Epitope mapping of aPS/PT antibodies from groups A and B. (A) Prothrombin fragments: GD-proT (residues 44-579); prethrombin-1, pre-1 (156-579); prethrombin-2, pre-2 (residues 285-579); fragment-1, F1 (residues 1-154); kringle-1, K1 (residues 44-155); and kringle-2, K2 (residues 156-271). Total IgG extracts from 7 patients from group A (B) (50 μL) (P4, P7, P9, P13, P14, P24, and P27) and 7 patients from group B (C) (50 μL) (P1, P3, P6, P17, P19, P21, and P25) were mixed with a solution (50 μl, 10 μM) of proTWT or specified fragment for 30 minutes at room temperature. Argatroban (Arg) was mixed with GD-proT at a concentration of 250 μM. The residual level of aPS/PT antibodies from group A (B) and group B (C) was quantified by using ELISA assays as described before. The effect of each competitor is reported as the percentage of inhibition relative to the effect of proTY93A (100%, dashed red line). (D) Visual abstract summarizing the main finding of the epitope mapping studies.