PTGDS and nasal cavity polyp: Our previous study (14) demonstrated over-expression of PGD2 and hematopoietic prostaglandin D2 synthase (hPGDS) in eosinophils of patients with aspirin-exacerbated respiratory disease (AERD), a condition that is characterized by recurrent nasal polyps (rNP), but the expression of CRTH2 receptors was not examined.