Tumour necrosis factor alpha (TNF-alpha) is a cytokine that induces physiological
and pathophysiological effects in the immune system. In this study we analyzed
its action on a human lymphoma cell line (Daudi cells) after 1 h, 6 h and 24 h of
incubation. Using vital DNA stains, DNA gel electrophoresis, in situ nick
translation, transmission electron microscopy and flow cytometry we showed that
as early as after 6 h of treatment, target cells were able to undergo death by
apoptosis. This was associated with cell shrinkage, chromatin condensation,
apoptotic bodies in the cytoplasm without the typical DNA fragmentation into low
molecular weight nucleosomes. Of interest was the observation of a significant
number (60%) of cells positive to the nick translation in specimens treated for 6
h, decreasing to 40% in samples treated for 24 h, when most of the cells were in
late apoptosis. In addition, no subdiploid peak was evident in flow cytometry
regardless of the time of incubation with TNF. Our study on Daudi cells clearly
supports the existence of alternative forms of apoptosis in which DNA degradation
does not result only in oligonucleosomal fragmentation