A Possible Role Of Microglia In Zika Virus Infection Of The Fetal Human Brain

Maternal Zika virus (ZIKV) infection during pregnancy is increasingly recognized as the cause of an epidemic of microcephaly and other neurological anomalies in human fetuses. However, it remains unclear how ZIKV gains access to the highly vulnerable population of neural progenitors of the fetal central nervous system (CNS), and which cell types of the CNS may serve as viral reservoirs. To model viral interaction with cells of the fetal CNS in vitro, we investigated the tropism of ZIKV for different iPS-derived human cells, with a particular focus on microglia-like cells derived from human pluripotent stem cells. We show that ZIKV infected isogenic neural progenitors, astrocytes and microglia-like cells, but was only cytotoxic to neural progenitors. Infected glial cells propagated the virus and maintained viral load over time, leading to viral spread to susceptible cells. ZIKV-infected microglia, when co-cultured with pre-established neural spheroids, invaded the tissue and initiated neural infection. Since microglia derive from primitive macrophages originating in anatomical proximity to the maternal vasculature of the placenta, we propose that they may act in vivo as a viral reservoir for ZIKV and, owing to their natural ability to traverse the embryo, can establish infection of the fetal brain. Infection of immature neural stem cells by invading microglia may occur in the early stages of pregnancy, before vascular circulation is established. Our data are also consistent with the virus affecting the integrity of the blood-brain barrier (BBB), which may allow infection of the brain at later stages.