Preparation and characterisation of liposomes containing mannosylated phospholipids capable of targetting drugs to macrophages.

We have prepared liposomes from mannosylated phosphatidylmyo-inositol, derived from mycobacteria, and cholesterol. The size of the particles so formed could be controlled by membrane filtration. The vesicles encapsulated a significant amount of aqueous phase (about 8 microliter per mg phospholipid). Markers of the liposomal membrane and aqueous phase rapidly associated with mouse peritoneal macrophages and, more slowly, with rat alveolar macrophages. The uptake was saturable at high liposome concentrations, although phagocytosis of latex particles of the same mean diameter was not saturable at these concentrations. An excess of unlabelled liposomes composed of phosphatidylcholine and phosphatidylserine, which were also taken up readily by macrophages, did not inhibit the uptake of mannosylated liposomes. The uptake of fluorescent mannosylated bovine serum albumin was inhibited by these liposomes, suggesting a specific interaction with the macrophage mannose-fucose receptor. We conclude that this type of liposome would be useful for the delivery of immunomodulators to reticuloendothelial cells.