VITT Abs induce procoagulant PLTs and increased TG via SYK-dependent signaling pathways. (A-B) PLTs were incubated with isolated IgG (A) or (B) serum from patients with VITT or HCs in the presence of exogenous PF4 (10 μg/mL) and tested for changes in the expression levels of P-selectin (CD62p) and PS with FC. As indicated, PLTs were preincubated with SYK inhibitors R406 (5 μM), PRT-060318 (1 μM), entospletinib (5 μM), and lanraplenib (5 μM), respectively. The number of patients tested is reported in each graph. Unpaired or paired t test is shown. (C) Representative TG curve induced on PLTs after incubation with IgGs from 1 patient with VITT in the presence of vehicle (red line), R406 (5 μM, blue solid line) or lanraplenib (5 μM, dashed blue line). Each curve represents the amounts of generated thrombin over time. (D) Data were quantified as peak thrombin generated (nM) using Thrombinoscope software and GraphPad Prism, version 10.1.0. Violin plots showing the distribution of the values were generated using GraphPad Prism, version 10.1.0. Paired t test is shown. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001. N, number of patients tested; ns, nonsignificant; PS, phosphatidylserine.