Mesothelial Cells Produce a Chemoattractant for Lung Fibroblasts: Role of Fibronectin

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Abstract
Pleural fibrosis may complicate several types of non-exudative pleural injury. Although the pathogenesis of such lesions is poorly understood, it is conceivable that mesothelial cells may recruit fibroblasts to sites of pleural damage. In order to test this possibility, conditioned medium from cultured rat mesothelial cells was tested for chemoattractant activity towards RL-87 rat lung fibroblasts. For this purpose, rat pleural or pericardial mesothelial cells were maintained in vitro for 6 to 96 h. Conditioned medium from each source was obtained at defined culture times and tested for chemotactic activity in a 48-well microchemotaxis assembly. A progressive, time-dependent increase in fibroblast chemoattractant activity was detected in both pleural and pericardial mesothelial cell conditioned medium samples. This effect was maximal in 96-h cultures. Checkerboard analysis revealed that the conditioned medium was truly chemotactic for lung fibroblasts. Characterization of the chemoattractant demonstrated that it was a nondialyzable (greater than 16 kD), thermolabile (100 degrees C for 15 min), acid-stable (pH 2.5), trypsin-sensitive, and pepsin-sensitive protein. The chemotaxin was shown to be fibronectin, since activity was abolished, in a dose-dependent manner, by treatment with anti-rat fibronectin antiserum as well as by passage through a gelatin agarose affinity column. This product consisted of two bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis of apparent molecular masses 250 and 220 kD. The secretion of a mesothelial cell-derived fibroblast chemoattractant may play a role in the response of the pleura to injury and in the pathogenesis of pleural fibrosis.