IL1RL1 and allergic disease: IL-33 and its receptor (known as ST2, IL-33R, IL1RL1, or IL-1R4) are part of the IL-1 cytokine family, but are unique in that they are associated with the promotion of predominantly Th2, not Th1, responses and are intimately involved in the promotion/maintenance of Th2-associated type 2 inflammation, such as allergy and host defense against helminth infection (114).