CD28-dependent CD40L expression is mediated via IL-2R signaling. (A) CD28-costimulated PBMCs were cultured with anti-CD80/86 or anti-CD25 mAb. (B) TCR-stimulated PBMCs were cultured with anti-CD80/86 mAb ± rIL-2. rIL-2 was added at 24 hours. All control cultures were incubated with the appropriate isotype mAb. Gating was performed on CD4⁺ lymphocytes. The means ± SE of 4 donors are shown.