Ultrastructural changes in the alveolar epithelium in response to mycobacterial infection

Electron microscopic examination of the lung of mice infected with a virulent strain of M. bovis (Ravenel) revealed marked alterations in the alveolar epithelial cells, particularly Type 2 cells (granular pneumocytes), in addition to the development of interstitial and intra-alveolar granuloma. Unlike the feature in uninfected mice, more than one Type 2 epithelial cells were often found adjacent to one another within a single alveolus. Some of these cells showed mitotic figures. Their characteristic lamellar inclusions were morphologically altered.