Soluble CD40L mediates the DC activation in supernatants derived from CD46-induced Tr1-like cells. (A-D) iDCs were incubated with control media containing GM-CSF/IL-4 (A) or supernatants derived from T cells activated with CD3 (B), CD3/CD28 (C), or CD3/CD46 (D). Each condition was performed with or without the addition of the indicated function neutralizing mAbs. A nonspecific isotype mAb was used as a control. This mAb had no effect on any of the tested activation conditions (data not shown). DC maturation was induced with LPS and the capacity of the DCs to induce allogeneic T-cell activation was analyzed in an MLR. Shown is 1 representative of 5 independently performed experiments (with each activation condition in triplicate). (E) Summary and statistical evaluation of all proliferation data obtained in this set of experiments, displayed as described in Figure 1E. F statistics and P values are shown for the comparison between untreated (gray bars) and anti-CD40L ligand mAb–treated conditions (black bars). 10, 40L, and G indicate the addition of function-neutralizing mAbs to IL-10, CD40L, and GM-CSF, respectively.