MORPHOLOGICAL OBSERVATIONS ON THE FATE OF LIPOSOMES IN THE REGIONAL LYMPH-NODES AFTER FOOTPAD INJECTION INTO RATS

Multilamellar liposomes composed of equimolar egg phosphatidylcholine and cholesterol and containing carboxyfluorescein or colloidal gold we re injected subcutaneously into the footpad of the hind-leg of rats. T he draining popliteal lymph nodes of animals killed at time intervals after injection were then dissected and sections examined by fluoresce nce microscopy (carboxyfluorescein), light microscopy using an immunog old silver kit to enhance gold particles or by transmission electron m icroscopy. Morphological observations confirmed that subcutaneously in jected liposomes accumulate in large numbers in the draining lymph nod e. The majority of liposomes arrived at the subcapsular sinuses, proba bly via afferent lymphatic vessels, as such, i.e., in a non-cell bound form. Subsequently, liposomes were dispersed throughout the lymph nod e either by permeation as free vesicles along the sinuses or by cells involved in vesicle uptake. The majority of such cells were free macro phages, littoral cells and reticular cells (fixed macrophages). Once w ithin cells, liposomes were seen digested by the lysosomal apparatus w ith varying loss of their lamellar structure, leaving free gold partic les within the lysosomes.