title: In vivo virulence of viral haemorrhagic septicaemia virus (VHSV) in rainbow trout Oncorhynchus mykiss correlates inversely with in vitro Mx gene expression.
abstract: The in vitro replication of viral haemorrhagic septicaemia virus (VHSV) isolates from each VHSV genotype and the associated cellular host Mx gene expression were analysed. All the isolates were able to infect RTG-2 cells and induce increased Mx gene expression (generic assay detecting isoforms 1 and 3 [Mx1/3]). A trout pathogenic, genotype Ia isolate (J167), showing high replication in RTG-2 cells (by infective titre and N gene expression) induced lower Mx1/3 gene expression than observed in VHSV isolates known to be non-pathogenic to rainbow trout: 96-43/8, 96-43/10 (Ib); 1p49, 1p53 (II); and MI03 (IVb). Paired co-inoculation assays were analysed using equal number of plaque forming units per ml (PFU) of J167 (Ia genotype) with other less pathogenic VHSV genotypes. In these co-inoculations, the Mx1/3 gene expression was significantly lower than for the non-pathogenic isolate alone. Of the three rainbow trout Mx isoforms, J167 did not induce Mx1 up-regulation in RTG-2 or RTgill-W1 cells. Co-inoculating isolates resulted in greater inhibition of Mx in both rainbow trout cell lines studied. Up-regulation of sea bream Mx in SAF-1 cells induced by 96-43/8 was also lower in co-inoculation assays with J167. The RTG-P1 cell line, expressing luciferase under the control of the interferon-induced Mx rainbow trout gene promoter, showed low luciferase activity when inoculated with pathogenic strains: J167, DK-5131 (Ic), NO-A-163/68 (Id), TR-206239-1, TR-22207111 (Ie), 99-292 (IVa), and CA-NB00-01 (IVc). Co-inoculation assays showed a J167-dose dependent inhibition of the luciferase activity. The data suggest that virulent VHSV isolates may interfere in the interferon pathways, potentially determining higher pathogenicity.
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe Weymouth, Dorset DT4 8UB, United Kingdom. Electronic address: irene.canocejas@cefas.co.uk.
authors.forename: Irene
authors.initials: I
authors.lastname: Cano
authors.affiliation: Marine Scotland, Marine Laboratory, 375 Victoria Road, Aberdeen AB11 9DB, United Kingdom.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Collet
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Clarissa
authors.initials: C
authors.lastname: Pereira
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Paley
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Ronny van
authors.initials: RV
authors.lastname: Aerle
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Stone
authors.affiliation: Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe Weymouth, Dorset DT4 8UB, United Kingdom.
authors.forename: Nick G H
authors.initials: NGH
authors.lastname: Taylor
mesh_terms: D000818:Animals; D002460:Cell Line; D005393:Fish Diseases / Q000503:physiopathology*; D005786:Gene Expression Regulation; D005838:Genotype; D031941:Hemorrhagic Septicemia, Viral / Q000503:physiopathology*; D064547:Myxovirus Resistance Proteins / Q000235:genetics*; D029141:Novirhabdovirus / Q000235:genetics / Q000472:pathogenicity*; D009698:Nucleoproteins / Q000235:genetics; D017686:Oncorhynchus mykiss / Q000235:genetics* / Q000821:virology*; D014774:Virulence; D014779:Virus Replication / Q000235:genetics
chemical_list: D064547:Myxovirus Resistance Proteins; D009698:Nucleoproteins
keywords: Inhibition; Luciferase; Mx; Pathogenicity; RTG-P1; Viral fitness; Viral haemorrhagic septicaemia virus