The reduction in release of cell-free HIV_Δvpu by tetherin is overcome in co-cultures.

<p>(<b>A</b>) A barrier was placed into the cell-free path of HIV at the step of virus release by expressing tetherin. (<b>B</b>) HEK293 cells producing HIV_LAI-Δvpu and increasing amounts of tetherin (ng) were analyzed for viral gene expression in cells and virus release into the culture supernatant by Western blotting using the α-p24 antibody. The expression of HA-tagged tetherin was confirmed using α-HA antibodies. (<b>C</b>) Relative HIV_{LAI-Δvpu-GLuc} infectivity released by HEK293 producer cells expressing increasing amounts of tetherin (red) or transmitted from producer cells to indicated target cell types in co-cultures. The ratio of infectivity to non-tetherin expressing cells was calculated. (<b>D</b>) Fold of rescue of co-culture over cell-free for the data shown in (C). Fold-rescue was determined by calculating the ratio of the infectivity in co-cultures over the infectivity of cell-free virus at the corresponding tetherin plasmid dose. Error bars represent the standard error of the mean from 3 experiments. The effects of tetherin expression on wild-type HIV_LAI are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053138#pone.0053138.s002" target="_blank">Figure S2</a>.