Interleukin (IL-)33 is a cytokine that possesses dichotomous functions in the gut. Whereas various cell types have been reported to produce IL-33, conventionally it is believed to be released from damaged intestinal epithelial cells. Many cell types express the ST2 receptor complex and respond to IL-33 signal, leading to context dependent pro- or anti-inflammatory responses. We have employed antibody staining and a novel IL-33-GFP reporter mouse to characterize the IL-33-producing cell types in the gut in health and various inflammatory or infection conditions.