Splenic B-cell subset phenotype and quantification. (A) B-cell subsets (naïve, memory, GC, pregerminal center [preGC], and PCs) were determined among CD19⁺ splenocytes by the expression of CD38 and IgD. Representative quantile contour plot of 1 ITP patient. (B) B-cell subset percentages were compared between 6 controls (open circles) and 11 ITP patients (black squares). Results are summarized in dot plots. The horizontal bar represents the median with interquartile range. P value derived by Mann-Whitney test. (C) The expression of IL-21R was assessed on B-cell subsets. IL-21R MFI measured in 6 controls and 11 ITP patients is depicted in dot plots. The horizontal bar represents the median with interquartile range. P value derived by Mann-Whitney test. *P < .05; ***P < .001. (D) TFH percentages correlate with the percentages of GC B cells, preGC B cells, and PCs. The graphs represent the results obtained in 6 controls (open circles) and 11 ITP patients (black squares). Spearman’s rank correlation coefficient (R) and P value are depicted. Line represents linear regression.