Patients with Alzheimer disease have lower levels of serum anti-amyloid peptide antibodies than healthy elderly individuals.

Active immunization with the human amyloid peptide (Abeta42) or passive immunization with anti-Abeta42 antibodies protects mice that express a mutant human amyloid precursor protein (APP) transgene from cerebral amyloid deposits. If anti-Abeta42 antibodies protect APP-transgenic mice, a model of Alzheimer's disease (AD), a high titer of anti-Abeta42 antibodies may protect humans from AD. The titer of anti-Abeta42 antibodies in serum from individuals with and without late onset AD was measured using an ELISA.