MKs present OVA peptides in MHC class I (MHCI) molecules. After a 60-minute chase, DQ-OVA and anti–MHCI-OVA (binds to the OVA SIINFEKL antigen in the groove of MHC class I molecules) colocalization was tested at 37°C (A) and on ice (B). In the same conditions, DQ-OVA colocalization with the α-granule marker CD62P was measured by confocal microscopy (C-D). DQ-OVA fluorescence and consistently expressed MHCI-OVA level at plasma membrane upon a pulse of 24 hours was determined by flow cytometry (500 µg/mL) (E-F). Unpaired t test; n = 13; mean with SD; ****P < .0001; each n corresponds to an independent MK donor mouse. Original magnification ×63 for panels A-D. Scale bars represent 10 μm, except in ROI images scale bars represent 2 μm.