CD4bs antibody binding to gp140 constructs in ELISA experiments. The CD4bs reactivity of the gp140 constructs NL4-3 (X4), ADA (R5) and the hybrid NL4-3/ADA was evaluated in ELISA experiments with CD4-Fc and five selected monoclonal antibodies: VRC01, VRC03 (both ), b12 , b13  and F105 . Where applicable, nonlinear regression fits are shown in the diagrams instead of connected data points. Derived KD values (PRISM software) are listed in the table of Additional file 5. The data is representative for at least three independent replicate experiments with each data point of the binding curves determined in triplicates with indicated mAb concentrations. Error bars indicate the standard deviation.