Zika virus (ZIKV) is spread by Aedes mosquitoe bites, and it can also be sexually and vertically transmitted. ZIKV has raised awareness after its association with congenital microcephaly and Guillain-Barré syndrome. Currently, there is no effective vaccine or specific treatment against ZIKV infection. Therefore, a better understanding of the virus-host interaction is needed to develop antiviral strategies. Innate host defense against viruses include type I interferons (IFN I). Recent studies on other flaviviruses have shown that non-structural proteins have manners to
hinder this response. In the present work, we analyzed whether one non-structural protein of ZIKV, NS4b, is able to inhibit IFN I response. For this purpose, we conducted transfection assays using RAW-Lucia ISG cells, an IFN reporter cell-line that secrete Lucia luciferase under ISRE promoter. Results showed that cells transfected with plasmid encoding NS4b were able to inhibit luciferase signals in a dose dependent manner compared to empty vector (two-way ANOVA, p<0.05). This inhibition was also significant after treatment with TLR ligand, LPS, and STING agonist, c-diAMP (two-way ANOVA+ Tukey´s, p<0.05). Furthermore, a fragment of NS4b (residues25-127) was successfully cloned in the pET21a vector and produced as inclusion bodies in E. coli BL21(DE3) cells. The recombinant protein was used to obtain specific antisera that could recognize NS4b in transfected cells. Immunofluorescent assay showed that NS4b can be involved in disrupting TBK1 /IRF3 cascade. Although further analysis should be carried out to elucidate how ZIKV NS4b is able to inhibit IFN I production, this results add evidence that flaviviruses are able to escape early host innate response. Because of this and the role of NS4b in assembling the replication complex, it may be a promising target for antiviral drug development.