RECOGNITION OF CHARGED LIPOSOMES BY RAT PERITONEAL AND SPLENIC MACROPHAGES - EFFECTS OF FIBRONECTIN ON THE UPTAKE OF CHARGED LIPOSOMES

Different recognition systems for charged liposomes were found in rat peritoneal and splenic macrophages. In peritoneal macrophages, significant uptake was observed in negatively charged liposomes, depending on the phosphatidylserine concentration, and receptor-mediated uptake of negatively charged liposomes was suggested. In contrast, splenic macrophages took up positively charged liposomes significantly, depending on the stearylamine concentration, and participation of receptor-mediated uptake process was also suggested. Fibronectin purified from rat plasma bound to saturation to positively charged liposomes preferentially. The addition of fibronectin caused significant increase in the uptake of liposomes containing stearylamine by splenic macrophages. The uptake of liposomes by peritoneal macrophages was not enhanced by fibronectin irrespective of liposomal charge. Rat plasma fibronectin may thus be concluded to function as an opsonin of positively charged liposomes for rat splenic macrophages.