Role of IL-21 and CD40 ligation in splenic B-cell differentiation and total IgG production. Sorted splenic CD19⁺ B cells were stimulated with a combination of anti-IgM antibody (αIgM), anti-CD40 agonist antibody (αCD40), and IL-21. At day 6, cells were stained for the determination of B-cell subsets using CD38 and IgD expression. (A) Quantile contour plots of 1 representative ITP patient are depicted with the percentages of PCs and GC, preGC, memory (mem.), and naive B cells. (B) The effect of each stimulation alone or in combination on B-cell subsets is summarized in dot plots. Results obtained from 3 controls (open circles) and 5 ITP patients (black squares). P value derived by Wilcoxon matched-pairs test. The horizontal bar represents the median with interquartile range. P value derived by Wilcoxon matched-pairs test. NS, nonsignificant; *P < .05; **P < .01.