IL-10/TGF-β–tolerized CD4⁺ T cells modestly down-regulate nonspecific responses. Tolerized cells exert a modest down-regulatory effect on naive OT-II responders. 10⁴ OT-II CD4⁺ T cells were cultured with or without 10⁴ tolerized B6 CD4⁺ T cells in the presence of B6 antigen-presenting cells. 0.5 μg/mL or 5 μg/mL OVAp was added to some wells as indicated. Tolerized B6 CD4⁺ T cells suppressed naive alloresponses by more than 90%. Shown is 1 of 2 replicate experiments with similar results.