Platelets and PEVs load and process OVA onto MHC-I. (A-B) Thrombin (0.1 U/mL)–activated murine platelets and their PEVs express MHC-I (detected by hs-FCM; n = 19). Data are the mean ± standard error of the mean (SEM). ****P < .0001 (Mann-Whitney U test). Activated platelets and their PEVs loaded the SIINFEKL peptide (C-D) or processed and loaded OVA (C-E) onto MHC-I (n = 19). Data are the mean ± SEM. ****P < .0001, pulsed (+) vs unpulsed (−) (Kruskal-Wallis test).