PTGS2 and Nasal polyposis: Reduced COX-2 expression, and consequently decreased PGE2 concentration, has previously been reported in peripheral blood leukocytes (PBLs) [27], urine [28], nasal polyps [29] and nasal polyp fibroblasts [7] in a variety of cells and samples from AIA patients, although the mechanism involved in this alteration remain unclear.