Abundant IL-33 receptors (ST2) are expressed on MCs and coordinate spatially and temporally with IL-33 signaling, which may trigger a key regulatory amplification loop involved in immune homeostasis.13,21,22 As key effector cells to IL-33 signaling, MCs are recognized as driving production of high amounts of the (T helper) Th2 cytokines IL-5, IL-9, and IL-13.23,24 In colitis, the interaction of MCs with epithelial cells depends on the inflammatory stage and activation of the tissue repair program. The gene discussed is IL33; the disease is colitis.