ISG15 and infection: In the mel Mtp cell line, despite a strong induction of IFN-β expression at 24 h post infection, only a small subset of ISGs was overexpressed during the first 24 h post infection correlated with a corresponding peak in IFN-β expression level, such as OAS1, ISG15, ISG6-16 (G1P3), ISG12 and STAT1 (Table 2), while at 96 h post infection, a substantial induction of XAF1 (7.8K-fold) and TNFSF10 genes (TRAIL, 62-fold), two known pro-apoptotic ISGs, was identified (Table 2).