Fig. 4. The minimal neutralizing antibody titers (NT₅₀) required for protection of pregnant mice.

a Experimental scheme for passive antibody transfer and efficacy test. Ten- to twelve-week-old A129 female mice (n = 28) were passively transferred with various amounts of neutralizing antibodies at E9.5. The NT₅₀ titers in recipient mice were determined at E10.5. The pregnant mice were then subcutaneously challenged with 10⁶ PFU ZIKV PRVABC59 at E10.5 and measured for viremia at E12.5. The maternal and fetal tissues/organs were harvested at E18.5 and measured for viral loads. b Correlation analysis between NT₅₀ titers at E10.5 and viremia at E12.5. c Plot of viremia levels versus different groups of NT₅₀ titers from (b). Correlation analyses between organ viral loads (detected at E18.5) and NT₅₀ titers (measured at E10.5) are presented for maternal brain (d, e), spleen (f, g), and placenta (h, i). The dotted lines indicate the minimal NT₅₀ titers required for protection of tissues/organs against viral infection. j Correlation analysis between fetal body weight (detected at E18.5) and NT₅₀ titers (measured at E10.5). P and R² values reflect significance and the correlation coefficient. Mann-Whitney test was performed to indicate significant differences (c, e, g, i, j). *p < 0.5, **p < 0.01, ***p < 0.001, ****p < 0.0001, non-significant (n.s.) p > 0.5. Error bars represent standard deviations. Source data are provided as a Source Data file.