Phagocytosed platelets in leukocytes from patients with PV or ET. The presence of neutrophils and monocytes with intracellular platelets was assessed by flow cytometry and confocal and electron microscopy, as described in “Flow cytometry” and “Confocal microscopy and electron microscopy.” For confocal microscopy, platelets were identified based on the expression of the glycoprotein Ib (red). Hoechst stain (blue) was used for counterstaining nuclei. (A) Symbols represent the fraction of neutrophils with intracellular platelet antigens. Horizontal lines indicate mean values. (B) Symbols represent the percentage of monocytes with intracellular platelet antigens. Horizontal lines indicate mean values. Representative confocal (panels C,E,G) and electron microscopy (panels D,F,H) images of neutrophils from a patient with PV (panels C-D), from a patient with ET (panels E-F), and from a healthy control (panels G-H) are shown.