Cell-permeable inhibitor of Lyn-dependent effects of the IL-5 receptor. Blocks binding of Lyn tyrosine kinase to βc subunit of IL-3/GM-CSF/IL-5 receptors, blocking Lyn activation. Inhibits IL-5 receptor-mediated eosinophil differentiation and survival in vitro. Inhibits airway eosinophilic inflammation in mouse model of asthma.