Immune Response In Atlantic Salmon Research Articles

Stimulation of type I IFN activity in Atlantic salmon ( Salmo salar L.) leukocytes: Synergistic effects of cationic proteins and CpG ODN

Unmethylated CpG motifs in DNA are recognised by vertebrate immune cells as pathogen signatures. Consequently, oligodeoxynucleotides containing CpG motifs (CpG ODNs) are able to enhance and direct immune responses. Recent studies have demonstrated that CpG ODNs activate antiviral immune responses in Atlantic salmon ( Salmo salar L.) leukocytes, and are therefore promising agents as vaccine adjuvants or immunostimulants in fish. In this work, we report synergy of CpG ODN and cationic proteins in the stimulation of type I IFN activity in Atlantic salmon leukocytes. Different fractions of cationic histone proteins derived from cod milt or poly- l-arginine and poly- l-lysine were screened for their ability to enhance CpG ODN induced type I IFN activity in Atlantic salmon leukocytes. Optimal ratio of histones to CpG ODN was identified, and effects on transcription of type I IFN and antiviral Mx genes were studied. Delivery of CpG ODN with cationic proteins enhanced the production of type I IFN and succeeding Mx transcripts after two and five days of stimulation at substimulatory concentrations of CpG ODN. These results indicate that co-delivery of CpG ODN and cationic proteins enhance antiviral mechanisms in Atlantic salmon leukocytes as compared to CpG ODN alone.

Changes in the innate immune response of Atlantic salmon, Salmo salar L., exposed to experimental infection with Neoparamoeba sp.

An experiment was conducted to determine the effect of Neoparamoeba sp. infection on the innate immune responses of Atlantic salmon. Atlantic salmon were experimentally infected with Neoparamoeba sp. and serially sampled 0, 1, 4, 6, 8 and 11 days post-exposure (dpe). Histological analysis of infected fish gill arches identified the presence of characteristic amoebic gill disease lesions as early as 1 dpe with a steady increase in the number of affected gill filaments over time. Immune parameters investigated were anterior kidney phagocyte function (respiratory burst, chemotaxis and phagocytosis) and total plasma protein and lysozyme. In comparison with non-exposed control fish basal respiratory burst responses were suppressed at 8 and 11 dpe, while phorbol myristate acetate-stimulated activity was significantly suppressed at 11 dpe. Variable differences in phagocytic activity and phagocytic rate following infection were identified. There was an increase in the chemotactic response of anterior kidney macrophages isolated from exposed fish relative to control fish at 8 dpe. Total protein and lysozyme levels were not affected by Neoparamoeba sp. exposure.

Expression, antigenicity and studies on cell receptor binding of the hemagglutinin of infectious salmon anemia virus

Infectious salmon anemia (ISA) virus belongs to the proposed genus Isavirus of Orthomyxoviridae and is an emerging pathogen in Atlantic salmon (Salmo salar) farming. The hemagglutinin-esterase (HE) of ISA virus share several characteristics with the influenza virus hemagglutinin. This study reports recombinant expression of different ISA virus HE mutants in fish cell lines. Some introduced mutations, representing minimal differences in single amino acid residues, resulted in remarkable effects on expression efficiency in general and on surface expression specifically. Receptor binding assays showed that amino acid residues in the N-terminal half part are important in receptor binding, either being directly involved in the binding, or by influencing the structure of the binding site. Deletion of the putative N-glycosylation sites of the ISA virus HE, located near the transmembrane region, did not influence expression, receptor binding properties or staining by either a neutralising MAb, or salmon convalescent sera. The humoral immune response of Atlantic salmon after ISA virus infection showed weak neutralising activity and the results indicated that it was directed against HE.

Pathogenesis and immune response in Atlantic salmon (Salmo salar L.) parr experimentally infected with salmon pancreas disease virus (SPDV)

Atlantic salmon parr were injected intraperitoneally with salmon pancreas disease virus (SPDV) grown on CHSE-214 cells. The viraemia, the histopathological changes in target organs and some immune parameters were taken at intervals up to 30 days post-infection (dpi). The earliest kind of lesion was necrosis of exocrine pancreas, appearing as soon as 2dpi. It progressed towards complete tissue breakdown at 9dpi before resolving gradually. Concurrent to this necrosis, a strong inflammatory response was in evidence from 9dpi in the pancreatic area for a majority of fish. A necrosis of the myocardial cells of the ventricle occurred in infected fish mainly at 16dpi and it faded thereafter. The monitoring of the plasma viral load showed a rapid haematogenous spreading of SPDV, peaking at 4dpi, but also the absence of a secondary viraemia. No interferon (IFN) was detected following the infection of parr with SPDV, probably owing to an IFN activity in Atlantic salmon below the detection level of the technique. Neutralising antibodies against SPDV were in evidence from 16dpi and they showed a time-related increasing titre and prevalence. The phagocytic activity in head-kidney leucocytes was always significantly higher in the infected fish than in the control fish, being particularly high by 9dpi. Lysozyme and complement levels were both increased and they peaked significantly in the infected fish at 9 and 16dpi respectively. These results demonstrated that an experimental infection of Atlantic salmon parr with SPDV provoked a stimulation of both specific and non-specific immunity with regards to the viraemia and the histopathology.

Suppression of the humoral immune response of Atlantic salmon, Salmo salar L. by the 64 kDa serine protease of Aeromonas salmonicida

Bacteria-free supernatants of broth cultures of Aeromonas salmonicida inhibited the humoral immune response, but not the cell-mediated immune response, of Atlantic salmon to bacteriophage MS2. The immunosuppressive factor was the 64kDa serine protease secreted by A. salmonicida. The suppressive activity was not due to degradation of epitopes of MS2, and although serine protease degraded the heavy chain of salmon IgM in vitro there was no evidence for significant degradation in vivo. The principal lethal toxin of A. salmonicida, the glycerophospholipid: cholesterol acyltransferase did not inhibit the immune response of salmon.

The humoral immune response of Atlantic salmon and rabbit against carbohydrate cell wall antigens ofRenibacterium salmoninarum

The humoral immune response of Atlantic salmon and rabbit against carbohydrate cell wall antigens ofRenibacterium salmoninarumwas studied after immunisation with whole bacterial cells (WC) and trypsinised cells (TC). Trypsination was shown to remove all proteins from theR. salmoninarumcells, and TC thus represents the carbohydrate skeleton of the bacterial cells. A galactose-rich polysaccharide (GPS) and peptidoglycan (PG) are the quantitatively most important carbohydrate constituents of theRenibacteriumcell wall. Antibodies to GPS were readily detectable in sera from rabbits immunised with TC, but not in sera from Atlantic salmon immunised with TC or WC. On the other hand, sera from Atlantic salmon immunised with TC showed relatively high titres of antibodies to PG, whereas sera from rabbits immunised with TC hardly contained antibodies to PG. The TC preparate contained mannose and glucose in its cell wall in addition to the monosaccharide constituents from GPS and PG. This indicates the presence of additional polysaccharide(s) and/or glycolipid(s) that may also be immunogenic which is also suggested by the immunological data presented.

Effects of dietary (n-3) and (n-6) polyunsaturated fatty acid ratio on the immune response of Atlantic salmon, Salmo salar L.

To examine the influence of the dietary ratio of (n-3) to (n-6) polyunsaturated fatty acids (PUFAs) on the immune system of Atlantic salmon, Salmo salar L., two dietary trials were carried out in which parr were maintained on diets containing either fish oil [(n-3)/(n-6) PUFA = 5.2] or sunflower oil [(n-3)/(n-6) PUFA = 0.3] and assessed for differences in immunological parameters. There were no significant differences in blood cell counts, differential leucocyte counts or haematocrit values between dietary groups, and while no apparent differences were observed in the non-specific immune parameters measured, there was a significantly higher number of B cells responding to Aeromonas salmonicida, in the kidney and spleen of vaccinated fish maintained on high (n-3)/(n-6) PUFAs diets. There was also a significant difference (P≤ 0.01) between the dietary groups in trial 1 and trial 2 when non-vaccinated fish were challenged with Aeromonas salmonicida and Vibrio anguillarum, respectively, with the (n-6) group succumbing to the bacterium before the (n-3) group. The results suggest that Atlantic salmon fed diets with a low ratio of (n-3)/(n-6) PUFA may be less resistant to infection than those fed diets containing lipid with a high (n-3)/(n-6) PUFA ratio.

Genetic variation in the humoral immune response in Atlantic salmon ( Salmo salar) against Aeromonas salmonicida A-layer

Antibody responses to Aeromonas salmonicida A-layer were analysed in family material of Atlantic salmon ( Salmo salar), consisting of 791 fish belonging to 34 full-sib groups within 12 paternal half-sib groups. The fish were immunized twice and blood samples were collected three times. Significant increase in antibody titre from first to second, and from second to third sampling, was observed. Genetic variation in antibody titres was observed at the three samplings with estimated heritabilities ranging from 0.16 to 0.20, and a significant heritability estimate was recorded in the antibody response after the second immunization ( h 2=0.16). Moderate to high genetic ( r=0.5–0.72) and phenotypic ( r=0.29–0.57) correlations were found between the titre values at different samplings, and between selected titres and titre increases. Production parameters, such as mean slaughter weight and mean survival rate were obtained for fish which were reared commercially in the sea, and which belonged to the same full-sib groups as those analysed for A. salmonicida A-layer antibodies. No significant correlation between the mean antibody titre to A. salmonicida A-layer in this study and mean slaughter weight and survival rate in full-sib family material in the sea was observed.

Gill Na+,K+‐ATPase activity, plasma cortisol level, and non‐specific immune response in Atlantic salmon (Salmo salar) during parr‐smolt transformation

Atlantic salmon (Salmo salar) yearling presmolts were reared under two different photoperiod regimes (simulated natural photoperiod, SNP, and continuous light, CL) and identical ambient temperature conditions from 21 November 1990 until 29 May 1991. Sampling was done biweekly from 21 February. Gill Na+,K+‐ATPase activity increased under both photoperiod regimes from early April, concurrently with the increase in ambient temperature. The initial increase and final levels (29 May) in enzyme activity were much lower in the CL regime fish. Seawater challenge tests (24 h, 35 ppt) on 2 and 15 May resulted in lower plasma chloride levels in the SNP regime fish, indicating better hypo‐osmoregulatory ability. This difference wasANNOUNCEMENT not present on 29 May. Resting plasma cortisol levels increased from March under both regimes, but the increase was much greater in the SNP regime fish (75 nm on 29 May v 22 nm in the CL regime). The individuals from the SNP regime were of lower weight and condition coefficient on 29 May, whereas length was uniform. Plasma lysozyme activity was unchanged throughout the sampling period, with the CL regime fish showing an overall higher activity. The in vitro leucocyte stimulation test did not indicate a reduced immune response in May in smolting fish exposed to the simulated natural photoperiod regime compared to fish reared under continuous light.

Gill Na+,K+-ATPase activity, plasma cortisol level, and non-specific immune response in Atlantic salmon (Salmo salar) during parr-smolt transformation

Gill Na+,K+-ATPase activity, plasma cortisol level, and non-specific immune response in Atlantic salmon (Salmo salar) during parr-smolt transformation

The effect of stress on the immune response of Atlantic salmon ( Salmo salar L.) fed diets containing different amounts of vitamin C

An experiment was performed to determine the effects of dietary vitamin C levels and stress on immunological parameters in Atlantic salmon ( Salmo salar L.). Atlantic salmon parr were maintained on diets containing 0.082 (low), 0.44 (normal) and 3.17 (high) g vitamin C/kg dry diet. After 23 weeks, tissue levels were found to reflect dietary input. Groups of fish were removed and subjected to a 2 h confinement stress prior to sacrifice and isolation of plasma and head kidney leucocytes. Leucocyte respiratory burst activity ( P<0.01) and bactericidal activity ( P<0.05) were both found to be significantly reduced by stress, but were unaffected by vitamin C status. Leucocyte migration was unaffected by stress or vitamin C status. Plasma bactericidal activity was also unaffected by vitamin C status but was significantly enhanced by stress ( P<0.05). Production of specific antibody following immunisation with Aeromonas salmonicida was found to be significantly reduced ( P<0.01) by stress, and there were significantly greater levels of specific antibody ( P<0.01) in fish fed the low vitamin C diet compared with fish fed high levels of vitamin C.

Relationship between diet and immune response in Atlantic salmon ( Salmo salar L.) after feeding various levels of ascorbic acid and omega-3 fatty acids

Juvenile Atlantic salmon ( Salmo salar L.) were fed experimental diets containing megadoses of vitamin C 1 and C 2, respectively, and increasing amounts of omega-3 fatty acids for periods of 52 and 72 days. General resistance to infection was assessed after challenge with Vibrio salmonicida. Development of specific immune response after vaccination against Yersinia ruckeri was assessed as likelihood of survival after challenge and antibody level. Cell wall strength was assessed by the erythrocyte fragility test, and occurrence of morphological changes in various body organs was investigated. In the present study, no significant increase in general or specific resistance to infection was seen. Fish fed diets with megadoses of vitamin C 2 had increased antibody levels and higher incidence of degenerative changes in skeletal muscle. Omega-3 fatty acids exerted an immunosuppressive action with both significantly lower likelihood of survival and lower antibody levels. An increased incidence of degenerative changes was also observed. On the other hand, increased levels of omega-3 fatty acids increased erythrocyte cell wall strength.

Humoral immune response in Atlantic salmon, Salmo salar L., to cellular and extracellular antigens of Aeromonas salmonicida

Abstract. The putative virulence factors of Aeromonas salmonicida, the aetiological agent of furunculosis in salmonids, are candidates for protective antigens in effective vaeeines against furunculosis. In this report, the authors have compared the immunogenieily of eell‐associated and extracellular antigens of A. salmonicida in Atlantic salmon, Salmo salar L., to that in rabbit. The animals were immunized with formalin‐killed whole cells and formalin‐inactivated extracellular products (ECP), either separately or in combination. The ability of the antigens to induce antibody production was studied by elisa and Western blotting techniques. These results confirm previous reports that far more structures are immunogenie in rabbit compared to the antibody responses elicited in salmon. However, in both species, some antigens were dominant, including a caseinolytic protease in addition to the A‐protein and high and low MW LPS.

The humoral immune response in Atlantic salmon ( Salmo salar L.) against the hapten carrier antigen NIP-LPH; the effect of determinant (NIP) density and the isotype profile of anti-NIP antibodies

The humoral immune response in Atlantic salmon ( Salmo salar L) against the semi-synthetic antigen NIP-LPH (4-hydroxy-3-iodo-5-nitrophenyl-acetic acid conjugated to Limulus polyphemus haemocyanin) was studied. The effect of the conjugation ratio on the antibody activity, affinity, specificity and shift of isotypic determinants of anti-NIP antibodies was tested. No affinity maturation of the antibody response similar to mammalian responses could be seen, except for the antigen having the lowest conjugation ratio (NIP 6 LPH) which demonstrated a moderate (two-fold) increase, of the average intrinsic association constant ( K 0 ) value from day 59–134 after immunisation. The NIP 6 LPH antigen also elicited anti-NIP antibodies having a 15-fold higher K 0 than the more substituted NIP 19 LPH or NIP 37 LPH. By using a panel of monoclonal antibodies binding determinants on salmon Igs, a different spectrum of such determinants could be recorded on anti-NIP molecules in normal and immune salmon sera. Although the specificity of these monoclonal is unproven (i.e. react with the C or V regions on salmon Ig) these data suggest that Atlantic salmon have more than one antibody isotype and possess the ability to alter the composition of antibody classes during an ongoing immune response, akin to higher vertebrates.

The immune response of Atlantic salmon, Salmo salar L., to the causative agent of bacterial kidney disease, Renibacterium salmoninarum

Abstract. Both under‐yearling and post‐yearling Atlantic salmon parr produced high agglutinating antibody titres in response to a single intraperitoneal injection of killed bacterial kidney disease (BKD) cells emulsified in. Freund's complete adjuvant (FCA), Low or no response was observed in animals injected with BKD cells in saline or in animals vaccinated by hyperosmotic immersion. Immunological duration was insufficient in fish vaccinated as under‐yearling parr to provide protective immunity 2 years later when the fish had become smolts. Atlantic salmon post‐yearling parr injected with BKD cells in FCA demonstrated a reduced prevalence of BKD lesions compared to control animals when both were observed as smolts 1 year after vaccination.