(A) Purified OT-I T cells were labeled with CFSE and infused into CD11c-DTR mice left untreated or treated i.p. with 4 ng/g body weight DT. The day after, mice were given i.v. with 10 × 10⁶ OVA-GMLs from β2m^–/– mice. Seventy-two hours later, spleen and LNs were harvested and analyzed for OT-I proliferation and for the percentage of CD11c⁺ DCs present in SLOs. Histograms (CFSE dilution on CD45.1-gated OT-I T cells) show sustained OT-I proliferation in untreated CD11c-DTR transgenic mice (48.1%; upper-right panel) compared with that observed in DC-depleted mice (23.9%; lower-right panel). The fraction of actively proliferating OT-I cells was remarkably different in the 2 groups of mice (38.1% vs. 8.2%). Accordingly, we found 2.07% CD11c⁺ DCs in untreated CD11c-DTR transgenic mice and only 0.7% in the DC-depleted mice (left panels). Data are representative of 2 experiments performed on splenocytes of 2 mice/group. (B) CD11c-purified DCs from mice treated with CFSE-labeled OVA β2m^–/– GMLs were analyzed by FACS for CFSE uptake and CD8α expression. Data are representative of 3 independent experiments. (C) Confocal microscopic analysis. CFSE-labeled GML are displayed as green staining. CD11c and CD8α molecules (DCs) are visualized with CD11c-PE and CD8α-Cy5 mAbs and displayed as red and blue staining, respectively. Arrowheads indicate CD11c⁺CD8α⁺ DCs engulfed by CFSE-labeled GMLs, shown at higher magnification in the inset. Original magnification, ×40. (D) TUNEL⁺CFSE⁺ apoptotic GMLs (red and green staining, respectively) were detected in SLOs of treated mice (left panels, white arrowheads) and displayed as yellow staining in the optically merged confocal image (original magnification, ×40). Right panels show apoptotic CFSE-labeled GMLs phagocytosed by SLO-resident CD11c⁺ DCs (blue staining). The white arrowhead indicates TUNEL⁺CFSE⁺ GML, whereas the yellow arrowhead shows a DC phagocytosing apoptotic bodies (triple staining; original magnification, ×63).