Interleukin 33 (IL-33), also known as NF-HEV and DVS27, is a member of the IL-1 family with a molecular weight of 30 kDa, and is secreted by a variety of cell types including fibroblasts, mast cells, dendritic cells, macrophages, osteoblasts, endothelial cells, and epithelial cells.IL-33 induces the secretion of type II cytokines by helper T cells, mast cells, eosinophils, and basophils. Type II cytokines are secreted by granulocytes.IL-33 mediates its biological functions by binding to the receptor ST2 and IL-1 receptor accessory protein (IL1RAP) and activating extracellular molecules in the NF-κB and MAP kinase signaling pathways that can induce the secretion of type II cytokines (e.g., IL-5 and IL-13) from polarized Th2 cells. After injection of IL-33, it induces type II cytokines in vivo, which is thought to induce severe pathological changes in mucosal organs.