IL-33 is expressed in the mouse mesentery. (A) Representative immunohistochemistry image depicting double-layer mesentery exhibiting strong IL-33 expression (red) in a majority of the cells, (green CD31, blue DAPI nuclear stain). (B) No endothelial cells (green, IB4) expressing IL-33 (red) were found in small or (C) medium-size blood vessels, (blue DAPI nuclear stain). (C) Numerous IL-33–positive cells (red) with elongated nuclei were found attached to medium-size vessels (green, IB4). Scale bars 50 μm.