Effects of anti-fXII antibodies on fXII and PK. fXII activation: conversion of fXII to fXIIa in the presence of (A) a silica-based aPTT reagent or (B) polyphosphate (2 μM) and vehicle (○), 9A2 (●), 15H8 (△), or the combination of 9A2 and 15H8 (▼). Results are means of 3 separate runs ± 1 standard deviation (SD). Prekallikrein activation: (C) PK (50 nM) was incubated in reaction buffer containing 250 μM CS-3102 at RT, in the absence (●) or presence (○) of fXIIa (1 nM). Cleavage of CS-3102 was monitoring by following changes in OD 405 nm. fXIIa at the concentration used does not cleave CS-3102 at an appreciable rate in the absence of PK (not shown). Addition of HK (□, 70 nM) or aPTT reagent (■, 5% v/v) to the reaction with PK and fXIIa had modest effects on the rate of activation, while addition of both aPTT reagent and HK (▲) had a greater effect. (D) The effects of vehicle (▲) 100 nM 9A2 (△) and 15H8 (♢) on activation of PK by fXIIa in the presence of aPTT reagent (5% v/v) and HK (70 nM).