Figure 2. sgp120 CD4-Ig binding and infection of CD4^low cells with BR24 viruses.

The binding of sgp120 to CD4-Ig together with the fold-increase in sCD4 sensitivity (A), infectivity of HeLa RC49 cells (B) and primary macrophages (mΦ; C) that express low levels of CD4 with pseudotyped viruses bearing CCR5-using Envs amplified over time from BR24 were determined. Properties of four envelope clones in the SHIV_SF162P3N inoculum (P3N) were also determined and shown for reference. sgp120 binding to CD4-Ig (A) was normalized to that of sgp120 binding to polyclonal serum from HIV-1 infected individuals. Infectivity in RC49 cells (B) and macrophages (C) that express low levels of CD4 was expressed as a ratio of infectivity in JC53 cells and autologous PBMCs that express high levels of CD4 and CCR5, respectively. The dashed vertical line indicates time of tropism switch. For sgp120 CD4-Ig binding, data are the means and standard deviations from at least two independent experiments. For infection of CD4^low cells, data are representative of at least 3 independent experiments (error bars, s.d.). * above the bars indicates normalized CD4-Ig binding and CD4^low cell infectivity ratios that are statistically different between the acute (w2) and the evolving R5 viruses.