Residual activity in HIV-1 strains. HIV-1IIIB cell-free viruses were exposed to serial dilutions of bDLE for 5 minutes. The viruses were then ultracentrifuged, washed twice and added to HeLa-CD4-LTR-β-gal cells. After 24 hours, β-gal activity was measured. Percentage values are relative to the positive control (infected cells without bDLE treatment). The data represent the means ± standard deviations from three separate experiments, each of which was carried out in duplicate.