Immunoultrastructural study of surfactant system. Distribution of specific protein of surface active material in rabbit lung.

Ducks were immunized with rabbit pulmonary surface active material that had been prepared with Sephadex chromatographic separation on lung washings. Specific antibody against a protein of surface active material was obtained after absorption of duck antisera with rabbit serum. Using the ultrastructural immunoperoxidase method, dense reaction product was recognized in alveolar lining material as granular deposits, closely associating with tubular myelin figures that were often observed in the basal layer of alveolar lining layer. In type I pneumocytes, reaction product was noted only in some pinocytotic vesicles. By contrast, in type II pneumocytes there was positivity in association with lamellar inclusion bodies, multivesicular bodies, Golgi complex, and endoplasmic reticulum. No reaction product was detected in bronchiolar and bronchial epithelial cells, including nonciliated bronchiolar and goblet cells. These findings indicate that specific protein in surfactant is synthesized in type II pneumocytes and secreted into the alveolar space to become a part of the alveolar lining layer, thus suggesting that specific protein plays an important role in surfactant system. Furthermore, reaction product could be detected in phagocytic vacuoles in alveolar macrophages and thus seems to be related to the clearance mechanism of the protein component of surfactant.