Annexin v.PE-/7-AAD assay for detection of cell apoptosis To determine the degree of apoptosis after exposure to HCV inocula or NHP, cells were stained with annexin v conjugated with phycoerythrin (PE), or 7 established aminoactinomycin D (7-AAD), as previously 16]. Briefly, 1 x 105 cells were washed with annexin buffer containing 10 mM HEPES (Invitrogen), 5 mM NaCl, 5 mM KC1 and 2 mM CaCl2 and centrifuged at 1,500 rpm for 10 min at 4 °C. Then, a cocktail containing 50 ug/mL of 7-AAD (Invitrogen) and 50 Hg/mL of annexin-V-PE (Invitrogen) were prepared in annexin buffer. Cells were suspended in 100 HL of apoptosis cocktail and kept on ice for 30 min. After staining, cells were washed once with annexin buffer, spun down and suspended in 500 HL of [1 annexin buffer to be analyzed by flow cytometry