Differentiation Of Cultured Type-Ii Cells Into Alveolar Epithelium-In-Vitro Organization Of Secreted Surfactant Membranes Into Tubular Myelin

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In view of the need for an in vitro model to study the pathobiology of surfactant tubular myelin, we cultured rat type II cells (purity 80-95%) in serum-free medium (ACL-4) on an extracellular matrix (Matrigel) for up to 2 weeks. In this model, type II cells progressively organize into colonies with lumina that are lined in part with flat type I-like cells with tight junctions to polarized type II cells. The lumina of these alveolar structures contain secreted surfactant membranes that begin to organize into tubular myelin at 3-4 days. After one week in culture the alveolar structures bear significant resemblance to the alveolar epithelium, and both lumina and culture supernatant contain abundant tubular myelin and other surfactant forms. Immunogold labeled sections of fixed, cryosubstituted alveolar structures demonstrated specific labeling for SP-A and lysozyme within the type II cells and secreted surfactant membranes, with preferential localization in tubular myelin. Our results indicate that the above model closely simulates the alveolar epithelium and provides an appropriate in vitro approach to study the surfactant system.

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FASEB Journal, v. 8, issue 6, p. 141