Hck deficiency results in reduced histamine release and cytokine production when mast cells are stimulated with high concentrations of antigen. IgE-sensitized WT and hck^−/− BMMCs were stimulated with the indicated concentrations of antigen for 45 minutes (A) or 20 hours (B). Histamine, tumor necrosis factor-α, and IL-6 secreted into culture media were measured. Representative results from 3 experiments are shown. Error bars represent SD.