FIG 10.

The CHIKV nsP2 mutants are cleared from NIH 3T3 cells without cytopathic effect and persistently replicate in Mavs KO NIH 3T3 cells. NIH 3T3 and Mavs KO derivative cells were infected with the indicated viruses at an MOI of 20 PFU/cell. Media were replaced every 24 h, and cells were split upon reaching confluency. Viral titers were determined by plaque assay on BHK-21 cells, and the samples harvested from infected NIH 3T3 cells were used for assessment of IFN-β concentration (black bars) as described in Materials and Methods. The fluorescence images of Mavs KO NIH 3T3 cells were acquired at day 9 p.i. using a Nikon A1 fluorescence microscope with a 20× objective to demonstrate that they remained GFP positive and thus contained persistently replicating viruses.