ISG15 and infection: Results showed that MX1, MX2 and OAS1 were over-expressed in SARS-CoV-2-infected A549 cells (p < 0.01 for MX1, ISG15, and OAS1; and p < 0.05 for MX2), and Calu-3 cells (p < 0.05 for MX1, ISG15, and OAS1; and p < 0.01 for MX2) compared with mock infection (Figure 5B).