DETECTION OF AMYLOID BETA-PROTEIN PRECURSOR IMMUNOREACTIVITY IN NORMAL AND ALZHEIMERS-DISEASE CEREBROSPINAL-FLUID

The amyloid A4 (or beta protein), a 4.2 kD polypeptide, is a major component of amyloid deposits in the brains of patients with Alzheimer's Disease (AD). The self-aggregating amyloid A4 protein of AD is encoded as part of three larger proteins by the amyloid A4 precursor gene. The corresponding proteins have 695, 751 and 770 amino acid residues. To investigate the utility of amyloid beta protein precursor (AβPP) as a diagnostic marker for AD an antiserum against a synthetic peptide (175-186), predicted from cDNA sequence for AβPP, was used. The immunoreactivity of AβPP in normal and AD cerebrospinal fluid (CSF) was measured by Western blot and detected with radiolabeled protein A. A total of fifty-seven CSF samples (AD=27 and normal=30) were analyzed for AβPP immunoreactivity. A polyclonal antibody detected two major protein bands with apparent molecular weights of 105kD and 90kD both in normal and AD CSF. The difference between normal and AD CSF was not significant. These results indicate that immunoreactivity of AβPP is present both in normal and AD CSF, and that the difference is too small to be used as a diagnostic marker. © 1990.