Immunosuppressive cytokines of CD4⁺CD25^high T cells. CD4⁺CD25^high T cells produce immunosuppressive cytokines, but their mode of suppression is cytokine independent. (A) First, 5 × 10⁴ CD4⁺CD25^high T cells, freshly sorted or expanded either on CD32⁺ L cells or with anti-CD3/anti-CD28–coated beads (TCE) were stimulated (or restimulated) under the indicated culture conditions for 3 days. Supernatants were harvested and analyzed by ELISA (TGF-β) or with a CBA kit (all others). One of 2 independent experiments with cells from 2 different donors is shown. (B) CD4⁺ T_resp cells were stimulated with allogeneic PBMCs for 5 days in the absence or presence of bead-expanded (left) or L cell–expanded CD4⁺CD25^high T cells (right) at a 1:1 ratio and neutralizing antibodies, as indicated. P < .001 for all cocultures versus T_resp cells alone.