Neutralizing activity against DENV2 of the serum from 2–8 week-old mice born to DENV1 immune mothers.

Serial dilution (2-fold) of the serum from 2, 3, 5 and 8 week-old mice born to DENV1 immune mothers were mixed with DENV2 prior to infection of BHK-21 cells. The number of plaques obtained was visually scored and compared to the number of plaques obtained with the virus alone (positive control). The plaque reduction neutralizing titer (PRNT50) was determined by nonlinear regression as the serum dilution factor for which 50% reduction in the number of plaques was obtained compared to the positive control.