Kinetics of IgG secretion, apoptosis, and IL6-R (CD126) expression. After thawing (RP5), CD20⁺cells were removed and the population was separated into CD138⁺ and CD138⁻ cells. (A) CD20⁻ CD138⁻ cells were cultured in RPMI 1640 10% FCS with 3 ng/mL IL-6 for 7 days. At days 0, 1, 2, and 7, supernatant was harvested and the amount of secreted Ig was determined by ELISA. The number of viable cells was determined by trypan-blue exclusion. (B and C) CD20⁻ CD138⁺cells (B) and CD20⁻ CD138⁻ (C) cells were cultured in RPMI 1640 10% FCS with 3 ng/mL IL-6. Apoptotic cells were determined by Apo2.7-PE staining. CD138-PECY5 and CD126-PE expression was determined in double staining in the viable cell population (R1 dot-plot FSC v SSC).