Receptor blocking.

We plated 6 × 10³ Huh7.5 cells per well in poly-d-lysine-coated 96-well plates and incubated the cells for 24 h. The next day, Huh7.5 cells were incubated in four replicates with dilution series of previously used monoclonal antibody against CD81 or SR-BI (38) or with four replicates of the respective control antibodies at the highest concentrations used in the assay. Following a 1-h incubation, a volume of the virus stock corresponding to a readout of 50 to 100 FFU/well was added to the cell-antibody mix and incubated for 4 h at 37°C. Cells were washed, and we added fresh medium and incubated the cells for a total infection time of 48 h. Cells were fixed and stained with 9E10 antibody as described previously (73), and the number of FFU was counted as described above (74, 75). The data were normalized to 8 replicates of virus only and analyzed using three-parameter curve fitting in GraphPad Prism 7.02.