In eosinophilic disorders such as asthma, there is increased eosinophilopoiesis and subsequent migration of eosinophils to the lung due to: (i) elevated levels of IL-3, IL-5, and GM-CSF to stimulate eosinophil development in bone marrow and survival in the blood and (ii) increased levels of type 2 cytokines (IL-4 and IL-13) to upregulate chemokine production, including CCL11 (eotaxin 1), CCL24 (eotaxin 2), CCL26 (eotaxin 3), CCL13 (MCP4), and CCL5 (RANTES), which enhance chemotaxis for eosinophil trafficking from the circulation to the airway (19). This evidence concerns the gene IL13 and asthma.