TFH quantification and mRNA expression. (A) The percentage of CXCR5⁺ among CD3⁺CD4⁺, of ICOS⁺PD-1^hi within CD3⁺CD4⁺CXCR5⁺ T cells and the percentage of TFHs defined as CD3⁺CD4⁺CXCR5⁺ICOS⁺PD-1^hi were determined in 6 controls (open circles) and 13 ITP (black squares). Data are summarized in dot plots. (B) CXCR5, CXCL13, BCL6, and IL-21 mRNA expression was quantified by RT-qPCR in total splenic CD4⁺ T cells of controls (n = 7, open circles) and ITP (n = 12, black squares). Results are expressed as fold change (FC) after normalization on GAPDH expression. Data 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 CXCL13 and IL-21 was correlated with TFH percentage measured by FCM. Spearman’s rank correlation coefficient (R) and P value are depicted. Line represents linear regression. (D) Circulating TFH frequency in 5 controls (open circles) and 10 ITP patients (black squares) is summarized in dot plots. The horizontal bar represents the median with interquartile range. P value derived by Mann-Whitney test.