DP1 is a Gs-coupled GPCR expressed in the colon, eye, platelets, eosinophils, that bind to PGD2 and PGE2. DP1 can inhibit platelet aggregation, and also inhibit leukotriene B4 and superoxide anion (O2-) release from human neutrophils. It can relax smooth muscle and regulate eosinophil apoptosis. DP receptor knockout OVA-challenged mice exhibit reduced Th2 cytokine levels and lymphocyte accumulation in the lung. In addition, they failed to produce asthmatic responses.