Eosinophils have been initially identified as important targets of PGD2, also emerged as important sources of PGD2 with both autocrine and paracrine roles in allergy and parasitic infections (Lewis et al., 1982; Tanaka et al., 2000; Shimura et al., 2010; Luna-Gomes et al., 2011; Ugajin et al., 2011) (Fig. 1a). The gene discussed is HPGDS; the disease is allergic disease.