MPs from GPA patients increase platelet reactivity to ADP. (A) Calcein-labeled platelets were exposed to GPA patient-derived MPs at an MP-to-platelet ratio of 10:1 and then treated with ADP (1uM) prior to assessment of activation by PAC-1 immunostaining. Mean fluorescence intensity is shown using 2 patient samples. (B) Flow cytometry scattergrams from the 2 patient sample studies showing PAC-1 fluorescence on X axis and calcein fluorescence on Y-axis. ADP, adenosine diphosphate; FL2-H, fluorescence label; GPA, granulomatosis with polyangiitis; IgM, immunoglobulin M; MP, microparticle; NT, non reated; PAC-1, platelet activation clone.