Quantification of uptake of liposomal carboxyfluorescein by professional phagocytes in-vitro. A flow microfluorimetric study on the J774 murine macrophage cell line

Abstract

Unilamellar egg phosphatidylcholine/cholesterol liposomes containing carboxyfluorescein were prepared by an ether injection method. The ability of cells of the J774.2 murine macrophage cell line to incorporate the liposomal fluorophore during incubation at 37 degrees C was measured by flow microfluorimetry. Liposomes incorporating additional phosphatidylserine or phosphatidic acid were taken up much more avidly than those lacking these phospholipids and the greatest uptake of carboxyfluorescein was observed with the phosphatidylserine species. Calculation of the number of liposomes taken up, greater than or equal to 0.2% of the number given, showed that this was an inefficient process. However these uptake data support previous findings based on the intracellular bactericidal activity of liposomal antibiotics determined in an identical in-vitro system.