Role of Alveolar Type II Epithelial Cells in the Repairing Process after Lung Injury; Stimulating Factors for Cell Proliferation and Ion Transport

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1. Isolation and culture of human alveolar type II cells from resected human lungs: Specimens were obtained from ll patients undergoing lobectomy or pneumonectomy for primary tumors. Alveolar type II cells were isolated by a modification of the method for isolating rat type II cells with elastase and density gradients. The yield of type II cells was 2.7 x10^6 cells/g of tissue weigh. the percentage of type ii cells as determined by the papanicolaou stain after one day in culture was 71.0 3.4 % in 8 of ll isolations. These human cells have more numerous and smaller granules than do isolated rat type II cells. EM of the cells showed characteristic surface microvilli and intracytoplasmic lamellar bodies, of which some were multicentric. Examining the cytoskeleton structure by an avidin-biotin stain, they have fine intermediate filaments such as actin and keratin. We measured the secretion of pulmonary surfactant apoprotein from human type II cells over 3-6 hours after one day in culture. … More Apoprotein was secreted about 33.1 ng/10^6 cells in 3 hrs, and 35.3 ng/10^6 cells in 6 hrs. This secretion was stimulated almost 2-fold by ADP 10^<-3>M.2. Functions of alveolar type II cells: (1) effect of silica in vitro; Alveolar type II cells appear hypertrophic and hyperlasic in silica-treated lungs, we investigated type II cell proliferations, measuring tritiated thymidine incorporation. Co-culturing type II cells with alveolar macrophages stimulated by silica, using transwell membrane, thymidine incorporation was inhibited to 46.9 % of the control. (2) in vivo culture; Altough the cells are necessarily damaged and lose surface receptors to some extent by the isolation procedure and conditions in vitro, we develop a new system of in vivo culture, which isolated cells are again implanted into the peritoneum or subcutaneous region of another rat, using diffusion chambers. The cells in vivo culture more proliferated and had more active ion transport. (3) effect of extracellular matrix; Fibronectin mediates alveolar type II cells adherence in vitro. Monolayers on fibronection coated filter have higher pothtial difference and resistance. Fluorescence microscopy of type II cells on fibronectin showed a marked accumulation of actin and keratin bundles in their periphery. Fibronectin is an important functional component of the extracellular matrix that may support alveolar type II cells during the alveolar re-epithelization after lung injury.3. Function of tracheal epithelium: The tracheal epithelium have some similar functions to those of alveolar type II cells, such as ion transport and cell proliferation. Less