To confirm the target protein of D29 Fab-IgG, Western blot analysis was carried out with DENV-infected Vero cell lysates and the recombinant ectodomain of DENV2 E protein (rE) under reducing and non-reducing conditions. Under non-reducing conditions, the control antibodies recognized their respective target proteins from the cell lysates: h4G2 detected the ,55 kDa E protein of all 4 serotypes and the ,50 kDa rE protein, and m2H2 detected the ,20 kDa prM of all 4 serotypes (Fig. 2B) . Remarkably, D29 Fab-IgG detected both E and prM of all 4 serotypes; however, the binding was abolished in the presence of reducing agent, indicating that the D29 epitope is conformational. All control antibodies except h3H5 lost binding to their target proteins under reducing condition (Fig. 2C) , which is expected since h3H5 recognizes a linear epitope on EDIII [22, 23] , whereas both h4G2 and m2H2 are conformationally sensitive [10, 24] . In agreement with the competition ELISA data, h3H5 and h4G2 did not compete with D29 Fab-IgG for epitopes in the Western blot format, whereas incubation with m2H2 abolished D29 binding to prM but not to E protein (Fig. 2D) .