Characterisation of proteins in excretory/secretory products collected from salmon lice, Lepeophtheirus salmonis

Abstract

BackgroundThe salmon louse, Lepeophtheirus salmonis, is an ectoparasitic copepod which feeds on the mucus, skin and blood of salmonid fish species. The parasite can persist on the surface of the fish without any effective control being exerted by the host immune system. Other ectoparasitic invertebrates produce compounds in their saliva, excretions and/or secretions which modulate the host immune responses allowing them to remain on or in the host during development. Similarly, compounds are produced in secretions of L. salmonis which are thought to be responsible for immunomodulation of the host responses as well as other aspects of crucial host-parasite interactions.MethodsIn this study we have identified and characterised the proteins in the excretory/secretory (E/S) products of L. salmonis using LC-ESI-MS/MS.ResultsIn total 187 individual proteins were identified in the E/S collected from adult lice and pre-adult sea lice. Fifty-three proteins, including 13 serine-type endopeptidases, 1 peroxidase and 5 vitellogenin-like proteins were common to both adult and pre-adult E/S products. One hundred and seven proteins were identified in the adult E/S but not in the pre-adult E/S and these included serine and cysteine-type endopeptidases, vitellogenins, sphingomyelinase and calreticulin. A total of 27 proteins were identified in pre-adult E/S products but not in adult E/S.ConclusionsThe assigned functions of these E/S products and the potential roles they play in host-parasite interaction is discussed.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-2885-6) contains supplementary material, which is available to authorized users.

Identification of proteins from the secretory/excretory products (SEPs) of the branchiuran ectoparasite Argulus foliaceus (Linnaeus, 1758) reveals unique secreted proteins amongst haematophagous ecdysozoa

“…Recent proteomic analysis of L. salmonis SEPs found a vitellogenin-like protein unique to adult females [55]. Dalvin et al [63] examining L. salmonis did not observe any transcription of this protein in the ovary but they did localise the presence of these proteins in the haemolymph [63] indicating the protein is circulated through the louse and thus may have a role in reproductive processes following feeding similar to ticks.…”

“…Anopheles culicifacies [54]) and sea lice (e.g. L. salmonis [55]) saliva/salivary glands and SEPs. Sea lice trypsins, vitellogenin-like proteins and proteins with immunomodulatory functions or host adhesion properties have similarly been studied with suggestions of their potential as vaccine antigen candidates [56][57][58].…”

“…135 in the saliva of the hard tick Haemaphysalis longicornis [36] or 187 in the SEPs of L. salmonis [55]. Parasite SEP protein yields can be enhanced by inducing salivation or stimulation of the salivary glands using dopamine and pilocarpine, but with varying success [34,36,51,55]. The overall number of identified proteins would also be anticipated to increase when a fully annotated genome becomes available.…”

“…Trypsin-like serine proteases secreted in the salmon louse gut act as a general digestive protease [88,89]. Trypsin-like proteases have been detected in the sea lice species C. rogercresseyi and L. salmonis and in their SEPs [35,55,77,90,91]. In addition, trypsin-like proteases have also been detected in the skin mucus of Atlantic salmon infected with L. salmonis, and have been suggested to play a role in facilitating feeding and evasion of the host immune response [92].…”

“…Due to the presence of VIT with a signal peptide in A. foliaceus SEPs, a similar mode of action may exist to that of H. longicornis VIT, but further validation is required. In terms of molecular function, GO analysis was very restricted but revealed that the majority of the identified A. foliaceus proteins are nominally involved in catalytic activity acting on a protein (8%) and hydrolase activity (50%), and 17% in ion binding and oxireducatase activity, which were found also from L. salmonis adult SEPs [55]. Notably, in terms of biological function, oxidationreduction processes accounted for 100% of the A. foliaceus SEPs identified, which may have roles in protection against host-derived reactive oxygen species [55,108].…”