Authors

O C Drysdale¹; D Smith¹; H Jewhurst¹; K Cwiklinski¹; J P Dalton¹;  ¹ Queen's University Belfast

Discussion

The liver fluke, Fasciola hepatica is a pathogen of economic importance in ruminants, such as sheep and cattle worldwide and is now recognised as an important zoonosis. Due to over-reliance on anthelmintics, drug-resistant parasites have emerged meaning that new control strategies are required. Vaccine development is becoming a greater focus of current research. F. hepatica-expressed molecules that act at the host-parasite interface, modify host cell function, and aid parasite development and survival are therefore of major interest as vaccine targets. Based on recent genome and associated stage specific transcriptome/proteome analysis, we have identified a number of molecules as potential vaccine candidates including Cystatin and Kunitz-type protease inhibitors. We have successfully expressed these inhibitors in Pichia pastoris, achieving a highly purified yield. Extensive characterisation of these inhibitors has been carried out and revealed that the Cystatins are broad range inhibitors of both host and parasite cysteine proteases compared with the Kunitz-type inhibitor that shows specific inhibition of Cathepsin L type proteases. The protease/anti-protease balance may be critical in the regulation of parasite processes including penetration, feeding, development and immune evasion, as well as modulation of host innate cell proteases involved in antigen processing and presentation. The potential of upsetting this balance is currently being assessed in sheep vaccine trials.