Background: Recently, a second prostaglandin D2 (PGD2) receptor, chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), was identified. Because PGD2 was reported to have chemotactic activity on eosinophils, CRTH2 expressed on eosinophils attracted interest as a receptor associated with eosinophil migration to, and accumulation at, inflammatory sites. To elucidate the mechanism regulating the expression of CRTH2 on eosinophils, the effects of PGD2, interleukin (IL)-4, IL-5 and interferon (IFN)-γ on CRTH2 expression were investigated.
Methods: Blood eosinophils were purified using Percoll and anti-CD16 antibody coated magnetic beads. Eosinophils were incubated with PGD2 and/or IL-4, IL-5 and IFN-γ. The expression of CRTH2 on eosinophils was measured using a FACScan cytometer (Becton Dickinson Immunocytometry Systems, San Jose, CA, USA).
Results: Prostaglandin D2 and IL-5, but not IL-4 and IFN-γ, downregulated the expression of CRTH2 on eosinophils. Furthermore, PGD2- and IL-5-induced downregulation of CRTH2 on human eosinophils was inhibited by phenylarsine oxide, a receptor internalization inhibitor.
Conclusions: These results suggest that PGD2 and IL-5 regulate CRTH2 expression on eosinophils through CRTH2 internalization. The decreased expression of CRTH2 on tissue eosinophils may make these cells remain at the site of allergic inflammation.