Identification of a residue in hepatitis C virus E2 glycoprotein that determines scavenger receptor BI and CD81 receptor dependency and sensitivity to neutralizing antibodies.

Hepatitis C virus (HCV) infection is dependent on at least three coreceptors: CD81, scavenger receptor BI (SR-BI), and claudin-1. The mechanism of how these molecules coordinate HCV entry is unknown. In this study we demonstrate that a cell culture-adapted JFH-1 mutant, with an amino acid change in E2 at position 451 (G451R), has a reduced dependency on SR-BI. This altered receptor dependency is accompanied by an increased sensitivity to neutralization by soluble CD81 and enhanced binding of recombinant E2 to cell surface-expressed and soluble CD81. Fractionation of HCV by density gradient centrifugation allows the analysis of particle-lipoprotein associations. The cell culture-adapted mutation alters the relationship between particle density and infectivity, with the peak infectivity occurring at higher density than the parental virus. No association was observed between particle density and SR-BI or CD81 coreceptor dependence. JFH-1 G451R is highly sensitive to neutralization by gp-specific antibodies, suggesting increased epitope exposure at the virion surface. Finally, an association was observed between JFH-1 particle density and sensitivity to neutralizing antibodies (NAbs), suggesting that lipoprotein association reduces the sensitivity of particles to NAbs. In summary, mutation of E2 at position 451 alters the relationship between particle density and infectivity, disrupts coreceptor dependence, and increases virion sensitivity to receptor mimics and NAbs. Our data suggest that a balanced interplay between HCV particles, lipoprotein components, and viral receptors allows the evasion of host immune responses

Acute stress response on Atlantic salmon: a time-course study of the effects on plasma metabolites, mucus cortisol levels, and head kidney transcriptome profile

Farmed Atlantic salmon (Salmo salar) welfare and performance can be strongly influenced by stress episodes caused by handling during farming practices. To better understand the changes occurring after an acute stress response, we exposed a group of Atlantic salmon parr to an acute stressor, which involved netting and transferring fish to several new holding tanks. We describe a time-course response to stress by sampling parr in groups before (T0) and 10, 20, 30, 45, 60, 120, 240, 300, and 330 min post-stress. A subgroup of fish was also subjected to the same stressor for a second time to assess their capacity to respond to the same challenge again within a short timeframe (ReStressed). Fish plasma was assessed for adrenocorticotropic hormone (ACTH), cortisol, and ions levels. Mucus cortisol levels were analyzed and compared with the plasma cortisol levels. At 5 selected time points (T0, 60, 90, 120, 240, and ReStressed), we compared the head kidney transcriptome profile of 10 fish per time point. The considerably delayed increase of ACTH in the plasma (60 min post-stress), and the earlier rise of cortisol levels (10 min post-stress), suggests that cortisol release could be triggered by more rapidly responding factors, such as the sympathetic system. This hypothesis may be supported by a high upregulation of several genes involved in synaptic triggering, observed both during the first and the second stress episodes. Furthermore, while the transcriptome profile showed few changes at 60 min post-stress, expression of genes in several immune-related pathways increased markedly with each successive time point, demonstrating the role of the immune system in fish coping capacity. Although many of the genes discussed in this paper are still poorly characterized, this study provides new insights regarding the mechanisms occurring during the stress response of salmon parr and may form the basis for a useful guideline on timing of sampling protocols.publishedVersio

Effects of dietary deoxynivalenol or ochratoxin A on performance and selected health indices in Atlantic salmon (Salmo salar)

Post-smolt Atlantic salmon (Salmo salar) were fed with standard feed added one of five concentrations of either pure deoxynivalenol (DON; 0.5–6 mg/kg) or pure ochratoxin A (OTA; 0.2–2.4 mg/kg), or no added toxins for up to 8 weeks. Performance effects (feed intake, feed efficiency, gain, length and condition factor), various clinical biochemical parameters, packed cell volume and vaccination response against Aeromonas salmonicidae were all inversely correlated with DON dose, whereas relative liver weight increased with DON dose. In fish fed OTA, however, the effects at the doses tested were rather small. We observed no effects of OTA exposure on performance parameters, but some clinical biochemical parameters tended to increase with OTA dose primarily at 3 weeks, and compared with controls OTA exposure caused increased mRNA expression of two immune markers in the spleen. No liver histopathological effects were found from DON or OTA exposure. For DON, we derived a BMDL20 of 0.3 mg/kg feed for reduced total protein in plasma, a BMDL5 of 0.5 mg/kg feed for reduced condition factor, and a NOAEL of 1 mg/kg feed for DON. For OTA, a BMDL or NOAEL could not be derived (>2.4 mg/kg).publishedVersio

Complement factor C5 in Atlantic salmon (Salmo salar): characterization of cDNA, protein and glycosylation

Complement component 5 (C5) is an essential factor of the defensive complement system in all vertebrates. We report the characterization of C5 cDNA and protein from Atlantic salmon (Salmo salar), a teleost fish species of high importance in aquaculture. The C5 cDNA cloned from liver is 5079 nucleotides long, whose translation product has a molecular weight of 190 kDa, with the classical β-α orientation and motifs/sites for β-α cleavage (678RPKR681) and cleavage by C5 convertases (R758). Mass spectrometric analysis show a single N-linked, biantennary, complex glycan at N1125. Moreover, the N-linked glycan displays an unusual modification in the form of acetylated sialic acid residues. Three anti-C5 antisera produced in mice using purified C5 worked in immunohistochemical analyses of formalin fixed liver tissue. The purification method, whereby inactive and activated (C5b) forms were isolated, opens for interesting studies on the complement function in fish, including possible connection to stress, disease and glycosylation.publishedVersio

Long-term persistence of piscine orthoreovirus-1 (PRV-1) infection during the pre-smolt stages of Atlantic salmon in freshwater

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Protective Immunization of Atlantic Salmon (Salmo salar L.) against Salmon Lice (Lepeophtheirus salmonis) Infestation

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A novel totivirus and piscine reovirus (PRV) in Atlantic salmon (Salmo salar) with cardiomyopathy syndrome (CMS)

<p>Abstract</p> <p>Background</p> <p>Cardiomyopathy syndrome (CMS) is a severe disease affecting large farmed Atlantic salmon. Mortality often appears without prior clinical signs, typically shortly prior to slaughter. We recently reported the finding and the complete genomic sequence of a novel piscine reovirus (PRV), which is associated with another cardiac disease in Atlantic salmon; heart and skeletal muscle inflammation (HSMI). In the present work we have studied whether PRV or other infectious agents may be involved in the etiology of CMS.</p> <p>Results</p> <p>Using high throughput sequencing on heart samples from natural outbreaks of CMS and from fish experimentally challenged with material from fish diagnosed with CMS a high number of sequence reads identical to the PRV genome were identified. In addition, a sequence contig from a novel totivirus could also be constructed. Using RT-qPCR, levels of PRV in tissue samples were quantified and the totivirus was detected in all samples tested from CMS fish but not in controls. <it>In situ </it>hybridization supported this pattern indicating a possible association between CMS and the novel piscine totivirus.</p> <p>Conclusions</p> <p>Although causality for CMS in Atlantic salmon could not be proven for either of the two viruses, our results are compatible with a hypothesis where, in the experimental challenge studied, PRV behaves as an opportunist whereas the totivirus might be more directly linked with the development of CMS.</p