IL33 and chronic obstructive pulmonary disease: IL-33 was discovered as an endothelial cell nuclear factor that is mostly expressed in large and small blood vessels in almost all human organs at steady state.62, 63, 64 Later, significant expression was also confirmed in epithelial cells from barrier tissues and fibroblastic stromal cells;65 and association studies have established a genome-wide significant association between variants in IL-33, eosinophil numbers, and risk for asthma or chronic obstructive pulmonary disease.47