Antibodies to amyloid β protein (Aβ) crossreact with glyceraldehyde-3-phosphate dehydrogenase (GAPDH)

In the present study, we characterized the epitope of a monoclonal antibody against purified amyloid plaque cores (Am-3). By immunocytochemical experiments, Am-3 stained cerebrovascular and senile plaque amyloid in brain sections of patients with Alzheimerʹs disease (AD) in a similar manner to that of antibodies against amyloid β-protein (Aβ). By Western blotting experiments, Am-3 recognized only a 35 kDa protein, which was revealed to be glyceraldehyde-3-phosphate dehydrogenase (GADPH), and not Aβ or β amyloid precursor protein (βPP). However, Am-3 recognized both GAPDH and purified native Aβ in a dot-binding assay. Therefore, we concluded that Am-3 recognized both GAPDH and native Aβ. Other monoclonal antibodies (6C6 and AmT-1) against the synthetic peptide corresponding to residues 1–28 of Aβ also recognized these proteins. Because the amino acid sequences of these two proteins are not homologous, we propose that the crossreactivity between Aβ and GAPDH is a consequence of their similar conformational epitopes. The possibility of crossreactions would complicate immunochemical and immunocytochemical studies of brain aging. AD and Downʹs syndrome. The implications of crossreactivity in developing immunological assays and in investigating the amyloid deposits of AD are discussed.