Interferon-inducible antiviral protein which plays a major role in the cell antiviral state induced by type I and type II interferon. Catalyzes the conversion of cytidine triphosphate (CTP to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP via a SAM-dependent radical mechanism. In turn, ddhCTP acts as a chain terminator for the RNA-dependent RNA polymerases from multiple viruses and directly inhibits viral replication. Therefore, inhibits a wide range of DNA and RNA viruses, including human cytomegalovirus (HCMV, hepatitis C virus (HCV, west Nile virus (WNV, dengue virus, sindbis virus, influenza A virus, sendai virus, vesicular stomatitis virus (VSV, zika virus, and human immunodeficiency virus (HIV-1. Promotes also TLR7 and TLR9-dependent production of IFN-beta production in plasmacytoid dendritic cells (pDCs by facilitating 'Lys-63'-linked ubiquitination of IRAK1 by TRAF6. Plays a role in CD4+ T-cells activation and differentiation. Facilitates T-cell receptor (TCR-mediated GATA3 activation and optimal T-helper 2 (Th