U937 dc sign cells

Vero E6 cells were purchased from the American Type Culture Collection (ATCC; Manassas, VA, USA) and were used for viral neutralization assays and to propagate DENV. Vero E6 cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM; Welgene, Gyeongsan, Korea) supplemented with 5% fetal bovine serum (FBS; Gibco, Thermo Fisher Scientific, Grand Island, NY, USA). In addition, U937-DC-SIGN cells (ATCC, U937 cells transfected with the human DC-SIGN gene, encoding an attachment factor for DENV) were used for the DENV binding and ADE experiments. U937-DC-SIGN cells were cultured in Roswell Park Memorial Institute (RPMI) medium (Welgene) containing 5% FBS, 2 mM L-glutamine, 0.1 mM non-essential amino acids, and 0.05 mM 2-mercaptoethanol.

Human dermal fibroblast HFF-1 cells (ATCC SCRC-1041) and U937-DC-SIGN cells (ATCC CRL-3253) were infected with all the Flavivirus isolates at an MOI of 0.1, and supernatants were harvested for titration every 24 h for 6 days.