Lineage-dependent differences and the role of IFITM3 in the type-I interferon-induced restriction of Zika virus

Abstract

28 Type-I interferon (IFN-I) is an important aspect of host innate antiviral response. Recent studies 29 have shown that IFN-I can inhibit Zika virus (ZIKV) replication and that this is mediated in part 30 by Interferon-induced transmembrane protein 3 (IFITM3). ZIKV infections in South America 31 have led to severe congenital syndrome in a subset of infected infants. ZIKV was first identified 32 in Africa, where there is limited evidence for the pathogenic effects associated with the 33 American outbreak, which is fueled by infection with Asian-lineage strains, raising the 34 possibility that the African and Asian ZIKV lineages have distinct pathogenic properties. Given 35 the observation that IFN-I can inhibit ZIKV replication in cell culture, we asked whether ZIKV 36 strains differed in their susceptibility to IFN-I. There was a range of susceptibilities to IFN-I 37 inhibition across virus strains. Virus production in A549 cells was reduced from 3-42-fold for 38 IFNα and 63-807-fold for IFNβ across a panel of nine viruses, five from the African-lineage and 39 four from the Asian-lineage. African-lineage ZIKV strains were more resistant to IFN-I than 40 Asian-lineage strains, but this difference was only significant for IFNα-mediated restriction (p = 41 0.049). Notably, over-expression of IFITM3 at similar levels induced by IFN-I did not 42 significantly restrict either a prototype African lineage (MR 766) or Asian lineage (PRVABC59) 43 isolate. Moreover, knocking out IFITM3 expression did not result in a significant increase in 44 viral replication or a diminishment of the inhibition by IFN-I. Overall, our findings show that 45 while diverse ZIKV strains are susceptible to the antiviral effects of IFN-I, African-lineage 46 strains are more resistant to IFNα. In addition, the majority of the IFN-I-induced inhibition of 47 ZIKV strains cannot be explained by IFITM3, suggesting that other unknown ISGs may be the 48 driving force of the type I IFN response against ZIKV. 3 49 Author summary 50 The innate immune system, and specifically the type-I interferon response, is a critical 51 component of the host response against viral infections. The recent unprecedented spread and 52 severe pathogenic features of Zika virus in the Americas have led to significant interest in 53 characterizing features of Zika virus strains that have fueled the American outbreak. Zika virus 54 was first identified in Africa, where there is limited evidence for the pathogenic effects 55 associated with the American outbreak. Here, we demonstrate that African-lineage Zika virus 56 strains are significantly more resistant to the effects of type-I interferon, and that type-I 57 interferon-mediated restriction of Zika virus strains is not explained by the host factor Interferon-58 induced transmembrane protein 3. This improved understanding of Zika virus-host interactions 59 may explain certain pathogenic features of Asian-lineage Zika virus strains that have fueled the 60 American Zika virus epidemic, and supports the search for as-yet-unident...