AbstractLight microscopy was used to study the pathologic alterations in the rat lung after timed diesel exposures to 6000 μg m−3of diesel particulates ranging from 6 h to 9 weeks. As a general reaction, an increase in alveolar macrophages containing diesel particles, an increase in type II pneumocytes, and an accumulation of inflammatory cells within the alveoli and septal walls was observed. Histochemical differentiation between type II cells and alveolar macrophages was clearly delineated by the use of the PAS (periodic acid Schiff) stain in which macrophages stained positive and type II cells negative for this reaction. After the 9‐week exposure, the accumulation of macrophages and accompanying type II cell reaction resulted in the formation of alveolar complexes that seemed to be preferentially localized near the terminal bronchioles. The similarity of the lesion to that of macrophage alveolitis' produced in animals repeatedly exposed to coal dust is emphasized, although the ultimate clinical significance of the complex formation cannot be assessed within the time limits of the experimental observa
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