Purified macrophages independently kill S180 cells through a combination of apoptosis and necrosis. SR/CR mice were injected with TG and infiltrating cells were washed from the peritoneal cavities after 3 d. Macrophages were further purified by adherence in culture DMEM with 10% FCS at 37°C for 30 min. Nonadherent cells were gently rinsed away with PBS. (A) Macrophages were cultured with S180 cells and viewed by time lapse video phase-contrast microscopy at 39°C in 5% CO₂ for 24 h to determine the mechanism of cancer cell killing. S180 cells targeted by macrophages (arrow) showed blebbing, followed by membrane rupture, characteristic of apoptosis. The time frame from the first to the last field was approximately 2 h 10 min. (B) Macrophages purified from SR/CR mice were cultured with S180 cells in standard in vitro killing assay conditions. After 12 h, rosettes of macrophages and S180 cells were fixed and viewed by phase contrast and immunohistochemistry. S180 cells were fluorescently labeled for activation of caspase 3 (arrow).