CPT-Tert cells were pre-treated with IFNT or UIFN for 20 h prior to infection with BTV-1 or BTV-8 (or mock infection) with MOIs ranging from 0.001 to 0.1. Both wt and the DNS4 mutants, destroyed 80 to 100% (depending on the MOI used) of the monolayer of infected cells in absence of IFN treatment ( Figure 6 ). On the other hand, pre-treatment with both types of IFN significantly reduced BTV-induced CPE. Interestingly, in the presence of IFN, BTV-8 wt consistently induced a more pronounced CPE than BTV8-DNS4. Conversely, only minor differences were observed in the CPE induced by both wt BTV-1 and BTV-1DNS4 in the presence of IFN ( Figure 6 ).