Electron micrographs showing apoptosis of megakaryocytes in immune thrombocytopenia (ITP)

Transmission electron micrographs show the ultrastructure of megakaryocytes (platelet precursor cells in the bone marrow), including mitochondria and the demarcation membrane system (DMS; the precursor to the plasma membrane of platelets). In immune thrombocytopenia (ITP), megakaryocytes can undergo apoptosis, contributing to reduced platelet production. Antibody destruction of platelets in the circulation also occurs. The images in panels B and C are taken at a higher magnification than A.
(A) Control megakaryocyte (from an individual without ITP). The inset shows a higher magnification of intact mitochondria (arrowheads) and a normal demarcation pattern. Original magnification, ×3000 (top panel); and ×18,000 (bottom panel).
(B) Megakaryocyte from an individual with ITP. Features of apoptosis are present, including nuclear fragmentation (arrow in inset), chromatin condensation (arrowheads), and shrinkage/rounding of the cell with decreased cell volume. Original magnification, ×7000 (top panel); and ×18,000 (bottom panel).
(C) Megakaryocyte from another individual with ITP. Features of para-apoptosis are present including mitochondrial swelling (short arrows), dilation of the endoplasmic reticulum, and dilation of the DMS. The enlarged cytoplasmic margin lacks organelles (arrowhead). Original magnification, ×7000 (top panel); and ×18,000 (bottom panel).