GPR44, also called CRTH2, is a Prostanoid Receptor that binds prostaglandin D2. PGD2 signals through CRTH2 to induce Th2, eosinophil, and basophil chemotaxis in a G-alpha(i) dependent manner. CRTH2 may play a role in mast cell-mediated immune responses such as those involved in allergic reactions. This receptor is upregulated in activated T helper-2 (Th2) cells, peripheral blood basophils, and eosinophils, but not in Th1 lineage cells. It may be a useful marker for Th2 and Tc2 cells.Synonyms: CRTH2, Chemoattractant receptor-homologous molecule expressed on Th2 cells, DL1R, Putative G-protein coupled receptor 44