Antibody-mediated growth of infectious salmon anaemia virus in macrophage-like fish cell lines.

Infectious salmon anaemia virus (ISAV), a pathogen in marine aquaculture, belongs to the genus Isavirus, family Orthomyxoviridae. There is limited information on how ISAV interacts with host defences. To study ISAV-antibody interactions, virus neutralization (VN) assays were performed in the cell lines CHSE-214, SHK-1 and TO using three strains of ISAV and rabbit or fish anti-ISAV sera. Homologous VN titres of >1 : 1280 in CHSE-214 cells corresponded to titres of only 1 : 80 in the macrophage-like fish cell lines SHK-1 and TO, despite using 1000 and 2000 times less virus, respectively. However, rabbit antiserum to infectious pancreatic necrosis virus (IPNV) had a VN titre of 1 : 10,260 against IPNV in both CHSE-214 and TO cells. Poor ISAV neutralization in TO cells was attributed to Fc receptors mediating virus infectivity, because (1) neutralization by rabbit antiserum to ISAV was increased 48-fold in the presence of staphylococcal Protein A and (2) when using FITC-labelled virus and spectrofluorometry, a significant increase (P=0.018) in the intensity of fluorescence of intracellular virus was observed in assays of virus-antiserum mixtures in the absence of Protein A as compared to those in the presence of Protein A. Neutralization of ISAV with fish antisera was observed only in CHSE-214 cells, as Protein A could not restore neutralization in TO cells. These findings demonstrate for the first time antibody-mediated infection of macrophage-like fish cell lines by a fish virus, ISAV, and, as ISAV in Atlantic salmon targets leukocytic and endothelial cells, this may have implications for ISA pathogenesis and vaccination.

Serological evidence of infectious salmon anaemia virus (ISAV) infection in farmed fishes, using an indirect enzyme-linked immunosorbent assay (ELISA).

Antibody detection tests are rarely used for diagnostic purposes in fish diseases. Infectious salmon anaemia (ISA) caused by ISA virus (ISAV) is an emerging disease of Atlantic salmon Salmo salar L. The virus has also been isolated from diseased coho salmon Oncorhynchus kisutch in Chile. An indirect enzyme-linked immunosorbent assay (ELISA) that should facilitate serodiagnosis of ISAV infection, the study of epidemiology, and the control of ISA in farmed fishes has been developed using purified ISAV as the coating antigen, and monoclonal antibodies that detect fish immunoglobulins bound to the antigen on the plate. Application of the test to a random sample of farmed Atlantic salmon from the Bay of Fundy, New Brunswick, Canada, positively identified 5 of the 7 ISAV RT-PCR-positive fish, and all 10 RT-PCR-negative fish were also negative in the ELISA. Some RT-PCR-negative fish had an elevated non-specific antibody reactivity suggestive of chronic infection or resistance to ISAV. This test was also able to detect 11 of the 14 coho salmon pooled serum samples from a clinically affected farm in Chile that were positive by the virus neutralization (VN) test, and 2 of the 4 VN-negative samples. We conclude that this ELISA would be suitable as a routine test for ISAV infection or for assessing ISAV vaccine efficacy before placing smolts in sea cages, and for testing fishes in sea cages to detect level of resistance to ISA. The assay enables vaccination in combination with depopulation control methods.

The effects of high-fat diet on exercise-induced changes in metabolic parameters in Zucker fa/fa rats.

The objectives of this study were to document the effects of moderate aerobic exercise on insulin secretion and other metabolic indices in fa/fa rats and to determine if a high-fat (HF) diet altered these effects. Six-week-old fa/fa and lean Zucker rats were either sedentary or exercised by daily swimming for 4 weeks. Half of the exercised and sedentary rats were fed a diet with 16% fat and 44% carbohydrate, while the control groups were fed a diet with 4.5% fat and 49% carbohydrate. At the end of 4 weeks, caloric intake, weight gain, plasma hormone and nutrient levels, and oral glucose tolerance were measured. The pancreatic islet beta-cell function was assessed by measuring glucose-stimulated insulin secretion, glucose phosphorylating activity, and free fatty acid (FFA) oxidation in cultured islets. In fa/fa rats fed the control diet, exercise reduced weight gain, caloric intake, and fasting plasma triglyceride (TG) concentrations without affecting fasting glucose and insulin concentrations. HF diet blocked the effects of exercise on weight gain and food intake and worsened insulin resistance of fa/fa rats. In vitro, neither exercise nor HF diet alone affected islet beta-cell function. However, in combination, exercise and high dietary fat reduced glucokinase sensitivity to glucose and increased islet cell response to mannoheptulose inhibitory actions. We conclude that beneficial effects of moderate exercise on metabolism are not mediated by effects on pancreatic beta cells. Diets elevated in fat decrease the beneficial effects of exercise on metabolic indices in vivo.