Characterization of the regulatory B cells. 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 mature DCs. 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. Mature DCs were cultured for 48 hours alone (ratio 1:0) or in the presence of nonstimulated (NS) or stimulated (S) B cells in their supernatant at a ratio (1 DC/4 B cells). (A) MFI of HLA-DR (9 samples), and percentages of CD80^low, CD86^low, and IL-12^low DCs (11 samples) were evaluated by flow cytometry on CD19-negative cells. *P < .05; **P < .01; ***P < .001; ns, nonsignificant. (B) Expression of IgD/CD38, CD24/CD38, CD19/CD27, and CD19/CD5 was evaluated by flow cytometry on CD19-positive B cells before stimulation (NS), after stimulation (S) and after a 48-hour coculture period (cocultured). (C) Expression of CD19/CD40, CD19/CD80, CD19/CD86, CD19/CD54, CD18/CD11a, and CD19/CD62L was similarly analyzed. Representative results are shown of 3 experiments.