LERD inhibits the activity of Fyn, but not Lyn. RBL-2H3 cells (1 × 107 cells/dish) were incubated with 50 ng/ml IgE for overnight and then stimulated with 25 ng/ml antigen for 7 min after pre-incubating with or without LERD for 1 h. (A) Cell lysates were subjected to immunoblot analysis with specific antibodies to detect each FcεRI subunit. Representative immunoblotting images are shown from three independent experiments. (B) Fyn or Lyn was immunoprecipitated from the cell lysates and the immunoprecipitates were incubated in the kinase assay buffer at room temperature for 40 min and the activity was measured as described in the “Methods” section. The values are expressed as the mean ± SEM from three independent experiments. Asterisks indicate significant differences from the controls, *P < 0.05 and **P < 0.01. PP2 is a general Src family kinase inhibitor.