IFN-α promotes the generation of DCs with a highly differentiated/activated phenotype. Monocyte-derived DCs were generated after 3 days of treatment with either IFN-α/GM-CSF or IL-4/GM-CSF as described in “Materials and methods.” Cells were then further treated with LPS for 20 hours (A) or left untreated (B). Flow cytometric analysis was performed on day 4. Top panels show the morphologic parameters (side versus forward scatter) of cells generated in the presence of the different cytokine combinations containing either IFN-α or IL-4 and subsequently exposed to LPS or left untreated. Staining with antibodies to the differentiation markers CD83 and CD14 or to the activation molecule CD80 is shown for the R1-gated cell cultures (bottom panels). Similar results were obtained using monocyte-derived DCs from 3 other patients.