Ultrastructural Studies on Human Myeloma Plasmacytes1

Myeloma plasmacytes were studied in six untreated pa tients to obtain more information on the nuclear ultrastruc tural abnormalities in these cells. Asynchrony of nucleolar, nuclear, and cytoplasmic maturation was frequently ob served in pleomorphic myeloma plasmacytes. Immature and mature myeloma plasmacytes of two patients contained intranuclear rodlets which consisted of fine filaments ar ranged in parallel. Myeloma plasmacytes in mitosis often contained persistent nucleoli, nucleolar fragments, and small nucleolus-like bodies. The mitotic division of the nu cleus was also noted in differentiated cytoplasm. In some cells in mitosis, the cytoplasm was differentiated and ap parently functional.