Nine ISGs mRNA levels were analyzed by qRT-PCR after PPRV infection, including GBP2, ISG15, ISG20, IFIT1, IFIT5, MX1, OASL, RASD2, and TRIM25. The results showed that mRNA levels of ISG15 and RSAD2 were significantly upregulated over time, with a maximum of about 100-fold and 1,000-fold, respectively (Figures 4A, B). Here, ISG15 is linked to infection.