Progressive cerebral deposition of amyloid-beta (Abeta) peptide, an early and essential feature of Alzheimer's disease (AD), is accompanied by an inflammatory reaction marked by microgliosis, astrocytosis, and the release of proinflammatory cytokines. Mucosal administration of disease-implicated proteins can induce antigen-specific anti-inflammatory immune responses in mucosal lymphoid tissue which then act systemically. We hypothesized that chronic mucosal administration of Abeta peptide might induce an anti-inflammatory process in AD brain tissue that could beneficially affect the neuropathological findings. To test this hypothesis, we treated PDAPP mice, a transgenic line displaying numerous neuropathological features of AD, between the ages of approximately 5 and approximately 12 months with human Abeta synthetic peptide mucosally each week. We found significant decreases in the cerebral Abeta plaque burden and Abeta42 levels in mice treated intranasally with Abeta peptide versus controls treated with myelin basic protein or left untreated. This lower Abeta burden was associated with decreased local microglial and astrocytic activation, decreased neuritic dystrophy, serum anti-Abeta antibodies of the IgG1 and IgG2b classes, and mononuclear cells in the brain expressing the anti-inflammatory cytokines interleukin-4, interleukin-10, and tumor growth factor-beta. Our results demonstrate that chronic nasal administration of Abeta peptide can induce an immune response to Abeta that decreases cerebral Abeta deposition, suggesting a novel mucosal immunological approach for the treatment and prevention of AD.