Detection of monovalent immune serum neutralizing antibody against DENV. Balb/c mice were immunized with 25 μg monovalent DENV VLP or virions a total of three times at a two week interval. On day 7 after the 3rd immunization, neutralizing antibodies against DENV1 (A), DENV2 (B), DENV3 (C), and DENV4 (D) were assessed using a 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 titers for each immune sera after immunization with each monovalent vaccine against the corresponding virus were 1:32, 1:64, 1:32, and 1:32, respectively. *indicates statistical significance (*P < 0.05; **P < 0.01).