(A) CD4+CD25− T cells cultured with OVA323–339 peptide-pulsed B cells (Day 0, 7, 14) for 3 days and then cells rested in medium supplement with recombinant IL-2 (Day 3 and 10) for 4 days. Treg-of-B (ToB)-1, -2, and -3 cells were collected by depleting B cells. (B) The suppressive assay. Splenic CD4+CD25− (T) cells seeded as responder cells with suppressor cells, including Treg-of-B cells and splenic CD4+CD25+ (Treg) cells, at a ratio of 1:1. Data shown were the representative of 3 individual experiments. (C) Representative intracellular cytokine staining in splenic naïve CD4+CD25− (T) and Treg-of-B cells. (D) The cumulative data of frequency of IL-10-, IFN-γ- and IL-4-producing populations in reactivated Treg-of-B cells from 4–6 individual experiments.