Pregnancy alters innate immune responses to Zika virus infection in the genital tract

Recent outbreaks of Zika virus (ZIKV) have been associated with birth defects, including microcephaly and neurological impairment. However, the mechanisms which confer increased susceptibility to ZIKV during pregnancy remain unclear. We hypothesized that poor outcomes from ZIKV infection during pregnancy are due in part to pregnancy-induced alteration of innate immune cell frequencies and cytokine expression. To examine the impact of pregnancy on innate immune responses, we inoculated pregnant and non-pregnant female C57BL/6 mice with 5×10 5 FFU of ZIKV intravaginally. Innate immune cell frequencies and cytokine expression were measured by flow cytometry at day 3 post infection. Compared to non-pregnant mice, pregnant mice exhibited higher frequencies of uterine macrophages (CD68+) and tolerogenic dendritic cells (CD11c+ CD103+ and CD11c+ CD11b+). Additionally, ZIKV-infected pregnant mice had lower frequencies of CD45+ IL-12+ and CD11b+ IL-12+ cells in the uterus and spleen. These data show that pregnancy results in an altered innate immune response to ZIKV infection in the genital tract of mice and that pregnancy-associated immune modulation may play an important role in the severity of acute ZIKV infection. Importance Pregnant females longer duration that viremia following infection with Zika virus but the mechanism of this is not established. Innate immune cellular responses are important for controlling virus infection and are important for development and maintenance of pregnancy. Thus, the acute immune response to Zika virus during pregnancy may be altered so that the pregnancy can be maintained. To examine this interaction, we utilized a mouse model of Zika virus infection during pregnancy using intravaginal inoculation. We found that following Zika virus infection, pregnant mice exhibited increased expression of tolerant or non-inflammatory dendritic cells. Additionally, we found that pregnant mice have significantly depressed ability to secrete the cytokine IL-12 from innate immune cells in the uterus and the spleen while maintaining MHCII expression. These findings show that pregnancy-induced changes in the innate immune cells are biased towards tolerance and can result in decreased antigen-dependent stimulation of immune responses.