Immunohistochemical detection of activated caspase-3 in ITP megakaryocytes. (A) Normal bone marrow megakaryocytes are negative for activated caspase-3. Some neutrophil granulocytes are positive (arrows). (B-C) Megakaryocytes of 2 ITP patients with extensive ultrastructural features of apoptosis are shown. These megakaryocytes stain positive for activated caspase-3. Original magnification, × 400.