BHK-21 cells and C6/36 mosquito cells were cultured as described previously [60] . 293T cells and T-REx TM -293 cells were cultured as previously described using tetracycline-deficient fetal calf serum for the latter cells [61] . The DENV2 New Guinea C (NGC) strain and the DENV1 Western Pacific (WP) strain were propagated in C6/36 cells in DMEM containing 2% heatinactivated fetal calf serum and 10 mM Hepes, pH 8.0, as previously described [41, 62] . Sindbis virus expressing green fluorescent protein was obtained as an infectious clone (a kind gift from Dr. Hans Heidner) and propagated in BHK cells [63] .