Comparison of the activation of ERK1 and ERK2 in human eosinophils and neutrophils. (A) ERK1 is constitutively phosphorylated in human eosinophils. Cells (2 × 106) were treated with either IL-5 (10−10 mol/L), PAF (10−6 mol/L) or IL-4 (10−8 mol/L) for the times indicated before lysis and SDS-PAGE analysis. (B) ERK1 is constitutively active, while ERK2 is inducible in human eosinophils. Cells (7.5 × 106) were stimulated with either IL-5 (10−10mol/L), PAF (10−6 mol/L), or IL-4 (10−8mol/L) for the times indicated. Samples were lysed and immunoprecipitated with either ERK1 or ERK2 specific antibodies. Kinase activity was analyzed as described in Materials and Methods. (C) ERK1 and ERK2 activity can both be induced in human neutrophils. Cells (107) were stimulated with either GM-CSF (10−10 mol/L), PAF (10−6 mol/L), or fMLP (10−6 mol/L) for the times indicated. Kinase activity was analyzed as described above.
