Reduced Amyloid Plaque Research Articles

A PPARdelta Agonist Reduces Amyloid Burden and Brain Inflammation in a Transgenic Mouse Model of Alzheimers Disease

Agonists of the peroxisome proliferator activated receptor gamma (PPARgamma) have been shown to reduce inflammatory responses in several animal models of neurological diseases and conditions and to reduce amyloid burden in transgenic mice expressing mutant forms of human amyloid precursor protein. However, the effects of activating the related receptor PPARdelta (PPARdelta), which is expressed at higher levels in the brain than PPARgamma, on inflammation and amyloid burden have not been explored. In this study we tested the effects of the selective PPARdelta agonist GW742 in 5xFAD mice which harbor 3 mutations in amyloid precursor protein and 2 mutations in presenilin 1, develop plaques by 5-6 weeks of age, and show robust inflammation and neuronal damage. Oral delivery of GW742 significantly reduced amyloid plaque burden in the subiculum region of 3-month old male and female 5xFAD mice. GW742 also significantly reduced astrocyte activation, suggesting anti-inflammatory effects on glia cells. The changes in plaque burden were accompanied by increased expression of the amyloid degrading enzymes neprilysin and insulin degrading enzyme, while in transfected HEK293 cells, GW742 activated a neprilysin promoter driving luciferase expression. These results suggest that, as found for some PPARgamma agonists, PPARdelta agonists can also reduce amyloid burden likely to be mediated by effects on amyloid clearance.

Characterizing the Appearance and Growth of Amyloid Plaques in APP/PS1 Mice

Amyloid plaques are primarily composed of extracellular aggregates of amyloid-beta (Abeta) peptide and are a pathological signature of Alzheimer's disease. However, the factors that influence the dynamics of amyloid plaque formation and growth in vivo are largely unknown. Using serial intravital multiphoton microscopy through a thinned-skull cranial window in APP/PS1 transgenic mice, we found that amyloid plaques appear and grow over a period of weeks before reaching a mature size. Growth was more prominent early after initial plaque formation: plaques grew faster in 6-month-old compared with 10-month-old mice. Plaque growth rate was also size-related, as smaller plaques exhibited more rapid growth relative to larger plaques. Alterations in interstitial Abeta concentrations were associated with changes in plaque growth. Parallel studies using multiphoton microscopy and in vivo microdialysis revealed that pharmacological reduction of soluble extracellular Abeta by as little as 20-25% was associated with a dramatic decrease in plaque formation and growth. Furthermore, this small reduction in Abeta synthesis was sufficient to reduce amyloid plaque load in 6-month-old but not 10-month-old mice, suggesting that treatment early in disease pathogenesis may be more effective than later treatment. In contrast to thinned-skull windows, no significant plaque growth was observed under open-skull windows, which demonstrated extensive microglial and astrocytic activation. Together, these findings indicate that individual amyloid plaque growth in vivo occurs over a period of weeks and may be influenced by interstitial Abeta concentration as well as reactive gliosis.

Alternative pathways for production of β-amyloid peptides of Alzheimer's disease

This highlight article describes three Alzheimer's disease (AD) studies presented at the 5th General Meeting of the International Proteolysis Society that address enzymatic mechanisms for producing neurotoxic beta-amyloid (Abeta) peptides. One group described the poor kinetics of BACE 1 for cleaving the wild-type (WT) beta-secretase site of APP found in most AD patients. They showed that cathepsin D displays BACE 1-like specificity and cathepsin D is 280-fold more abundant in human brain than BACE 1. Nevertheless, as BACE 1 and cathepsin D show poor activity towards the WT beta-secretase site, they suggested continuing the search for additional beta-secretase(s). The second group reported cathepsin B as an alternative beta-secretase possessing excellent kinetic efficiency and specificity for the WT beta-secretase site. Significantly, inhibitors of cathepsin B improved memory, with reduced amyloid plaques and decreased Abeta(40/42) in brains of AD animal models expressing amyloid precursor protein containing the WT beta-secretase site. The third group addressed isoaspartate and pyroglutamate (pGlu) posttranslational modifications of Abeta. Results showed that cathepsin B, but not BACE 1, efficiently cleaves the WT beta-secretase isoaspartate site. Furthermore, cyclization of N-terminal Glu by glutaminyl cyclase generates highly amyloidogenic pGluAbeta(3-40/42). These presentations suggest cathepsin B and glutaminyl cyclase as potential new AD therapeutic targets.

P2-310: Exebryl-1: A novel small-molecule drug that markedly reduces amyloid plaque load and improves memory, enters human clinical trials

P2-310: Exebryl-1: A novel small-molecule drug that markedly reduces amyloid plaque load and improves memory, enters human clinical trials

Ultrasound Enhanced Delivery of Molecular Imaging and Therapeutic Agents in Alzheimer's Disease Mouse Models

Alzheimer's disease is a neurodegenerative disorder typified by the accumulation of a small protein, beta-amyloid, which aggregates and is the primary component of amyloid plaques. Many new therapeutic and diagnostic agents for reducing amyloid plaques have limited efficacy in vivo because of poor transport across the blood-brain barrier. Here we demonstrate that low-intensity focused ultrasound with a microbubble contrast agent may be used to transiently disrupt the blood-brain barrier, allowing non-invasive, localized delivery of imaging fluorophores and immunotherapeutics directly to amyloid plaques. We administered intravenous Trypan blue, an amyloid staining red fluorophore, and anti-amyloid antibodies, concurrently with focused ultrasound therapy in plaque-bearing, transgenic mouse models of Alzheimer's disease with amyloid pathology. MRI guidance permitted selective treatment and monitoring of plaque-heavy anatomical regions, such as the hippocampus. Treated brain regions exhibited 16.5±5.4-fold increase in Trypan blue fluorescence and 2.7±1.2-fold increase in anti-amyloid antibodies that localized to amyloid plaques. Ultrasound-enhanced delivery was consistently reproduced in two different transgenic strains (APPswe:PSEN1dE9, PDAPP), across a large age range (9–26 months), with and without MR guidance, and with little or no tissue damage. Ultrasound-mediated, transient blood-brain barrier disruption allows the delivery of both therapeutic and molecular imaging agents in Alzheimer's mouse models, which should aid pre-clinical drug screening and imaging probe development. Furthermore, this technique may be used to deliver a wide variety of small and large molecules to the brain for imaging and therapy in other neurodegenerative diseases.

Thromboxane Receptor Activation Mediates Isoprostane-Induced Increases in Amyloid Pathology in Tg2576 Mice

Alzheimer's disease (AD) amyloid plaques are composed of amyloid-beta (Abeta) peptides produced from proteolytic cleavage of amyloid precursor protein (APP). Isoprostanes, markers of in vivo oxidative stress, are elevated in AD patients and in the Tg2576 mouse model of AD-like Abeta brain pathology. To determine whether isoprostanes increase Abeta production, we delivered isoprostane iPF(2alpha)-III into the brains of Tg2576 mice. Although treated mice showed increased brain Abeta levels and plaque-like deposits, this was blocked by a thromboxane (TP) receptor antagonist, suggesting that TP receptor activation mediates the effects of iPF(2alpha)-III on Abeta. This hypothesis was supported by cell culture studies that showed that TP receptor activation increased Abeta and secreted APP ectodomains. This increase was a result of increased APP mRNA stability leading to elevated APP mRNA and protein levels. The increased APP provides more substrate for alpha and beta secretase proteolytic cleavages, thereby increasing Abeta generation and amyloid plaque deposition. To test the effectiveness of targeting the TP receptor for AD therapy, Tg2576 mice underwent long-term treatment with S18886, an orally available TP receptor antagonist. S18886 treatment reduced amyloid plaques, insoluble Abeta, and APP levels, thereby implicating TP receptor signaling as a novel target for AD therapy.

Curcumin Structure-Function, Bioavailability, and Efficacy in Models of Neuroinflammation and Alzheimer's Disease

Curcumin can reduce inflammation and neurodegeneration, but its chemical instability and metabolism raise concerns, including whether the more stable metabolite tetrahydrocurcumin (TC) may mediate efficacy. We examined the antioxidant, anti-inflammatory, or anti-amyloidogenic effects of dietary curcumin and TC, either administered chronically to aged Tg2576 APPsw mice or acutely to lipopolysaccharide (LPS)-injected wild-type mice. Despite dramatically higher drug plasma levels after TC compared with curcumin gavage, resulting brain levels of parent compounds were similar, correlating with reduction in LPS-stimulated inducible nitric-oxide synthase, nitrotyrosine, F2 isoprostanes, and carbonyls. In both the acute (LPS) and chronic inflammation (Tg2576), TC and curcumin similarly reduced interleukin-1beta. Despite these similarities, only curcumin was effective in reducing amyloid plaque burden, insoluble beta-amyloid peptide (Abeta), and carbonyls. TC had no impact on plaques or insoluble Abeta, but both reduced Tris-buffered saline-soluble Abeta and phospho-c-Jun NH(2)-terminal kinase (JNK). Curcumin but not TC prevented Abeta aggregation. The TC metabolite was detected in brain and plasma from mice chronically fed the parent compound. These data indicate that the dienone bridge present in curcumin, but not in TC, is necessary to reduce plaque deposition and protein oxidation in an Alzheimer's model. Nevertheless, TC did reduce neuroinflammation and soluble Abeta, effects that may be attributable to limiting JNK-mediated transcription. Because of its favorable safety profile and the involvement of misfolded proteins, oxidative damage, and inflammation in multiple chronic degenerative diseases, these data relating curcumin dosing to the blood and tissue levels required for efficacy should help translation efforts from multiple successful preclinical models.

Inhibitors of Cathepsin B Improve Memory and Reduce β-Amyloid in Transgenic Alzheimer Disease Mice Expressing the Wild-type, but Not the Swedish Mutant, β-Secretase Site of the Amyloid Precursor Protein

Elucidation of Abeta-lowering agents that inhibit processing of the wild-type (WT) beta-secretase amyloid precursor protein (APP) site, present in most Alzheimer disease (AD) patients, is a logical approach for improving memory deficit in AD. The cysteine protease inhibitors CA074Me and E64d were selected by inhibition of beta-secretase activity in regulated secretory vesicles that produce beta-amyloid (Abeta). The regulated secretory vesicle activity, represented by cathepsin B, selectively cleaves the WT beta-secretase site but not the rare Swedish mutant beta-secretase site. In vivo treatment of London APP mice, expressing the WT beta-secretase site, with these inhibitors resulted in substantial improvement in memory deficit assessed by the Morris water maze test. After inhibitor treatment, the improved memory function was accompanied by reduced amyloid plaque load, decreased Abeta40 and Abeta42, and reduced C-terminal beta-secretase fragment derived from APP by beta-secretase. However, the inhibitors had no effects on any of these parameters in mice expressing the Swedish mutant beta-secretase site of APP. The notable efficacy of these inhibitors to improve memory and reduce Abeta in an AD animal model expressing the WT beta-secretase APP site present in the majority of AD patients provides support for CA074Me and E64d inhibitors as potential AD therapeutic agents.

CD40L disruption enhances Aβ vaccine-mediated reduction of cerebral amyloidosis while minimizing cerebral amyloid angiopathy and inflammation

Amyloid-β (Aβ) immunization efficiently reduces amyloid plaque load and memory impairment in transgenic mouse models of Alzheimer's disease (AD). Active Aβ immunization has also yielded favorable results in a subset of AD patients. However, a small percentage of patients developed severe aseptic meningoencephalitis associated with brain inflammation and infiltration of T-cells. We have shown that blocking the CD40–CD40 ligand (L) interaction mitigates Aβ-induced inflammatory responses and enhances Aβ clearance. Here, we utilized genetic and pharmacologic approaches to test whether CD40–CD40L blockade could enhance the efficacy of Aβ 1–42 immunization, while limiting potentially damaging inflammatory responses. We show that genetic or pharmacologic interruption of the CD40–CD40L interaction enhanced Aβ 1–42 immunization efficacy to reduce cerebral amyloidosis in the PSAPP and Tg2576 mouse models of AD. Potentially deleterious pro-inflammatory immune responses, cerebral amyloid angiopathy (CAA) and cerebral microhemorrhage were reduced or absent in these combined approaches. Pharmacologic blockade of CD40L decreased T-cell neurotoxicity to Aβ-producing neurons. Further reduction of cerebral amyloidosis in Aβ-immunized PSAPP mice completely deficient for CD40 occurred in the absence of Aβ immunoglobulin G (IgG) antibodies or efflux of Aβ from brain to blood, but was rather correlated with anti-inflammatory cytokine profiles and reduced plasma soluble CD40L. These results suggest CD40–CD40L blockade promotes anti-inflammatory cellular immune responses, likely resulting in promotion of microglial phagocytic activity and Aβ clearance without generation of neurotoxic Aβ-reactive T-cells. Thus, combined approaches of Aβ immunotherapy and CD40–CD40L blockade may provide for a safer and more effective Aβ vaccine.

Cytochrome c oxidase deficiency in neurons decreases both oxidative stress and amyloid formation in a mouse model of Alzheimer's disease

Defects in the mitochondrial cytochrome c oxidase (COX) have been associated with Alzheimer's Disease, in which the age-dependent accumulation of beta-amyloid plays an important role in synaptic dysfunction and neurodegeneration. To test the possibility that age-dependent decline in the mitochondrial respiratory function, especially COX activity, may participate in the formation and accumulation of beta-amyloid, we generated mice expressing mutant amyloid precursor protein and mutant presenilin 1 in a neuron-specific COX-deficient background. A neuron-specific COX-deficient mouse was generated by the Cre-loxP system, in which the COX10 gene was deleted by a CamKIIalpha promoter-driven Cre-recombinase. COX10 is a farnesyltransferase involved in the biosynthesis of heme a, required for COX assembly and function. These KO mice showed an age-dependent COX deficiency in the cerebral cortex and hippocampus. Surprisingly, COX10 KO mice exhibited significantly fewer amyloid plaques in their brains compared with the COX-competent transgenic mice. This reduction in amyloid plaques in the KO mouse was accompanied by a reduction in Abeta42 level, beta-secretase activity, and oxidative damage. Likewise, production of reactive oxygen species from cells with partial COX activity was not elevated. Collectively, our results suggest that, contrary to previous models, a defect in neuronal COX does not increase oxidative damage nor predispose for the formation of amyloidgenic amyloid precursor protein fragments.

Reducing Amyloid Plaque Burden via Ex Vivo Gene Delivery of an Aβ-Degrading Protease: A Novel Therapeutic Approach to Alzheimer Disease

BackgroundUnderstanding the mechanisms of amyloid-β protein (Aβ) production and clearance in the brain has been essential to elucidating the etiology of Alzheimer disease (AD). Chronically decreasing brain Aβ levels is an emerging therapeutic approach for AD, but no such disease-modifying agents have achieved clinical validation. Certain proteases are responsible for the catabolism of brain Aβ in vivo, and some experimental evidence suggests they could be used as therapeutic tools to reduce Aβ levels in AD. The objective of this study was to determine if enhancing the clearance of Aβ in the brain by ex vivo gene delivery of an Aβ-degrading protease can reduce amyloid plaque burden.Methods and FindingsWe generated a secreted form of the Aβ-degrading protease neprilysin, which significantly lowers the levels of naturally secreted Aβ in cell culture. We then used an ex vivo gene delivery approach utilizing primary fibroblasts to introduce this soluble protease into the brains of β-amyloid precursor protein (APP) transgenic mice with advanced plaque deposition. Brain examination after cell implantation revealed robust clearance of plaques at the site of engraftment (72% reduction, p = 0.0269), as well as significant reductions in plaque burden in both the medial and lateral hippocampus distal to the implantation site (34% reduction, p = 0.0020; and 55% reduction, p = 0.0081, respectively).ConclusionsEx vivo gene delivery of an Aβ-degrading protease reduces amyloid plaque burden in transgenic mice expressing human APP. These results support the use of Aβ-degrading proteases as a means to therapeutically lower Aβ levels and encourage further exploration of ex vivo gene delivery for the treatment of Alzheimer disease.

Active Aβ vaccination-induced Aβ clearance enhanced by suppression of the CD40-CD40L interaction (48.11)

Abstract Active and passive Aβ immunization efficiently reduces amyloid plaque load and memory impairment in transgenic mouse models of Alzheimer’s disease. Immunization has also yielded favorable results for many patients; but a significant percentage also developed severe meningioencephalitis. Prior studies by our group suggest CD40 receptor-CD40 ligand interaction between T-cells and microglia initiates release of proinflammatory factors, which drive phenotypic switching from a phagocytic to an antigen presenting cell phenotype thus impairing the clearance of Aβ. We therefore tested whether a CD40 blockade could enhance Aβ vaccination-mediated Aβ clearance in vivo. Importantly in our present study, Aβ vaccinated CD40 deficient heterozygous transgenic mice over-expressing mutant amyloid precursor protein and presenilin-1 demonstrated enhanced Aβ clearance; compared with vaccinated PSAPP mice. Similar results were obtained with Aβ vaccinated PSAPP mice passively immunized with CD40L antibody injections. Taken together with our previous studies these data suggest that CD40 blockade, in the context of active Aβ vaccination, acts to enhance CNS Aβ clearance by maintaining microglia in a phagocytic phenotype. These data also may provide the basis for a method whereby enhancing Aβ vaccination-mediated Aβ clearance strategies.

Selection and characterization of Affibody ligands binding to Alzheimer amyloid β peptides

Affibody (Affibody) ligands specific for human amyloid beta (Abeta) peptides (40 or 42 amino acid residues in size), involved in the progress of Alzheimer's disease, were selected by phage display technology from a combinatorial protein library based on the 58-amino acid residue staphylococcal protein A-derived Z domain. Post-selection screening of 384 randomly picked clones, out of which 192 clones were subjected to DNA sequencing and clustering, resulted in the identification of 16 Affibody variants that were produced and affinity purified for ranking of their binding properties. The two most promising Affibody variants were shown to selectively and efficiently bind to Abeta peptides, but not to the control proteins. These two Affibody ligands were in dimeric form (to gain avidity effects) coupled to affinity resins for evaluation as affinity devices for capture of Abeta peptides from human plasma and serum. It was found that both ligands could efficiently capture Abeta that were spiked (100 microgml(-1)) to plasma and serum samples. A ligand multimerization problem that would yield suboptimal affinity resins, caused by a cysteine residue present at the binding surface of the Affibody ligands, could be circumvented by the generation of second-generation Affibody ligands (having cysteine to serine substitutions). In an epitope mapping effort, the preferred binding site of selected Affibody ligands was mapped to amino acids 30-36 of Abeta, which fortunately would indicate that the Affibody molecules should not bind the amyloid precursor protein (APP). In addition, a significant effort was made to analyze which form of Abeta (monomer, dimer or higher aggregates) that was most efficiently captured by the selected Affibody ligand. By using Western blotting and a dot blot assay in combination with size exclusion chromatography, it could be concluded that selected Affibody ligands predominantly bound a non-aggregated form of analyzed Abeta peptide, which we speculate to be dimeric Abeta. In conclusion, we have successfully selected Affibody ligands that efficiently capture Abeta peptides from human plasma and serum. The potential therapeutic use of these optimized ligands for extracorporeal capture of Abeta peptides in order to slow down or reduce amyloid plaque formation, is discussed.

PKCε increases endothelin converting enzyme activity and reduces amyloid plaque pathology in transgenic mice

Deposition of plaques containing amyloid beta (Abeta) peptides is a neuropathological hallmark of Alzheimer's disease (AD). Here we demonstrate that neuronal overexpression of the epsilon isozyme of PKC decreases Abeta levels, plaque burden, and plaque-associated neuritic dystrophy and reactive astrocytosis in transgenic mice expressing familial AD-mutant forms of the human amyloid precursor protein (APP). Compared with APP singly transgenic mice, APP/PKCepsilon doubly transgenic mice had decreased Abeta levels but showed no evidence for altered cleavage of APP. Instead, PKCepsilon overexpression selectively increased the activity of endothelin-converting enzyme, which degrades Abeta. The activities of other Abeta-degrading enzymes, insulin degrading enzyme and neprilysin, were unchanged. These results indicate that increased neuronal PKCepsilon activity can promote Abeta clearance and reduce AD neuropathology through increased endothelin-converting enzyme activity.

Antibodies against β‐amyloid reduce aβ oligomers, glycogen synthase kinase‐3β activation and τ phosphorylation in vivo and in vitro

Although active and passive immunization against the beta-amyloid peptide (Abeta) of amyloid plaque-bearing transgenic mice markedly reduces amyloid plaque deposition and improves cognition, the mechanisms of neuroprotection and impact on toxic oligomer species are not understood. We demonstrate that compared to control IgG2b, passive immunization with intracerebroventricular (icv) anti-Abeta (1-15) antibody into the AD HuAPPsw (Tg2576) transgenic mouse model reduced specific oligomeric forms of Abeta, including the dodecamers that correlate with cognitive decline. Interestingly, the reduction of soluble Abeta oligomers, but not insoluble Abeta, significantly correlated with reduced tau phosphorylation by glycogen synthase kinase-3beta (GSK-3beta), a major tau kinase implicated previously in mediating Abeta toxicity. A conformationally-directed antibody against amyloid oligomers (larger than tetramer) also reduced Abeta oligomer-induced activation of GSK3beta and protected human neuronal SH-SY5Y cells from Abeta oligomer-induced neurotoxicity, supporting a role for Abeta oligomers in human tau kinase activation. These data suggest that antibodies that are highly specific for toxic oligomer subspecies may reduce toxicity via reduction of GSK-3beta, which could be an important strategy for Alzheimer's disease (AD) therapeutics.

Estrogen increases brain expression of the mRNA encoding transthyretin, an amyloid beta scavenger protein.

Estrogen replacement therapy in postmenopausal women is associated with a reduced risk of Alzheimer's Disease (AD). The multiple mechanisms by which estrogen protects against AD are still unknown. To conduct a broad screen for estrogen-regulated AD-related genes in the brain, we used cDNA array assays of brain mRNA samples from ovariectomized (ovx) adult female mice treated with either 17beta-estradiol or vehicle at 1 or 5 weeks post-ovx. The gene encoding transthyretin (TTR), which has been reported to scavenge amyloid beta peptides and reduce amyloid plaque formation, is increased by estradiol treatment at both 1 and 5 weeks post-ovx. Northern blot analyses and RNase protection assays performed on whole brain samples obtained from estradiol- or vehicle-treated mice confirmed the cDNA array assays showing a significant increase in TTR mRNA with estradiol treatment. Qualitative in situ hybridization or immunocytochemistry performed on brain sections demonstrated that TTR mRNA is expressed only in choroid plexus and leptomeninges, and that both estrogen receptor proteins, alpha and beta, are present in choroid plexus cells. These novel findings suggest that estrogen may reduce the risk of AD by acting on choroid plexus cells to increase TTR gene expression, leading to enhanced sequestration and reduced aggregation of amyloid beta peptides.

Reduction of amyloid load and cerebral damage in a transgenic mouse model of Alzheimer's disease by treatment with a beta-sheet breaker peptide.

Genetic, neuropathological, and biochemical studies have provided strong evidence for a central role of amyloid in the pathogenesis of Alzheimer's disease (AD). We have proposed previously that peptides designed as beta-sheet breakers may be useful in preventing the formation of amyloid plaques. In this study, we describe a modified beta-sheet breaker peptide with improved pharmacological properties, a high rate of penetration across the blood-brain barrier, and the ability to induce a dramatic reduction in amyloid deposition in two different transgenic AD models. In addition, we report for the first time a significant increase in neuronal survival and a decrease in brain inflammation associated with the reduction of amyloid plaques. These results demonstrate that the process of amyloid deposition is one of the causes of neurodegeneration in AD. Moreover, our findings indicate that beta-sheet breaker peptides provide a valuable tool for evaluating further the importance of amyloid in the etiology of AD and suggest that these peptides or some of their derivatives might be good candidates for AD treatment.

Reduced levels of amyloid beta-peptide antibody in Alzheimer disease.

To investigate whether it was possible to detect the presence and different levels of naturally occurring anti-beta-amyloid (Abeta) antibodies in the CSF of patients with AD and age-matched controls by employing a sensitive ELISA. Immunization with preaggregated amyloid beta-peptide (Abeta(1-42)) and administration of antibodies against Abeta into amyloid precursor protein APP(V717F)- transgenic mice (an animal model of AD) have recently been reported to dramatically reduce amyloid plaque deposition, neuritic dystrophy, and astrogliosis, most likely by enhancing Abeta clearance from brain. A sensitive ELISA was performed to detect levels of naturally occurring anti-Abeta antibodies in the CSF of patients with AD and age-matched controls. Additionally, an immunoprecipitation assay was performed to confirm that naturally occurring anti-Abeta antibodies also exist in the human blood. - Naturally occurring antibodies directed against Abeta were found in the CSF and plasma of patients with AD and healthy control subjects. Moreover, CSF anti-Abeta antibody titers are significantly lower in patients with AD compared with healthy control subjects. Naturally occurring antibodies directed against Abeta exist in human CSF and plasma. The CSF anti-Abeta antibody titers may be helpful in better understanding the effects of future immunologic therapies for AD.