FIG. 3.

CD28 intracellular region is not required for enhancing Fas-mediated apoptosis. (A) Fas and CD28 expression were analyzed by flow cytometry analysis on the bulk populations of sorted CD28-negative Jurkat cells stably transfected with the CD28Δ construct (thick line) or the control empty vector (thin line). The dashed line is the negative IgG control MAb. (B) CD28Δ (filled bars) or control (open bars) Jurkat cells were incubated with beads coated with the anti-Fas (0.08 μg/ml) and the negative IgG control MAb (upper panel) or the anti-CD28 MAb (lower panel) at the indicated ratios. Cell death was measured using the ⁵¹Cr release assay. Results represent the means and errors of three independently repeated experiments.