The alveolar epithelium of the newborn rat,and the significance of the osmiophilic lamellated bodies in cellular autophagy

Abstract

An attempt was made to determine the nature, origin, and fate of the membrane material of osmiophilic lamellated bodies, using lung tissue from neonate rats. The cytoplasm of the type II alveolar pneumonocyte contains centrioles, multivesicular bodies, and minute free vesicles similar to those in the multivesicular bodies. Autolysosomes, comprising membrane-bounded cytoplasmic regions and osmiophilic lamellated material, also occur in the type II pneumonocytes. The mitochondria often contain concentric membrane accumulations and membranous whorls. The type II alveolar cells are characterised by an intensive autophagy; this is apparently correlated with glycogenolysis, and with a radical cytodifferentiation by which the cells transform to the type I pneumonocyte. The osmiophilic lamellae of the autolysosomes are probably emptied isolation membranes. The mitochondria possibly serve as repositories for the massive membrane accumulations remaining after cytoplasmic lysis, which may invaginate into the organelles. The osmiophilic lamellated bodies typical of type II alveolar pneumonocytes may be mitochondrial membranes packed with the residual membranous material. Myeloid matter in the alveolar spaces (derived from the osmiophilic lamellated bodies) is best interpreted, not as an organised secretory product, but rather as a residue of cellular autophagy.