An Investigation into the Microglial Response to Neonatal ZIKV Infection

Zika Virus (ZIKV), unlike other Flaviviruses , has an apparent selective tropism for developing neural stem cells. As a result, the fetal brain is acutely more vulnerable to ZIKV infection than the adult brain. ZIKV can cross the placental barrier to directly enter the fetal brain. In the fetal brain, ZIKV appears to specifically target developing radial glia. In embryonic mice, ZIKV infection of neural progenitor cells (NPCs) arrests the cell cycle and hinders apoptotic cell death by 24 hours post‐infection. However, by 3 days post‐infection, ZIKV induces apoptosis in NPCs and stimulates pro‐inflammatory cytokine expression from microglial cells – the resident immune cells of the brain. It is unclear whether neural progenitor cells are the only cells targeted by ZIKV. It is also unclear what role microglia have in the mitigation or exacerbation of cell death associated with ZIKV infection. We hypothesized that ZIKV infection of NPCs would induce microglia to express high levels of pro‐inflammatory cytokines (IL‐1β and IL‐6), either mitigating or contributing to the resultant cell death of developing neural cells. To test this hypothesis using a rat model, we collected hippocampal and cortical tissue from P2 Sprague Dawley rat pups and either (A) fixed the cells for ICC to study which specific cell types are primarily targeted by ZIKV or (B) collected the cells for qPCR to measure cytokine expression and determine the impact of ZIKV on neonatal microglial activation. We infected these freshly isolated neural cells with ZIKV at 0, 0.1, 1, and 10 MOI for 4, 8, or 16 hours. The fixed cells were immunofluorescently stained for analysis of cell type specific ZIKV infection and apoptosis. A separate set of similarly‐treated cell cultures were collected for qPCR analysis of pro‐inflammatory cytokine expression, markers of microglial activation, and production of anti‐viral proteins. This experimental design is unique in its use of a rat animal model as well as its use of a primary cell culture model over a complex in‐vivo model. These infection studies will allow us to better characterize Zika virus‐host interactions in the developing brain, including how the developing neural immune system responds to this emergent virus. In our preliminary results we found that after cells were treated with the virus for 2 hours and allowed to rest for 2 hours the immune activation response significantly differed in IL‐6 and IFN‐b expression. Cells infected at 10 MOI showed a significant increase in IL‐6 whereas cells infected at 0.1 MOI and 1 MOI showed a significant increase in IFN‐ β. However, in the following experiment we found that at 4 hours post‐infection there was significantly more CD11b expressed at 0.1 MOI ZIKV. At 8 hours post‐infection there was significantly more IFN‐β 0.1 MOI as well as significantly more Mx1 expressed at both 0.1 and 1 MOI. Our preliminary ICC data indicates that ZIKV replication can be detected in rat neural cells following a 16‐hour incubation at 1 MOI, an unprecedented result in a rat animal model. Still, the infected cell type remains to be determined. Support or Funding Information There is no current funding for this project This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .