CRTH2, an orphan receptor of T-helper-2-cells, is expressed on basophils and eosinophils and responds to mast cell-derived factor(s).

We have recently cloned a putative chemoattractant receptor, named CRTH2, which is preferentially expressed on human T-helper- (Th) 2 but not Th1 cells. In this study, we demonstrated that CRTH2 is also highly expressed on peripheral blood basophils and eosinophils. Our search for a CRTH2 ligand identified mast cells as the possible producers of a ligand. When stimulated with an anti-FcepsilonR1 antibody, cord blood-derived mast cells secreted factor(s) that induced Ca(2+) mobilization in CRTH2-expressing K562 cells but not in mock transfected cells. These findings implied the involvement of CRTH2 in mast cell-mediated immune responses such as allergic reactions.