Effect of cytokines and chemoattractants on the phosphorylation of ERK2 in human eosinophils. After stimulation, the eosinophils (2 × 10⁶) were immediately lysed in Laemmli buffer. Phosphorylation of ERK2 (ppERK2) was detected as described in Materials and Methods. (A) Time-course of IL-5 (5 × 10⁻¹⁰ mol/L) induced ERK2 phosphorylation. (B) Time course of phosphorylation of ERK2 by PAF (10⁻⁶ mol/L). (C) IL-5 (5 × 10⁻¹⁰ mol/L, 5 minutes), but not IL-4 (10⁻⁸ mol/L, 5 minutes) induced ERK2 phosphorylation. (D) Time course of ERK2 activation by IL-5 (10⁻¹⁰ mol/L) and PAF (10⁻⁶ mol/L) as measured by MBP phosphorylation. Kinase assays with 7.5 × 10⁶ eosinophils were performed as described in Materials and Methods.