Figure 1. Mice born to ZIKV-immune mothers have increased dengue disease severity and DENV burden.

Four- to 5-week-old LysMCre⁺Ifnar1^fl/fl mice born to mothers previously infected with ZIKV strain SD001 (10⁶ FFU via retro-orbital route) or to naïve mothers were challenged with DENV2 strain S221 (10⁶ FFU via tail vein). (A) Clinical scores of infected mice (n=11) from naïve mothers (n=2). (B) Clinical scores of infected mice (n=15) from ZIKV-immune mothers infected for 8-12 months (n=3). (C-D) Weight loss and survival data of infected mice from naïve (open squares) versus ZIKV-immune mothers infected for 8-12 months (black circles). (E) Clinical scores of infected mice (n=8) from naïve mothers (n=2) (F) Clinical scores of infected mice (n=8) from ZIKV-immune mothers infected for 2 months (n=2). (G-H) Weight loss and survival data of infected mice from naïve (open squares) versus ZIKV-immune mothers infected for 2 months (grey circles). To determine DENV viral burden, mice were euthanized at 3 days p.i. and serum, spleens, and livers were harvested. (I) The levels of DENV RNA from each tissue were measured via qRT-PCR. Viral RNA levels in the serum, spleen, and liver of DENV2-infected pups (open squares, n=11) from naïve mothers (n=2) were compared to pups (black circles, n=13) from ZIKV-immune mothers infected for 6-13 months (n=4). (J) The levels of infectious DENV2 were measured via focus forming assay in the serum, spleen, and liver of DENV2-infected pups (open squares, n=7) from naïve mothers (n=2) and pups (grey circles, n=7) from ZIKV-immune mothers infected for 2 months (n=2). Data were pooled from two independent experiments and are expressed as mean ± standard error of mean (C and G). Unpaired Student’s t test of groups for each day. (D and H) log-rank test (*** P ≤ 0.001, ** P < 0.01). (I and J) Data were pooled from 2 independent experiments. Mann-Whitney test (*** P< 0.001, ** P < 0.01).