Kinetics of plasma cell differentiation.

Resting memory cells were activated for 4 days with CD40L⁺fibroblasts in the presence of 50 U/mL IL-2 and 100 ng/mL IL-10 as described in “Materials and methods.” At the end of activation, cells were harvested and washed. Activated B cells (day 0) were then recultured for 7 days with IL-2 and IL-10 in the presence of anti-CD40L mAb. The cell phenotype was analyzed in double-staining with anti-CD38–PE mAb and anti-CD20–FITC mAb (A, B) or in triple-staining with anti-CD38–PE, anti-CD20–FITC, and anti-CD138–PECy5 mAbs (C-F). (A) Activated B cells CD20⁺CD38^±; (B) preplasmablasts CD20^±CD38⁺; (C, E) plasmablasts CD20⁻CD38⁺⁺CD138⁻; and (D, F) early plasma cells CD20⁻CD38⁺⁺⁺CD138⁺⁺. Results are representative of 1 out of more than 10 experiments. Insert: Changes in viable cell number during PC generation. Apoptotic cells were identified and counted by Apo2.7 staining. Results are given as the mean ± SD of 6 experiments.