CHIKV nsP2 mutants, but not the parental CHIKV 181/25, are potent inducers of IFN-β in both murine and human cell lines. NIH 3T3 (A), MRC-5 (B), and HFF-1 (C) cells were infected at an MOI of 20 PFU/cell with nsP2 mutants and parental CHIKV 181/25. At 18 h PI, the supernatants were harvested to determine viral titers and the levels of IFN-β. n.d. indicates that the concentration of IFN-β was below the limit of detection. Similar experiments were made multiple times with consistent results. The results of one of the representative experiments are presented.