We next investigated whether STING cleavage by DENV NS2B3 had an impact on its ability to mediate the signaling necessary for type I IFN production. We transfected 293T cells with either hSTING (Figures 2A and 2B ) or mSTING (Figures 2C and 2D) and the three different versions of the DENV protease: wild type, the proteolytically inactive version (NS2B3-S135A) and the proteolytic core (NS2Bh-NS3pro) alongside luciferase reporter constructs driven by either an IFNb promoter (IFNb-Luc) or by three IRF3/7 binding sites (p55-C1B-Luc) (kindly provided by Dr. Megan Shaw and shown in figure 2E schematically) [34] . As shown in figures 2A and 2B, cleavage of hSTING by the DENV NS2B3-WT and NS2Bh-NS3pro greatly inhibited its ability to activate both reporter constructs, while transfection of the mutant version of the protease did not. Conversely, the DENV NS2B3 had minimal or no impact on the ability of mSTING to induce activation of either of the reporter constructs used. We did not observe any DENV NS2B3-dependent inhibition when the human adaptor TBK1 was used as a positive control to induce the IFNb promoter, demonstrating that the inhibition during dengue infection occurs upstream of this adaptor (data not shown). Taking together, these data demonstrate that cleavage of hSTING by the DENV NS2B3 precludes the induction of type I IFN responses. Moreover, to validate the observed results in human primary cells, we used E. coli DNA, a known inducer of STING signaling [35] to treat human MDDCs previously infected with DENV, UV-inactivated DENV or mock treated (as shown schematically in figure 2F ). Figures 2G, 2H and 2I show that only live DENV but not UV inactivated DENV was able to inhibit the induction of IFNb, IFNa or ISG15 by this ligand in human MDDCs.