Hck deficiency results in reduced mast cell proliferation. (A) Flow cytometric analysis of FcϵRI and c-Kit expression on the surface of WT and hck^−/− BMMCs. (B) Growth curves of bone marrow cells cultured in IL-3–containing medium. (C) Proliferation of WT and hck^−/− BMMCs in response to the indicated concentrations of IL-3 or SCF were measured by thymidine uptake. Error bars represent standard deviation (SD) unless otherwise mentioned. (D) Growth factor-deprivation–induced apoptosis in WT and hck^−/− BMMCs. Percentages of annexin V⁻/7AAD⁻ live cells are plotted as a function of incubation time. Representative results from at least 3 independent experiments are shown.