Schematic representation of eosinophil maturation and trafficking. Eosinophils differentiate from hematopoietic progenitor cells into mature eosinophils in the bone marrow under the control of critical transcription factors, especially GATA-1. The eosinophil-promoting cytokines, IL-3, GM-CSF, and IL-5, regulate eosinophil expansion. Eosinophil migration from the bone marrow into the peripheral circulation is primarily regulated by IL-5. Circulating eosinophils interact with the endothelium in the gastrointestinal tract by a regulated process involving the coordinated interaction between adhesion molecules, chemokines and their receptors.