Pleural mesothelial cells stimulated by asbestos release chemotactic activity for neutrophils in vitro

The development of the pleural inflammatory response to asbestos remains poorly defined. Importantly, the role of the pleural mesothelial cell in recruitment of neutrophils to the pleural space is not known. We hypothesized that rabbit pleural mesothelial cells stimulated by asbestos fibers release chemotactic factor(s) for neutrophils. Primary cultures of rabbit pleural mesothelial cells were established, and their purity verified by the presence of keratin and hyaluronic acid mucin. Mesothelial cells in serum-free media, in the presence of 30 micrograms/ml of crocidolite asbestos, released chemotaxins for neutrophils. This activity was not dependent on the type of asbestos fiber or fiber length. It was dose-dependent until 30 micrograms/ml of asbestos. The chemotactic fractions had the ability to increase both directed and random migration of neutrophils. The chemotactic activity was not present in sonicated fractions of unstimulated mesothelial cells, nor in supernates of asbestos fibers alone. Characterization of the chemotactic activity showed that it was heat stable (56 degrees C per 30 min) and sensitive to digestion with trypsin and papain. On Sephadex G-50 chromatography, it had a molecular weight between 6,000 and 9,000. Production of the chemotactic activity was inhibitable by cycloheximide. These results demonstrate that pleural mesothelial cells can actively synthesize a protein fraction with chemotactic activity for neutrophils. Production of this mesothelial cell-derived chemotactic activity for neutrophils may play an important role in the initiation of the inflammatory response of the pleura to asbestos.