Three-step in vitro model of PC generation. Peripheral blood human MBCs were purified and cultured with sCD40L, ODN, and IL-2 + IL-10 + IL-15, then with IL-2 + IL-6 + IL-10 + IL-15 for 3 days, and then with IFN-α + IL-6 + IL-15 for 3 days. Cells were labeled with anti-CD20, CD38, and anti-CD138 mAbs, CD20⁺CD38⁻ D4 actBCs, CD20⁻CD38⁺⁺ D4 or D7 PBs, and CD20⁻CD38⁺⁺CD138⁺ D10 PCs were FACS sorted and stained with May-Grünwald-Giemsa (original magnification, ×1000). The percentage of cells in the S hase of the cell cycle was determined using propidium iodide, and data were analyzed with the ModFit LT software. Histograms are those of 1 experiment representative of 3.