PLEURAL MACROPHAGES DIFFERENTIALLY ALTER PLEURAL MESOTHELIAL CELL GLYCOSAMINOGLYCAN PRODUCTION

Glycosaminoglycans are produced in abundance by the pleural mesotheliu m and likely participate in the inflammatory response to pleural injur y. Because intrapleural tetracycline (TCN) results in pleural macropha ge influx and pleural fibrosis, this study attempted to define the rol e of pleural macrophage products on mesothelial glycosaminoglycan (GAG ) production. Pleural macrophages were isolated 72 h after intrapleura l TCN or intrapleural carrageenan (CAR), a substance that recruits ple ural macrophages without Producing plural fibrosis. Macrophage culture d for 24 h produced a conditioned medium that was added to pleural mes othelial cell culture containing [H-3]-glucosamine and was compared to control cultures treated with RPMI culture media alone or with the ad dition of TCN or CAR. After 72 h, GAGs were isolated by pronase digest ion, cetyl pyridinium precipitation, and MgCl2 and ethanol extraction. The majority of GAGs were found in, the culture media as compared to the combined mesothelial cell and basement membrane fractions of contr ol mesothelial cells (883 +/- 33 vs. 216 +/- 16, cpm, counts per minut e), TCN-treated (792 +/- 48 vs. 204 +/- 18 cpm), CAR-treated (849 +/- 45 vs. 223 +/- 13 cpm), and macrophage-conditioned media-treated mesot helial cells (TCN macrophage-conditioned media 1420 +/- 42 vs. 356 +/- 11 cpm; CAR macrophage-conditioned media: 1241 +/- 38 vs. 339 +/- 10 cpm) (all p <.05). Media samples were enzymatically digested and indiv idual GAG species were separated by Sephadex G-50 column chromatograph ). TCN macrophage-conditioned media induced more GAG production by the mesothelial cell into the cell media (1420 +/- 42 cpm) than CAR macro phage-conditioned media (1241 +/- 38 cpm) (p <.05), which was predomin antly a difference in hyaluronate production. (342 +/- 53 cpm vs. 186 +/- 7 cpm) (p <.05). The results show that pleural macrophages modulat e mesothelial GAC production during tetracycline pleural injury. Incre ases in mesothelial cell hyaluronate production may be important in th e fibrotic response to chemical pleural injury.