Interleukin 3 (IL-3) is a species-specific pleiotropic cytokine that promotes the survival and proliferation of pluripotent hematopoietic stem cells and lineage-committed progenitor cells and their differentiation into mature cells of most lineages, including mast cells, basophils, neutrophils, eosinophils, macrophages, dendritic cells, erythrocytes, and megakaryocytes (Fung et al.; Metcalf et al.; Broughton et al.). IL-3 is produced by activated T cells, and has a physiological role in inflammation and allergies by promoting the secretion of inflammatory mediators such as histamine, IL-4, and IL-6 by mast cells, basophils and eosinophils. The mouse IL-3 receptor consists of a unique alpha-subunit (CD123) and two beta subunits, one specific for IL-3 (βIL-3), the other shared with the receptors for IL-5 and GM-CSF (beta common chain, βc or CD131). IL-3 binding to heterodimeric receptors containing the alpha subunit and one of either beta subunits activates JAK/STAT, MAPK, and PI3K signaling pathways (Scott and Begley).