The ADE assay was performed as described previously [20] . Briefly, pre-formed immune complexes were prepared by incubating serially diluted antibody with DENV2 or imDENV2 at a multiplicity of 25 GCP per cell (MOG 25) in RPMI MM at 37 o C for 1 hr before applying to 2610 4 K562 cells in 96-well U-bottom plate (Nunc). Supernatant was harvested 48 hr postinfection and virus titer was quantified by plaque assay.