Unlike IL‐25, the complicating factor in the study of IL‐33 sources is the breadth of its expression: a study characterising IL‐33 reporter mice showed expression in epithelial cells from the lung, skin, stomach, and vagina; retinal glial cells; vasculature endothelial cells of the colon during DSS‐induced colitis; and fibroblastic reticular cells in various lymphoid tissues [47]. This evidence concerns the gene IL33 and colitis.