Mast cells and inhalation of asbestos in rats.

Mast cell counts were performed on sections taken from the lungs of rats exposed by inhalation to different UICC samples of asbestos fibres for periods ranging from a few days to two years. A comparison of mast cell counts with grades of fibrosis showed that there is a sevenfold increase when there is interlobular linking of the fibrotic lesions (grade 5). Submesothelial mast cells showed a trend of increasing numbers with increasing exposure and with increasing subpleural thickening. Each type of asbestos produced a steady increase in mast cell numbers with increasing exposure. Two samples from animals exposed to chrysotile and two from animals exposed to amphiboles (crocidolite and amosite respectively) had 10 times as many cells as the control group after six and 24 months' exposure. Another amphibole, anthophyllite, produced 50 times more cells than were present in the control specimen appropriate for the heaviest exposure. These results are briefly discussed in relation to further exposure, smoking, and characteristics of the dusts.