Production of protease inhibitors by postsurgical macrophages

The deposition and lysis of fibrin are important processes in normal peritoneal healing. Since macrophages secrete a neutral plasminogen activator, we studied the production of plasminogen-dependent, fibrinolytic activity by postsurgical macrophages. Peritoneal exudate macrophages were collected from rabbits after resection and reanastomosis of their ileum. Intracellular plasminogen activator (PA) activity of resident (nonsurgical) macrophages was 8.4 +/- 1.8 milli-Plough units (mPU)/10(6) cells. Postsurgical Day 1 macrophages had significantly less activity (0.33 +/- 0.056 mPU/10(6) cells) compared to resident cells. Thereafter, the PA activity gradually increased and reached control levels by Postsurgical Day 7. The PA activity secreted by postsurgical macrophages into serum-free medium after 48 hr of culture was also determined. Conditioned medium from macrophages collected on Postoperative Days 1-5 exhibited less PA activity than buffer controls. PA activity was detected after acid treatment of the conditioned medium to remove acid-labile inhibitors. The activities of PA in acid-treated conditioned medium increased gradually and reached nonsurgical levels by Postsurgical Day 7. In spent medium from macrophages collected on Postsurgical Days 1-3, high levels of urokinase inhibitory activities were secreted; production gradually decreased during the later postoperative period. This inhibitory activity of macrophage-conditioned medium on urokinase-like PA activity was partially diminished by acidification of the media. These results support the hypothesis that macrophages in the postsurgical exudate may play an important role in the fibrinolytic process during peritoneal wound healing, perhaps through production and secretion of plasminogen activator as well as acid-labile and resistant protease inhibitors.