Cytochemistry and ultrastructural morphometry of cultured HL60 myeloid leukemia cells

Cultured human myeloid leukemia (HL60) cells were characterized using ultrastructural cytochemical methods and differences identified when cells were compared for low (17 to 47), middle (69 to 100), and high (214 to 244) passages or to normal promyelocytes aspirated from bone marrow. Endoplasmic reticulum and transition structures (pre-Golgi compartment) of HL60 cells stained positively for peroxidase using diaminobenzidine but stained sparsely for reducing groups with osmium-zinc iodide. Staining of Golgi elements was relatively indistinct with diaminobenzidine and strong with osmium-zinc iodide, in comparison to freshly harvested promyelocytes which have intense diaminobenzidine and osmium-zinc iodide staining of the pre-Golgi and Golgi compartments. Cytoplasmic polyribosomes were more numerous in middle and high passage cells, whereas dilatation of endoplasmic reticulum was less prominent in these cells. The mean granule size was significantly increased in low passage cells, and staining of peroxidase was more prominent by light and electron microscopy when compared to high passage cells. Cytoplasmic granules demonstrated strong complex carbohydrate staining, indicating a lack of granule maturation in HL60 cells. Terminally differentiated myeloid cells were more frequent in low passage samples, and some neutrophil granule maturation appeared to occur within these cells, whereas all eosinophil granules consistently remained immature with intense complex carbohydrate staining and lack of crystalloid formation. These studies demonstrate significant differences between HL60 cells and normal promyelocytes, and also passage-dependent maturational differences in HL60 cells. These differences should be considered in evaluating parameters of cell growth and maturation and in the biochemical and enzymatic characterization of these cells.