Destruction of murine lymphoma cells by allogeneic immune peritoneal macrophages in vitro: an ultrastructure study.

SL2 lymphoma cells from inbred DBA/2 mice were added to monolayers of peritoneal macrophages isolated from immunized inbred C57BL/10ScCr mice. Tumor cells were removed from the supernatant most rapidly during the first few hours. Once tumor cells were bound to the macrophages, however, their destruction apparently proceeded at a constant rate. Most tumor cells initially had only very small areas of contact with macrophages. The first tumor cell changes were loss of microvilli and the formation of surface blebs that ultimately detached from the cell. Subsequently, the tumor cell rapidly rounded up while the nucleus became pyknotic and the cytoplasm vacuolated; finally, the plasma membrane lost its integrity. It was only in this stage that the macrophages actively phagocytized the tumor cells. The recorded extracellular killing of tumor cells, followed by phagocytosis of their remnants, was compared with the widely divergent descriptions of macrophage-tumor cell interaction in the literature.