Interleukin 33 (IL-33) is a pro-inflammatory cytokine from the IL-1 family. It binds to the ST2 receptor and activates NF-kB and MAPK pathways. IL-33 is expressed by epithelial cells, smooth muscle cells, and fibroblasts in various tissues and organs, as well as resting basophils, mast cells, eosinophils, natural helper cells, group 2 innate lymphoid cells, dendritic cells, and activated macrophages (Schmitz et al.; Yasuda et al.). It contributes to allergic inflammation by stimulating production of the cytokines IL-4, IL-5, and IL-13 in Th2 cells, and stimulates host defense against microbial and viral infections (Liew; Yasuda et al.). In the central nervous system, IL-33 is produced by endothelial cells and astrocytes. It induces proliferation of microglia and mediates production of pro-inflammatory cytokines (Yasuoka et al.).