Electron microscopic study of chronic eosinophilic pneumonia.

Two cases of chronic eosinophilic pneumonia were examined electron microscopically to study the role of eosinophil granulocytes. Eosinophils, together with macrophages and lymphocytes, were observed to have infiltrated prominently in the lung tissues of the two cases. Degeneration and necrosis of pneumocytes were observed, and denuded basement membranes and destroyed alveolar structures were occasionally found. In the alveolar septa, swelling of the endothelial cells of the blood capillaries, edema of the stroma and fibrin deposition were observed. Eosinophils, released eosinophil granules and macrophages phagocytosing eosinophil granules were found frequently near the degenerated and necrotic alveolar tissues. These findings suggest that the tissue injuries were induced by the cytotoxic effects of the eosinophil granules.