PTGDR2 and inflammation: Due to the widespread expression of the prostaglandin D2 receptor CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells) on several immune-inflammatory cells [180] including eosinophils, some oral CRTH2 antagonists have been tested in order to evaluate their potential therapeutic effects on eosinophilic inflammation in the airways [101].