Oncogenic suppressor 2 (ST2), also known as IL-1R4, is a member of the IL-1 receptor family of glycoproteins that prompts the Th2 immune response.ST2 is expressed on the surface of mast cells, activated Th2 cells, macrophages, and cardiomyocytes. It binds to IL-33, a member of the pro-inflammatory IL-1 family with intracellular and extracellular activity. In addition to its mast cell-promoting and Th2-dependent inflammatory effects, activation of transmembrane ST2 enhances inflammation-associated responses and protects the organism from atherosclerosis and cardiomyocyte hypertrophy. Serum soluble ST2 expression levels are elevated during inflammation, including allergic asthma, sepsis, trauma, dengue, and lung disease. Elevated serum ST2 is also affected by multiple aspects of heart failure, including aortic stenosis, congestive cardiomyopathy and risk of cardiovascular failure and death.