Fig 1. Anti-envelope mAb binding to HIV_JRFL virions in solution measured by Fluorescence Correlation Spectroscopy (FCS).

HIV_JRFL virions (10μg/ml p24 equivalent concentrations) were allowed to interact in solution with Alexa Fluor 647-conjugated test Mabs b12, 2G12, A32, C11, and 17b, or negative control antibody Synagis in a 100μL volume at 4.5–6.6μg/ml final concentrations (see Methods). The relative fraction of Mabs that adopts a slower diffusion coefficient (D _b~8 μm² /sec) as a result of virion binding is indicated by black bars. The percentage of Mab binding to virions treated with 100μg/ml sCD4 is shown in grey bars. As a control for nonspecific binding, Mabs were tested for interactions with particles not expressing HIV Env (HIV_ΔENV). All experiments were repeated at least four times, and average values are shown. Error bars indicate standard deviation.