Activation of the FXIIa-driven contact system in AD patient plasma from group 2. (A) Western blot analysis of HK and transferrin loading control in plasma of 10 AD patients and 10 ND controls from group 2. (B) Intact HK levels normalized to transferrin were significantly lower in AD (P < 0.0001) compared with ND plasma. (C) Kallikrein-like activity was higher in AD plasma compared with ND (P = 0.03). (D) Levels of CSF Aβ42, which decrease with AD, were positively correlated with intact HK levels (r = 0.63; P = 0.003). (E) Levels of CSF tau, which increase with AD, were not correlated with intact HK levels (r = −0.11; P = 0.64). (F) Levels of CSF p-tau, which increase with AD, were not correlated with intact HK levels (r = −0.25; P = 0.28). Samples were analyzed three separate times with similar results. Results are presented as vertical scatter plots with medians, with statistical significance determined using the Mann–Whitney test.