Tα1-induced IDO⁺ DCs activate Treg cells in vitro. (A) Frequency of IFN-γ–/IL-10–producing splenic CD4⁺ T cells activated by Aspergillus-pulsed Tα1-treated GM-DCs or FL-DCs. The 1-MT was present in selected cultures. Plates were read with the AID-EliSpot Reader System (Amplimedical). Values are means ± SE per 10⁶ cells of samples from 3 to 5 experiments, calculated using replicates of serial 2-fold dilutions of cells. *P < .05, conidia-exposed versus unexposed cells; **P < .05, thymosin-exposed versus unexposed cells. (B) Phenotypic analysis of CD4⁺ cells cultured alone (–) or as in panel A. Numbers represent the percentage of double-positive cells.