ISG15 and viral infectious disease: Although not statistically significant, we did find that average ΔCT values were higher for ISGs including IFIT1, IFIT2, RSAD2 (the ISG that encodes the protein viperin), and ISG15 in cultures from patients with CRSwNP, suggesting lower basal levels and consistent with previous reports demonstrating lower levels of interferon and ISGs in cultures from patients with CRSwNP.23,34 However, we wanted to further investigate what happens to ISG levels relative to these respective mock values when the cultures were challenged with a viral infection.