Fig. 2

The effect of DENV2-immune sera on ZIKV infection in vitro and in Ifnar1 ^−/− mice. Ifnar1 ^−/− mice were immunized intraperitoneally with DENV2 (2 × 10² FFU) for 28 days. Naive Ifnar1 ^−/− mouse sera (n = 10) and DENV2-immune Ifnar1 ^−/− mouse sera (n = 10) were examined for their ability to neutralize DENV2 or ZIKV using U937 DC-SIGN cells and a flow cytometry-based neutralization assay (a). Data were pooled from two independent experiments with n = 5 mouse sera per group and expressed as mean ± SEM. Different volumes of naive and DENV2-immune Ifnar1 ^−/− mouse sera were passively transferred (retro-orbital route) to naive recipient Ifnar1 ^−/− mice (b, c). Three days post retro-orbital challenge with 1 × 10⁴ FFU of ZIKV FSS13025, viral burdens in sera and indicated organs were measured using FFA. In b, data are pooled from two independent experiments (n = 3–4 mice per group per experiment), while results in c represent one experiment. Data are expressed as mean ± SEM. **p < 0.01. b A Kruskal–Wallis one-way ANOVA. c Two-tailed Mann–Whitney test. Supplementary Tables 1 and 2 provide exact values of n and p