Bronchial Epithelial Cells Produce Chemotactic Activity for Bronchial Epithelial Cells: Possible Role for Fibronectin in Airway Repair

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Abstract
Bronchial mucosal injury initiates a complex series of repair mechanisms, one of which is reepithelialization of a denuded lumenal surface. This suggests the hypothesis that bronchial epithelial cells, the cells initially affected by bronchial injury, might be able to initiate repair of an injured area by producing a chemotactic activity for intact bronchial epithelial cells. To evaluate this, bronchial epithelial cells were prepared from bovine lung by protease digestion and cultured in medium 199 (M199) with 10% fetal calf serum (FCS) until confluence, after which the cells were rinsed with Hanks'' balanced salt solution, and serum-free fresh M199 was added. This conditioned medium was then collected and used to test the chemotactic response of bronchial epithelial cells using a blindwell chamber technique. Target cells for this assay were isolated from airways by protease digestion, grown to confluence in M199 with 10% FCS, and then harvested with trypsin. Bronchial epithelial cell-conditioned medium harvested after 3 days attracted more cells (197.0 .+-. 5.7 cells/10 high power fields) than did M199 without FCS alone (4.3 .+-. 0.9) (p < 0.01). Checkerboard analysis showed that the migration was chemotactic. The chemotactic activity accumulated in the culture medium with time. The addition of 25 .mu.g/ml of cycloheximide inhibited this accumulation. Column chromatography with Sephadex G-150 revealed a single peak of chemotactic activity in the high molecular weight range. The chemotactic activity was bound to gelatin-Sepharose 4B and was eluted with 6 M urea. Enzyme-linked immunosorbent assay of the column fractions demonstrated that the chemotactic activity, strongly suggesting that the chemotactic activity may be fibronectin. Finally, bronchial epithelial cell-derived fibronectin was compared with plasma-derived fibronectin and found to be 10- to 50-fold more potent as a chemotactic factor. The ability of bronchial epithelial cells to produce chemotactic activity may play an important role during tissue repair after airway injury by initiating prompt and efficient reepithelialization of bronchial wall.