Dasatinib is a multitargeted drug that blocks several tyrosine kinases. Apart from its well-known antileukemic activity, the drug has attracted attention because of potential immunosuppressive and anti-inflammatory effects. We report that dasatinib at 1 microM completely blocks anti-IgE-induced histamine release in blood basophils in healthy donors, and allergen-induced release of histamine in sensitized individuals. In addition, dasatinib inhibited FcepsilonRI-mediated release of IL-4 and IgE-mediated up-regulation of CD13, CD63, CD164, and CD203c in basophils. The effects of dasatinib were dose-dependent (IC(50): 50-500 nM) and specific for FcepsilonRI activation in that the drug failed to inhibit C5a-induced or Ca-ionophore-induced histamine release. Interestingly, at lower concentrations, dasatinib even promoted FcepsilonRI-dependent histamine release in basophils in allergic subjects. In consecutive studies, dasatinib was found to interact with and block several FcepsilonRI downstream targets in basophils, including Btk. Correspondingly, FcepsilonRI-mediated histamine secretion in basophils was markedly reduced in Btk knockout mice and in a patient with Btk deficiency. However, the remaining "low-level" mediator secretion in Btk-deficient cells was fully blocked down again by 1 muM dasatinib. Together, these data suggest that dasatinib inhibits FcepsilonRI-mediated activation of basophils through multiple signaling molecules including Btk. Dasatinib may be an interesting agent for immunologic disorders involving Btk-dependent responses or/and FcepsilonRI activation of basophils.