Filamentary tubular inclusions in type II pneumocytes of the guinea pig.

The type II pneumocytes of guinea pigs were studied with a transmission electron microscope. It was shown that 5-20% of type II cells contained filamentary tubular inclusions. No reports of similar structures in type II cells of any species have been found in the literature to date. These inclusions measured 90 nm in diameter, varying up to 3 micron in length, and were generally present in the basal and lateral portions of the cells with a close association to the lamellar bodies. They were usually straight but could be curved and tended to aggregate into parallel stacks. In cross-sections, these filamentary tubular inclusions were surrounded by a thickened unit membrane and were composed of microfilaments arranged in circular fashion around a central core. In longitudinal sections, they consisted of rod-like bodies with three lines of filaments. The possible function of the filamentary tubular inclusions is also discussed.