ISG15 and infection: As expected, expression of genes involved in the TLR-mediated IFN-I response to infection, including interferon stimulated gene 15 (ISG15), which is upregulated in response to IFN-I and TLR-signaling (reviewed in refs. 48,49), LY96, and interferon-inducible protein-6 (IFI6) (PU.1-IRF regulated genes) and IFITM3 were very low in uninfected, unexposed cells (Fig. 3C).