Ultrastructural features of alveolitis in sarcoidosis.

Seventy-nine specimens of lung parenchyma from 61 patients with sarcoidosis were examined ultrastructurally with a focus on alveolitis, and they were compared with specimens of hypersensitivity pneumonitis (HP) and the percentage of lymphocytes in bronchoalveolar lavage fluid (BALF). Lymphocytes and monocytes were frequently observed in the capillary lumina, and these cells and macrophages were found in the interstitium of the alveolar walls in the specimens with alveolitis of sarcoidosis and HP. Increases in the percentage of lymphocytes in BALF correlated with the degree of alveolitis. Swelling and bleb formation of the endothelium of alveolar capillaries and changes in the capillary basement membrane were commonly found and were significantly increased in the specimens with alveolitis. The frequency of bleb formation was significantly higher in alveolitis of sarcoidosis than in that of HP. However, the changes in alveolar epithelium were not significant in sarcoidosis. Microvascular changes in alveolitis are not specific for sarcoidosis, but they are observed in other interstitial lung diseases. These alterations may play an important role in the development of pulmonary sarcoidosis.