Endocytic and tumoricidal heterogeneity of rat liver macrophage populations.

We demonstrate that all liver macrophages in the rat can be activated to a tumoricidal state by the i.v. injection of liposomal muramyl dipeptide (MDP). No significant differences in cytotoxicity between the macrophage subfractions were observed after i.v. injection of liposomal MDP, although endocytic uptake of liposomes per cell increased proportionally to cell size, both in vitro and in vivo. We found that in vitro uptake of MDP-containing liposomems by the subfractions produced the highest cytolytic activity in the small to intermediate-size macrophages