Quantification of Alzheimer amyloid beta peptides ending at residues 40 and 42 by novel ELISA systems

Background: The amyloid beta (A beta) peptide is a key molecule in the path ogenesis of Alzheimer's disease. Reliable methods to detect and quantify so luble forms of this peptide in human biological fluids and in model systems , such as cell cultures and transgenic animals, are of great importance for further understanding the disease mechanisms. In this study, the applicati on of new and highly specific ELISA systems for quantification of A beta 40 and A beta 42 (A beta peptides ending at residues 40 or 42, respectively) in human cerebrospinal fluid (CSF) are presented. Materials and Methods: Monoclonal antibodies W0-2, G2-10 and G2-11 were tho roughly characterized by (SPOT) epitope mapping and immunoprecipitation/mas s spectrometry. We determined whether aggregation affected the binding capa cities of the antibodies to synthetic peptides and whether components of th e CSF affected the ability of the antibodies to bind synthetic A beta 1-40 and A beta 1-42 peptides. The stability of A beta 40 and A beta 42 in CSF d uring different temperature conditions was also studied to optimize sample handling from lumbar puncture to A beta assay. Results: The detection range for the ELISAs were 20-250 pM. The intra-assay variations were 2% and 3%, and the inter-assay variations were 2%and 10% f or A beta 40 and A beta 42, respectively. The antibodies specifically detec ted the expected peptides with equal affinity for soluble and fibrillar for ms of the peptide. The presence of CSF obstructed the recognition of synthe tic peptides by the antibodies and the immunoreactivity of endogenous CSF A beta decreased with increasing storage time and temperature. Conclusions: This study describes highly sensitive ELISAs with thoroughly c haracterized antibodies for quantification of A beta 40 and A beta 42, an i mportant tool for the understanding of the pathogenesis of Alzheimer's dise ase. Our results pinpoint some of the difficulties associated with A beta q uantification and emphasize the importance of using a well-documented assay .