Intravenous immunoglobulin (IVIg) Gammagard liquid contains anti-RAGE IgG and sLRP

Abstract

Baxter's IVIg preparation Gammagard Liquid (GGL) has shown encouraging results in a phase II trial treating patients with mild Alzheimer's disease (AD) [Relkin et al, Neurobiol. Aging, 2008]. GGL, which is manufactured from large pools of human plasma donations, has been shown to contain amyloid-β conformer-specific IgG autoantibodies that could be involved in the beneficial effects observed in the phase II study [O'Nuallain et al, Biochemistry, 2008]. Here we asked the question whether GGL contains other antibodies and soluble proteins that can modulate the amyloid-β pathway apart from these naturally occurring anti-amyloid-β IgGs. In particular, we checked for the presence of antibodies against the receptor for advanced glycation end products (RAGE), a receptor involved in the amyloid-β influx from plasma into the brain, and for the presence of soluble low density lipoprotein receptor-related protein (sLRP), a high-affinity Aβ binding protein that can modulate amyloid-β efflux from the brain into plasma. We investigated 20 lots of GGL. We checked for the presence of anti-RAGE IgG by a direct ELISA using a synthetic peptide. For the sLRP measurement, we used plate-immobilized recombinant receptor-associated protein (RAP) to capture sLRP from the sample and detected the bound sLRP with a monoclonal anti-LRP and an anti-mouse IgG peroxidase [Quinn et al, J. Biol. Chem., 1997]. Furthermore, we ran inhibition studies for checking the specificity of our assays. We detected naturally occurring anti-RAGE IgG in all GGL lots investigated and measured sLRP levels in the μg range (up to 40 μg/mL) with only moderate lot-to-lot variations among the different GGL lots. Inhibition with the RAGE peptide and RAP proved both assays to be specific. Anti-RAGE antibodies present in GGL could block RAGE and inhibit the uptake of amyloid-β peptide by the brain, whereas sLRP also present in GGL could lower the amyloid-β burden of the brain consistent with the peripheral sink hypothesis. These findings that GGL contains anti-RAGE IgG and sLRP broaden the possible mode of action of GGL in AD beyond the effects of anti-amyloid-β antibodies.