Effect of HIT patients on PF4 enhancement of aPC formation. aPC generation was performed as in Figure 1B, but in the absence or presence of a single concentration of PF4 (3.2μM) and 400 μg/mL of either control hIgG, HIT anti-PF4/heparin IgG antibodies from patients 1 to 4 or KKO. Experiments were done 3 times. Data are mean plus or minus SD. *P < .03 vs control hIgG.