Interference of SLAM homoassociation–induced signaling with CD40L-induced IL-12 production of DCs. (A) DCs were activated in the presence of CD40L-L cells or with various SLAM-expressing CD40L-L cells, including polyclonal SLAM-transfected CD40L-L cells (which contained SLAM^– cells as well) and 2 independent SLAM/CD40L-L clones (F8 and G4). IL-12 concentrations were measured by ELISA at 24 hours. (B) Relative expression levels of IL-12p40 mRNA in DCs activated with CD40L-L or SLAM/CD40L-L cells determined by quantitative RT-PCR. (C) IL-12p70 production of DCs in the presence of Jurkat T cells, or a Jurkat cell line expressing SLAM in the presence or absence of anti-CD3 mAbs. Error bars represent the standard deviation of triplicate cultures.