Interferon activates macrophages to produce plasminogen activator.

Macrophages and monocytes become activated, by a variety of mechanisms, to exhibit cytotoxicity. Associated with this activation for cytotoxicity is the production of certain neutral proteases, especially plasminogen activator (PA), which may be involved in the mechanism of cytolysis. Supernatants from concanavalin A (Con A) or antigen-stimulated spleen cells contain factor(s) which render macrophages and monocytes activated in vitro (MAF/MIF). We have found that in addition to such spleen cell supernatants murine interferon was able to activate peptone-induced C57BL/6 peritoneal macrophages to produce PA but had no effect on human monocytes. Similarly, human recombinant interferon activated human monocytes but not murine macrophages to produce PA. In addition to displaying this species specificity, interferon was able to function as a monocyte/macrophage activator in this system just as in cytotoxicity and may be a regulator of monocyte/macrophage function in vivo by modulation of proteolytic enzymes.