Expression of SLAM molecules on immature DCs inhibits IL-12 production upon CD40 stimulation. Immature (nonactivated), monocyte-derived DCs were transiently transfected with the human SLAM cDNAby electroporation (Nucleofection; AMAXA). SLAM expression was measured 5 hours following transfection by flow cytometry. A representative of 4 independent experiments is shown (A). The filled histogram shows SLAM expression on DCs following transfection; the dashed line represents staining with an isotype control antibody. SLAM-transfected SLAM⁺ and SLAM^– cells were separated 5 hours after transfection on a cell sorter. IL-12 (B) or IL-10 (C) present in the supernatants of CD40L-Lcell–activated, SLAM-sorted SLAM⁺ and SLAM^– populations or vector-transfected controls were measured at 24 hours by ELISA. Error bars represent the standard deviation of triplicate cultures.