All these findings on the crucial regulatory role played by the PGE-EP2 axis in airway inflammatory diseases, such as asthma and CRSwNP, support the notion that the low PGE2 production by the airway epithelium in AERD results in an ongoing activation of inflammatory cells, which in turn increases the release of pro-inflammatory cytokines and metabolites, such as PGD2 and Cys-LTs (Figure 2). Here, PTGDS is linked to asthma.