Figure 3. ZIKV I39V mutation increases placental transmission in DENV2-immune Ifnar1^−/− mice and infectivity in human fetal neural progenitor cells.

DENV2-immune Ifnar1^−/− mice were generated by intraperitoneal injection of 10³ FFU DENV2 S221 for 30 days, and DENV-immune dams were then mated with BALB/c sires. On embryonic day 7.5 (E7.5), pregnant mice were injected intra-footpad with 10⁴ FFU of recombinant wild-type ZIKV (rZIKV-WT) or rZIKV-NS2B-I39V. On E14.5, the mice were euthanized, and fetuses and maternal tissues were harvested for analysis.

(A and B) Body weights (A) and body length (B) of fetuses on E14.5. Blue and red symbols represent viable and resorbed fetuses, respectively.

(C) Representative placenta and fetuses from dams in each mouse group. Blue and red arrows indicate viable and resorbed fetuses, respectively.

(D) RT-qPCR analysis of ZIKV RNA levels in maternal serum, brain, spleen, and placenta/decidua on E14.5. Data are presented as the mean ± SEM and were pooled from independent experiments with a total of 28 fetuses from four mothers for the rZIKV-WT group and 40 fetuses from six mothers for the rZIKV-NS2B-I39V group.

(E) Kinetics of rZIKV-WT and rZIKV-NS2B-I39V replication in human fetal NPCs. Human fetal NPCs were infected with the indicated viruses at an MOI of 1. RT-qPCR and FFA were performed on days 1 and 3 post-infection (1 dpi and 3 dpi) to measure levels of ZIKV RNA and infectious virus in culture supernatants, respectively. Data are presented as the mean ± SEM of triplicates and represent pooled results from three independent experiments with cells derived from three donors. *p < 0.05, **p < 0.01, ****p < 0.0001 by the two-tailed Mann–Whitney test.