COMPARISON OF DNA FRAGMENTATION AND COLOR THRESHOLDING FOR OBJECTIVE QUANTITATION OF APOPTOTIC CELLS

Apoptosis is a process of cell death characterized by distinctive morp hological changes and fragmentation of cellular DNA. Using video imagi ng and color thresholding techniques, we objectively quantitated the n umber of cultured CD4+ T-lymphoblastoid cells (HUT78 cells, RH9 subclo ne) displaying morphological signs of apoptosis before and after expos ure to gamma-irradiation. The numbers of apoptotic cells measured by o bjective video imaging techniques were compared to numbers of apoptoti c cells measured in the same samples by sensitive apoptotic assays tha t quantitate DNA fragmentation. DNA fragmentation assays gave consiste ntly higher values compared with the video imaging assays that measure d morphological changes associated with apoptosis. These results sugge st that substantial DNA fragmentation can precede or occur in the abse nce of the morphological changes which are associated with apoptosis i n gamma-irradiated RH9 cells.