Differential modulation of human basophil functions through prostaglandin D₂ receptors DP and chemoattractant receptor-homologous molecule expressed on Th2 cells/DP2

Background: Both prostaglandin (PG) D receptor (DP) and CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells)/DP2 are high-affinity receptors for PGD₂. Previous studies have demonstrated that PGD₂ enhances releasability and induces CRTH2/DP2-mediated migration in human basophils, but the precise effects of PGD₂ on basophils as well as receptor usage have not been fully clarified. Objective: We comprehensively explored the roles of DP and CRTH2/DP2 in basophil functions by using selective agonists and antagonists for each receptor. Methods: DP and CRTH2/DP2 transcripts were quantified by real-time PCR. We studied the effects of selective agonists (DP: BW245C; CRTH2/DP2: 13,14-dihydro-15-keto (DK)-PGD₂) and/ or antagonists (DP: BWA868C; CRTH2/DP2: ramatroban) on Ca²⁺ mobilization, migration, degranulation, CD11b expression and survival of human basophils. Results: Basophils expressed transcripts of both DP and CRTH2/DP2, but the levels of CRTH2/ DP2 transcripts were ca. 100-fold higher compared with DP transcripts. Ca²⁺ influx was induced in basophils by either PGD₂ or DK-PGD₂/CRTH2 agonist but not by BW245C/DP agonist. Basophils treated with PGD₂ were completely desensitized to subsequent stimulation with DK-PGD₂, but not vice versa. DK-PGD₂ as well as PGD₂ up-regulated CD11b expression, induced migration and enhanced degranulation, and those effects were completely antagonized by ramatroban/CRTH2 antagonist. In contrast, BW245C/DP agonist exhibited an inhibitory effect on basophil migration and IgE-mediated degranulation, and the migration inhibitory effect was effectively antagonized by BWA868C/DP antagonist. On the other hand, while PGD₂ significantly shortened the basophil lifespan, neither DK-PGD₂/CRTH2 agonist nor BW245C/DP agonist did. Conclusion: CRTH2/DP2 is primarily responsible for the pro-inflammatory effects of PGD₂ on human basophils, while DP introduces negative signals capable of antagonizing the effects of CRTH2/DP2 in these cells. The effects of PGD₂ on longevity imply a mechanism(s) other than via DP or CRTH2/DP2. CRTH2/DP2 on basophils may afford opportunities for therapeutic targeting in allergic inflammation.