Association of target NB4 and APL cells with MΦs. NB4 and APL cells treated with 1μM DNR for 24 hours were used as PS-exposed target cells for all subsequent coculture assays. MΦs were differentiated from monocytes or THP-1 cells. Target cells incubated with MΦs at a 2:1 ratio at 37°C for different times were analyzed. (A) Confocal microscopy image of CMTPX-stained THP-1–derived MΦs (red) with bound CMFDA-labeled target NB4 cells (green, arrows) after 30 minutes of incubation. A scattered target NB4 cell (green, arrowhead). (B) Scanning (left) and transmission (right) electron microscopic examination of anchored (square) and adhered (stars) target APL cells to the surface of THP-1–derived MΦs (triangles) after 30 minutes. (C) After 1-hour incubation, scanning electron microscopy of grasped (left, star) and internalized (right, square) target NB4 cells by THP-1–derived MΦs (triangles). (D) Scanning electron microscopy of a THP-1–derived MΦ (triangle) extending pseudopodia over a target APL cell (star) after 1-hour incubation. (E) After 2 hours of incubation, transmission microscopy of NB4 material (left, square) and a morphologically apoptotic target NB4 cell with karyopyknosis (right, star) engulfed by THP-1–derived MΦs (triangles). (F) Transmission micrograph showing phagocytosed target APL material (square) in a monocyte-derived MΦ (triangle) after 2 hours of incubation. (G) Transmission microscopy image of a THP-1–derived MΦ (triangle) with digested APL apoptotic bodies (arrows) after 3 hours of incubation. Scale bars represent 10 μm (A) or 4 μm (B-G).