The regulation of DC functions is independent of IL-10 but requires cell-to-cell contact. Monocytes were purified from the peripheral blood of healthy donors and stimulated with GM-CSF (1000 U/mL) and IL-4 (500 U/mL) for 6 days. The differentiated immature DCs were stimulated with LPS (100 ng/mL) and IFN-γ (1000 U/mL) for 24 hours to generate mDCs. Tonsillar B cells were purified and stimulated for 5 days on CD40L-transfected NIH3T3 murine fibroblasts in the presence of 0.25μM CpG-ODN 2006. mDCs were cultured for 48 hours with or without anti–IL-10–blocking Abs (α-IL-10), at 1 or 4 μg/mL final concentration (A) in the supernatant of activated B cells (1:0), or (B) with activated B cells in their supernatant (ratio 1 DC/4 B cells). (C) Experiments were repeated in Transwells with mDCs in the lower chamber and B cells with their supernatant in the upper chamber. Cocultures without Transwells were used as controls. MFI of HLA-DR and percentages of CD80^low, CD86^low, and IL-12^low mDCs were evaluated by flow cytometry on CD19-negative cells. (D) mDCs were cocultured with or without 10 μg/mL of anti–TGF-β–blocking Ab (α-TGF-β) in the supernatant of activated B cells (1:0) or in the presence of activated B cells with their supernatant (ratio 1 DC/4 B cells). The percentage of IL-12^lowmDCs was evaluated by flow cytometry. *P < .05; **P < .01; ns, nonsignificant.