Neutralizing properties of sera from DENV1-immune mothers and their offspring.

Serially diluted (2-fold) heat-inactivated sera from DENV1-immune mothers (6 weeks p.i.), age-matched naïve mothers and 5–6 weeks old mice born to their respective mothers were mixed with either DENV1 or DENV2 prior to infection of BHK cells. The PRNT50 value was determined by nonlinear regression of the serum dilution factor that results in 50% reduction in the number of plaques as compared to the positive control (virus alone). Samples with PRNT50 values less than 1:10 were arbitrarily assigned a value of 5. Sera from DENV1-immune and naïve mothers were pooled whereas sera from mice born to their respective mothers were tested individually (n = 5) and are expressed as average ± SEM.