Platelets and PEVs loaded with OVA peptide express activation and costimulatory molecules. (A-B) Activated platelets and (C-D) PEVs loaded with OVA peptide (25D1.16⁺) express higher levels of proteasome (LWA300), activation (annexin V, P-selectin), and costimulatory molecules (CD40, CD40L, and OX40L). (A,C) Mean fluorescence intensity (MFI) of the different markers assessed by hs-FCM (n = 7). Data are mean ± standard error of the mean (SEM). *P < .05 (Student t test). NS nonsignificant. (B,D) Representative MFI histograms of the 25D1.16⁻ and 25D1.16⁺ populations for each marker shown on CD41⁺proteasome+ events.