Induction of Mx protein by interferon and double-stranded RNA in salmonid cells

Mr protein is one of several antiviral proteins that are induced by the typ e I interferons (IFN), IFN alpha and beta, in mammals. In this work inducti on of a 76 kDa Mr protein by double-stranded RNA (dsRNA) or type I IFN-like activity in Atlantic salmon macrophages, Atlantic salmon fibroblast cells (AS cells) and in Chinook salmon embryo cells (CHSE-214) is reported. Type I IFN-like activity was produced by the stimulation of Atlantic salmon macr ophages with the synthetic dsRNA polyinosinic polycytidylic acid (poly I:C) . A correlation appeared to exist between Mr protein expression and protect ion against infectious pancreatic necrosis virus (IPNV) induced by IFN in C HSE-214 cells. Several observations in the present work suggest that, as in mammals, the induction of Mr protein by dsRNA in fish cells primarily occu rs via induction of type I IFN. First, type I IFN-like activity but not pol y I:C, induced Mx protein expression in CHSE-214 cells. These cells apparen tly lack the ability to produce IFN in response to poly I:C. Second, the pu tative IFN induced maximal Mr protein expression 48 h earlier than poly I:C in AS cells. Third, the peak expression of Mr protein in macrophages induc ed by poly I:C occurred after 48 h whereas peak in IFN-like activity was ob served by 24 h after addition of poly I:C. The present work supports the no tion of using Mr protein as a molecular marker for the production of putati ve type I IFN in fish. (C) 2000 Academic Press.