Filopodia engulf and then pull myelin into phagocyte. Successive steps during phagocytosis of a myelin particle by a wild-type BalbC macrophage. (A) Arrows mark a filopodium-like structure (green and red) that engulfs a myelin particle (purple). Then (B to D), the filopodium retracts, pulling the myelin into the phagocyte. Phagocytosis was monitored continuously by confocal fluorescence microscopy at a single plane of focus. The macrophage cytoplasm was visualized by Ca+2 indicator Fura-4 (green), macrophage cell membrane by RH237 (red), and myelin by DiIc18 (blue). However, RH237 that was initially localized to the macrophage plasma membrane diffused out and became incorporated into myelin that turned purple (blue + red). Bar: 5 μm.