Purified serum IgG cross-neutralization.

(a) IgG neutralization curves derived from mean values for each data point of three independent TZM-bl-based neutralization assays. Error bars represent the standard deviation. The rabbits are designated by the Group number first (1, 2 or 3) followed by a dash and the animal index number as indicated in Fig 7 (i.e., #3–5). If specified otherwise, the serum was analyzed following the fourth immunization. The “control rabbit” was immunized four times with blank liposomes in adjuvant and IgG was purified similarly to the experimental rabbit IgGs; the mean values of two experimental replicates are shown for this negative specificity control (b) ID₅₀ values were derived from the curves described above and are color-coded as indicated. Weak neutralizing values were extrapolated based on the two highest IgG dilution data points and are indicated in italics. (c) Cross-neutralization of IAVIC22Δ276 and BG505Δ276 viruses analyzed by depletion with the 16055 gp120 TriMut protein. Purified IgG from the serum of rabbit #2–5 and rabbit #3–5 were titrated at the concentrations indicated (horizontal axis) in the absence or presence of the 16055 gp120 TriMut (two left panels). The 16055 gp120 TriMut protein was used at fixed concentration of 100 mg/ml. The mean values of two independent TZM-bl-based neutralization assays are shown with the bars at each dilution indicating the individual values. VRC13 IgG was used as a CD4bs-directed antibody positive control (two right panels) and in case of BG505Δ276 virus representative control experiment is shown.