Efficiency of virus capture by DC-SIGN +Raji cells and the subsequent transmission of captured virus to C8166 T cells. A. Raji/DC-SIGN cells were exposed to virus during 1 h, after which unbound virions were removed by thourough washing. The levels of captured virus were quantified using a p24 ELISA and were used as a measurement for capture efficiency. All data were normalized to the capture efficiency of virus lacking envelope glycoprotein expression (WT∆Env). B. Virus-captured Raji/DC-SIGN cells were brought into contact with C8166 T cells, resulting in transmission of virus to, and infection of, the C8166 cells. Virion production by the C8166 cells, as quantified by p24 ELISA, was used as a measurement for transmission efficiency. Results represent transmission efficiency, normalized to equal levels of virus capture by the Raji/DC-SIGN cells. Results are means ± SEM of at least 3 independent experiments. The difference between WT and mutant gp41 virus was considered to be significant when the p value calculated using the student’s t-test was <0.05 (* = p < 0.05, ** = p < 0.005).