The Sigma Class Glutathione Transferase from the Liver Fluke Fasciola hepatica

BackgroundLiver fluke infection of livestock causes economic losses of over US$ 3 billion worldwide per annum. The disease is increasing in livestock worldwide and is a re-emerging human disease. There are currently no commercial vaccines, and only one drug with significant efficacy against adult worms and juveniles. A liver fluke vaccine is deemed essential as short-lived chemotherapy, which is prone to resistance, is an unsustainable option in both developed and developing countries. Protein superfamilies have provided a number of leading liver fluke vaccine candidates. A new form of glutathione transferase (GST) family, Sigma class GST, closely related to a leading Schistosome vaccine candidate (Sm28), has previously been revealed by proteomics in the liver fluke but not functionally characterised. Methodology/Principal FindingsIn this manuscript we show that a purified recombinant form of the F. hepatica Sigma class GST possesses prostaglandin synthase activity and influences activity of host immune cells. Immunocytochemistry and western blotting have shown the protein is present near the surface of the fluke and expressed in eggs and newly excysted juveniles, and present in the excretory/secretory fraction of adults. We have assessed the potential to use F. hepatica Sigma class GST as a vaccine in a goat-based vaccine trial. No significant reduction of worm burden was found but we show significant reduction in the pathology normally associated with liver fluke infection. Conclusions/SignificanceWe have shown that F. hepatica Sigma class GST has likely multi-functional roles in the host-parasite interaction from general detoxification and bile acid sequestration to PGD synthase activity.研究背景： 家畜肝片吸虫感染每年在全球范围内造成超过30亿美元的经济损失。该疾病在全球家畜种群中发病率持续攀升，同时也是一种重新出现的人体感染疾病。目前尚无商业化获批疫苗，且仅有一种药物对成虫和童虫具有显著疗效。由于易产生耐药性的短期化疗方案在发达国家与发展中国家均非可持续的防控策略，因此肝片吸虫疫苗被认为是必不可少的防控手段。蛋白质超家族已为肝片吸虫疫苗研发提供了多个优质候选体。谷胱甘肽S-转移酶（glutathione transferase, GST）家族的新亚型——Sigma类GST，与主流血吸虫（Schistosome）疫苗候选体Sm28具有高度同源性，此前已通过蛋白质组学技术在肝片吸虫中被鉴定，但尚未完成功能表征。 材料与方法及主要研究结果： 本研究证实，经纯化的重组肝片吸虫Sigma类GST具有前列腺素合酶活性，并可调控宿主免疫细胞的活性。免疫细胞化学（immunocytochemistry）与蛋白质免疫印迹（western blotting）实验结果显示，该蛋白定位于肝片吸虫体表附近，可在虫卵与新脱囊童虫中表达，并存在于成虫的排泄分泌组分（excretory/secretory fraction）中。本研究通过山羊疫苗接种试验，评估了肝片吸虫Sigma类GST作为疫苗的应用潜力。试验未观察到虫荷的显著降低，但证实该疫苗可显著减轻肝片吸虫感染通常引发的病理损伤。 结论与意义： 本研究证实，肝片吸虫Sigma类GST在宿主-寄生虫互作中可能发挥多重功能，涵盖广谱解毒、胆汁酸螯合以及前列腺素D合酶（PGD synthase）活性调控等多个方面。