CHANGES IN ULTRASTRUCTURES AND ENZYME-ACTIVITIES DURING DIFFERENTIATION OF MYELOID-LEUKEMIA CELLS TO NORMAL MACROPHAGES

Changes in ultrastructures and in enzyme activities were investigated electron microscopically, cytochemically and biochemically when mouse myeloid leukemia cells, Ml cell line, successfully differentiated to normal macrophages after incubation with a conditioned medium harvested from secondary embryo fibroblasts, or a lipopolysaccharide from Salmonella typhosa. The number of mitochondria increased significantly accompanied by the enhanced activity of cytochrome oxidase per cell, although the activity in each mitochondrion remained unchanged. The rough-surfaced endoplasmic reticulum elongated and often exhibited a concentrically multilayered lamellae. Glucose-6-phosphatase activity, a marker enzyme for the endoplasmic reticulum, also increased. Primary lysosomes were newly formed where acid phosphatase activity was positively demonstrated. Ten-nm cytoplasmic microfilaments, mainly forming bundles, and other microfilaments less than 6 nm wide were formed newly and abundant. Budding of type C viruses from the plasma membranes was reduced strikingly. Another established cell line, Mm-1, which spontaneously differentiated from the Ml cell line, was characterized completely by a macrophage, in which azurophilic granules (primary lysosomes), secondary lysosomes possessing strong activity of acid phosphatase and 10-nm microfilaments were most remarkable. These non-transplantable Mm-1 cells sometimes exhibited budding of viruses. © 1979.