The pDCs fail to activate CD8⁺transgenic T-cell responses in vivo. Rag^–/–γc^–/– mice were injected intravenously with naive CFSE-labeled HY Tg T cells alone or with total DCs (totDCs), pDCs, or cDCs from male 129sv mice as indicated. One uninjected Rag^–/–γc^–/– mouse was used as a control (no HY). (A) Seven days later, spleen cells were harvested. CFSE profiles (top) and CD44 markers (bottom) on CD8⁺ Tg T cells were analyzed. Dot plots show representative results obtained in one of the mice tested in the experiment. (B) HY-specific IFN-γ production by CD8⁺ T cells from injected mice in culture supernatants of splenocytes. (C) Frequency of HY-specific IFN-γ–producing T cells in the spleens of injected mice was quantified by ELISPOT. (D) HY-specific T cells from injected mice were assessed for their ability to lyse peptide-coated EL-4 target cells ex vivo (left). Unspecific lysis of unloaded EL-4 cells is also shown (right). (B-D) Results are means ± SDs of 2 (HY, HY+ totDCs, and HY+ cDCs) or 3 mice (HY + pDCs) and are representative of 3 independent experiments. Error bars represent SDs. E/T indicates effector-to-target ratio.