Activation of mouse peritoneal macrophages in vitro and in vivo by interferon-gamma.

Abstract

To determine the role of IFN-.gamma. in the activation of resident mouse peritoneal macrophages, crude macrophage-activating lymphokines were incubated with a monoclonal anti-murine IFN-.gamma. antibody. This treatment abolished the capacity of mitogen-induced lymphokines to enhance either H2O2 release or activity against the intracellular protozoa Toxoplasma gondii and Leishmania donovani. All macrophage-activating factor detected by these assays was also removed by passing the lymphokines over a Sepharose column to which the monoclonal anti-IFN-.gamma. antibody had been coupled. Therefore, pure murine rIFN-.gamma. was tested both in vitro and in vivo as a single activating agent. After 48 h or pretreatment in vitro with 0.01-1 antiviral U/ml, macrophage H2O2-releasing capacity was enhanced an average of 6.4-fold; half-maximal stimulation was induced by 0.03 U/ml. Resident macrophages infected with T. gondii half-maximally inhibited parasite replication after 24 h of preincubation with 0.14 U/ml of rIFN-.gamma., and near complete inhibition was achieved by pretreatment with 100 U/ml. Half-maximal leishmanicidal activity was induced by 0.08 U/ml of rIFN-.gamma., and 67-75% of intracellular L. donovani amastigotes were killed after macrophages were preincubated with 10-100 U/ml. Eighteen hours after parenteral injection of rIFN-.gamma., peritoneal macrophages displayed a dose-dependent enhancement of H2O2-releasing capacity and antiprotozoal activity. Half-maximal enhancement required 85-250 U of rIFN-.gamma. given i.p. Peritoneal macrophages were also activated by rIFN-Y injected i.v. and i.m. The results suggest that, in the mouse model, IFN-.gamma. is likely to be a primary factor within mitogen-induced lymphokines responsible for activating macrophage oxidative metabolism and antiprotozoal activity, and indicate that rIFN-.gamma. is a potent activator of these effector functions both in vitro and in vivo. These findings provide a rationale for evaluating rIFN-.gamma. in the treatment of systemic intracellular infections, and indicate that murine models are appropriate for such studies.