Interleukin 4 (IL-4) is a type I cytokine produced by Th2 T cells, NK T cells, γ/δ T cells, eosinophils, mast cells, and activated basophils. IL-4 receptors are present on a number of cells, including hematopoietic, endothelial, epithelial, muscle, and brain tissues. IL-4 receptor engagement initiates signaling through the JAK/STAT pathway, and leads to the activation of PI3K and Ras/MAPK pathways (Nelms et al.). IL-4 plays a key role in immunoglobulin class switching in B cells and in regulating the differentiation of naïve T cells into T helper 2 (Th2) cells, while inhibiting Th1 differentiation. IL-4 acts together with tumor necrosis factor to stimulate expression of adhesion molecules on vascular endothelial cells and to downregulate expression of E-selectin, thus recruiting T cells and eosinophils to the site of inflammation (Nelms et al.).