A new myelin-like laminated body found in two cases of pulmonary alveolar proteinosis.

Electron microscopic observations were made on lung tissue, broncho-pulmonary lavage fluid and sputum in 2 cases of pulmonary alveolar proteinosis. Diagnosis was established by open lung biopsy in both cases. In Case 1 the electron microscopic samples were obtained from the surgical specimen. In Case 2 an electron microscopic observation was made only on the lavage fluid and sputum. The alveolar air spaces were full of amorphous or fine granular-appearing material intermingled with two kinds of laminated bodies (abbreviated to "Lamella A" and "Lamella B"). Lamella A, about 0.2 approximately 4 micrometer in diameter, presented a concentric laminated structure with approximately 300 A periodicity and was found in the alveolar air spaces, lung washings and sputum. It corresponded to what has hitherto been reported in the same disease and was always located outside the cells. Lamella B showed a laminated structure of high electron density, approximately 50 A in periodicity, usually looking like a concentric circle with a diameter of 0.5 micrometer or less. It was intensely stained with methenamine silver. It was mainly observed in mesenchymal cells of the alveolar septa and free macrophages in the alveolar air spaces, although it also occurred in the type I and type II alveolar epithelial cells. Furthermore, the Lamella B could be found in the alveolar air spaces outside the cells and in the bronchopulmonary lavage fluid. This body has not been demonstrated previously and, although its significance in this disease is still uncertain, the structural similarity of the Lamella B to the intra-alveolar material suggests a possible role of it in the production of intra-alveolar material.