Efficiency of B-cell polyclonal activation. CD19⁺ CD27⁺ B cells from 1 representative healthy control (no. 7) were analyzed by flow cytometry for size features and the expression of CD20, CD38, and CD138 over the culture period. Cells were gated on CD19 and CD27 membrane expression. (A) The phenotype of stimulated cells was shown at day 0, day 3, and day 6, which included the cell incubation of the ELISpot assay. (B) Histogram dot plots of unstimulated cells represented the level of spontaneous differentiation at day 6.