Isolation, Culturing and in Vitro Activation of Liver Macrophages

Abstract

Systemic administration of particulate drug carriers such as liposomes generally leads to rapid accumulation of the carrier in cells of the mononuclear phagocyte system (MPS) (Scherphof et al., 1983). The mechanism of entry is most likely to be of endocytic nature (Scherphof et al., 1985), implying that the carrier-drug complex will be subject to intralysosomal processing. For a drug to be released from the lysosomal compartment in an active or activatable form it will have to be dissociated from the carrier and pass the lysosomal membrane when, as will most often be the case, its action is required in the cytosol. The great majority of the MPS is concentrated in the liver and the spleen, the organs which usually are responsible for the bulk of the removal of the drug carrier from the circulation. In order to be able to study the intracellular fate of such drug carriers as a function of various carrier parameters such as size and composition without being bothered by the involvement, either directly or indirectly, of other cell types, it might be advantageous to perform such studies in vitro with isolated cells. Since the liver macrophage population comprises the largest population of MPS cells in any one organ and as such contributes most extensively to the elimination of particulate drug carriers from the blood, we set out to investigate in detail the uptake and intracellular processing of one of the most versatile drug carriers, the liposome, by isolated liver macrophages (Kupffer cells) in monolayer culture. Also the action of a biologically active compound, the immunomodulator muramyl dipeptide (MDP), encapsulated in liposomes, was studied in this system.