[Electron-microscopic observations on rat lungs after long term inhalation of diesel emissions--non-neoplastic...

Non-neoplastic lesions in the respiratory organs of rats (F344) were investigated after exposure to heavy and light duty diesel emissions for 30 months. Pathological examinations of the lungs after every 6 months of exposure were performed by light and electron microscopy. Anthracosis caused by the inhaled diesel soot was the main morphological change observed in the lung. Foci of alveoli filled with alveolar macrophages engorged with diesel particles were scattered in the lung parenchyma. Marked changes observed in these areas consisted of intake of diesel particles by type 1 epithelium, hypertrophy and glandular proliferation of type 2 epithelium with many extended microvilli and increased number and size of lamellar inclusion bodies, focal increase of collagen fibers in the interstitium, and infiltration of particle-laden macrophages, neutrophils, mast cells and plasma cells into the interstitium of alveolar septa. Within the alveolar lumina there was marked accumulation of particle-laden macrophages or neutrophils and their debris, as well as laminated or scrolled materials discharged from the type 2 epithelium. The most marked changes observed in the airways were focal shortening of cilia and protrusions of non-ciliated cells, which were attributable mainly to the effects of gaseous components in the diesel exhaust. These morphological changes appeared in all the groups exposed to particle concentrations greater than 1 mg/m3 after 6 months' exposure, and were more marked with increase in particle concentration and with time.