B cell subsets at iTTP presentation and ADAMTS13 relapse. Percentages of transitional cells (IgD⁺CD38⁺⁺) (A), naïve cells (IgD⁺CD38⁺) (B), IgD⁺ memory B cells (IgD⁺CD38^–) (C), postgerminal center memory B cells (IgD^–CD38⁺) (D), double–negative memory B cells (IgD^–CD38^–) (E), and plasmablasts (IgD^–CD38⁺⁺) (F) in patients with acute iTTP episodes (n = 22), ADAMTS13 relapse (n = 24), and HC (n = 27). A13 relapse, ADAMTS13 relapse; double-negative memory cells, double-negative memory cells; Post GC memory, postgerminal center memory cells.