Copper Ions Enhance Signal Intensity of Sandwich ELISA for Amorphous Aggregates of Amyloid-β₄₂

Abstract

Amyloid-β 42 (Aβ 42 ) accumulates within senileplaque, a pathological hall mark of Alzheimer’s disease (AD). Our previous reports showed that the monoclonal antibodies 37-11 and 77-3 react with conformational epitopes on the surface of the soluble aggregates of Aβ 42 and that sandwich ELISA using these two monoclonal antibodies yields high reactivity to detect soluble aggregates of Aβ 42 . Here, the reactivity of the sandwich ELISA was shown to increase in the presence of 50 μM Cu 2+ . However, the addition of Cu 2+ had only a small effect on the reactivity of a direct ELISA using antibody 37-11 or 77-3, suggesting that Cu 2+ has a small effect on the number of epitopes on the surface of the aggregates. Atomic force microscopy images showed that larger aggregates were formed in the presence of Cu 2+ , as shown in the other reports. Cu 2+ may gather the aggregates with distinct epitopes recognized by antibodies 37-11 and 77-3, leading to increased signal intensity of the sandwich ELISA.