IDO-competent DCs stimulate T-cell regulatory activity on allogeneic rather than autologous stimulation. DCs were activated with LPS/IFN-γ for 48 hours and used to stimulate an allogeneic or an autologous, TT triggered, response (see “T-cell stimulation and mixed lymphocyte reaction”). CD4⁺ T cells were recovered from the DC/T-cell cocultures, sorted, and subjected to subsequent suppressor assays as in Figure 4. (Left) The CD4⁺ T cells were retrieved from DC/T-cell cocultures stimulated by allogeneic DCs. (Right) The CD4⁺ T cells were retrieved from DC/T-cell cocultures stimulated by autologous, TT pulsed, DCs. Proliferative responses of fresh CFSE-stained and anti-CD3–stimulated T cells are shown by CFSE dilution (open histograms with thick black line) on coculture with the sorted CD4⁺CD25⁻ (top) and CD4⁺CD25⁺ T cells (bottom). Filled gray histograms indicate CFSE dilution of anti-CD3–stimulated fresh T cells only; open histograms with thin line, CFSE dilution of unstimulated fresh T cells only. The numbers indicate the percentage of CFSE-negative cells in suppressor assays. Results of 1 experiment, representative of 3 experiments, are shown.