Morphological changes in HL-60 cells at low or high IDR doses. Cells were exposed to 0.05 μmol/L IDR for 24 hours (A and B) or 10 μmol/L IDR for 6 hours (C and D). At these time points, maximum apoptosis was reported by the MiCK assay in respective cultures (see Fig 8). Giemsa-stained cytospin preparations show three distinctive morphological types of cells: (1) Cells displaying morphological features of interphase or mitotic promyelocytes with no visible changes in cell structure; two large cells in (A) and predominant cells in (B); (2) cells in the early stage of apoptosis (ap, in [A] and [C]) with aggregated chromatin abutting the nuclear membrane, and condensed, basophilic cytoplasm; (3) necrotic cells (nec, in [A] and [C]) with faintly stained nuclear “ghosts,” indistinct vacuolated cytoplasm which appears light due to loss of basophilia, and ruptured plasma membranes; predominant cells in (D). Low magnification (B and D) is used to show proportions of apoptotic and necrotic cells in cultures. Scale marker indicates 10 μm for (A) and (C) and 50 μm for (B) and (D).