On the use of Percoll as a marker for liposomes in electron microscopy of mouse spleen tissue.

Liposomes encapsulating Percoll were prepared by reverse phase evaporation and characterized by electron microscopy (EM). Encapsulated Percoll was contained between lipid bilayers and in the lumen of the liposomes. The largest population of liposomes had diameters between 110 and 140 nm (22.6 per cent of total vesicle population). Percoll proved to be a good marker for liposomes in spleen tissue. It is inherently electron dense, has dimensions which are uniform and not easily confused with subcellular organelles, and can be encapsulated and visualized by EM examination of tissue by routine procedures. Electron microscope examination of spleen tissue excised 20 min after intravenous injection of liposomes encapsulating Percoll showed the presence of both liposome-encapsulated Percoll and free Percoll in phagolysosomes, suggesting that liposomes had been phagocytosed by macrophages in a way similar to circulating blood cells and that enzymatic digestion had already begun. On the other hand, intravenously injected free Percoll did not localize in phagolysosomes, but its fate appeared similar to that of intravenously injected colloidal carbon, being phagocytosed by what appeared to be macrophages and platelets.