Optimal cross-presentation requires CD40L and type I IFN stimulation of conventional DCs. BALB/c or BALB/c-OVA mice were irradiated and reconstituted with B6 (CD45.2) BM, 10⁶ CD8, and 10⁵ CD4 cells from B6 CD45.1 mice. (A) Representative flow cytometry of spleen, LN, and blood on day 14 (gated on CD8⁺CD45.1⁺ cells). (B) Time course (at least 3 mice/group at each time). At day 14 after transplantation, unpulsed (cyan) or SIINFEKL-pulsed (CFSE) B6 splenocytes were infused and spleens were harvested 18 hours later. Note the selective killing of SIINFEKL-pulsed cells (C). Mice were transplanted as in panel A, except that they received donor B6 BM from WT, MHC class II⁻, CD11c-cre x ROSA26-flox-stop-DTA, CD40^−/−, or IFNAR1^−/− mice. Recipients were killed on day 14. Shown is representative Tet^SIINFEKL staining (D; gated on CD8⁺CD45.1⁺ cells). Percentages of CD8 cells that were Tet^SIINFEKL+ are shown in panel E. Data from 3 experiments combined. P = .02, comparing recipients of WT BM compared with recipients of IFNAR1^−/− or CD40^−/− BM.