FIG 4.

CD4-dependent binding of gp120 from multiple HIV-1 subtypes to human PBMCs. Biotinylated gp120s from HIV-1 subtypes A, B, and C were tested for binding to RA-treated PBMCs by flow cytometry. In addition, PBMCs preincubated with a saturating concentration of Leu3a prior to the addition of biotinylated gp120 were tested in parallel. Biotinylated MAdCAM-1 was used as a positive control to confirm the presence of the α₄β₇ integrins on the PBMCs. Black curves in the histograms, unstained PBMCs; gray curves, PBMCs incubated with avidin-PE only; red curves, PBMCs incubated with gp120 from HIV-1 isolates 92US715.6 (subtype B), 92UG37 (subtype A), BaL (subtype B), AN-1 (deduced ancestral subtype), SF162 (subtype B), and 96ZM651 (subtype C), in which binding was detected with avidin-PE. The results also correspond to those for PBMCs incubated with biotinylated MAdCAM-1, in which binding was detected with avidin-PE.