ISG15 and infection: As shown in Figure 2C, both MVA recombinants expressing the wild-type (ISG15GG) or the mutated (ISG15AA) ISG15 forms induced the secretion of IFN-I in infected macrophages at 6 and 16 hpi compared with the parental MVA-Δ3-GFP, with the highest levels detected after MVA-Δ3-ISG15AA infection (Figure 2C, right panel).