The binding sites for CD4 and m2-phage are different. CD4 was applied to ELISA wells and used to capture gp120 BaL. Subsequently m2-phage was added and detection of phage and gp120 was achieved with anti-M13 mAb, HIVIg or b12 mAb as indicated. Note that whereas CD4 capture inhibits b12 binding as expected, occupation of the CD4bs does not interfere with m2 binding. The experiment was carried out in duplicate.