Fig. 1

Cellular sources and cellular targets of IL-33. IL-33 is released from endothelial cells, epithelial cells and fibroblasts in response to tissue damage and/or mechanical stress (indicated as dotted arrow). After release, IL-33 functions as an alarmin and activates various types of cells (indicated as solid arrow), including Th2 cells, Tregs, basophils, mast cells, eosinophils, macrophages, dendritic cells, innate lymphoid cells (ILC2s), NK cells and NKT cells. These cells respond to IL-33/ST2 signaling by producing both pro-inflammatory and anti-inflammatory mediators depending on the immune context in different tissues and diseases