Incorporation of recombinant gamma interferon into liposomes enhances its ability to induce peritoneal macrophage antitoxoplasma activity.

In this study we compared the ability of free- and liposome-incorporated murine recombinant gamma interferon (rIFN-gamma) to enhance peritoneal macrophage H2O2 release and antitoxoplasma activity in vitro. rIFN-gamma was efficiently (37 to 47%) incorporated into multilamellar vesicles composed of phosphatidylglycerol/cholesterol in a 2:1 molar ratio. The amount of rIFN-gamma incorporated into multilamellar vesicles and added to macrophages (0.1 to 1,000 U/ml) was quantitated with [3H]rIFN-gamma. The concentration of liposomal rIFN-gamma required to enhance macrophage H2O2 release (1 U/ml) and maximally inhibit Toxoplasma gondii growth (10 U/ml) was one-tenth the concentration required for free rIFN-gamma (10 and 100 U/ml, respectively). This increase in potency was observed in both thioglycolate-elicited and resident peritoneal macrophages. Control liposomes containing encapsulated buffer had no effect on the potency of free rIFN-gamma. The duration of macrophage activation induced by 24 h of liposomal rIFN-gamma treatment was also considerably longer than that induced by free rIFN-gamma (2 days versus less than 1 day). These data indicate that liposomal rIFN-gamma is more active than free rIFN-gamma as an inducer of macrophage microbicidal properties in vitro. This enhanced activity, combined with the potential for selective delivery of liposomal rIFN-gamma to phagocytic cells in vivo, may improve the therapeutic efficacy of rIFN-gamma in infections characterized by parasitization of phagocytes.