blocked by an antibody to PDGF (data not shown). Antibodies to PDGF, FGF, TGF-beta and TNF-alpha did not reduce the enhanced mesothelial growth, and anti-EGF reduced it by only 15%.
  • The antibody to KGF produced the greatest inhibition, blocking the growth-promoting effect of pleural lavage fluid on mesothelial cells. Pure KGF increased DNA synthesis in normal mesothelial cells.
  • In cell counts after 2 days, mesothelial cells numbered 6.4 ± 0.4 (x 10^4) with KGF and 5.9 ± 0.3 with pleural lavage fluid, versus 4.5 ± 0.3 serum free. Adding anti-KGF to pleural lavage fluid gave 4.3 ± 0.5.
• The authors' conclusion: The authors concluded that there are at least 2 cytokine effects in the lung and pleural space after asbestos exposure. One stimulates fibroblasts and is seen up to 6 weeks later. The other, probably involving KGF, stimulates mesothelial cell proliferation early after a single crocidolite exposure.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Fibroblast, Alveolar Macrophage, Crocidolite, Deposition, Cytokine, Fibrosis, Interstitial.

Related studies

• KGF and HGF are growth factors for mesothelial cells in pleural lavage fluid after intratracheal asbestos — I.Y. Adamson, J. Bakowska (2001)
• Mesothelial cell proliferation: a nonspecific response to lung injury associated with fibrosis — I.Y. Adamson, J. Bakowska, et al. (1994)
• Alveolar macrophage cytokine and growth factor production in a rat model of crocidolite-induced pulmonary inflammation and fibrosis — K.E. Driscoll, J.K. Maurer, et al. (1995)
• Differential proliferation of rat lung fibroblasts induced by the platelet-derived growth factor-AA, -AB, and -BB isoforms secreted by rat alveolar macrophages — J.C. Bonner, A.R. Osornio-Vargas, et al. (1991)
• Nitric oxide (NO) synthase activity in the lung and NO synthesis in alveolar macrophages of rats increased on exposure to asbestos — H. Iguchi, S. Kojo, et al. (1996)
• Long-lasting production of TGF-beta1 by alveolar macrophages exposed to low doses of asbestos without apoptosis — Y. Nishimura, T. Nishiike-Wada, et al. (2007)

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