Development of an in vitro system to measure the sensitivity to the antiviral Mx protein of fish viruses

Mx is a structural protein, induced by type I interferon (IFN), with direct antiviral properties. In fish the inherent contribution of Mx protein to viral protection is unknown. The transgenic Chinook salmon embryonic (CHSE)-TOF cell line was genetically modified to express the rainbow trout Mx (rbtMx1) protein under the control of the tetracycline derivative, doxycycline (DOX). Two clones CHSE-TOF-MX8 and CHSE-TOF-MX10 were isolated and characterised by qPCR. The level of resistance to Infectious Pancreatic Necrosis Virus (IPNV), Salmon Alphavirus (SAV), Infectious Haematopoietic Necrosis Virus (IHNV) and Epizootic Haematopoietic Necrosis Virus (EHNV) of the CHSE-TOF, CHSE-TOF-MX8 and CHSE-TOF-MX10 cell lines cultivated with and without DOX was measured. A novel method was established to measure accurately the level of sensitivity of any given viral isolate to Mx protein. IPNV and SAV viruses were highly sensitive to the presence of rbtMx1 in the cells whereas IHNV and EHNV showed partial resistance suggesting contrasting viral evasion strategies between these categories of viruses.

► Generation of CHSE-TOF-MX8/10 cell lines expressing Mx under the Tet-Off regulation.
► High Mx sensitivity of IPNV and SAV, low Mx sensitivity of IHNV and EHNV.
► Higher Mx sensitivity of SAV isolate 4640 compared to SAV isolate F93-125.