Figure 1.

Contact activation in vitro. (A) Filtration with Minisart filters does not cause significant contact activation: FXIIa generation was measured before (control) and after filtration of plasma with the filters used in our Blood paper,¹ and kaolin (100 μg/mL) was used as positive control (n = 4, ns, nonsignificant Student t test). (B) Amelung KC4 causes contact activation, leading to substantial thrombin generation: pooled citrated plasma samples with or without CTI corn trypsin inhibitor (CTI) were incubated for 20 minutes at 37°C in Amelung KC4, ReoRox4, or polypropylene (PP) tubes. FXIIa generation was measured as described previously¹ with the fluorescent substrate present during incubation in the instrument. Bars represent FXIIa substrate fluorescence as percentage of the PP tubes (n = 8, background fluorescence of inhibitor/vehicle additions were compensated). Aliquots from incubated plasma were used for subsequent real-time thrombin generation measurements in the presence of 10 μM phospholipids. Curves represent means of 4 independent experiments.