Ultrastructure of megakaryocytes in healthy control and ITP. (A) Mature megakaryocyte (stage III) from a healthy donor, showing the characteristic ultrastructure. The right panel shows a higher magnification of intact mitochondria (arrowheads) and a normal demarcation pattern. Original magnification, × 3000 (left panel); and × 18 000 (right panel). (B) Mature megakaryocyte of an ITP patient showing apoptotic characteristics. The right panel shows a detail of the nuclear fragmentation (arrow) and chromatin condensation to the margins of the nucleus (arrowheads). The cells shown in panels B-C are taken at a higher magnification than those in panel A. The shrinkage of the cells and rounding up has reduced cellular volume considerably. Original magnification, × 7000 (left panel); and × 18 000 (right panel). (C) Mature megakaryocyte of another ITP patient showing ultrastructural features of para-apoptosis. In the inset details are shown of cytoplasmic vacuolization, partly as a result of swollen mitochondria (arrowheads), dilation of endoplasmic reticulum, and dilation of the demarcation membrane system. The thick, enlarged peripheral margin (open arrow) in the cytoplasm lacks organelles. Original magnification, × 7000 (left panel); and × 18 000 (right panel). N indicates nucleus.