Infection of virtually non-infectious imDENV was also significantly enhanced by D29 Fab-IgG to a level similar to m2H2, causing an 80-100 fold increase in infection relative to control IgG (Fig. 7C) . The enhancement of imDENV infection by h3H5 was similar to that observed for DENV2, since its epitope was not affected by the maturity state hence it enhanced both equally well; h4G2 failed to enhance imDENV2 infection in K562 cells possibly be due to the occlusion of its epitope by the pr peptide [29, 30] , and indicated by the immunoprecipitation protein profile (Fig. 3B ).