Expression of mitochondrial Apo2.7 molecules and caspase-3 activation in human lymphocytes treated with the ribosome-inhibiting mistletoe lectins andthe cell membrane permeabilizing viscotoxins

Background: It is unclear whether expression of newly described mitochondri al Apo2.7 molecules (7A6 antigen) is specific for apoptosis or may also occ ur in necrosis. Methods: We incubated human lymphocytes with the apoptosis-inducing mistlet oe lectin (ML) I and the cell membrane-permeabilizing viscotoxins (VT), and measured cell death-associated changes by flow cytometry. Results: In ML I-treated lymphocytes, Apo2.7 expression and caspase-3 activ ation was recognized within 24 h. In VT-treated cells, we observed an Apo2. 7 expression with low fluorescence level, while active caspase-3 and DNA fr agments (TUNEL) were not detected within 24 h. In these cells, caspase-3 ac tivation was recognized 48 h later. As a major subset of ML-treated cells e xpressing Apo2.7 molecules did not activated caspase-3, while all caspase-3 (+) cells did express Apo2.7, one may suggest that the caspase pathway is a ctivated secondarily to mitochondrial events. Conclusions: Expression of Apo2.7 is sensitive marker of cell death but may not be specific for apoptosis alone as it can be detected also in cells tr eated with cell membrane-permeabilizing toxins. On the other hand, this exp ression may be the consequence of an induction of distinct "death signals" resulting in apoptosis later on. Cytometry 37: 133-139, 1999. (C) 1999 Wile y-Liss, Inc.