Intestinal IL-33 increases platelet reactivity, hemostasis, and inflammation via serotonin release. Constitutive IL-33 secretion from IECs supports serotonin (5-HT) release from enterochromaffin cells. 5-HT is taken up by platelets, increasing platelet reactivity, hemostasis, and wound repair. After intestinal inflammation induced by DSS or LPS, IL-33 release from damaged IECs supports 5-HT secretion and platelet-dependent neutrophil recruitment.