Chronic intranasal treatment with an anti-Aβ(30-42) scFv antibody ameliorates amyloid pathology in a transgenic mouse model of Alzheimer's disease

Amyloid-beta peptide (Aβ)-directed active and passive immunization therapeutic strategies reduce brain levels of Aβ, decrease the severity of beta-amyloid plaque pathology and reverse cognitive deficits in mouse models of Alzheimer's disease (AD). As an alternative approach to passive immunization with full IgG molecules, single-chain variable fragment (scFv) antibodies can modulate or neutralize Aβ-related neurotoxicity and inhibit its aggregation in vitro. In this study, we characterized a scFv derived from a full IgG antibody raised against the C-terminus of Aβ, and studied its passage into the brains of APP transgenic mice, as well as its potential to reduce Aβ-related pathology. We found that the scFv entered the brain after intranasal application, and that it bound to beta-amyloid plaques in the cortex and hippocampus of APP transgenic mice. Moreover, the scFv inhibited Aβ fibril formation and Aβ-mediated neurotoxicity in vitro. In a preventative therapeutic approach chronic intranasal treatment with scFv reduced congophilic amyloid angiopathy (CAA) and beta-amyloid plaque numbers in the cortex of APPswe/PS1dE9 mice. This reduction of CAA and plaque pathology was associated with a redistribution of brain Aβ from the insoluble fraction to the soluble peptide pool. Due to their lack of the effector domain of full IgG, scFv may represent an alternative tool for the treatment of Aβ-related pathology without triggering Fc-mediated effector functions. Additionally, our observations support the possibility that Aβ-directed immunotherapy can reduce Aβ deposition in brain vessels in transgenic mice.     

Amyloid-beta-anti-amyloid-beta complex structure reveals an extended conformation in the immunodominant B-cell epitope

Alzheimer's disease (AD) is the most common form of dementia. Amyloid-β (Aβ) peptide, generated by proteolytic cleavage of the amyloid precursor protein, is central to AD pathogenesis. Most pharmaceutical activity in AD research has focused on Aβ, its generation and clearance from the brain. In particular, there is much interest in immunotherapy approaches with a number of anti-Aβ antibodies in clinical trials. We have developed a monoclonal antibody, called WO2, which recognises the Aβ peptide. To this end, we have determined the three-dimensional structure, to near atomic resolution, of both the antibody and the complex with its antigen, the Aβ peptide. The structures reveal the molecular basis for WO2 recognition and binding of Aβ. The Aβ peptide adopts an extended, coil-like conformation across its major immunodominant B-cell epitope between residues 2 and 8. We have also studied the antibody-bound Aβ peptide in the presence of metals known to affect its aggregation state and show that WO2 inhibits these interactions. Thus, antibodies that target the N-terminal region of Aβ, such as WO2, hold promise for therapeutic development.     

Nonhuman Amyloid Oligomer Epitope Reduces Alzheimer’s-Like Neuropathology in 3xTg-AD Transgenic Mice

Accumulation of beta-amyloid (Aβ) is an important pathological event in Alzheimer’s disease (AD). It is now well known that vaccination against fibrillar Aβ prevents amyloid accumulation and preserves cognitive function in transgenic mouse models. To study the effect of vaccination against generic oligomer epitopes, Aβ oligomers, islet amyloid polypeptide oligomers, random peptide oligomer (3A), and Aβ fibrils were used to vaccinate 3xTg-AD, which develop a progressive accumulation of plaques and cognitive impairment. Subcutaneous administration of these antigens markedly reduced total plaque load (Aβ burden) and improved cognitive function in the 3xTg-AD mouse brains as compared to controls. We demonstrated that vaccination with this nonhuman amyloid oligomer generated high titers of specifically antibodies recognizing Aβ oligomers, which in turn inhibited accumulation of Aβ pathology in mice. In addition to amyloid plaques, another hallmark of AD is tau pathology. It was found that there was a significant decline in the level of hyper-phosphorylated tau following vaccination. We have previously shown that immunization with 3A peptide improves cognitive function and clears amyloid plaques in Tg2576 mice, which provides a novel strategy of AD therapy. Here, we have shown that vaccination with 3A peptide in 3xTg-AD mice not only clears amyloid plaques but also extensively clears abnormal tau in brain.     

Conversion of Aβ42 into a Folded Soluble Native-like Protein using a Semi-random Library of Amphipathic Helices

The amyloid cascade model hypothesizes that neurotoxic oligomers or aggregates formed by the Alzheimer amyloid peptide (Aβ) cause disease pathology in Alzheimer's disease. Attempted treatment strategies for Alzheimer's disease have involved either inhibiting Aβ oligomerization or aggregation, or dissolving existing aggregates. Blocking such downhill processes, however, has proved daunting. We have used a different approach that targets Aβ before the oligomerization cascade begins. We predicted that an amphipathic helix could convert Aβ into a native-like protein and inhibit initiation of oligomerization and aggregation. This idea was tested with a designed library and genetic screen. We exhaustively screened a library of semi-randomized amphipathic helical sequences, each expressed as a fusion protein with an Aβ42-yellow fluorescent protein sequence serving as a reporter for folding and solubilization. This yielded an amphipathic helix capable of initiating native-like folding in Aβ42 and preventing aggregation. This amphipathic helix has direct application to Alzheimer's disease therapy development.     

Calmodulin antagonizes amyloid-β peptides-mediated inhibition of brain plasma membrane Ca(2+)-ATPase

The synaptosomal plasma membrane Ca(2+)-ATPase (PMCA) plays an essential role in regulating intracellular Ca(2+) concentration in brain. We have recently found that PMCA is the only Ca(2+) pump in brain which is inhibited by amyloid-β peptide (Aβ), a neurotoxic peptide implicated in the pathology of Alzheimer's disease (AD) [1], but the mechanism of inhibition is lacking. In the present study we have characterized the inhibition of PMCA by Aβ. Results from kinetic assays indicate that Aβ aggregates are more potent inhibitors of PMCA activity than monomers. The inhibitory effect of Aβ could be blocked by pretreating the purified protein with Ca(2+)-calmodulin, the main endogenous activator of PMCA, and the activity of truncated PMCA lacking the calmodulin binding domain was not affected by Aβ. Dot-overlay experiments indicated a physical association of Aβ with PMCA and also with calmodulin. Thus, calmodulin could protect PMCA from inhibition by Aβ by burying exposed sites on PMCA, making them inaccessible to Aβ, and also by direct binding to the peptide. These results suggest a protective role of calmodulin against neuronal Ca(2+) dysregulation by PMCA inhibition induced by Aβ.     

Curcumin promotes A-beta fibrillation and reduces neurotoxicity in transgenic Drosophila

The pathology of Alzheimer's disease (AD) is characterized by the presence of extracellular deposits of misfolded and aggregated amyloid-β (Aβ) peptide and intraneuronal accumulation of tangles comprised of hyperphosphorylated Tau protein. For several years, the natural compound curcumin has been proposed to be a candidate for enhanced clearance of toxic Aβ amyloid. In this study we have studied the potency of feeding curcumin as a drug candidate to alleviate Aβ toxicity in transgenic Drosophila. The longevity as well as the locomotor activity of five different AD model genotypes, measured relative to a control line, showed up to 75% improved lifespan and activity for curcumin fed flies. In contrast to the majority of studies of curcumin effects on amyloid we did not observe any decrease in the amount of Aβ deposition following curcumin treatment. Conformation-dependent spectra from p-FTAA, a luminescent conjugated oligothiophene bound to Aβ deposits in different Drosophila genotypes over time, indicated accelerated pre-fibrillar to fibril conversion of Aβ(1-42) in curcumin treated flies. This finding was supported by in vitro fibrillation assays of recombinant Aβ(1-42). Our study shows that curcumin promotes amyloid fibril conversion by reducing the pre-fibrillar/oligomeric species of Aβ, resulting in a reduced neurotoxicity in Drosophila.     

A cyclic undecamer peptide mimics a turn in folded Alzheimer amyloid β and elicits antibodies against oligomeric and fibrillar amyloid and plaques

The 39- to 42-residue amyloid β (Aβ) peptide is deposited in extracellular fibrillar plaques in the brain of patients suffering from Alzheimer's Disease (AD). Vaccination with these peptides seems to be a promising approach to reduce the plaque load but results in a dominant antibody response directed against the N-terminus. Antibodies against the N-terminus will capture Aβ immediately after normal physiological processing of the amyloid precursor protein and therefore will also reduce the levels of non-misfolded Aβ, which might have a physiologically relevant function. Therefore, we have targeted an immune response on a conformational neo-epitope in misfolded amyloid that is formed in advance of Aβ-aggregation. A tetanus toxoid-conjugate of the 11-meric cyclic peptide Aβ(22-28)-YNGK' elicited specific antibodies in Balb/c mice. These antibodies bound strongly to the homologous cyclic peptide-bovine serum albumin conjugate, but not to the homologous linear peptide-conjugate, as detected in vitro by enzyme-linked immunosorbent assay. The antibodies also bound--although more weakly--to Aβ(1-42) oligomers as well as fibrils in this assay. Finally, the antibodies recognized Aβ deposits in AD mouse and human brain tissue as established by immunohistological staining. We propose that the cyclic peptide conjugate might provide a lead towards a vaccine that could be administered before the onset of AD symptoms. Further investigation of this hypothesis requires immunization of transgenic AD model mice.     

Novel approaches for immunotherapeutic intervention in Alzheimer's disease

Immunotherapy can attenuate amyloid neuropathology and improve cognitive function in transgenic models of Alzheimer's disease. However, the first clinical trial was halted when 6% of the Alzheimer's patients developed aseptic meningoencephalitis. Postmortem analysis of two cases with meningoencephalitis showed robust glial activation, T-cell infiltration and sporadic clearance of Abeta. Interestingly, transgenic mouse models of Alzheimer's disease failed as predictors of these adverse inflammatory events. However there are now several studies with amyloid precursor protein transgenic mice that have reported an increased risk of microhemorrhages at sites of cerebrovascular amyloid deposits and because approximately 80% of Alzheimer's patient's have cerebrovascular pathology, there is concern regarding clinical trials using passive administration of humanized anti-Abeta antibodies. Although many studies have now been published on immunotherapy in mouse models, the mechanism(s) of antibody-mediated clearance of beta-amyloid from the brain, and the cause of the antibody-induced microhemorrhages remain unclear. In this review, we will discuss the most recent results from the first clinical trial, offer speculation on possible causes for the failure of the trial, review data on antibody-mediated clearance mechanisms, explore the role of complement and inflammation in the clearance of beta-amyloid, and suggest novel strategies for avoiding problems in future clinical trials. The central hypothesis being proposed in this review is that anti-Abeta antibodies delivered directly to the CNS at the sites of amyloid deposits will be far more effective at clearing Abeta and safer than active or passive immunization strategies where the majority of the antibodies are in the periphery.     

Protective effects of positive lysosomal modulation in Alzheimer's disease transgenic mouse models

Alzheimer's disease (AD) is an age-related neurodegenerative pathology in which defects in proteolytic clearance of amyloid β peptide (Aβ) likely contribute to the progressive nature of the disorder. Lysosomal proteases of the cathepsin family exhibit up-regulation in response to accumulating proteins including Aβ(1-42). Here, the lysosomal modulator Z-Phe-Ala-diazomethylketone (PADK) was used to test whether proteolytic activity can be enhanced to reduce the accumulation events in AD mouse models expressing different levels of Aβ pathology. Systemic PADK injections in APP(SwInd) and APPswe/PS1ΔE9 mice caused 3- to 8-fold increases in cathepsin B protein levels and 3- to 10-fold increases in the enzyme's activity in lysosomal fractions, while neprilysin and insulin-degrading enzyme remained unchanged. Biochemical analyses indicated the modulation predominantly targeted the active mature forms of cathepsin B and markedly changed Rab proteins but not LAMP1, suggesting the involvement of enhanced trafficking. The modulated lysosomal system led to reductions in both Aβ immunostaining as well as Aβ(x-42) sandwich ELISA measures in APP(SwInd) mice of 10-11 months. More extensive Aβ deposition in 20-22-month APPswe/PS1ΔE9 mice was also reduced by PADK. Selective ELISAs found that a corresponding production of the less pathogenic Aβ(1-38) occurs as Aβ(1-42) levels decrease in the mouse models, indicating that PADK treatment leads to Aβ truncation. Associated with Aβ clearance was the elimination of behavioral and synaptic protein deficits evident in the two transgenic models. These findings indicate that pharmacologically-controlled lysosomal modulation reduces Aβ(1-42) accumulation, possibly through intracellular truncation that also influences extracellular deposition, and in turn offsets the defects in synaptic composition and cognitive functions. The selective modulation promotes clearance at different levels of Aβ pathology and provides proof-of-principle for small molecule therapeutic development for AD and possibly other protein accumulation disorders.     

Tau-targeted immunization impedes progression of neurofibrillary histopathology in aged P301L tau transgenic mice

In Alzheimer's disease (AD) brains, the microtubule-associated protein tau and amyloid-β (Aβ) deposit as intracellular neurofibrillary tangles (NFTs) and extracellular plaques, respectively. Tau deposits are furthermore found in a significant number of frontotemporal dementia cases. These diseases are characterized by progressive neurodegeneration, the loss of intellectual capabilities and behavioral changes. Unfortunately, the currently available therapies are limited to symptomatic relief. While active immunization against Aβ has shown efficacy in both various AD mouse models and patients with AD, immunization against pathogenic tau has only recently been shown to prevent pathology in young tau transgenic mice. However, if translated to humans, diagnosis and treatment would be routinely done when symptoms are overt, meaning that the histopathological changes have already progressed. Therefore, we used active immunization to target pathogenic tau in 4, 8, and 18 months-old P301L tau transgenic pR5 mice that have an onset of NFT pathology at 6 months of age. In all age groups, NFT pathology was significantly reduced in treated compared to control pR5 mice. Similarly, phosphorylation of tau at pathological sites was reduced. In addition, increased astrocytosis was found in the oldest treated group. Taken together, our data suggests that tau-targeted immunization slows the progression of NFT pathology in mice, with practical implications for human patients.     

Membrane and surface interactions of Alzheimer's Aβ peptide--insights into the mechanism of cytotoxicity

Alzheimer's disease is the most common form of dementia and its pathological hallmarks include the loss of neurones through cell death, as well as the accumulation of amyloid fibres in the form of extracellular neuritic plaques. Amyloid fibrils are composed of the amyloid-β peptide (Aβ), which is known to assemble to form 'toxic' oligomers that may be central to disease pathology. Aβ is produced by cleavage from the amyloid precursor protein within the transmembrane region, and the cleaved peptide may retain some membrane affinity. It has been shown that Aβ is capable of specifically binding to phospholipid membranes with a relatively high affinity, and that modulation of the composition of the membrane can alter both membrane-amyloid interactions and toxicity. Various biomimetic membrane models have been used (e.g. lipid vesicles in solution and tethered lipid bilayers) to examine the binding and interactions between Aβ and the membrane surfaces, as well as the resulting permeation. Oligomeric Aβ has been observed to bind more avidly to membranes and cause greater permeation than fibrillar Aβ. We review some of the recent advances in studying Aβ-membrane interactions and discuss their implications with respect to understanding the causes of Alzheimer's disease.     

靶向β淀粉样蛋白的阿尔茨海默病疫苗研究进展

阿尔茨海默病(AD)是一种以认知功能障碍和记忆减退为主要临床特征的神经退行性疾病。目前,β淀粉样蛋白(Aβ)被认为是AD免疫治疗的关键靶标,其疫苗研究包括多肽疫苗、DNA表位疫苗及病毒载体疫苗等。我们简要地对近年来AD疫苗研究进展进行了综述。     

Colloidal properties of biodegradable nanoparticles influence interaction with amyloid-β peptide

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the extracellular deposition of amyloid-β peptides (Aβ). During the past few years, promising approaches based on nanotechnologies have emerged to alter Aβ aggregation and its related toxicity. This study aims to investigate the influence of the nanoparticle colloidal properties over the interaction with Aβ peptide 1-42 (Aβ(1-42)). Using capillary electrophoresis with laser-induced fluorescence detection, it was shown that biodegradable poly(ethylene glycol)-block-polylactide (PEG-b-PLA) nanoparticles were able to interact with Aβ(1-42) peptide leading to its uptake in rather short time periods. In addition, we highlighted the crucial role of the nanocarrier colloidal properties on the uptake kinetics. Whereas nanoparticles stabilized by sodium cholate (lower size and higher negative surface charge) gave optimum uptake kinetics, nanoparticles stabilized with others surfactants presented lower interactions. In contrast, PEG density seemed to have no influence on the interaction when sodium cholate was used for the preparation. This study intends to give new insights into Aβ(1-42) peptide interaction with nanoparticulate systems by helping to determine suitable nanoparticle characteristics regarding forthcoming therapeutic strategies against AD.     

阿尔茨海默病免疫治疗的临床研究进展

阿尔茨海默病免疫治疗以淀粉样蛋白Aβ或tau蛋白为治疗靶点。通过疫苗刺激产生靶标抗体的主动免疫或直接给予抗体的被动免疫,可减轻AD病理改变,有望延缓或阻止AD病程进展。动物研究显示了广阔的治疗前景,临床免疫治疗的部分药物已完成III期试验,但未达到预期效果。综述近年来免疫治疗AD的临床研究进展。     

Point mutations in Aβ result in the formation of distinct polymorphic aggregates in the presence of lipid bilayers

A hallmark of Alzheimer's disease (AD) is the rearrangement of the β-amyloid (Aβ) peptide to a non-native conformation that promotes the formation of toxic, nanoscale aggregates. Recent studies have pointed to the role of sample preparation in creating polymorphic fibrillar species. One of many potential pathways for Aβ toxicity may be modulation of lipid membrane function on cellular surfaces. There are several mutations clustered around the central hydrophobic core of Aβ near the α-secretase cleavage site (E22G Arctic mutation, E22K Italian mutation, D23N Iowa mutation, and A21G Flemish mutation). These point mutations are associated with hereditary diseases ranging from almost pure cerebral amyloid angiopathy (CAA) to typical Alzheimer's disease pathology with plaques and tangles. We investigated how these point mutations alter Aβ aggregation in the presence of supported lipid membranes comprised of total brain lipid extract. Brain lipid extract bilayers were used as a physiologically relevant model of a neuronal cell surface. Intact lipid bilayers were exposed to predominantly monomeric preparations of Wild Type or different mutant forms of Aβ, and atomic force microscopy was used to monitor aggregate formation and morphology as well as bilayer integrity over a 12 hour period. The goal of this study was to determine how point mutations in Aβ, which alter peptide charge and hydrophobic character, influence interactions between Aβ and the lipid surface. While fibril morphology did not appear to be significantly altered when mutants were prepped similarly and incubated under free solution conditions, aggregation in the lipid membranes resulted in a variety of polymorphic aggregates in a mutation dependent manner. The mutant peptides also had a variable ability to disrupt bilayer integrity.     

Engineered antibody approaches for Alzheimer's disease immunotherapy

The accumulation of amyloid-β-peptide (Aβ or A-beta) in the brain is considered to be a key event in the pathogenesis of Alzheimer's disease (AD). Over the last decade, antibody strategies aimed at reducing high levels of Aβ in the brain and or neutralizing its toxic effects have emerged as one of the most promising treatments for AD. Early approaches using conventional antibody formats demonstrated the potential of immunotherapy, but also caused a range of undesirable side effects such meningoencephalitis, vasogenic edema or cerebral microhemorrhages in both murine and humans. This prompted the exploration of alternative approaches using engineered antibodies to avoid adverse immunological responses and provide a safer and more effective therapy. Encouraging results have been obtained using a range of recombinant antibody formats including, single chain antibodies, antibody domains, intrabodies, bispecific antibodies as well as Fc-engineered antibodies in transgenic AD mouse and primate models. This review will address recent progress using these recombinant antibodies against Aβ, highlighting their advantages over conventional monoclonal antibodies and delivery methods.     

The amyloid precursor protein and its homologues: structural and functional aspects of native and pathogenic oligomerization

Over the last 25 years, remarkable progress has been made not only in identifying key molecules of Alzheimer's disease but also in understanding their meaning in the pathogenic state. One hallmark of Alzheimer pathology is the amyloid plaque. A major component of the extracellular deposit is the amyloid-β (Aβ) peptide which is generated from its larger precursor molecule, i.e., the amyloid precursor protein (APP) by consecutive cleavages. Processing is exerted by two enzymes, i.e., the β-secretase and the γ-secretase. We and others have found that the self-association of the amyloid peptide and the dimerization and oligomerization of these proteins is a key factor under native and pathogenic conditions. In particular, the Aβ homodimer represents a nidus for plaque formation and a well defined therapeutic target. Further, dimerization of the APP was reported to increase generation of toxic Aβ whereas heterodimerization with its homologues amyloid precursor like proteins (APLP1 and APLP2) decreased Aβ formation. This review mainly focuses on structural features of the homophilic and heterophilic interactions among APP family proteins. The proposed contact sites are described and the consequences of protein dimerization on their functions and in the pathogenesis of Alzheimer's disease are discussed.     

Macromolecular and small-molecule modulation of intracellular Aβ42 aggregation and associated toxicity

Aβ (amyloid β-peptide) has a central role in AD (Alzheimer's disease) where neuronal toxicity is linked to its extracellular and intracellular accumulation as oligomeric species. Searching for molecules that attenuate Aβ aggregation could uncover novel therapies for AD, but most studies in mammalian cells have inferred aggregation indirectly by assessing levels of secreted Aβ peptide. In the present study we establish a mammalian cell system for the direct visualization of Aβ formation by expression of an Aβ(42)-EGFP (enhanced green fluorescent protein) fusion protein in the human embryonic kidney cell line T-REx293, and use this to identify both macromolecules and small molecules that reduce aggregation and associated cell toxicity. Thus a molecular shield protein AavLEA1 [Aphelenchus avenae LEA (late embryogenesis abundant) protein 1], which limits aggregation of proteins with expanded poly(Q) repeats, is also effective against Aβ(42)-EGFP when co-expressed in T-REx293 cells. A screen of polysaccharide and small organic molecules from medicinal plants and fungi reveals one candidate in each category, PS5 (polysaccharide 5) and ganoderic acid DM respectively, with activity against Aβ. Both PS5 and ganoderic acid DM probably promote Aβ aggregate clearance indirectly through the proteasome. The model is therefore of value to study the effects of intracellular Aβ on cell physiology and to identify reagents that counteract those effects.     

D-amino acid-based peptide inhibitors as early or preventative therapy in Alzheimer disease

Beta amyloid (Aβ) accumulation is recognized as a hallmark of Alzheimer disease (AD) pathology and the aggregation of Aβ peptide is hypothesized to drive pathogenesis. As such, Aβ is a logical target for therapeutic intervention and there have been many studies looking at diverse classes of drugs that target Aβ. Of concern is the recent failure of several clinical trials, highlighting the need for earlier, possibly preventative intervention, and raising the question of what form of Aβ is the best target. The Aβ oligomers are considered to be the toxic species, but many therapies, such as antibody therapies, target monomers, removing them as substrates for aggregation. Peptide inhibitors, in contrast, are able to interfere with the aggregation process itself. Designing peptide inhibitors requires some knowledge of Aβ structure; while there is structural information about the amyloid core of Aβ fibrils, the transient nature of oligomers makes them difficult to characterize. Fortunately, some interaction sites have been identified between monomers and oligomers of Aβ and these, plus known aggregation-prone sequences in Aβ, can serve as a basis for inhibitor design. In this mini-review we focus on D-amino acid based peptide inhibitors and discuss how their non-toxic and stable nature can be beneficial, while they specifically target aggregation-prone sequences within the Aβ peptide. Many peptide inhibitors have been designed using the LVFFA domain within Aβ to disrupt the self-assembly of Aβ peptide. While this may be sufficient to stop aggregation in vitro, other aggregation sites at the C-terminus may promote aggregation independently and the flexible N terminus may be a good target to induce clearance of aggregates. Ultimately, it may be a combination of targets that provides the best therapeutic strategy.     

Active immunization with amyloid-beta 1-42 impairs memory performance through TLR2/4-dependent activation of the innate immune system

Active immunization with amyloid-β (Aβ) peptide 1-42 reverses amyloid plaque deposition in the CNS of patients with Alzheimer's disease and in amyloid precursor protein transgenic mice. However, this treatment may also cause severe, life-threatening meningoencephalitis. Physiological responses to immunization with Aβ(1-42) are poorly understood. In this study, we characterized cognitive and immunological consequences of Aβ(1-42)/CFA immunization in C57BL/6 mice. In contrast to mice immunized with myelin oligodendrocyte glycoprotein (MOG)(35-55)/CFA or CFA alone, Aβ(1-42)/CFA immunization resulted in impaired exploratory activity, habituation learning, and spatial-learning abilities in the open field. As morphological substrate of this neurocognitive phenotype, we identified a disseminated, nonfocal immune cell infiltrate in the CNS of Aβ(1-42)/CFA-immunized animals. In contrast to MOG(35-55)/CFA and PBS/CFA controls, the majority of infiltrating cells in Aβ(1-42)/CFA-immunized mice were CD11b(+)CD14(+) and CD45(high), indicating their blood-borne monocyte/macrophage origin. Immunization with Aβ(1-42)/CFA was significantly more potent than immunization with MOG(35-55)/CFA or CFA alone in activating macrophages in the secondary lymphoid compartment and peripheral tissues. Studies with TLR2/4-deficient mice revealed that the TLR2/4 pathway mediated the Aβ(1-42)-dependent proinflammatory cytokine release from cells of the innate immune system. In line with this, TLR2/4 knockout mice were protected from cognitive impairment upon immunization with Aβ(1-42)/CFA. Thus, this study identifies adjuvant effects of Aβ(1-42), which result in a clinically relevant neurocognitive phenotype highlighting potential risks of Aβ immunotherapy.