Ultrastructure of lamellar bodies of type II pneumocytes after osmium—zinc impregnation

Sections from normal rat, dog, and human lungs and from atelectatic rat lungs and autografted and allografted dog lungs were impregnated with an OsO 4 -ZnI 2 mixture, examined with light and electron microscopes, and compared to sections fixed with glutaraldehyde and osmium tetroxide. The interlamellar clefts of the lamellar bodies of the type II pneumocytes, which were electron lucent after glutaraldehyde and osmium tetroxide fixation, had a great affinity for OsO 4 -ZnI 2 while the lamellae did not react. After lipid extraction, no reaction products could be detected. This suggests that the interlamellar clefts contain a substance which is, in part at least, lipid in nature. Electron microprobe analysis indicates that this substance reacts with OsO 4 -ZnI 2 to yield electron-dense precipitates of only osmium and zinc. Although early precursors of the lamellar bodies had no osmium-zinc impregnation, later precursors had increasing amounts of precipitates of various sizes and shapes. During extrusion from the cell and subsequent fragmentation of mature lamellar bodies, the osmium-zinc positive interlamellar substance maintained its morphologic relationship to the lamellae suggesting that this substance may be related to surfactant. Alveolar exudates of atelectatic rat lungs and transplanted dog lungs had an increase in the number and size of type II pneumocytes and of particles resulting from the extrusion and fragmentation of lamellar bodies. These changes were most marked in the allografted lungs during the later phases of rejection.