HIT IgG stimulates ROS production in neutrophils. Luminescence accumulation by neutrophils isolated from (A-C) 3 healthy donors incubated with PMA (25 nM, 50 nM, and 100 nM), or heparin (Hep) and purified PF4 and normal IgG (mouse isotype control [mIgG] or normal human IgG [nIgG]) or HIT IgG (KKO, or IgG from 3 HIT patients, HIT1 to HIT3). (D) Quantification of peak luminescence induced by neutrophils stimulated by PMA, normal IgG, or HIT IgG. Data expressed as mean plus or minus the standard error of the mean (SEM) (n = 3). *P < .05, **P < .01, ***P < .001, and ****P < .0001 by Student t test for comparisons between KKO and mIgG; 1-way ANOVA with Bonferroni correction was used for multiple comparisons (HIT1-3 and nIgG).