Toscana virus (TOSV) is a phlebotomus-transmitted virus that belongs to the family and causes widespread infections in humans; about 30 % of these cases result in aseptic meninigitis. In the present study, it was shown that TOSV is an inducer of beta interferon (IFN-), although its non-structural protein (NSs) could inhibit the induction of IFN- if expressed in a heterologous context. A recombinant Rift Valley fever virus expressing the TOSV NSs could suppress IFN- expression in infected cells. Moreover, in cells expressing NSs protein from a cDNA plasmid, IFN- transcripts were not inducible by poly(I : C). Unlike other members of the family , TOSV appears to express an NSs protein that is a weak antagonist of IFN induction. Characterization of the interaction of TOSV with the IFN system will help our understanding of virus–host cell interactions and may explain why the pathogenesis of this disease is mostly mild in humans.


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