Phosphorylation of Syk by HRF/TCTP and inhibition of HRF/TCTP and anti-IgE–induced histamine release by a Syk inhibitor. (Inset) A total of 2 million basophils per lane were stimulated with buffer (“C”) or 2.8 μM HRF/TCTP. Pelleted cells were lysed, and a Western blot was probed with anti-4G10 to detect phosphorylated Syk (p-Syk/anti-PY). The blot was reprobed with anti-Syk to determine total cellular levels of Syk (syk). The levels of Syk phosphorylation were normalized to the stimulation index (SI) of 1 for control and calculated to be 3.45 after HRF/TCTP stimulation. Data are representative of 2 separate experiments. The graph shows partially purified double percoll basophils from HRF/TCTP-R donors preincubated with NVP-QAB205, the Syk inhibitor (.03–3μM), for 10 minutes at 37°C, and then stimulated with suboptimal concentrations of HRF/TCTP (●) or anti-IgE (□) (n = 3). The standard error is represented by the error bars. Inhibition is illustrated as percentage of control, which is stimulus without inhibitor.