Cell death induced in L-cells by treatment with thymidine: staging of the process and relationship to apoptosis.

The purpose of this study was to characterize the stages in the development of thymidine-induced cell death. L-cells were characterized by both morphologic and quantitative techniques and evaluated at 24, 48, and 72 h of treatment. Cells first enlarged (stage I); about 50% of these enlarged cells then decreased in size with blebbing and compacting (stage II). This residual cell body transformed into a smooth eosinophilic hyaline body (stage III) by 72 h, many of which could be identified within the vacuolar system of viable cells. These changes were reflected in morphologic counts and Coulter sizing. Cell death (loss of labeled DNA) began in stage II and was most prominent in stage III. No cleavage of DNA into oligonucleosomal fragments was detected by agarose gel electrophoresis at any stage. The similarity of these changes to the complete spectrum of apoptosis in vivo is discussed.