Detection of tetravalent immune serum neutralizing antibody against DENV. Balb/c mice were immunized with 100 μg tetravalent DENV-VLP (total of 25 μg for each DENV-VLP serotype) a total of three times at a two week interval. Neutralizing antibodies against DENV1-4 were assessed seven days after the 3rd immunization, using the PRNT50 assay. 150-200PFU DENV were incubated with serially diluted mouse antisera in 24-well plates, using BHK-21 cell lines. Data from each group is expressed as the mean percentage of plaque reduction with an SD bar (n = 3). The PRNT50 titer of the tetravalent immune sera against the four DENV serotypes were 1:32, 1:32, 1:16, and 1:16, respectively. (A) the PRNT50 titer of tetravalent immune serum; (B) the plaque morphology.