Osmiophilic Lamellated Bodies and Associated Material in Lung Alveolar Spaces

The presence of osmiophilic, lamellated bodies in cells of the pulmonary surface epithelium of both immature and mature animals now is established. Such inclusions were described first by Schlipk6ter (1954), and there have been numerous reports of their presence in the lungs of many mammals and in the gill epithelium of amphibia and fish (e.g., Campiche, 1960; Policard et al., 1957). There have been suggestions that they are transformations of mitochondria (Woodside and Dalton, 1958; Schulz, 1959) and that similar bodies "in specific (epithelial) cells" may be observed occasionally to burst and discharge their osmio-philic content into the alveolar spaces (Kisch, 1960). Buckingham and Avery (1962) and Klaus et al. (1962) have proposed that these bodies may be the source of the "surface active agent," the presence of which in the fluid film lining the pulmonary alveoli is now generally accepted is believed to function as an anti-atelectasis factor, in that not only is it capable of changing surface tension but it also can achieve a low tension. The material probably is a lipoprotein, perhaps containing dipalmitoyl lecithin (Clements, 1962). Surface-active agent (surfactant) is present also in the newborn as well as the adult, and osmio-philic inclusion bodies in pulmonary epithelium have been reported in embryonic, neonate, and adult mice (Woodside and Dalton, 1958) and rats (Leeson and Leeson, 1964). Thus, it is possible to postulate a chain of events whereby the osmio-philic, lamellated inclusion bodies in pulmonary surface epithelium, perhaps derived from mito-chondria, discharge a lipoprotein into the alveolar spaces where it acts as a surface-active agent in the fluid film lining the alveoli. MATERIALS AND METHODS Small pieces of lung tissue were obtained from adult male and female rats and from neonate rats delivered by Caesarian section on the estimated day of parturi-tion. Some of the neonates from each of two litters were sacrificed before breathing; others were delivered and permitted to breathe for 5 min before killing by decapitation. Tissue was fixed either in 1% osmium tetroxide buffered to pH 7.4 with Veronal-acetate or in 1.5% glutaraldehyde in 0.1 M phosphate buffer at pH 7.20 at 4°C for periods of 0.5 to 12 hr. The glutaraldehyde-fixed material was postfixed in osmium tetroxide for 2 hr after washing in sucrose buffer. After dehydration, all material was infiltrated with and embedded in Maraglas (Freeman and Spurlock, 1962). Various staining methods and combinations were employed, usually lead hydroxide (Watson, 1958) …