WNV can infect and induce apoptosis in human neuroblastoma cell line, SK-N-SH. (A) WNV titers in culture supernatant from SK-N-SH cell line collected at 2 h and from days 1 to 4 after infection were determined by plaque assay using Vero cells. Viral titers are expressed as plaque forming units (PFU)/mL of supernatant. Data are expressed as mean ± SD for two independent experiments conducted in duplicate. (B) Cell toxicity of SK-N-SH cells from days 1 to 3 after WNV infection was assessed by cell proliferation assay and percentage cell toxicity was calculated by comparing to mock-infected cells at corresponding time points. Data are expressed as mean ± SD for three independent experiments conducted in triplicate. (C) Mock (i and ii), and WNV (MOI-1)-infected SK-N-SH cells (iii and iv) were fixed at day 2 after infection and TUNEL assay was conducted (red; i and iii). Cells were counterstained with DAPI to label nucleus. TUNEL plus DAPI images (ii and iv) indicate that number of cells in each field were similar. DNase I-treated cells were used as positive control (v). The images depict representative results of three independent experiments.