Interferon-λ signaling to maternal dendritic cells protects against congenital Zika virus infection.

Interferon-λ (IFN-λ, type III IFN) mediates antiviral immunity at anatomic barriers, including the maternal-fetal interface. To investigate the effects of IFN-λ during congenital Zika virus (ZIKV) infection, we infected mice lacking the IFN-αβ receptor (Ifnar1-/-) or both the IFN-αβ and IFN-λ receptors (Ifnar1-/-Ifnlr1-/-) at embryonic day 9 and found that loss of maternal IFN-λ signaling resulted in greater transplacental transmission, highlighting a protective effect of IFN-λ at the maternal-fetal interface. To investigate the spatial relationship between ZIKV infection and antiviral responses, we used HiPlex RNAscope on the entire gravid uterus and found that IFN-λ was expressed more proximal to the site of ZIKV infection in Ifnar1-/- dams compared to Ifnar1-/-Ifnlr1-/- dams. We performed immunophenotyping of the placenta and uterus by flow cytometry and found a decrease in dendritic cells and natural killer (NK) cells in the uterus of Ifnar1-/-Ifnlr1-/- dams compared to Ifnar1-/- dams, but NK cell depletion did not affect fetal infection. Using conditional knockout mice, we identified maternal dendritic cells as the key IFN-λ-responsive cell type mediating protection against ZIKV congenital infection. Together, our data support a model in which IFN-λ signaling to maternal dendritic cells increases dendritic cell accumulation in the uterus, which facilitates a protective antiviral response that restricts ZIKV congenital infection.