Effect of plasma on human platelet aggregation test. The plasma from patients with confirmed αIIbβ3 integrin autoantibodies was used with matched blood group, healthy donor platelets labeled with either CFSE or PKH26 and mixed in 1:1 ratio before stimulation. Ristocetin stimulation (left) was used as a control of the plasma quality because GPIb-induced platelet aggregation is independent of αIIbβ3 integrin function. PMA stimulation (right) was used to test the potential inhibitory effects of patient autoantibodies on αIIbβ3 integrin function. Aggregation percentages were normalized to those obtained with the same platelets incubated with healthy EDTA pool plasma (set to 100%) and either agonist. Average and standard deviation are depicted for the group of control plasmas on each condition, n = 4. Some of the patient plasmas were tested in 2 independent experiments.