PTGDR2 and chronic rhinosinusitis with nasal polyps: The linkage of CRTH2 to the underlying biology is complicated in CRSwNP, as besides eosinophils, Th2, ILC2, and other inflammatory cells are also likely to be the source of CRTH2 over-expression and thus contribute to the recurrence of NP through this receptor, we cannot exclude the effects of these cells.