Serial dilutions of mAbs were mixed with DENV-2 (16681) at MOI of 1 at 4uC for 1 h. The 100 ml mixture were incubated with 5610 4 K562 cells [39] in 96-well plates at 37uC for 2 h. After infection, the cells were washed and incubated with RPMI (Gibco) plus 2% (v/v) FBS at 37uC for 2 days. The cells were washed with PBS supplemented with 1% FBS, fixed with 3.7% formaldehyde, and permeabilized in PBS supplemented with 1% FBS, 0.1% saponin (Sigma) at 4uC for 10 min. For staining, cells were incubated with DB42-3 at a concentration of 3 mg/ml at 4uC for 30 min. After two times washes, R-Phycoerythrin (PE)-conjugated AffiniPure F(ab9) 2 fragment goat anti-mouse IgG (H+L) (Jackson ImmunoResearch Laboratories, West Grove, PA) diluted 1:250 was then added at 4uC for 30 min follow by two times wash steps and analyzed by flow cytometry.