Inhibition by neutralizing antibodies. A. Locations of mutation and reversions on the structure of gp120 relative to the epitopes for neutralizing antibodies b12 and 2G12. Colors are the same as in fig. 4A. Residues important for b12 binding  are indicated in blue and the asparagines which anchor the glycans involved in 2G12 binding [10-12] are indicated in magenta. B. Neutralization of the virus variants with selected monoclonal antibodies on CD4+ enriched lymphocytes. Neutralization curves are depicted for the various viruses in limiting dilutions of the b12 (top panel) and 2G12 (bottom panel) antibodies.