Plasminogen activator secreted from macrophages stimulated by lymphokines

In our previous study, we have demonstrated that plasminogen activators (PAs) with Mr=24, 000 and Mr=48, 000 play an important role in tissue fibrinolysis during the development of hypersensitivity granulomas. In order to investigate the cellular source of these PAs, we cultured mouse peritoneal macrophages in different conditions. C57BL/6N mice were used with or without infection by Mycobacterium lepraemurium. Antigen stimulated peritoneal exudate macrophages were obtained by intraperitoneal injection of sonicated M. lepraemurium to the infected mice. PA activity in conditioned media was assayed by using two-stage colorimetric method and electrophoretic enzymography. Resident peritoneal macrophages secreted PA with Mr=48, 000. However antigen stimulated peritoneal exudate macrophages secreted a high activity of PA with Mr=24, 000 in addition to Mr=48, 000. In order to investigate secretion mechanism, in vitro stimulation of macrophages was carried out by lymphokines which were obtained from culture supernatants of splenic cells exposed with antigen or splenic T cells with Concanavalin A. The results clearly demonstrated that macrophages became secretable of PA with Mr=24, 000 by lymphokine stimulation. Further experiments showed that the effect of lymphokine to induce secretion of PA was partially represented by γ-Interferon. These data indicated that the immunological stimulation induced macrophages to secrete PA, the molecular weight of which was altered from resident macrophages.