The surfactant system of human fetal lung organotypic cultures: Ultrastructural preservation by a lipid-carbohydrate retention method

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Abstract
Human fetal lung organotypic cultures consisted of epithelial elements (≃40-100 m̈m in diameter) formed by the reaggregation of single cells from a monodisperse suspension of enzymatically dissociated fetal lung. These elements, termed alveolar-like structures, were composed primarily of type II alveolar epithelial cells whose apical surfaces bordered the central lumen of the alveolar-like structure. Pulmonary surfactant secreted by the type II cells was retained within the lumen and accumulated in close association with the epithelium. These characteristics made this culture system an advantageous model for the morphological study of human pulmonary surfactant in vitro. A lipid-carbohydrate retention procedure which reduced the extraction of tissue components and thus provided improved preservation of multilamellar bodies and tubular myelin surfactant was used in an ultrastructural study of organotypically cultured surfactant. Human surfactant was observed for the first time with most of its structural components intact. In vitro human surfactant was found to be similar to in vivo rodent and non-human primate surfactant, but with certain differences. Long surfactant tubules were not observed. There were more transformed multilamellar bodies present with more foci undergoing transformation. Each focus contained fewer layers of tubular myelin surfactant than occurs in rodent surfactant. No epiphase-hypophase areas were observed, only tubular myelin surfactant. In addition, a previously unreported intrasurfactant matrix material was observed.