CAT and viral infectious disease: To test whether I64T mutation diminishes the NS1 protein's ability to counteract host innate immune responses in the context of virus infection, MDCK cells constitutively expressing GFP and Fluc reporter genes under the control of the IFN-β promoter (MDCK IFN-β GFP-CAT/IFN-β Fluc) (30) were mock infected or infected (MOI, 4) with either r85 or r87 virus (Fig. 8A).