O2–05–05: IVIg contains antibodies against oligomers and fibrils of beta amyloid

Abstract

Intravenous immunoglobulin (IVIg) is a polyclonal human IgG preparation that contains antibodies against beta amyloid (Aβ). In our Phase I immunotherapy trial involving eight patients with mild to moderate Alzheimer's disease (AD), IVIg improved cognitive function, increased Aβ levels in plasma and decreased Aβ levels in the cerebrospinal fluid (CSF). However, the magnitude of change in Aβ40 and Aβ42 levels after treatment was unexpectedly large relative to the known titers of anti-Aβ antibodies in IVIg. To clarify the mechanisms responsible for IVIg's effects on amyloid levels in AD patients. We carried out binding and competition studies to examine the capacity of IVIg to bind to various forms of synthetic Aβ in vitro. Pure monomer solutions were created by dissolving HFIP-treated Aβ peptide films in DMSO and suspending in PBS. Monomers were confirmed by Western blot. Extended incubation times and agitation permitted creation of oligomers and fibrils of Aβ. Aggregate formation was confirmed by ThioT fluorescence and EM. Dot blots were employed to compare binding of IVIg to monomers, oligomers and fibrils of Aβ. ELISA techniques were used to measure antibody titers. Antibodies in IVIg did not bind significantly to freshly dissolved monomers of synthetic Aβ. Antibodies in IVIg did bind to synthetic Aβ prepared under conditions that led to Aβ oligomerization and fibril formation. The presence of antibodies in IVIg against oligomers and fibrils of Aβ was confirmed by dot blot analyses. Titers of antibodies in IVIg against fibrillar Aβ were higher than those against monomeric Aβ. IVIg contains antibodies that bind to oligomeric and fibrillar forms of Aβ to a greater extent than to monomers. The substantial alterations of Aβ40 and Aβ42 peptide levels in blood and spinal fluid following infusion of IVIg may be explained by the binding of anti-Aβ antibodies to multimeric forms of Aβ. Studies now in progress will address whether IVIg's positive effects on cognition in AD patients correlate with the titers of antibodies against monomeric, oligomeric and/or fibrillar forms of Aβ.