Immunosuppression of Aquaglyceroporins in Salmon Lice

Parasitic sea lice pose a great threat to the health of wild and farmed salmonids, but their increased resistance to multiple drugs means that alternative treatments need to be developed to reduce infections. The most efficient, sustainable, safe and environmentally friendly method for the prevention of infectious diseases is vaccination. We have thus identified specific proteins that are important for the louse´s osmoregulation and metabolism and conducted multiple immunizations of salmon with synthetic fragments to form an immune response. Two separate peptide fragments from the identified proteins were used to immunize salmon parr using standard protocols. Our results reveal that each peptide had a stable half-life of between 2 to 7 days and induced a specific immune response in 78 and 87% of the immunized fish, respectively. Repeated immunizations further demonstrated a boost effect. The experiments thus trained the salmon immune system to specifically respond to the louse peptides. To ensure that there would be no autoimmune response in the immunized salmon, we conducted comprehensive evolutionary studies to identify all of the glycerol transporters in the salmon genome. This revealed a complex history of gene evolution in the salmon and also uncovered novel glycerol transporters. By expressing each of the functional gene products in frog oocytes, we tested whether the antibodies raised against the louse peptides could immunosuppress the function of either the salmon or louse glycerol-transporting proteins. The results showed that only the function of the louse glycerol transporters was immunosuppressed, with no risk of an autoimmune response in immunized salmon. In our final analyses we conducted a comprehensive evolutionary analysis of the glycerol transporters in crustaceans to understand the origins of the louse genes. This revealed that the genes and translated proteins are unique to the genus, with specific motifs in the intracellular domains potentially associated with membrane trafficking. Experiments to test the identified motifs, revealed which signal transduction pathways control the membrane insertion of the proteins. This is important for understanding how exposure of the proteins to salmon antibodies can be enhanced, thus improving the possibility for future vaccine development.

Å finne ikke-kjemiske miljøvennlige løsninger på det utbredte problemet med lakselusangrep, er av stor betydning for samfunnet. Vaksiner er velkjente løsninger som kan løse store samfunnsproblemer. Dette prosjektet har med hell lagt grunnlaget for vaksineutvikling i laksen mot glyseroltransportproteiner i lusen. Fremtidige studier kan øke tilnærmingene som er utviklet i prosjektet, og utvide muligheten for suksess ved å studere den grunnleggende biologien av veier som forbedrer lusttransportørens eksponering for laksens immunrespons. Prosjektet integrerte partnernes innsats for å oppnå disse resultatene og bidro videre til den akademiske utviklingen av to postdoktorer. Hver doktorgradsstipendiat publiserte og leverte artikler til internasjonalt anerkjente vitenskapelige tidsskrifter, og har nå med suksess søkt og fått nye stillinger.

Epizootics caused by ectoparasitic sea lice are a severe threat to wild and domestic salmonids and the extended food networks and human activities that depend upon them. The increasing instances of multiple levels of drug resistance in Norway means that alternative therapeutic approaches to dealing with this pest are needed. The most effective, sustainable, safe and environmentally friendly method of preventing infectious diseases is vaccination. Due to the ectoparasitic lifestyle of sea lice, however, antigenic targets are challenging to identify. Amongst other ectoparasitic arthropods which feed on the blood of their hosts, including malaria mosquitoes and cattle ticks, immunogenic targeting of proteins involved in osmoregulation and nutrient mobilisation is proving highly successful. Since osmoregulation represents a major vulnerability of sea lice compared to their hosts, where cell volume regulation breaks down in fresh or brackish waters, this project aims to lay the groundwork for developing a vaccine in Atlantic salmon against sea lice osmoregulatory proteins as a part of a future integrated louse management strategy.