Zika virus productively infects primary human placenta-specific macrophages

Abstract

The strong association of Zika virus infection with congenital defects has led to questions of how a flavivirus is capable of crossing the placental barrier to reach the fetal brain. Here, we demonstrate permissive Zika virus infection of primary human placental macrophages, commonly referred to as Hofbauer cells, and placental villous fibroblasts. We also demonstrate Zika virus infection of Hofbauer cells within the context of the tissue ex vivo using term placental villous explants. In addition to amplifying infectious virus within a usually inaccessible area, the putative migratory activities of Hofbauer cells may aid in dissemination of Zika virus to the fetal brain. Understanding the susceptibility of placenta-specific cell types will aid future work around and understanding of Zika virus-associated pregnancy complications.

Figure 1. Primary human placental-specific macrophages and fibroblasts are permissive to ZIKV infection.

(A) The indicated primary placental cells and Vero cell line were infected with ZIKV^CAM, ZIKV^MEX, and ZIKV^MR766 for 48 hours (MOI of 1), fixed, and stained with mouse monoclonal anti-ZIKV E (4G2). Data are shown as the percentage of positive ZIKV E cells relative to the total number of nuclei (as determined by DAPI) of an average of 3 biological replicates (± SD) from 3 separate placenta preparations. (B) Representative immunofluorescence images of ZIKV-infected Hofbauer cells at ×20 magnification. Infected cells were costained with anti-ZIKV E and anti-CD163 (host rabbit). (C) Viral growth kinetics of the indicated cells that were infected with an MOI of 1. Two hours after infection, cells were washed twice in PBS and fresh medium was applied. Quantitative PCR analysis was performed 2, 24, 48, and 72 hours after infection. Data are presented as the log relative expression of ZIKV RNA over GAPDH (average ± SD, n = 3). (D) Collected supernatants at 48 hours from C were assessed for the presence of infectious virus via plaque assays. Data are presented as log PFU/ml of supernatant (average ± SD, n = 3).

Figure 2. Primary human placental-specific macrophages are infected within the context of placental tissue.

Villous tissue explants (60 mg) were infected with ZIKV within 2 hours of delivery, formalin fixed after 48 hours, and paraffin embedded. Sections were fluorescently labeled with mouse monoclonal J2 to detect viral dsRNA or NS1 to detect viral nonstructural protein and anti-CD163 macrophage cell marker. White arrows indicate infected HBCs.