study, we aim to adapt the Luc-DENV for anti-DNEV neutralizing selleck inhibitor and enhancing antibodies evaluation. This newly developed reporter virus-based assay is validated using various known monoclonal antibodies (mAbs) and clinical samples from infected animal and patients, demonstrating well correlation with the traditional plaque-based assays. Results Development of check details Luc-based neutralizing assay The Luc-DENV was developed by engineering the Renilla luciferase gene into the capsid-coding region by reverse genetic technology . We have shown that Luc-DENV replicates efficiently in both mammalian and mosquito cells with high stability. As shown in Additional file 1: Figure S1 and Additional file 2: Figure S2, increasing amounts of luciferase signal were observed from 24 to 96 h post-infection in Luc-DENV infected BHK-21 and K562 cells. To adapt Luc-DENV for neutralizing assay, we firstly assayed three identified neutralizing mAbs 4G2 , 2B8  and 2A10G6  by using plaque-based and Luc-based assay, respectively. Standard PRNT was performed in 12-well plates using 10-fold selleck dilution of each mAb. The results showed that all three mAbs significantly reduced the numbers of plaques in a dose-dependent manner (Figure 1,ABC, right ordinate). The PRNT50 of 4G2, 2B8 and 2A10G6 was 8.55, 0.45 and 0.35 μg/mL, respectively. The RLU based assay was performed in the 12-well plate using the same dilutions
of each mAb. The results demonstrated that all three mAbs significantly decreased RLU in a dose-dependent manner (Figure 1, ABC, left ordinate). LRNT50 of three mAbs calculated from a fitting curve were 6.80, 0.86 and 0.26 μg/mL, respectively, which was of the same order of magnitude with PRNT50. An unrelated mAb against EV71 showed no neutralization for both plaque and Luc-based assay (data not shown). Data fitting was made between values above. As expected, a linear correlation (R2 > 0.95) was demonstrated between PFU and RLU assay,
and the linear equation between RLU and PFU is calculated as RLU = 86.74 PFU + 2256 (Figure 1D). Our results supported the application of Luc-based assay for neutralization antibodies against DENV. Figure 1 Comparison of the new and conventional antibody neutralization assay system. Neutralization activities mediated by various concentrations of mAbs (A: Oxymatrine 4G2, B: 2B8, C: 2A10G6) specific for E protein of DENV in BHK-21 cells were performed with the new (square) and conventional (round) antibody neutralization assay system. Error bars indicate the standard deviations from two independent experiments. (D) Linear correlation between RLU and PFU values for neutralization assay. Development of Luc-based ADE assay To develop the Luc-DENV for ADE assay, K562 cells were infected with Luc-DENV in the presence of serial 10-fold dilutions of 2A10G6. The viral titers in the supernatants were measured by standard plaque-based assay and Rlu-based assay, respectively.