THE ULTRASTRUCTURE OF MEGAKARYOCYTES IN POLYCYTHAEMIA VERA AND CHRONIC GRANULOCYTIC LEUKAEMIA

Megakaryocytes from patients with normal haematopoiesis, patients with polycythaemia vera (PCV) and patients with chronic granulocytic leukaemia (CGL) were examined in the electron microscope. In addition to the usual cytoplasmic organelles, a regular finding in normal megakaryocytes was the presence of specific granules. The normal megakaryocytes were also characterized by the presence of the platelet demarcation system. The first evidence of this system was small vesicles, which increased in number, became elongated, and formed demarcation tubules and membranes, delimiting the future platelets. Finally, the platelets were demarcated. After platelet production was completed, the end result was a naked nucleus almost completely devoid of cytoplasm. Megakaryocytes from patients with PCV differed from normal megakaryocytes in certain aspects. They could show hypertrophy of both nucleus and cytoplasm, as well as an increase in the amount of ribosomes. Rough-surfaced endoplasmic reticulum, which was not a regular finding in normal cells, appeared in most megakaryocytes from patients with PCV. Some cells appeared abnormal in that they showed no signs of differentiation towards thrombopoietic activity although the cytoplasm was abundant. In occasional cells, tubular-like double-membrane limited profiles enclosing stranded material were found. The megakaryocytes from patients with CGL were generally hypotrophic, but had a well-developed platelet demarcation system. In two patients with CGL, defective development of the demarcation system was encountered in some cells. These cells showed actual demarcation of platelets in spite of very sparse development of the demarcation system.