DHL4 B cells were preincubated with PRT318 at concentrations indicated for 1 hour before activation with 5 μg/mL anti-IgG for 30 minutes. Lysates underwent sodium dodecyl sulfate-polyacrylamide gel electrophoresis and were transferred to nitrocellulose membranes. Blots were probed with rabbit anti–phospho-SYK(Y352). The blot shown is representative of 2 independent experiments.