Cultured CD4⁺CD25⁺ cells markedly suppress cytokine accumulation in MLRs. Analysis of suppressor cell function in MLR assays by assessment of cytokine levels. (A) Assessment of cytokines produced by activated T cells reveals marked impairment of accumulation. Inhibition of IL-2, IFN-γ, GM-CSF, TNF-α, IL-5, and IL-10 is observed. No alteration in TGF-β1 accumulation is noted. Shown are IL-2 levels on day 2 and other cytokines on day 6, respective times of peak of accumulation in control MLR cultures. (B) Assessment of chemokine levels reveals minimal alterations at early time points (day 2) and modest decrements in levels at late time points (day 7) for RANTES, IL-8, and MIP-1α. Representative of 4 MLR experiments.