IL33 and Arthritis: In mouse models of experimental arthritis induced by active immunization, such as collagen- and antigen-induced arthritis, the use of ST2-knockout (KO) mice, ST2 blockade, or injection of soluble ST2 led to decreased immune responses and severity of arthritis, which suggested a pathogenic role for IL-33 signaling through ST2 in these experimental models [10, 11].