CD63 and neoplasm: IL-33 is known to lead to activation of eosinophils52,53 which is accompanied by upregulation of molecules important for eosinophil transmigration (CD11b) and degranulation (CD63).13,25,39,54 We could confirm these observations in our experiments for in vitro-activated eosinophils as well as for tumor-infiltrated eosinophils in vivo.