Monoclonal antibodies raised against covalently crosslinked complexes of human immunodeficiency virus type 1 gp120 and CD4 receptor identify a novel complex-dependent epitope on gp 120.
The binding of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein, gp120, to its cell surface receptor, CD4, represents a molecular interaction involving distinct alterations in protein structure. Consequently, the pattern of epitopes presented on the gp120-CD4 complex should differ from those on free gp120. To investigate this concept, mice were immunized with covalently crosslinked complexes of viral HIV-1IIIBgp120 and soluble CD4. Two monoclonal antibodies (MoAbs) obtained from the immunized mice exhibited a novel epitope specificity. The MoAbs were marginally reactive with HIV-1IIIBgp120, highly reactive with gp120-CD4 complexes, and unreactive with soluble CD4. The same pattern of reactivity was seen in solid-phase assays using HIV-1(451)gp120. A similar specificity for complexes was evident in flow cytometry experiments, in which MoAb reactivity was dependent upon the attachment of gp120 to CD4-positive cells. In addition, MoAb reactivity was detected upon the interaction of CD4 receptors with purified HIV-1IIIB virions. Notably, seroantibodies from HIV-positive individuals competed for MoAb binding, indicating that the epitope is immunogenic in humans. The results demonstrated that crosslinked gp120-CD4 complexes elicit antibodies to cryptic gp120 epitopes that are exposed during infection in response to receptor binding. These findings may have important implications for the consideration of HIV envelope-receptor complexes as targets for virus neutralization.
DeVico
A L
AL
Advanced BioScience Laboratories, Inc., Kensington, Maryland 20895, USA.
Rahman
R
R
Welch
J
J
Crowley
R
R
Lusso
P
P
Sarngadharan
M G
MG
Pal
R
R
D000818:Animals; D000911:Antibodies, Monoclonal / Q000096:biosynthesis / Q000276:immunology*; D001666:Binding Sites, Antibody; D015704:CD4 Antigens / Q000276:immunology*; D000939:Epitopes / Q000276:immunology*; D005434:Flow Cytometry; D015483:HIV Antibodies / Q000096:biosynthesis / Q000276:immunology*; D015699:HIV Envelope Protein gp120 / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D011994:Recombinant Proteins / Q000276:immunology
D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D000939:Epitopes; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D011994:Recombinant Proteins; C076613:recombinant soluble CD4