Intracisternal protein in the type II pneumocyte of the ferret, guinea pig, and mongrel dog.

An intracisternal protein in the type II pneumocyte of the ferret, guinea pig, and mongrel dog was examined by light and electron microscopy and morphometry. The basic pattern of layering in this membrane-bound, ribosome-studded structure (cisternal body) was visualized in cross section as dense layers separated by approximately 0.1 micron with seven fine layers between. In all species the central fine band of the seven was occasionally more prominent than the other six. In the guinea pig the seven fine layers alternated in density from light to dark. The cisternal body of the dog was similar to that of the ferret, but was very much smaller and encountered infrequently. No function has been ascribed to this structure; however, its relation to lamellar bodies, the perinuclear membrane, and surfactant apoprotein is discussed.