ADAMTS13 conformation index and activity and anti-ADAMTS13 antibody titer before and after preemptive rituximab administration in patients with iTTP in clinical remission. ADAMTS13 conformation index (A) and activity (%) (B) and anti-ADAMTS13 antibody titers (C) before and after preemptive rituximab treatment. Closed ADAMTS13 (conformation index <0.5) is represented as filled circles, and open ADAMTS13 (conformation index >0.5) is represented as open circles. Patient samples with open ADAMTS13 conformation during remission are indicated in color. Horizontal dashed lines indicate ADAMTS13 conformation index of 0.5 with conformation index <0.5 representing closed ADAMTS13 (A), ADAMTS13 activity <10% (B), and anti-ADAMTS13 antibody titers of 12 IU/mL, with detectable anti-ADAMTS13 antibody titers when >12 IU/mL (C). (D) ADAMTS13 activity and conformation during follow-up in 1 patient treated preemptively with rituximab (red arrows). Conformation index <0.5 represents closed ADAMTS13.