Destruction of murine lymphoma cells by allogeneic peritoneal macrophages in vitro: Influence of antiserum

Peritoneal macrophages isolated from intact inbred C57BL/10ScCr mice and from inbred C57BL/10ScCr mice previously immunized with the allogeneic SL2 lymphoma were incubated with SL2 cells with and without antiserum. The mode of interaction of the cells during the first 4 hours was studied ultrastructurally. Normal macrophages interacted with the tumor cells only when antiserum was present. The main feature was a partial enveloping of the tumor cells by thin lamellipodia without any visible cell damage. Immune macrophages without antiserum killed the tumor cells extracellularly by a process of apoptosis and subsequently phagocytized the cell remnants, as described previously. In the presence of antiserum, immune macrophages phagocytized intact tumor cells with very long, slender lamellipodia. Subsequently, the tumor cells underwent intracellular necrosis that seemed to be initiated by the release by the macrophage of complete lysosomes into the phagosome containing the tumor cell. In addition to altering the mode of interaction, antiserum greatly increased the degree of cytotoxicity.