Figure 5.

The cytokine environment modulates naïve but not memory CD4⁺ T cell response to Fas ligation. (A) Differentiation cytokines IL-4 (Th2) and IL-12 (Th1) reverse the Fas responsiveness of naïve cells but do not affect the Fas responsiveness of memory cells. Naïve or memory CD4⁺ T cells were stimulated with 1 μg/ml of anti-CD3 alone (open bars) or 5 μg/ml of anti-Fas antibody (solid bars) in the presence of optimal concentrations of IL-4 or IL-12. Proliferation was assessed by [³H]thymidine incorporation after 48 hr in culture. (B) CD28-mediated costimulation, but not IL-2, reverses the Fas responsiveness of naïve cells. Cells were cultured as in A except that the growth factor IL-2 (10 ng/ml) or anti-CD28 antibody (5 μg/ml) was added instead of differentiation cytokines.