The m1-phage binds gp120 and locks it into a CD4i conformation without interfering with CD4 binding. A. Dot blot illustrating the stringent dependence of mAb CG10 on CD4. CDC451 gp120 was spotted onto nitrocellulose and detected with HIVIg, mAb CG10 or mAb CG10 in the presence of CD4. CG10 is strictly dependent on the presence of CD4 for gp120 binding. B. Equal amounts of phages displaying the m1-peptide, phages with no insert (fth-1) or CD4 were spotted to nitrocellulose filters. Filters were incubated with gp120 CDC451 or in blocking solution without gp120 (no signals developed in the absence of gp120, not shown) and bound gp120 was detected using HIVIg or the CD4i CG10 mAb. C. Equal amounts of phages displaying the m1-peptide or phages with no insert (fth-1) were captured on ELISA wells using an anti-M13 mAb. Wells were incubated with pre-formed gp120 CDC451:CD4 complex (stoichiometric molar ratio of 1:1), gp120 or CD4 alone, as indicated. Bound gp120 was detected using a biotinylated anti-gp120 9G3 mAb; bound CD4 was detected by a biotinylated anti-CD4 mAb CG9. The experiment was carried out in triplicate.