Interleukin 33 (IL-33), also known as DVS27 or NF-HEV (Nuclear Factor from High Endothelial enules), is a proinflammatory protein and a chromatin-associated cytokine of the IL-1 family with high sequence and structural similarity to IL-1 and IL-18. IL-33 protein is expressed highly and rather selectively by high endothelial venule endothelial cells (HEVECs) in human tonsils, Peyers's patches, and lymph nodes. IL-33 protein has transcriptional regulatory properties, and the researches suggested that IL-33 is a dual-function protein that might act both as a cytokine and as an intracellular nuclear factor. As a type 2 cytokines, IL-33 protein also play a pivotal role in helminthic infection and allergic disorders.