A newly developed DP1 antagonist (S-555739, asapiprant) showed improved affinity and bioavailability, and reversed antigen- and PGD2-induced nasal congestion and airway hyperresponsiveness in guinea pigs and sheep, respectively, along with significantly decreased eosinophils and other inflammatory cells in nasal lavage fluid (100). This evidence concerns the gene PTGDR and airway hyperresponsiveness.