The Effect of Conditioned Medium from Isolated Alveolar Type II Cell on Lung Fibroblast Proliferation

Tadashi Igishi, Yutaka Hitsuda, Yuji Kawasaki, Katsuhiko Fukuda, Kazuhito Yasuda, Yukio Matsumoto and Takao Sasaki

Third Department of Internal Medicine, Faculty of Medicine, Tottori University, Yonago 683, Japan

Alveolar epithelial cell is thought to play an important role to keep normal architecture of alveolus. Little is known about the effect of alveolar epithelial cell on lung fibroblast. The effects of conditioned medium (CM) from isolated alveolar type II cell on lung fibroblast proliferation were investigated. Type II cells were isolated from rat lung by digesting with elastase and cultured for 8 days. Lung fibroblasts were obtained from lung explants. Fibroblast proliferation was assessed by MTT assay. Type II cells lost their phenotype with the time in culture becoming flatter and losing lamellar bodies. CM at 2 days after the isolation inhibited fibroblast proliferation in a volume dependent manner. Those at 5 and 8 days after the isolation had no effect on fibroblast proliferation. The inhibition was not affected by treatment of type II cells with indomethacin. Heat treatment (56°C, 1 h) of CM had no effect on this growth inhibitory activity. The results suggest that only CM from freshly isolated type II contains soluble factor which inhibits fibroblast proliferation and this activity is specific for type II cell rather than whole alveolar epithelial cell. This activity is not derived from prostaglandin E₂ which was proved to be secreted by type II cell and different from that derived from macrophage.

key words: alveolar type II cell; conditioned medium; fibroblast proliferation; inhibition

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