Figure 1.

The production and roles of IL-33 in immune responses. Under pathological conditions, full length IL-33 is released by endothelial cells, epithelial cells of barrier tissues such as lung, intestine, skin, and fibroblasts, and also glial cells and astrocytes, smooth muscle cells and platelets and several types of immune cells, including macrophages, dendritic cells (DCs), and mast cells. After cleavage by proteases, highly active IL-33, interacting with ST2, activates different immune cells to generate different cytokines or polarize into the corresponding phenotypes in different pathological conditions.