Decreased serum amyloid β1-42 autoantibody levels in Alzheimer's disease, determined by a newly developed immuno-precipitation assay with radiolabeled amyloid β1-42 peptide

Background: Autoantibodies against amyloid beta (A beta) peptide found in patients with Alzheimer's disease (AD) also occur naturally in the general population independently of the cognitive status. Methods: We compared serum A beta(1-42) autoantibody levels (A beta(1-42)-AL) of 96 AD patients and 30 healthy elderly control subjects (HC), assessing their diagnostic value for AD with a newly developed immunoprecipitation assaywith radiolabeled A beta(1-42) peptide. Results: We found a highly significant decrease of A beta(1-42)-AL in AD patients (p =.001) independently of age, cognitive status, and apolipoprotein E epsilon 4 carrier status. Amyloid beta(1-42) autoantibody levels were correlated with gender in AD, with a higher level occurring in women. When A beta(1-42) autoantibody sensitivity (specificity) was set > 80%, specificity (sensitivity) was below 50% to correctly allocate patients and healthy control subjects. Conclusions: Our data indicate a potentially pathophysiologic decrease of serum. A beta(1-42) antibodies in AD. Amyloid beta(1-42) antibodies in the serum alone, however, seem not to be useful as a diagnostic marker of AD.