The CD4 binding site is not compromised by m2-phage binding. The m2 and fth-1 phages were applied to nitrocellulose filters along with CD4. The filters were incubated with gp120 BaL or without gp120 (no signals developed in the absence of gp120, not shown) and probed with three stringent CD4i mAbs and three CD4bs mAbs as indicated. Binding is also illustrated for mAb 2G12 which recognizes a mannose-rich epitope on gp120. Note that m2-phage induces binding for all three of the CD4i mAbs and does not interfere with the binding of the CD4bs mAbs. The binding of the CD4bs mAbs is sensitive to the capture of gp120 by CD4 as expected.