E2- and CD81-mediated entry of HCV-pp into small primate hepatic cells. (A) H77(1a)opt-pp were preincubated with increasing concentrations (0.2, 1, 5, 25, and 100 μg/ml, from dark gray to white bars) of anti-HCV E2 or anti-GBV-B E2 (nonspecific scFv) single-chain antibodies or in the absence of antibody (black bars) prior to infection of Huh7.5 (top) or TH1-14S (bottom) cells. (B) Huh7.5 and TH1-14S cell lines and PMH cultures were preincubated with increasing concentrations (0.1, 1, 3, 10, and 30 μg/ml for cell lines or 1 and 10 μg/ml for PMH, from dark gray to white bars) of anti-CD81 monoclonal antibody (MAb) or nonspecific isotype-matched MAb or in the absence of MAb (black bars) prior to infection with H77(1a)opt-pp. Relative infection ratios were determined at 72 h p.i. by scoring FLuc activities in the presence of antibodies relative to FLuc activities in the absence of antibodies set at 100% and are represented with a logarithmic scale.