Effect of protein knockdown on virus uptake by cells. (A) Rab5A, SNX3 and SNX10 were knocked down in CEM.CCR5 cells and the ability of shRNA-transduced cells to internalize HXB2pp, Bal26pp or VSVpp was measured after stripping of cell surface-associated virus with trypsin 1 h post-inoculation (see Methods). The fraction of internalized virus for each condition is plotted. The data points are means and SEM from two independent triplicate experiments. *, P < 0.05; **, P < 0.01; NS, not significant. (B) Correlation between virus uptake by and fusion with CEM.CCR5 cells depleted of Rab5A, SNX3 or SNX10 (data from Figure 2B and Figure 4A) plotted as fractions of the shScr control.