Figure 3.

Fas and CD28 ligation have opposite effects on CD4⁺ naïve T cell proliferation (A and C) but identical costimulatory effects on CD4⁺ memory cells (B and D). Purified naïve (A and C) or memory (B and D) CD4⁺ T cells from B6 mice were cultured with 1 μg/ml of anti-CD3 antibody and indicated concentrations of anti-CD28 (thin line) or anti-Fas (thick line) antibody. Kinetics were determined by harvesting the cells after 48 hr (A and B) or 72 hr (C and D) of stimulation. Incorporation of [³H]thymidine was measured as an indicator of proliferation.