F. hepatica infections are associated with a T-helper-cell type 2 (Th2) immune response dominating during the chronic phases of infection [61] , but pro-inflammatory responses are suppressed [62] . Suppression of allergic responses during chronic parasitic worm infections has a mutually beneficial effect on the parasites' proliferation and the hosts' survival. Prostanoids, including PGD 2 , are important in mediating these allergic inflammatory responses. While generally regarded as pro-inflammatory molecules, these important lipid molecules are also involved in mediating antiinflammatory responses [63] . Helminth-derived molecules are thought to be involved in driving the Th2 response stereotypical of parasitic worm infections. DC and macrophage cell cultures Figure 6 . rFhGST-SI stimulates the production PGE2 and PGD2 from the macrophage cell lines J774 and RAW264.7. J744 and RAW264.7 macrophage cell lines were cultured in vitro with medium, rFhGST-S1 (10 mg/ml) or LPS (100 ng/ml) for 18 hours, and the production of total prostaglandin, PGE2 and PGD2 released into supernatants determined by competitive EIA. Data are presented as the mean 6 SEM following subtraction of medium controls and are representative of two experiments. doi:10.1371/journal.pntd.0001666.g006