CHANGES IN CELLULAR ULTRASTRUCTURE INDUCED BY GAMMA-INTERFERON IN K-562 CELLS MAY BE PREREQUISITE FOR APOPTOSIS

We report here the time-course of electron microscopic changes induced by gamma-interferon (IFN-gamma) in the human erythromyeloid leukemia cell line K562. In K562 cells treated with IFN-gamma for 6 h, the nucl ei were polygonal in shape and microvilli were far more abundant on ce ll membranes compared with control K562 cells, and invaginations were often seen in the cell membranes. There was a reduction in the number of cell-membrane microvilli and an increase in the number of lysosomal bodies in the cytoplasm of K562 cells treated with IFN-gamma for 12 h . After treatment with IFN-gamma for 24 h, the cell membrane microvill i disappeared, large numbers of cellular organelles were observed, suc h as mitochondria and lysosomes, and the cytoplasm became electron-den se. Cytoplasmic vesicles and vacuoles were also observed. These vesicl es may correspond to an intermediate step in the ultimate cellular dis integration associated with apoptosis caused by IFN-gamma.