Migration and maturation of pDCs transferred into the host spleen. CD11c⁺ spleen cells purified from untreated (B,E,H), CpG-injected (C,F,I), or heat-inactivated (HI) influenza virus-injected (D,G,J) Ly5.2⁺ 129sv mice were intravenously transferred into Ly5.1⁺ C57BL/6 recipient mice. Fifteen hours later, mice were killed and total DCs were isolated from spleens and labeled with either CD11c, B220, CD45.1, and CD45.2 mAbs or CD11c, B220, CD45.1, and CD40 mAbs and analyzed. (A) Control Ly5.1 mouse that did not receive Ly5.2⁺ DCs. (B-D) Ly5.2⁺ cells (labeled with CD45.2 mAbs) were found in the spleens of Ly5.1 recipient mice. (E-G) Analysis of CD11c and B220 expression by recovered Ly5.2⁺ cells. (H-J) Analysis of CD40 expression by Ly5.1^–CD11c⁺B220⁺ cells. For all analyses, we checked that the Ly5.1^– population corresponded to the injected Ly5.2⁺ DCs. Gray histograms represent CD40 expression by unstimulated endogenous Ly5.1⁺ pDCs. Open histograms represent CD40 expression by transferred Ly5.2⁺ pDCs. Percentages indicate the proportion of transferred pDCs that strongly up-regulated the expression of CD40 at their surface. The mean intensity of the fluorescence signal of the main peak of transferred DCs is indicated in the top left corners of histograms. Results are representative of 2 independent experiments. FITC indicates fluorescein isothiocyanate.