FIGURE 5.

Effects of apoptotic targets on BU.MPT responder cell viability are dependent on cell-cell interaction. Serum-starved BU.MPT responder cells were exposed to apoptotic (Apo) targets at a target/responder cell ratio of 10:1 continuously for 24 h, as depicted in the inset, either unimpeded, enabling direct target-responder physical interaction (Control), or with separation of targets and responders by a 0.4-μm polycarbonate membrane in a Transwell support system (Transwell). The source of apoptotic targets was DO11.10 cells treated with actinomycin D (Act D), staurosporine (Stauro), or dexamethasone (Dex). After 24 h, relative cell number by MTT assay (A) or [³H]thymidine incorporation (B) was determined. All values were normalized against those for BU.MPT responder cells not exposed to targets. Each data point in the graphs represents the mean and S.E. from a minimum of three separate experiments. Absolute A_570/650 values (A) for responders unexposed to targets in the absence and presence of a Transwell support system were 0.915 ± 0.023 and 0.450 ± 0.02, respectively. Absolute cpm (B) for responders unexposed to targets in the absence and presence of a Transwell support system were 2571 ± 185 and 2805 ± 47, respectively. All experimental A_570/650 values (A) and cpm (B) were normalized to these values as represented by the dotted lines at relative cell number (A) and relative thymidine incorporation (B) equal to 1.0. A, p < 0.0001, apoptotic targets (actinomycin D) and apoptotic targets (staurosporine) versus no targets in the absence of Transwell; p = not significant, apoptotic targets versus no targets in the presence of Transwell. B, p < 0.05, apoptotic targets (actinomycin D), apoptotic targets (staurosporine), and apoptotic targets (dexamethasone) versus no targets in the absence of Transwell; p = not significant, apoptotic targets versus no targets in the presence of Transwell. Error bars (A and B) denote S.E.