FIG. 8.

Soluble factors in MEF culture supernatants do not interfere with VSV-GFP challenge of Vero cells. (a to e) VSV-GFP-induced CPE. Images of mock (a) and VSV-GFP-infected cells (b to e) were acquired by using a light microscope. Cultures were treated as follows: a and b, untreated cultures of Vero cells; c, Vero cells pretreated with IFN-α 2a (500 U/ml); d and e, cultures pretreated with clarified supernatants (1 ml) recovered at 96 h postinfection from WNV-NY-infected or mock-infected wt MEFs, respectively. Vero cells were pretreated for 24 h and then infected with VSV-GFP at an MOI of 0.1 in panels b to e. At 16 h postinfection the supernatants were removed, and VSV-GFP titers were assessed by plaque formation assays. (f) The relative infectivity of viral particles produced under each condition was derived by dividing the number of PFU/milliliter in supernatants from each sample by the number of PFU/milliliter in supernatants from untreated control cultures. For comparison, the relative infectivity of the nontreated control culture was set at 1.0.