Human Anti-Aβ IgGs Target Conformational Epitopes on Synthetic Dimer Assemblies and the AD Brain-Derived Peptide

Abstract

Soluble non-fibrillar assemblies of amyloid-beta (Aβ) and aggregated tau protein are the proximate synaptotoxic species associated with Alzheimer’s disease (AD). Anti-Aβ immunotherapy is a promising and advanced therapeutic strategy, but the precise Aβ species to target is not yet known. Previously, we and others have shown that natural human IgGs (NAbs) target diverse Aβ conformers and have therapeutic potential. We now demonstrate that these antibodies bound with nM avidity to conformational epitopes on plate-immobilized synthetic Aβ dimer assemblies, including synaptotoxic protofibrils, and targeted these conformers in solution. Importantly, NAbs also recognized Aβ extracted from the water-soluble phase of human AD brain, including species that migrated on denaturing PAGE as SDS-stable dimers. The critical reliance on Aβ’s conformational state for NAb binding, and not a linear sequence epitope, was confirmed by the antibody’s nM reactivity with plate-immobilized protofibrills, and weak uM binding to synthetic Aβ monomers and peptide fragments. The antibody’s lack of reactivity against a linear sequence epitope was confirmed by our ability to isolate anti-Aβ NAbs from intravenous immunoglobulin using affinity matrices, immunoglobulin light chain fibrils and Cibacron blue, which had no sequence similarity with the peptide. These findings suggest that further investigations on the molecular basis and the therapeutic/diagnostic potential of anti-Aβ NAbs are warranted.

Should development of Alzheimer’s disease-specific intravenous immunoglobulin be considered?

“…Some studies have reported that IVIG’s anti-Aβ antibodies are limited to those that are ‘conformation-specific’ (they do not recognize linear Aβ) [ 62 ], while others suggest that they may bind to monomeric Aβ, as well as Aβ aggregates [ 26 , 54 , 58 ]. Aβ25-40 is a major region for IVIG binding, while its binding to Aβ’s N-terminus is minimal [ 25 ].…”

Should development of Alzheimer¿s disease-specific intravenous immunoglobulin be considered?

“…Anti-Amyloid-beta (Aβ) antibodies Some studies have reported that IVIG's anti-Aβ antibodies are limited to those that are 'conformation-specific' (they do not recognize linear Aβ) [62], while others suggest that they may bind to monomeric Aβ, as well as Aβ aggregates [26,54,58]. Aβ25-40 is a major region for IVIG binding, while its binding to Aβ's N-terminus is minimal [25].…”

IgG Conformer's Binding to Amyloidogenic Aggregates

“…Anti-amyloid IgG conformers were isolated from preparations of IVIg and mAbs using Aβ and Cibacron blue affinity chromatography, as described [ 20 , 27 ]. The Aβ column consisted of S26C Aβ that was solubilized with 0.1 NH 4 OH and then aggregated at ~0.2 mg/mL in PBS, pH 7.4, for 5 days at 37°C.…”

“…Moreover, we have demonstrated that Aβ-reactive IVIg IgGs are cross-reactive against conformational epitopes on other amyloidogenic proteins and peptides. Thus, anti-amyloid pAbs isolated from normal human blood have demonstrated therapeutic potential not only for AD but for other amyloid diseases [ 20 , 21 , 27 ].…”