Notch triggering by DL1, but not Jag1, blocks pDC development from thymic progenitor cells. (A) CD34⁺CD1a^- cells were cocultured with OP9-DL1, OP9-Jag1, or control cells in the presence or absence of 10 μM γ-secretase inhibitor DAPT. Cultures were analyzed for the presence of CD123^hiBDCA2⁺ pDCs after 1 week of culture. Experiment is representative of 3. (B) At day 5 after culture of CD34⁺CD1a^- cells on OP9 control cells, either CpG-ODN (2216) was added at different concentrations (10 or 50 μg/mL), or HSV-1 was added at 1 pfu/cell for 18 hours. Supernatants were analyzed in duplicate for the presence of IFN-α by ELISA. One representative experiment of 2 is shown.