HL60 CELLS EXHIBIT PARTICULAR ULTRASTRUCTURAL FEATURES DURING ALL-TRANS-RETINOIC ACID-INDUCED APOPTOSIS

Ultrastructural features induced by 1 mu mol/l all-trans retinoic acid (ATRA) treatment of HL60 cells were observed with transmission electr on microscopy. Whilst some cells were unaffected, most of the others u nderwent granulocytic differentiation, starting point for apoptosis an d then, possibly, secondary necrosis. First steps of apoptosis led to nuclear fragmentation into dense bodies. Then three different ways wer e observed: i) cells shrank and dense bodies were expelled, mostly ass ociated with a fine lamellae of cytoplasm, ii) a secondary necrosis in volved the release of apoptotic bodies without cytoplasm or iii) cells showed a dual or bipolar structure, not previously described.