An electron microscope study of the response of mesothelial cells to the intrapleural injection of asbestos dust

Our plain-English summary of An electron microscope study of the response of mesothelial cells to the intrapleural injection of asbestos dust, by J.M. Davis (British Journal of Experimental Pathology, 1974).

The study

• Author: J.M. Davis
• Journal: British Journal of Experimental Pathology
• Published: 1974;55(1):64-70
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Studies of the pleural mesothelium in rats, mice, and guinea-pigs following the intrapleural injection of asbestos dust, showed that for 6 months at least this dust did not induce mesothelial hyperplasia. During the first few days after injection some areas of mesothelial cells became rounded and less clearly attached to one another, and a few were found to contain small numbers of asbestos fibres. During this period there was evidence of the penetration of asbestos fibres between the mesothelial cells, into the submesothelial connective tissues. Later in the studies the mesothelium covering most of the pleural cavity returned to normal, but where mesothelium covered asbestos granulomata, the cells were found to be extremely flattened, and without surface microvilli. Usually the mesothelial covering was complete, but in some areas pores were found penetrating the mesothelial cell cytoplasm and leaving areas of connective tissue in direct contact with the pleural cavity. In a few cases mesothelial cells were found lining clefts within the connective tissue of asbestos granulomata.

In plain English

In this animal experiment, the author used light and electron microscopes to examine the mesothelial cells lining the pleural (chest) cavity after asbestos dust was injected there. Groups of 20 guinea-pigs, 20 rats and 20 mice were used; in each, 10 received crocidolite and 10 chrysotile. Animals were killed 7 days to 6 months later. Most of the dust ended up in large cellular granulomata (clusters of reacting cells), which were fully formed by 14 days. The mesothelial cells showed no signs of hyperplasia (overgrowth) at any stage. In the first weeks some cells became rounded and loosely attached, a few held at most three or four dust particles, and some fibres passed between the cells into the tissue beneath. Most mesothelium later returned to normal. Cells covering granulomata, however, were extremely flattened, lacked surface processes, and sometimes had pores through them. Mesothelial findings were very similar for both fiber types, although crocidolite tended to spread faster and form smaller, more numerous and more widely scattered granulomata. The author concluded that most mesothelial cells looked normal throughout.

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 (intrapleural injection), with tissue examined by light and electron microscopy at intervals after injection
• Who was studied: 20 guinea-pigs (Bernard Hartley strain), 20 rats (Wistar strain) and 20 mice (Balb/C strain), taken from the animals used in a study of experimental mesotheliomata; Institute of Occupational Medicine, Edinburgh
• Exposure: Intrapleural injection of crocidolite (10 animals per species) or chrysotile (10 animals per species). Doses were 25 mg in 1 ml distilled water for guinea-pigs and rats, and 10 mg in 0.5 ml distilled water for mice.
• Main results:
  • In all three species, most of the injected dust was taken into large cellular granulomata, which were fully formed by 14 days and did not grow after that.
  • Crocidolite dust tended to spread more rapidly than chrysotile, and crocidolite granulomata tended to be smaller but more numerous and more widely scattered than chrysotile granulomata.
  • The mesothelial cells showed no signs of hyperplasia at any stage.
  • After injection, mesothelial cells in some areas became more rounded than usual.
  • Contact between neighbouring mesothelial cells was much looser than usual.
  • A few mesothelial cells contained asbestos particles, but none held more than three or four.
  • In some places asbestos fibres passed between the mesothelial cells into the connective tissue beneath.
  • From 6 weeks after injection no changes were seen in any mesothelial surfaces, and dust-containing mesothelial cells were no longer found.
  • In most cases the rounded cells quickly returned to normal. The exceptions were on the surfaces of granulomata and the fibrous tissue around them.
  • Mesothelial cells covering granulomata were extremely extended. They often lacked a normal basement membrane and had no surface processes.
  • In some cases pores ran through these cells, leaving collagen or basement membrane in direct contact with the body cavity.
  • Near the surfaces of granulomata, some narrow clefts were lined with mesothelial cells.
  • The electron microscope findings on the mesothelial cells were very similar for chrysotile and crocidolite.
• The authors' conclusion: The author concluded that the majority of mesothelial cells appeared normal for the whole study and that no areas of mesothelium showed hyperplasia.
• Limitations the authors state:
  • Crocidolite in tissue made sectioning for electron microscopy very difficult, so no high-definition images were obtained from crocidolite-treated animals. All illustrations are from chrysotile-treated animals.
  • The author could not determine whether mesothelial cells actively took up the dust or whether particles were physically pushed into them.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Mesothelium, Reactive Mesothelial Hyperplasia, Pleural Cavity.

Related studies

• Epithelial outgrowths from lung tissue following intrapleural injection of asbestos dust in experimental animals — J.M. Davis (1971)
• The calcification of fibrous pleural lesions produced in guinea-pigs by the injection of chrysotile asbestos dust — J.M. Davis (1971)
• The long term fibrogenic effects of chrysotile and crocidolite asbestos dust injected into the pleural cavity of experimental animals — J.M. Davis (1970)
• Evaluation of the tumorigenic potential of vermiculite by intrapleural injection in rats — B. Hunter, C. Thomson (1973)
• The effects of chrysotile asbestos dust on lung macrophages maintained in organ culture. An electron-microscope study — J.M. Davis (1967)
• Quantitative assessment of inorganic fibrous particulates in dust samples with an analytical transmission electron microscope — F.D. Pooley, N.J. Clark (1979)

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