Prolymphocytic leukemia. An ultrastructural study

The ultrastructural features of the leukemic cells from three patients with prolymphocytic leukemia were examined. In all patients, the prolymphocytes were characterized by a single prominent nucleolus and a chromatin structure intermediate between that of a mature lymphocyte and a lymphoblast. The cytoplasm contained a few short segments of rough endoplasmic reticulum and a poorly-developed Golgi apparatus. Polyribosomes and lysosomes were scarce. These ultrastructural features help in distinguishing prolymphocytic leukemia from other malignant lymphoproliferative disorders. A unique feature of the leukemic cells from one patient was the presence of intracytoplasmic inclusions. These were concentrated in the region of the Golgi zone, were surrounded by a smooth, trilaminar membrane, and had a substructure of parallel lines with a periodicity of approximately 60 A. To the authors' knowledge, similar inclusions have not been previously described in prolymphocytic leukemia.