This study demonstrates that Mks can endocytose ovalbumin and proteolytically generate its immunogenic peptide ligand, which is cross-presented on their surface in association with MHC class I. The authors also found that MKs can present Mk-associated (CD61) peptides to activate CD61-specific CD8+ T cells and mediate immune thrombocytopenia in vivo. This evidence concerns the gene ITGB3 and autoimmune thrombocytopenic purpura.