Roles of three putative salmon louse (Lepeophtheirus salmonis) prostaglandin E2 synthases in physiology and host–parasite interactions

Abstract

Background The salmon louse (Lepeophtheirus salmonis) is a parasite of salmonid fish. Atlantic salmon (Salmo salar) exhibit only a limited and ineffective immune response when infested with this parasite. Prostaglandins (PGs) have many biological functions in both invertebrates and vertebrates, one of which is the regulation of immune responses. This has led to the suggestion that prostaglandin E2 (PGE2) is important in the salmon louse host–parasite interaction, although studies of a salmon louse prostaglandin E2 synthase (PGES) 2 gene have not enabled conformation of this hypothesis. The aim of the present study was, therefore, to characterize two additional PGES-like genes. Methods Lepeophtheirus salmonis microsomal glutathione S-transferase 1 like (LsMGST1L) and LsPGES3L were investigated by sequencing, phylogenetics, transcript localization and expression studies. Moreover, the function of these putative PGES genes in addition to the previously identified LsPGES2 gene was analyzed in double stranded (ds) RNA-mediated knockdown (KD) salmon louse. Results Analysis of the three putative LsPGES genes showed a rather constitutive transcript level throughout development from nauplius to the adult stages, and in a range of tissues, with the highest levels in the ovaries or gut. DsRNA-mediated KD of these transcripts did not produce any characteristic changes in phenotype, and KD animals displayed a normal reproductive output. The ability of the parasite to infect or modulate the immune response of the host fish was also not affected by KD. Conclusions Salmon louse prostaglandins may play endogenous roles in the management of reproduction and oxidative stress and may be a product of salmon louse blood digestions. Graphic Abstract

Small, charged proteins in salmon louse (Lepeophtheirus salmonis) secretions modulate Atlantic salmon (Salmo salar) immune responses and coagulation

“…It is also unlikely that such enzymes are deposited on the host skin during infestation given the low severity of lice induced lesions 6 , 7 , 23 , 25 . Furthermore, it has not been possible to experimentally confirm that lice derived PGE 2 is in fact taking part in the host-parasite interaction 59 , 60 , emphasizing that more studies like this, directly addressing the regulation and mode of action of glandular proteins, are needed to analyse the interaction taking place at the site of infestation. New knowledge on this topic may represent a promising fundament for the development of new immune based anti-salmon louse treatments.…”

The effect of different intensities of the ectoparasitic salmon lice (Lepeophtheirus salmonis) on Atlantic salmon (Salmo salar)

“…It has also been suggested that the immunosuppressive effect of the parasite increase with parasite intensity (Holm et al, 2015). However, the mechanism behind salmon lice immunosuppression is not elucidated (Dalvin, Eichner, Dondrup, & Øvergård, 2021; Eichner, Øvergård, Nilsen, & Dalvin, 2015; Øvergård et al, 2016). A parasite intensity‐dependent host immune response in the skin is not supported by our findings here.…”

Temperature affects settlement success of ectoparasitic salmon lice (Lepeophtheirus salmonis) and impacts the immune and stress response of Atlantic salmon (Salmo salar)

“…The immune response of Atlantic salmon against salmon lice is weak and delayed compared to other salmonids resulting in low levels of resistance to infestations (Braden et al., 2020). The inefficient immune response against lice, could in parts be due to the immunomodulatory capabilities of the parasite (Braden et al., 2020; Fast et al., 2007; Øvergård et al., 2016, 2018), but the mechanism is currently not known (Dalvin et al., 2021; Eichner et al., 2015). However, the lack of an efficient immune response towards the ectoparasitic lice may also result from selection for tolerance rather than resistance in Atlantic salmon.…”