Fig. 4.

mda-5 stimulates the production of endogenous IFN, and this activity can be blocked by coexpression of the SV5 V protein. (a and b): 293 cells were transfected with control “empty vector” (5 μg), mda-5 (1.25 μg and “empty vector” 3.75 μg), or mda-5 (1.25 μg) and SV5-V (3.75 μg) expression vectors. After 24 h, cells were either mock-treated or treated with dsRNA for a further 18 h. The amount of IFN present in the culture media was estimated by either a virus reduction assay (a) or an IFN-stimulated regulatory element reporter assay (b, as described in ref. 6) in Vero cells. (c) As a above, but increasing amounts (1.25–5 μg) of the mda-5 expression vector were transfected with 3.75 μg of the SV5 V plasmid.