Effect of anti-FXII IgG 15H8 on protease activity and HK cleavage. (A) Effect of IgG 15H8 on activity of FXII-WT and FXII-T. PK (50 nM) was incubated in standard buffer at 37°C with 200 μM S-2302 and 50 nM FXII-WT (left) or FXII-T (right) in the absence () or presence () of 15H8 IgG (50 nM). For FXII-WT, a control reaction without FXII was run (). Continuous cleavage of S-2302 at 405 nM was followed. Data are means of 3 runs. (B) Western blot showing the effect of 15H8 antibody infusion on HK in WT mice supplemented with FXII-WT. The blot was processed as in Figure 5. Arrows on the right indicate the positions of cleaved HK (HKa), and positions of molecular mass standards in kilodaltons are shown to the left of the image. (C-E) Effect of IgG 15H8 on FXIIa generation. Plasma FXII (200 nM) was incubated in standard buffer at 37°C with vehicle (control) (C), 20 nM kallikrein (D), or 20 nM plasmin (E) in the absence () or presence () of 15H8 (400 nM). At various time points, aliquots were mixed with stop solution (containing HO3 for kallikrein, aprotinin for plasmin) and FXIIa concentration was determined by chromogenic assay. Data show means ± 1 SD.