Three independent tools have been used to disclose the role of IL-33 in promoting airway allergy and asthma [63]; these are (1) genetic studies: in the case of IL-33 and/or ST2 gene polymorphisms or genomewide association studies (GWAS), (2) evaluations of IL-33/ST2 cellular gene expression and intracellular signaling pathways in allergic and asthmatic mice, for example, by ST2 blockage or IL-33 inhibition, and (3) study of IL-33-defective mice, and also evaluation of IL-33 administration to such mice. Here, IL1RL1 is linked to allergic respiratory disease.