FIG. 2.

The positive effect on HIV-1 infectivity mediated by the amount of virion-bound host ICAM-1 is also seen in primary human cells. Similar amounts of Null-, Lo-, and Hi-ICAM-1 virus preparations were used to inoculate freshly isolated PBMCs from three different healthy donors (5 ng of p24). Virions and target cells were incubated together for 90 min at 37°C and washed with PBS, and incubation at 37°C was pursued for an additional 72 h. Next, cells were lysed and luciferase activity was monitored as described in Materials and Methods. Results are the means ± standard errors of the means for quadruplicate samples and are representative of three independent experiments. Negative controls consisted of mock-infected PBMCs. Luciferase activity values for mock-infected cells were 0.44 ± 0.07 RLU for donor A, 0.41 ± 0.02 RLU for donor B, and 0.43 ± 0.03 RLU for donor C.