AChE activity in normal and abnormal BM MK. Presented is cytochemical staining of AChE activity (right) and immunochemical staining with GPIIb/IIIa antibodies (left) of normal, normal TPO-expanded, and ITP BM cells. (A and B) Normal BM grown ex vivo in the presence of TPO; (C and D) normal BM cells; and (E and H) ITP BM cells. Small (I, diameter < 10 μm), intermediate (II, diameter 10 to 25 μm), and large (III, diameter < 25 μm) MK are marked. Note the pronounced staining of AChE activity in small megakaryoblasts and the gradual decrease in AChE activities from cells at stage I to cells at stages II and III towards nonproliferating MK in the normal BM MK and the visible activity staining in a representative mature stage III MK in BM from an ITP patient (G and H). Pictures are representative of one of three tested normal, one of three tested ITP preparations, and one of five normal TPO-expanded BM cultures. Size bar = 10 μm.