Isolation, Cultivation and Differentiation of Lung Type II Epithelial Cells

Abstract

Type II alveolar epithelial cells account for approximately 5 % of the epithelial cell population of the alveoli and play many roles in the physiology and biology of the lung. They function as stem cells of the alveolar epithelium and proliferate and differentiate into type I cells during lung growth or after injury. These thin, squamous type I cells account for the other 95 % of the alveolar lining and form the barrier over which gas exchange takes place in the lung. Following damage to these fragile cells, type II cells proliferate and differentiate into type I cells to restore the integrity of the alveolar surface. Type II cells also function in the metabolism of xenobiotics (Baron and Voight 1990) and the regulation of ion transport (Liu and Mantone 1996) and in the immune responses of the lung (Cunningham et al. 1994). They also function in the synthesis and secretion of surfactant (Bates et al. 1994). The ability to obtain pure isolates in vitro of type II cells from animal lungs is of considerable benefit to investigate the activities of this extremely specialized cell type. Once placed into culture, type II cells begin to differentiate and to acquire morphological and biological characteristics of type I cells (Borok et al. 1994). Type II to type I differentiation, which can be controlled to some extent in culture, serves as an extremely useful model for examining the mechanisms involved in both spontaneous and chemically induced epithelial differentiation.