FIGURE 6.

Granulomatous inflammation in the lungs of rats instilled with Iraq and silica dusts. Hematoxylin and eosin-stained sections are shown. Iraq dust. At 3 d following intratracheal injection of 5 mg/kg bw of Ir8 dust, there is a localized inflammatory response around the alveolar ducts (AD) in which a granuloma is seen. The surrounding alveoli appear relatively normal. There is moderate interstitial acute and chronic inflammation around the lesion together with alveolar epithelial hyperplasia. The terminal bronchiole (TB) is indicated (8×). By 150 d, the inflammation is substantially reduced (see Figures 3 and 4 and the following). In the section shown, two small granulomas are seen, persisting in an otherwise normal lung. Incident light microscopy revealed brown and black particles and polarizing light microscopy revealed birefringent particles consistent with silicates (20×). Silica. In this section of lung taken from rat 150 d after instillation of 150 mg/kg bw of silica dust, there are several well-formed granulomas, intra-alveolar foamy macrophages (blue arrow), interstitial and intra-alveolar inflammation, distortion of the small airways and bronchiole, and alveolar epithelial proliferative changes (8×).