Donor-derived MR-DCs are processed by recipient DCs in vivo. (A) Migration of intravenously injected BALB/c MR-DCs (CD45.2⁺) into B6 mouse (CD45.1⁺) spleen, analyzed by fluorescence microscopy on tissue sections, 24 hours after MR-DC injection. Arrow points to a BALB/c MR-DC homed in the T-cell area of a splenic follicle. Nuclei were stained blue with DAPI (original magnification × 200). (B) Detection by PCR of the BALB/c IgG2a^a allele after BALB/c MR-DC injection intravenously into B6 mice. (Top) Assay sensitivity. (Bottom) Detection by PCR of BALB/c MR-DCs mobilized to spleens of B6 mice 1, 6, or 24 hours after MR-DC injection. Host B6 mice were treated (+) or not (−) with the NK cell-depleting Ab NK1.1. The housekeeping gene S15 is shown to confirm equal DNA loading between samples. (C) Confocal image of a cytospin showing one recipient (eGFP⁺) splenic DC with fragments (in red) derived from PKH26-labeled BALB/c MR-DCs injected intravenously 12 hours earlier (original magnification × 400). Percentages of recipient splenic eGFP⁺ DCs with material acquired from PKH26-labeled BALB/c MR-DCs, assessed on cytospins by microscopy at different times after MR-DC injection. (D) Cytospin showing one recipient (B6) splenic DC (CD11c⁺, far red) containing phagocytosed apoptotic cell fragments (TUNEL⁺, green) derived from CD45.2⁺ (red) BALB/c MR-DCs injected intravenously. Nuclei were stained with DAPI. The area marked in the figure is shown in detail in the inset. Confocal, fluorescence microscopy (original magnification ×400).