Fig. 2. T. gondii downregulates activation of caspases 3 and 9 after induction of apoptosis in human-derived cell lines. HL-60 and U937 cells were infected at a parasite to host ratio of 30:1 and were 30 minutes later treated with actinomycin D or TNF-
in combination with cycloheximide as indicated. Eight hours after infection, antigenic extracts were prepared from equal numbers of cells and were separated by standard SDS-PAGE. After transfer to nitrocellulose membranes, caspase 3 (A), caspase 9 (B) and caspase 8 (C) were visualized by immunostaining using enhanced chemiluminescence detection. T. gondii-induced alterations of caspase activation were quantified densitometrically by determining the levels of the active subunits (caspase 3) or the levels of the inactive proforms (caspases 8 and 9) (D). Bars represent the relative changes in caspase levels after parasitic infection of untreated cells (open bars) or those treated with pro-apoptotic stimuli (closed bars) compared with levels in uninfected cells. Horizontal dashed lines indicate an unchanged protein level after parasitic infection compared with levels in uninfected controls.
