FIG. 4.

The ISP acts via the induction of IFN-α/β. MEF and primary murine spleen cells were plated in 96-well tissue culture dishes and treated with 0.5 μg of ISP/ml in the presence or absence of either polyclonal antibodies specific for all murine IFN-α/β (diluted 1:16), anti-murine IFN-β (150 μg/ml), or anti-murine IFN-γ (150 μg/ml) for 24 h. (A) MEF were washed and treated directly with VSV. (B) The conditioned media from the spleen cells were transferred to MKF for 24 h prior to the addition of VSV. Cells were monitored for cytopathic effect and stained with crystal violet ∼18 h after infection. Each bar represents the mean of triplicate wells ± the standard deviation.