The Role of Antibody Polyspecificity and Lipid Reactivity in Binding of Broadly Neutralizing Anti-HIV-1 Envelope Human Monoclonal Antibodies 2F5 and 4E10 to Glycoprotein 41 Membrane Proximal Envelope Epitopes

Abstract

Two neutralizing human mAbs, 2F5 and 4E10, that react with the HIV-1 envelope gp41 membrane proximal region are also polyspecific autoantibodies that bind to anionic phospholipids. To determine the autoantibody nature of these Abs, we have compared their reactivities with human anti-cardiolipin mAbs derived from a primary antiphospholipid syndrome patient. To define the role of lipid polyreactivity in binding of 2F5 and 4E10 mAbs to HIV-1 envelope membrane proximal epitopes, we determined the kinetics of binding of mAbs 2F5 and 4E10 to their nominal gp41 epitopes vs liposome-gp41 peptide conjugates. Both anti-HIV-1 mAbs 2F5 and 4E10 bound to cardiolipin with Kd values similar to those of autoimmune anti-cardiolipin Abs, IS4 and IS6. Binding kinetics studies revealed that mAb 2F5 and 4E10 binding to their respective gp41 peptide-lipid conjugates could best be defined by a two-step (encounter-docking) conformational change model. In contrast, binding of 2F5 and 4E10 mAbs to linear peptide epitopes followed a simple Langmuir model. A mouse mAb, 13H11, that cross-blocks mAb 2F5 binding to the gp41 epitope did not cross-react with lipids nor did it neutralize HIV-1 viruses. Taken together, these data demonstrate the similarity of 2F5 and 4E10 mAbs to known anti-cardiolipin Abs and support the model that mAb 2F5 and 4E10 binding to HIV-1 involves both viral lipid membrane and gp41 membrane proximal epitopes.

Evolving concepts of specificity in immune reactions

“…In some HIVinfected individuals, it is increased even more, to about 75% of the B cells that make mAbs that bind gp140, a prominent antigenic glycoprotein spike on the HIV-1 virus (53). Many of these mAbs, like the multireactive 2F5 and 4E10 mAbs from other HIV-infected individuals, also bind cardiolipin, a phospholipid in many cell membranes (32,33). The remarkably high frequency of these multireactive Abs, which have switched H chains and mutated V domains, suggests that they are selected by the HIV-1 virus, particularly during affinity maturation.…”

“…A mAb (7G12) raised against a porphyrin bound an unrelated polyether (31). Moreover, two mAbs (2F5 and 4E10) from HIV-infected individuals reacted with a viral protein (gp41) and also bound cardiolipin and other phospholipids (32,33). Yet another mAb (IgG1b12) from an HIV-infected person, in addition to binding the gp120 protein of the virus, reacted with dsDNA, histones, and "centromere B" (33).…”

Aromatic residues at the edge of the antibody combining site facilitate viral glycoprotein recognition through membrane interactions

“…Since the initial findings by Grunder et al and Ofek et al (12,22), a number of publications have also shown that 2F5, 4E10, and Z13e1 improve binding to Env and epitope peptides in a lipid environment (21,23,24). In addition, it has become increasingly clear that 4E10 binds to lipids in the absence of the MPER (21,(23)(24)(25)(26)(27)(28)(29).…”

“…In addition, it has become increasingly clear that 4E10 binds to lipids in the absence of the MPER (21,(23)(24)(25)(26)(27)(28)(29). These studies have generated models of 4E10 epitope recognition (21,23), but they have not yet fully addressed which antibody region(s) bind lipid and, of particular importance for vaccine design, whether lipid interaction is an essential component of MPER-mediated neutralization.…”

Recognition of synthetic glycopeptides by HIV-1 broadly neutralizing antibodies and their unmutated ancestors

“…V1V2 glycopeptide-binding K d and rate-constant measurements were carried out on BIAcore 3000 instruments (GE Healthcare) as described earlier (41,42). Anti-human IgG Fc antibody (Sigma Chemicals) was immobilized on either a CM3 or CM5 (CM3 for kinetics and K d determination) sensor chip (to minimize nonspecific binding of peptides to the chip matrix) to about 5,000 resonance units (RUs), and each antibody was captured to about 100-200 RU on individual flow cells in addition to one flow cell with the control Synagis mAb on the same sensor chip.…”