Figure 4

Removal of protection against DEN-2 by filtrate treatment with proteinase K. Bar Mock = Mock-treated, naïve cells exposed to DEN-2 stock; Bar Filtrate = Cells pre-exposed for 48 h to the 5 kDa filtrate from cultures persistently infected with DEN-2 (passage 16) and showing more than 2 logs decrease in DEN-2 titer; Bar Pro-K = Cells pre-exposed for 48 h with proteinase-K-treated 5 kDA filtrate and showing a major recovery in DEN-2 titer. Bars indicate mean titers ± SD for 3 replicates and those labeled with different letters are significantly different (p < 0.05) while those with the same letter are not (p > 0.05).