Evidence linking neuronal cell death to autoimmunity in Alzheimer's disease

Serum immunoglobulin and the threshold of Fc receptor-mediated immune activation

Antibodies can mediate immune recruitment or clearance of immune complexes through the interaction of their Fc domain with cellular Fc receptors. Clustering of antibodies is a key step in generating sufficient avidity for efficacious receptor recognition. However, Fc receptors may be saturated with prevailing, endogenous serum immunoglobulin and this raises the threshold by which cellular receptors can be productively engaged. Here, we review the factors controlling serum IgG levels in both healthy and disease states, and discuss how the presence of endogenous IgG is encoded into the functional activation thresholds for low- and high-affinity Fc receptors. We discuss the circumstances where antibody engineering can help overcome these physiological limitations of therapeutic antibodies. Finally, we discuss how the pharmacological control of Fc receptor saturation by endogenous IgG is emerging as a feasible mechanism for the enhancement of antibody therapeutics.

Antibody-Mediated Clearance of Brain Amyloid-β: Mechanisms of Action, Effects of Natural and Monoclonal Anti-Aβ Antibodies, and Downstream Effects

Immunotherapeutic efforts to slow the clinical progression of Alzheimer's disease (AD) by lowering brain amyloid-β (Aβ) have included Aβ vaccination, intravenous immunoglobulin (IVIG) products, and anti-Aβ monoclonal antibodies. Neither Aβ vaccination nor IVIG slowed disease progression. Despite conflicting phase III results, the monoclonal antibody Aducanumab received Food and Drug Administration (FDA) approval for treatment of AD in June 2021. The only treatments unequivocally demonstrated to slow AD progression to date are the monoclonal antibodies Lecanemab and Donanemab. Lecanemab received FDA approval in January 2023 based on phase II results showing lowering of PET-detectable Aβ; phase III results released at that time indicated slowing of disease progression. Topline results released in May 2023 for Donanemab's phase III trial revealed that primary and secondary end points had been met. Antibody binding to Aβ facilitates its clearance from the brain via multiple mechanisms including promoting its microglial phagocytosis, activating complement, dissolving fibrillar Aβ, and binding of antibody-Aβ complexes to blood-brain barrier receptors. Antibody binding to Aβ in peripheral blood may also promote cerebral efflux of Aβ by a peripheral sink mechanism. According to the amyloid hypothesis, for Aβ targeting to slow AD progression, it must decrease downstream neuropathological processes including tau aggregation and phosphorylation and (possibly) inflammation and oxidative stress. This review discusses antibody-mediated mechanisms of Aβ clearance, findings in AD trials involving Aβ vaccination, IVIG, and anti-Aβ monoclonal antibodies, downstream effects reported in those trials, and approaches which might improve the Aβ-clearing ability of monoclonal antibodies.

Immune Regulatory Functions of Macrophages and Microglia in Central Nervous System Diseases

Macrophages can be characterized as a very multifunctional cell type with a spectrum of phenotypes and functions being observed spatially and temporally in various disease states. Ample studies have now demonstrated a possible causal link between macrophage activation and the development of autoimmune disorders. How these cells may be contributing to the adaptive immune response and potentially perpetuating the progression of neurodegenerative diseases and neural injuries is not fully understood. Within this review, we hope to illustrate the role that macrophages and microglia play as initiators of adaptive immune response in various CNS diseases by offering evidence of: (1) the types of immune responses and the processes of antigen presentation in each disease, (2) receptors involved in macrophage/microglial phagocytosis of disease-related cell debris or molecules, and, finally, (3) the implications of macrophages/microglia on the pathogenesis of the diseases.

Alzheimer’s Disease and Inflammaging

Alzheimer’s disease is one of the most common age-related neurodegenerative disorders. The main theory of Alzheimer’s disease progress is the amyloid-β cascade hypothesis. However, the initial mechanisms of insoluble forms of amyloid-β formation and hyperphosphorylated tau protein in neurons remain unclear. One of the factors, which might play a key role in senile plaques and tau fibrils generation due to Alzheimer’s disease, is inflammaging, i.e., systemic chronic low-grade age-related inflammation. The activation of the proinflammatory cell phenotype is observed during aging, which might be one of the pivotal mechanisms for the development of chronic inflammatory diseases, e.g., atherosclerosis, metabolic syndrome, type 2 diabetes mellitus, and Alzheimer’s disease. This review discusses the role of the inflammatory processes in developing neurodegeneration, activated during physiological aging and due to various diseases such as atherosclerosis, obesity, type 2 diabetes mellitus, and depressive disorders.

Increased plasma and brain immunoglobulin A in Alzheimer’s disease is lost in apolipoprotein E ε4 carriers

Background

Alzheimer’s disease (AD) is foremost characterized by β-amyloid (Aβ)-extracellular plaques, tau-intraneuronal fibrillary tangles (NFT), and neuroinflammation, but over the last years it has become evident that peripheral inflammation might also contribute to the disease. AD patients often demonstrate increased levels of circulating proinflammatory mediators and altered antibody levels in the blood. In our study, we investigated the plasma Immunoglobulin A (IgA) levels in association with apolipoprotein E (APOE) ε4 status and Aβ pathology.

Methods

IgA levels in antemortem-collected (cohort I) and postmortem-collected (cohort II) plasma samples from AD patients (n = 30 in cohort I and n = 16 in cohort II) and non-demented age-matched controls (NC) (n = 42 in cohort I and n = 7 in cohort II) were measured using ELISA. Hippocampal sections from cohort II were immunostained against IgA, and the IgA area fraction as well as the number of IgA positive (IgA+) cells in the cornu ammonis region were analysed using ImageJ. The relationship between plasma IgA levels and cognition, C-reactive protein (CRP), and cerebrospinal fluid (CSF) AD biomarkers in cohort I as well as neuropathology, IgA+ cell number, and IgA area fraction in cohort II was analysed before and after grouping the cohorts into APOEε4 carriers and APOEε4 non-carriers.

Results

Plasma IgA levels were higher in AD patients compared to NC in both cohorts. Also, AD patients demonstrated higher IgA area fraction and IgA+ cell number compared to NC. When APOEε4 status was considered, higher plasma IgA levels in AD patients were only seen in APOEε4 non-carriers. Finally, plasma IgA levels, exclusively in APOEε4 non-carriers, were associated with cognition, CRP, and CSF Aβ levels in cohort I as well as with IgA area fraction, IgA+ cell number, and Aβ, Lewy body, and NFT neuropathology in cohort II.

Conclusions

Our study suggests that AD pathology and cognitive decline are associated with increased plasma IgA levels in an APOE allele-dependent manner, where the associations are lost in APOEε4 carriers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01062-z.

Systematic review of human post-mortem immunohistochemical studies and bioinformatics analyses unveil the complexity of astrocyte reaction in Alzheimer's disease

AIMS

Reactive astrocytes in Alzheimer's disease (AD) have traditionally been demonstrated by increased glial fibrillary acidic protein (GFAP) immunoreactivity; however, astrocyte reaction is a complex and heterogeneous phenomenon involving multiple astrocyte functions beyond cytoskeletal remodelling. To better understand astrocyte reaction in AD, we conducted a systematic review of astrocyte immunohistochemical studies in post-mortem AD brains followed by bioinformatics analyses on the extracted reactive astrocyte markers.

METHODS

NCBI PubMed, APA PsycInfo and WoS-SCIE databases were interrogated for original English research articles with the search terms 'Alzheimer's disease' AND 'astrocytes.' Bioinformatics analyses included protein-protein interaction network analysis, pathway enrichment, and transcription factor enrichment, as well as comparison with public human -omics datasets.

RESULTS

A total of 306 articles meeting eligibility criteria rendered 196 proteins, most of which were reported to be upregulated in AD vs control brains. Besides cytoskeletal remodelling (e.g., GFAP), bioinformatics analyses revealed a wide range of functional alterations including neuroinflammation (e.g., IL6, MAPK1/3/8 and TNF), oxidative stress and antioxidant defence (e.g., MT1A/2A, NFE2L2, NOS1/2/3, PRDX6 and SOD1/2), lipid metabolism (e.g., APOE, CLU and LRP1), proteostasis (e.g., cathepsins, CRYAB and HSPB1/2/6/8), extracellular matrix organisation (e.g., CD44, MMP1/3 and SERPINA3), and neurotransmission (e.g., CHRNA7, GABA, GLUL, GRM5, MAOB and SLC1A2), among others. CTCF and ESR1 emerged as potential transcription factors driving these changes. Comparison with published -omics datasets validated our results, demonstrating a significant overlap with reported transcriptomic and proteomic changes in AD brains and/or CSF.

CONCLUSIONS

Our systematic review of the neuropathological literature reveals the complexity of AD reactive astrogliosis. We have shared these findings as an online resource available at www.astrocyteatlas.org.

Alzheimer Disease Pathogenesis: The Role of Autoimmunity

BACKGROUND

In addition to deposits of amyloid β (Aβ) plaques and neurofibrillary tangles, growing evidence demonstrates that complex and multifaceted biological processes can arise during Alzheimer disease (AD) pathogenesis. The recent failures of clinical trials based on the amyloid hypothesis and the presence of Aβ plaques in cognitively healthy elderly persons without AD point toward a need to explore novel pathobiological mechanisms of AD.

CONTENT

In the search for alternative AD mechanisms, numerous genome-wide association studies and mechanistic discoveries suggest a potential immunologic component of the disease. However, new experimental tools are needed to uncover these immunogenic components. The current methods, such as ELISAs or protein microarrays, have limitations of low throughput and/or sensitivity and specificity. In this article, we briefly discuss evidence of potential autoimmune contributions to AD pathobiology, describe the current methods for identifying autoantibodies in patient fluids, and outline our own efforts to develop new techniques for novel autoantibody biomarker discovery.

SUMMARY

Uncovering the putative autoimmune components of AD may be crucial in paving the way to new concepts for pathogenesis, diagnosis, and therapy.

IMPACT STATEMENT

In addition to deposits of amyloid β plaques and neurofibrillary tangles, growing evidence demonstrates that complex and multifaceted biological processes can arise during Alzheimer disease (AD) pathogenesis. Numerous research directions, including genome-wide association, clinical correlation, and mechanistic studies, have pointed to a potential autoimmunologic contribution to AD pathology. We present research suggesting the association between autoimmunity and AD and demonstrate the need for new laboratory techniques to further characterize potential brain antigen-specific autoantibodies. Uncovering the putative autoimmune components of AD may be crucial in paving the way to new concepts for pathogenesis, diagnosis, and therapy.

The Functional Roles and Applications of Immunoglobulins in Neurodegenerative Disease

Natural autoantibodies, immunoglobulins (Igs) that target self-proteins, are common in the plasma of healthy individuals; some of the autoantibodies play pathogenic roles in systemic or tissue-specific autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus. Recently, the field of autoantibody-associated diseases has expanded to encompass neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD), with related studies examining the functions of Igs in the central nervous system (CNS). Recent evidence suggests that Igs have various effects in the CNS; these effects are associated with the prevention of neurodegeneration, as well as induction. Here, we summarize the functional roles of Igs with respect to neurodegenerative disease (AD and PD), focusing on the target antigens and effector cell types. In addition, we review the current knowledge about the roles of these antibodies as diagnostic markers and immunotherapies.

AMBAR, an Encouraging Alzheimer's Trial That Raises Questions

Grifols' recent Alzheimer Management by Albumin Replacement (“AMBAR”) study investigated the effects of plasmapheresis with albumin replacement, plus intravenous immunoglobulin (IVIG) in some subjects, in patients with mild-to-moderate Alzheimer's disease (AD). AMBAR was a phase IIb trial in the United States and a phase III trial in Europe. There were three treatment groups (plasmapheresis with albumin replacement; plasmapheresis with low dose albumin and IVIG; plasmapheresis with high dose albumin and IVIG) and sham-treated controls. Disease progression in pooled treated patients was 66% less than control subjects based on ADAS-Cog scores (p = 0.06) and 52% less based on ADCS-ADL scores (p = 0.03). Moderate AD patients had 61% less progression, based on both ADAS-Cog and ADCS-ADL scores, than their sham-treated counterparts (p-values 0.05 and 0.002), and their CDR-Sb scores declined 53% less than their sham-treated counterparts. However, ADAS-Cog and ADCS-ADL scores were not significantly different between actively-treated and sham-treated mild AD patients, although CDR-Sb scores improved vs. baseline for treated mild AD patients. Patients administered both IVIG and albumin had less reduction in brain glucose metabolism than sham-treated patients. Questions raised by these findings include: what mechanism(s) contributed to slowing of disease progression? Is this approach as effective in mild AD as in moderate AD? Must IVIG be included in the protocol? Does age, sex, or ApoE genotype influence treatment response? Does the protocol increase the risk for amyloid-related imaging abnormalities? How long does disease progression remain slowed post-treatment? A further study should allow this approach to be optimized.

Alzheimer's Disease: From Amyloid to Autoimmune Hypothesis

Although Alzheimer's disease (AD) was described over a century ago, there are no effective approaches to its prevention and treatment. Such a slow progress is explained, at least in part, by our incomplete understanding of the mechanisms underlying the pathogenesis of AD. Here, I champion a hypothesis whereby AD is initiated on a disruption of the blood-brain barrier (BBB) caused by either genetic or non-genetic risk factors. The BBB disruption leads to an autoimmune response against pyramidal neurons located in the allo- and neocortical structures involved in memory formation and storage. The response caused by the adaptive immune system is not strong enough to directly kill neurons but may be sufficient to make them selectively vulnerable to neurofibrillary pathology. This hypothesis is based on the recent data showing that memory formation is associated with epigenetic chromatin modifications and, therefore, may be accompanied by expression of memory-specific proteins recognized by the immune system as "non-self" antigens. The autoimmune hypothesis is testable, and I discuss potential ways for its experimental and clinical verification. If confirmed, this hypothesis can radically change therapeutic approaches to AD prevention and treatment.

Putative autoantibodies in the cerebrospinal fluid of Alzheimer's disease patients

Background: Recent efforts have described an immunogenic component to the pathobiology of Alzheimer's disease (AD) and Parkinson's disease (PD). However, current methods of studying fluid autoantibodies, such as enzyme-linked immunosorbent assays and immunohistochemistry, are hypothesis-driven and not optimal for discovering new autoantibody biomarkers by proteome-wide screening. Recently, we developed a general mass spectrometry-based approach to identify tissue-specific autoantibodies in serum, at a proteome-wide level. In this study, we adapted the method to explore novel autoantibody biomarkers in the cerebrospinal fluid (CSF) of AD and PD patients. Methods: CSF samples were obtained from 10 headache control individuals, 10 AD patients and 10 PD patients. Antibodies present in the CSF were isolated by immobilization to protein-G magnetic beads. These antibodies were incubated with a brain tissue extract, prepared from frontal cortex, pons, cerebellum and brain stem. Protein antigens captured by the protein-G magnetic bead-bound antibodies were digested with trypsin and analyzed using mass spectrometry. Autoantibody candidates were selected by 1) detection in one or less individuals of the control group and 2) identification in at least half of the patient groups. Results: There were 16 putative autoantibody biomarkers selected from the AD group. Glia-derived nexin autoantibody was detected in eight of ten AD patients and was absent in the control group. Other AD pathology-related targets were also identified, such as actin-interaction protein, quinone oxidoreductase, sushi repeat-containing protein, metalloproteinase inhibitor 2, IP3 receptor 1 and sarcoplasmic/endoplasmic reticulum calcium ATPase 2. An additional eleven autoantibody targets were also identified in the present experiment, although their link to AD is not clear. No autoantibodies in the PD group satisfied our selection criteria. Conclusion: Our unbiased mass spectrometry method was able to detect new putative CSF autoantibody biomarkers of AD. Further investigation into the involvement of humoral autoimmunity in AD and PD pathobiology may be warranted.

Tau-Reactive Endogenous Antibodies: Origin, Functionality, and Implications for the Pathophysiology of Alzheimer's Disease

In Alzheimer's disease (AD), tau pathology manifested by the accumulation of intraneuronal tangles and soluble toxic oligomers emerges as a promising therapeutic target. Multiple anti-tau antibodies inhibiting the formation and propagation of cytotoxic tau or promoting its clearance and degradation have been tested in clinical trials, albeit with the inconclusive outcome. Antibodies against tau protein have been documented both in the brain circulatory system and at the periphery, but their origin and role under normal conditions and in AD remain unclear. While it is tempting to assign them a protective role in regulating tau level and removal of toxic variants, the supportive evidence remains sporadic, requiring systematic analysis and critical evaluation. Herein, we review recent data showing the occurrence of tau-reactive antibodies in the brain and peripheral circulation and discuss their origin and significance in tau clearance. Based on the emerging evidence, we cautiously propose that impairments of tau clearance at the periphery by humoral immunity might aggravate the tau pathology in the central nervous system, with implication for the neurodegenerative process of AD.

Women's Pregnancy Life History and Alzheimer's Risk: Can Immunoregulation Explain the Link?

BACKGROUND

Pregnancy is associated with improvement in immunoregulation that persists into the geriatric phase. Impaired immunoregulation is implicated in Alzheimer's disease (AD) pathogenesis. Hence, we investigate the relationship between pregnancy and AD.

METHODS

Cross-sectional cohort of British women (N = 95). Cox proportional hazards modeling assessed the putative effects of cumulative months pregnant on AD risk and the mutually adjusted effects of counts of first and third trimesters on AD risk.

RESULTS

Cumulative number of months pregnant, was associated with lower AD risk (β = -1.90, exp(β) = 0.15, P = .02). Cumulative number of first trimesters was associated with lower AD risk after adjusting for third trimesters (β = -3.83, exp(β) = 0.02, P < .01), while the latter predictor had no significant effect after adjusting for the former.

CONCLUSIONS

Our observation that first trimesters (but not third trimesters) conferred protection against AD is more consistent with immunologic effects, which are driven by early gestation, than estrogenic exposures, which are greatest in late gestation. Results may justify future studies with immune biomarkers.

Amyloid-Beta 1-42 Cross-Reactive Antibody Prevalent in Human Sera May Contribute to Intraneuronal Deposition of A-Beta-P-42

Antibodies against many neural antigens are detected in the sera of both patients with Alzheimer's disease (AD) and some healthy individuals. Blood-brain barrier dysfunction could make it possible for brain-reactive autoantibodies to reach the brain, where they can react with amyloid ß peptide (AßP). The origin of these autoreactive antibodies in the blood is unclear. The goals of this study were as follows: (1) to examine the immune reactivity of anti-AßP-42 with 22 neuronal and other associated antigens, some of which are involved in the pathophysiology of AD; (2) to classify antibodies to these 22 different antigens into those that cross-react with AßP-42 and those that do not; (3) to determine whether these antibodies react with BBB proteins, nerve growth factors, and enteric neuronal antigens. Using monoclonal AßP-42 antibody and ELISA methodology, we found that the antibody was highly reactive with Aß protein, tau protein, presenilin, rabaptin-5, β-NGF, BDNF, mTG, and enteric nerve. The same antibody produced equivocal to moderate reactions with glutamate-R, S100B, AQP4, GFAP, MBP, α-synuclein, tTG-2, and tTG-3, and not with the rest. These antibodies were also measured in blood samples from 47 AD patients and 47 controls. IgG antibodies were found to be elevated against AßP-42 and many other antigens in a significant percentage of controls. Overall, the mean OD values were significantly higher against 9/23 tested antigens (p <0.001) in the samples with AD. We were indeed able to classify the detected neuronal antibodies into those that cross-react with AßP-42 and those that do not. Our main finding is that although these antibodies may be harmless in a subgroup of controls, in individuals with compromised BBBs these antibodies that cross-react with AßP-42 can reach the brain, where their cross-reactivity with AßP-42 may contribute to the onset and progression of AD, and perhaps other neurodegenerative disorders.

Peptides of the variable IgG domain as potential biomarker candidates in primary open-angle glaucoma (POAG)

Autoantibody profiling has gained increasing interest in the research field of glaucoma promising the detection of highly specific and sensitive marker candidates for future diagnostic purposes. Recent studies demonstrated that immune responses are characterized by the expression of congruent or similar complementarity determining regions (CDR) in different individuals and could be used as molecular targets in biomarker discovery. Main objective of this study was to characterize glaucoma-specific peptides from the variable region of sera-derived immunoglobulins using liquid chromatography--mass spectrometry (LC-MS)-based quantitative proteomics. IgG was purified from sera of 13 primary open-angle glaucoma patients (POAG) and 15 controls (CTRL) and subsequently digested into Fab and Fc by papain. Fab was further purified, tryptic digested and measured by LC-MS/MS. Discovery proteomics revealed in total 75 peptides of the variable IgG domain showing significant glaucoma-related level changes (P < 0.05; log2 fold change ≥ 0.5): 6 peptides were high abundant in POAG sera, whereas 69 peptides were low abundant in comparison to CTRL group. Via accurate inclusion mass screening strategy 28 IgG V domain peptides were further validated showing significantly decreased expression levels in POAG sera. Amongst others 5 CDR1, 2 CDR2 and 1 CDR3 sequences. In addition, we observed significant shifts in the variable heavy chain family distribution and disturbed κ/λ ratios in POAG patients in contrast to CTRL. These findings strongly indicate that glaucoma is accompanied by systemic effects on antibody production and B cell maturation possibly offering new prospects for future diagnostic or therapy purposes.

Age-dependent increase of blood-brain barrier permeability and neuron-binding autoantibodies in S100B knockout mice

S100B is a calcium-sensor protein that impacts multiple signal transduction pathways. It is widely considered to be an important biomarker for several neuronal diseases as well as blood-brain barrier (BBB) breakdown. In this report, we demonstrate a BBB deficiency in mice that lack S100B through detection of leaked Immunoglobulin G (IgG) in the brain parenchyma. IgG leaks and IgG-binding to selected neurons were observed in S100B knockout (S100BKO) mice at 6 months of age but not at 3 months. By 9 months, IgG leaks persisted and the density of IgG-bound neurons increased significantly. These results reveal a chronic increase in BBB permeability upon aging in S100BKO mice for the first time. Moreover, coincident with the increase in IgG-bound neurons, autoantibodies targeting brain proteins were detected in the serum via western blots. These events were concurrent with compromise of neurons, increase of activated microglia and lack of astrocytic activation as evidenced by decreased expression of microtubule-associated protein type 2 (MAP2), elevated number of CD68 positive cells and unaltered expression of glial fibrillary acidic protein (GFAP) respectively. Results suggest a key role for S100B in maintaining BBB functional integrity and, further, propose the S100BKO mouse as a valuable model system to explore the link between chronic functional compromise of the BBB, generation of brain-reactive autoantibodies and neuronal dysfunctions.

No relationship between lipoprotein-associated phospholipase A2, proinflammatory cytokines, and neopterin in Alzheimer's disease

OBJECTIVE

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a reported risk factor for dementia. However, the relationship between Alzheimer's disease (AD) and Lp-PLA2 is still debatable and, to the best of our knowledge, no study has evaluated the associations between levels of Lp-PLA2, proinflammatory cytokines, and neopterin in AD.

METHODS

In total, 59 patients with AD and 38 non-demented individuals were included in the case-control study. Fasting serum concentrations of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), neopterin, and Lp-PLA2 were determined using ELISA. The associations between AD and each of the variables were analyzed by logistic regression.

RESULTS

The median Lp-PLA2 levels in AD and controls were similar (P=0.29, not significant). Median serum neopterin and IL-6 levels were significantly higher in patients with AD than in controls (P=0.0001 and P=0.03, respectively). In regression analyses, median neopterin levels, a lower level of education, and female gender were significantly associated with AD when compared with controls (OR, 31.44, 95% CI 3.59-275.28, P=0.002; OR, 4.35, 95% CI 1.13-16.61, P=0.032; OR, 7.25, 95% CI 1.88-28.00, P=0.004, respectively).

CONCLUSION

In contrast to previous evidence suggesting its role in dementia and AD, Lp-PLA2 enzyme levels were higher in the controls, and no relationship between Lp-PLA2 and either proinflammatory cytokines or neopterin was identified in AD. Elevated neopterin levels may be considered inflammatory markers of AD.

Autoantibodies in Alzheimer's disease: potential biomarkers, pathogenic roles, and therapeutic implications

Alzheimer’s disease (AD) is a prevalent and debilitating neurodegenerative disorder in the elderly. The etiology of AD has not been fully defined and currently there is no cure for this devastating disease. Compelling evidence suggests that the immune system plays a critical role in the pathophysiology of AD. Autoantibodies against a variety of molecules have been associated with AD. The roles of these autoantibodies in AD, however, are not well understood. This review attempts to summarize recent findings on these autoantibodies and explore their potential as diagnostic/ prognostic biomarkers for AD, their roles in the pathogenesis of AD, and their implications in the development of effective immunotherapies for AD.

Extremely low frequency electromagnetic fields stimulation modulates autoimmunity and immune responses: a possible immuno-modulatory therapeutic effect in neurodegenerative diseases

Increasing evidence shows that extremely low frequency electromagnetic fields (ELF-EMFs) stimulation is able to exert a certain action on autoimmunity and immune cells. In the past, the efficacy of pulsed ELF-EMFs in alleviating the symptoms and the progression of multiple sclerosis has been supported through their action on neurotransmission and on the autoimmune mechanisms responsible for demyelination. Regarding the immune system, ELF-EMF exposure contributes to a general activation of macrophages, resulting in changes of autoimmunity and several immunological reactions, such as increased reactive oxygen species-formation, enhanced phagocytic activity and increased production of chemokines. Transcranial electromagnetic brain stimulation is a non-invasive novel technique used recently to treat different neurodegenerative disorders, in particular Alzheimer's disease. Despite its proven value, the mechanisms through which EMF brain-stimulation exerts its beneficial action on neuronal function remains unclear. Recent studies have shown that its beneficial effects may be due to a neuroprotective effect on oxidative cell damage. On the basis of in vitro and clinical studies on brain activity, modulation by ELF-EMFs could possibly counteract the aberrant pro-inflammatory responses present in neurodegenerative disorders reducing their severity and their onset. The objective of this review is to provide a systematic overview of the published literature on EMFs and outline the most promising effects of ELF-EMFs in developing treatments of neurodegenerative disorders. In this regard, we review data supporting the role of ELF-EMF in generating immune-modulatory responses, neuromodulation, and potential neuroprotective benefits. Nonetheless, we reckon that the underlying mechanisms of interaction between EMF and the immune system are still to be completely understood and need further studies at a molecular level.

Histamine Induces Alzheimer's Disease-Like Blood Brain Barrier Breach and Local Cellular Responses in Mouse Brain Organotypic Cultures

Among the top ten causes of death in the United States, Alzheimer's disease (AD) is the only one that cannot be cured, prevented, or even slowed down at present. Significant efforts have been exerted in generating model systems to delineate the mechanism as well as establishing platforms for drug screening. In this study, a promising candidate model utilizing primary mouse brain organotypic (MBO) cultures is reported. For the first time, we have demonstrated that the MBO cultures exhibit increased blood brain barrier (BBB) permeability as shown by IgG leakage into the brain parenchyma, astrocyte activation as evidenced by increased expression of glial fibrillary acidic protein (GFAP), and neuronal damage-response as suggested by increased vimentin-positive neurons occur upon histamine treatment. Identical responses-a breakdown of the BBB, astrocyte activation, and neuronal expression of vimentin-were then demonstrated in brains from AD patients compared to age-matched controls, consistent with other reports. Thus, the histamine-treated MBO culture system may provide a valuable tool in combating AD.

Brain Atrophy, Anti-Smooth Muscle Antibody and Cognitive Impairment: An Association Study

Cortical atrophy, neuronal loss, beta-amyloid deposition, neuritic plaques, and neurofibrillary tangles are neuropathological key features in the Alzheimer's disease (AD). Antibodies against beta-amyloid, neurotransmitters, microvascular endothelium components and microglial cells have been detected in AD serum suggesting that AD could be another autoimmune disease and provides a link between vascular pathology, endothelium dysfunction and neuronal cells death. Aim of the present study was to evaluate the association between autoantibody profile and cognitive impairment in geriatric patients, accounting for ApoE genotype as a potential confounding factor. Three hundred and forty-four geriatric patients, attending the clinic for the cognitive decline, underwent a biochemical and immunological profile, chest X-ray, cerebral computed tomography scan and complete cognitive evaluation. All patients were also screened for the ApoE genotype. A significantly higher prevalence of Anti-Smooth Muscle Antibody (ASMA) positivity was found in 89/204 (43.63%) patients with diagnosed neuroradiological signs of cerebral atrophy compared with 15/140 (10.71%) patients without the condition (p<0.001). Multivariable logistic model evidenced that such association was independent of patient's age, gender and Mini-Mental State Examination (OR=8.25, 95%CI: 4.26-15.99) and achieved a good discriminatory power (c-statistic=0.783). Results were also independent of ApoE genotype, which resulted not associated both with the presence of brain atrophy and with the presence of ASMA positivity. Our results shows a strong association between brain atrophy and ASMA positivity and are consistent with several studies that focused attention on the mechanisms of endothelial immune response in the development of dementia.

Myelin basic protein associates with AβPP, Aβ1-42, and amyloid plaques in cortex of Alzheimer's disease brain

The goal of this study was to show that myelin and axons in cortical gray matter are damaged in Alzheimer's disease (AD) brain. Superior temporal gyrus gray matter of AD patients (9 male, 14 female) was compared to cognitively normal controls (8 male, 7 female). Myelin basic protein (MBP) and a degraded myelin basic protein complex (dMBP) were quantified by Western blot. Brain sections were immunostained for MBP, dMBP, axonal neurofilament protein (NF), autophagy marker microtubule-associated proteins 1A/B light chain 3B precursor (LC3B), amyloid-β protein precursor (AβPP), and amyloid markers amyloid β1-42 (Aβ1-42) and FSB. Co-immunoprecipitation and mass spectroscopy evaluated interaction of AβPP/Aβ1-42 with MBP/dMBP. Evidence of axonal injury in AD cortex included appearance of AβPP in NF stained axons, and NF at margins of amyloid plaques. Evidence of myelin injury in AD cortex included (1) increased dMBP in AD gray matter compared to control (p < 0.001); (2) dMBP in AD neurons; and (3) increased LC3B that co-localized with MBP. Evidence of interaction of AβPP/Aβ1-42 with myelin or axonal components included (1) greater binding of dMBP with AβPP in AD brain; (2) MBP at the margins of amyloid plaques; (3) dMBP co-localized with Aβ1-42 in the core of amyloid plaques in AD brains; and (4) interactions between Aβ1-42 and MBP/dMBP by co-immunoprecipitation and mass spectrometry. We conclude that damaged axons may be a source of AβPP. dMBP, MBP, and NF associate with amyloid plaques and dMBP associates with AβPP and Aβ1-42. These molecules could be involved in formation of amyloid plaques.

Is Alzheimer's Disease Autoimmune Inflammation of the Brain That Can be Treated With Nasal Nonsteroidal Anti-Inflammatory Drugs?

The Alzheimer's Association recently reported that a woman's estimated lifetime risk of developing Alzheimer's at age 65 is 1 in 6, compared to nearly 1 in 11 for a man (ie, female to male ratio 1.8). Based on female to male ratio, Alzheimer's disease could well be an autoimmune disorder. Like Alzheimer's, multiple sclerosis, an autoimmune inflammation of the central nervous system, has a female to male ratio of 2.3. Also based on female to male ratio, Alzheimer's resembles the autoimmune inflammatory disease rheumatoid arthritis, which has a female to male ratio of 2.7. The reasons for the female preponderance in autoimmune disease are unclear, but nonsteroidal anti-inflammatory drugs (NSAIDs) are widely and successfully employed to treat autoimmune anti-inflammatory disease and dramatically relieve symptoms. Moreover, oral NSAIDs consistently reduce the risk of Alzheimer's disease, although they have been totally ineffective as a treatment in multiple failed clinical trials. A basis for this failure might well be that the brain dose after oral administration is too small and not sufficiently early in the pathogenesis of the disorder. But NSAID brain dose could be significantly increased by delivering the NSAIDs intranasally.

Autoimmune manifestations in the 3xTg-AD model of Alzheimer's disease

BACKGROUND

Immune system activation is frequently reported in patients with Alzheimer's disease (AD). However, it remains unknown whether this is a cause, a consequence, or an epiphenomenon of brain degeneration.

OBJECTIVE

The present study examines whether immunological abnormalities occur in a well-established murine AD model and if so, how they relate temporally to behavioral deficits and neuropathology.

METHODS

A broad battery of tests was employed to assess behavioral performance and autoimmune/inflammatory markers in 3xTg-AD (AD) mice and wild type controls from 1.5 to 12 months of age.

RESULTS

Aged AD mice displayed severe manifestations of systemic autoimmune/inflammatory dise6ase, as evidenced by splenomegaly, hepatomegaly, elevated serum levels of anti-nuclear/anti-dsDNA antibodies, low hematocrit, and increased number of double-negative T splenocytes. However, anxiety-related behavior and altered spleen function were evident as early as 2 months of age, thus preceding typical AD-like brain pathology. Moreover, AD mice showed altered olfaction and impaired "cognitive" flexibility in the first 6 months of life, suggesting mild cognitive impairment-like manifestations before general learning/memory impairments emerged at an older age. Interestingly, all of these features were present in 3xTg-AD mice prior to significant amyloid-β or tau pathology.

CONCLUSION

The results indicate that behavioral deficits in AD mice develop in parallel with systemic autoimmune/inflammatory disease. These changes antedate AD-like neuropathology, thus supporting a causal link between autoimmunity and aberrant behavior. Consequently, 3xTg-AD mice may be a useful model in elucidating the role of immune system in the etiology of AD.

New roles for Fc receptors in neurodegeneration-the impact on Immunotherapy for Alzheimer's Disease

There are an estimated 18 million Alzheimer's disease (AD) sufferers worldwide and with no disease modifying treatment currently available, development of new therapies represents an enormous unmet clinical need. AD is characterized by episodic memory loss followed by severe cognitive decline and is associated with many neuropathological changes. AD is characterized by deposits of amyloid beta (Aβ), neurofibrillary tangles, and neuroinflammation. Active immunization or passive immunization against Aβ leads to the clearance of deposits in transgenic mice expressing human Aβ. This clearance is associated with reversal of associated cognitive deficits, but these results have not translated to humans, with both active and passive immunotherapy failing to improve memory loss. One explanation for these observations is that certain anti-Aβ antibodies mediate damage to the cerebral vasculature limiting the top dose and potentially reducing efficacy. Fc gamma receptors (FcγR) are a family of immunoglobulin-like receptors which bind to the Fc portion of IgG, and mediate the response of effector cells to immune complexes. Data from both mouse and human studies suggest that cross-linking FcγR by therapeutic antibodies and the subsequent pro-inflammatory response mediates the vascular side effects seen following immunotherapy. Increasing evidence is emerging that FcγR expression on CNS resident cells, including microglia and neurons, is increased during aging and functionally involved in the pathogenesis of age-related neurodegenerative diseases. Therefore, we propose that increased expression and ligation of FcγR in the CNS, either by endogenous IgG or therapeutic antibodies, has the potential to induce vascular damage and exacerbate neurodegeneration. To produce safe and effective immunotherapies for AD and other neurodegenerative diseases it will be vital to understand the role of FcγR in the healthy and diseased brain. Here we review the literature on FcγR expression, function and proposed roles in multiple age-related neurological diseases. Lessons can be learnt from therapeutic antibodies used for the treatment of cancer where antibodies have been engineered for optimal efficacy.

Characterization of immune response to neurofilament light in experimental autoimmune encephalomyelitis

BACKGROUND

Autoimmunity to neuronal proteins occurs in several neurological syndromes, where cellular and humoral responses are directed to surface as well as intracellular antigens. Similar to myelin autoimmunity, pathogenic immune response to neuroaxonal components such as neurofilaments may contribute to neurodegeneration in multiple sclerosis.

METHODS

We studied the immune response to the axonal protein neurofilament light (NF-L) in the experimental autoimmune encephalomyelitis animal model of multiple sclerosis. To examine the association between T cells and axonal damage, pathology studies were performed on NF-L immunized mice. The interaction of T cells and axons was analyzed by confocal microscopy of central nervous system tissues and T-cell and antibody responses to immunodominant epitopes identified in ABH (H2-Ag7) and SJL/J (H2-As) mice. These epitopes, algorithm-predicted peptides and encephalitogenic motifs within NF-L were screened for encephalitogenicity.

RESULTS

Confocal microscopy revealed both CD4+ and CD8+ T cells alongside damaged axons in the lesions of NF-L immunized mice. CD4+ T cells dominated the areas of axonal injury in the dorsal column of spastic mice in which the expression of granzyme B and perforin was detected. Identified NF-L epitopes induced mild neurological signs similar to the observed with the NF-L protein, yet distinct from those characteristic of neurological disease induced with myelin oligodendrocyte glycoprotein.

CONCLUSIONS

Our data suggest that CD4+ T cells are associated with spasticity, axonal damage and neurodegeneration in NF-L immunized mice. In addition, defined T-cell epitopes in the NF-L protein might be involved in the pathogenesis of the disease.

Hygiene and the world distribution of Alzheimer's disease: Epidemiological evidence for a relationship between microbial environment and age-adjusted disease burden

People living in sanitized environments may be at greater Alzheimer's risk. We compare Alzheimer's rates in different countries in light of countries' historical and contemporary pathogen prevalence, sanitation, and urbanization. We find that countries that are less urbanized, with more pathogens and lower degree of sanitation have lower Alzheimer's rates.

Background and objectives: Alzheimer’s disease (AD) shares certain etiological features with autoimmunity. Prevalence of autoimmunity varies between populations in accordance with variation in environmental microbial diversity. Exposure to microorganisms may improve individuals’ immunoregulation in ways that protect against autoimmunity, and we suggest that this may also be the case for AD. Here, we investigate whether differences in microbial diversity can explain patterns of age-adjusted AD rates between countries.

Methodology: We use regression models to test whether pathogen prevalence, as a proxy for microbial diversity, across 192 countries can explain a significant amount of the variation in age-standardized AD disability-adjusted life-year (DALY) rates. We also review and assess the relationship between pathogen prevalence and AD rates in different world populations.

Results: Based on our analyses, it appears that hygiene is positively associated with AD risk. Countries with greater degree of sanitation and lower degree of pathogen prevalence have higher age-adjusted AD DALY rates. Countries with greater degree of urbanization and wealth exhibit higher age-adjusted AD DALY rates.

Conclusions and implications: Variation in hygiene may partly explain global patterns in AD rates. Microorganism exposure may be inversely related to AD risk. These results may help predict AD burden in developing countries where microbial diversity is rapidly diminishing. Epidemiological forecasting is important for preparing for future healthcare needs and research prioritization.

Inflammation in Alzheimer disease-a brief review of the basic science and clinical literature

Biochemical and neuropathological studies of brains from individuals with Alzheimer disease (AD) provide clear evidence for an activation of inflammatory pathways, and long-term use of anti-inflammatory drugs is linked with reduced risk to develop the disease. As cause and effect relationships between inflammation and AD are being worked out, there is a realization that some components of this complex molecular and cellular machinery are most likely promoting pathological processes leading to AD, whereas other components serve to do the opposite. The challenge will be to find ways of fine tuning inflammation to delay, prevent, or treat AD.

The senescence hypothesis of disease progression in Alzheimer disease: an integrated matrix of disease pathways for FAD and SAD

Alzheimer disease (AD) is a progressive, neurodegenerative disease characterised in life by cognitive decline and behavioural symptoms and post-mortem by the neuropathological hallmarks including the microtubule-associated protein tau-reactive tangles and neuritic plaques and amyloid-beta-protein-reactive senile plaques. Greater than 95 % of AD cases are sporadic (SAD) with a late onset and <5 % of AD cases are familial (FAD) with an early onset. FAD is associated with various genetic mutations in the amyloid precursor protein (APP) and the presenilins (PS)1 and PS2. As yet, no disease pathway has been fully accepted and there are no treatments that prevent, stop or reverse the cognitive decline associated with AD. Here, we review and integrate available environmental and genetic evidence associated with all forms of AD. We present the senescence hypothesis of AD progression, suggesting that factors associated with AD can be seen as partial stressors within the matrix of signalling pathways that underlie cell survival and function. Senescence pathways are triggered when stressors exceed the cells ability to compensate for them. The APP proteolytic system has many interactions with pathways involved in programmed senescence and APP proteolysis can both respond to and be driven by senescence-associated signalling. Disease pathways associated with sporadic disease may be different to those involving familial genetic mutations. The interpretation we provide strongly points to senescence as an additional underlying causal process in dementia progression in both SAD and FAD via multiple disease pathways.

Allergy influences the inflammatory status of the brain and enhances tau-phosphorylation

Despite the existing knowledge regarding the neuropathology of Alzheimer's disease (AD), the cause of sporadic forms of the disease is unknown. It has been suggested that systemic inflammation may have a role, but the exact mechanisms through which inflammatory processes influence the pathogenesis and progress of AD are not obvious. Allergy is a chronic inflammatory disease affecting more than 20% of the Western population, but the effects of allergic conditions on brain functions are largely unknown. The aim of this study was to investigate whether or not chronic peripheral inflammation associated with allergy affects the expression of AD-related proteins and inflammatory markers in the brain. On the basis of previously described models for allergy in mice we developed a model of chronic airway allergy in mouse, with ovalbumin as allergen. The validity of the chronic allergy model was confirmed by a consistent and reproducible eosinophilia in the bronchoalveolar lavage (BAL) fluid of allergic animals. Allergic mice were shown to have increased brain levels of both immunoglobulin (Ig) G and IgE with a widespread distribution. Allergy was also found to increase phosphorylation of tau protein in the brain. The present data support the notion that allergy-dependent chronic peripheral inflammation modifies the brain inflammatory status, and influences phosphorylation of an AD-related protein, indicating that allergy may be yet another factor to be considered for the development and/or progression of neurodegenerative diseases such as AD.

Intracerebral immune complex formation induces inflammation in the brain that depends on Fc receptor interaction

In this study, we investigate the underlying mechanisms of antibody-mediated inflammation in the brain. We show that immune complexes formed in the brain parenchyma generate a robust and long-lasting inflammatory response, characterized by increased expression of the microglia markers CD11b, CD68 and FcRII/III, but no neutrophil recruitment. In addition to these histological changes, we observed transient behavioural changes that coincided with the inflammatory response in the brain. The inflammatory and behavioural changes were absent in Fc-gamma chain (Fcγ)-deficient mice, while C1q-deficient mice were not different from wild-type mice. We conclude that, in the presence of antigen, antibodies can lead to a local immune complex-mediated inflammatory reaction in the brain parenchyma and indirectly induce neuronal tissue damage through recruitment and activation of microglia via Fcγ receptors. These observations may have important implications for the development of therapeutic antibodies directed against neuronal antigens used for therapeutic intervention in neurological diseases.

Enhanced characterization of serum autoantibody reactivity following HSP 60 immunization in a rat model of experimental autoimmune glaucoma

PURPOSE

Antibodies against heat shock proteins have been identified in sera of human glaucoma patients in several studies and immunization with heat shock protein 60 (HSP 60) causes retinal ganglion cell (RGC) loss in an animal model of experimental autoimmune glaucoma. The aim of this study was to observe the time course of increased anti-retina antibody appearance in the serum and characterize the identification of prominent autoantibodies that accompany HSP 60 immunization in a rat model of experimental autoimmune glaucoma.

METHODS

Eight weeks after immunization with HSP 60 retinal flatmounts were prepared and RGCs were counted in eight predefined areas and compared to controls. Serum collected before, as well as four and eight weeks after, immunization was used to detect antibody patterns against bovine retinal antigens using Western blotting techniques. These patterns were analyzed by multivariate statistical methods. Autoantibodies that were prominently increased were further identified through mass spectrometry. Intraocular pressure was measured throughout the study.

RESULTS

After eight weeks, animals immunized with HSP 60 showed significant RGC loss of retinal flatmounts (P = 0.02), which was intraocular pressure independent. Early changes in antibody profiles, many of them significant upregulations, were detected. Antigens with significantly upregulated antibody reactivity after four weeks were identified as histone H2B type 1, S-arrestin, glial fibrillary acidic protein, vimentin, and heat shock protein 60. These upregulated autoantibodies returned to normal levels four weeks following their initial upregulation. Antibodies against retinaldehyde binding protein 1 on the other hand became upregulated after eight weeks.

CONCLUSION

This is the first study to identify the appearance and disappearance of retinal autoantibodies in the serum of rats at several time-points following their initial upregulation in response to HSP 60 immunization in a model of experimental autoimmune glaucoma.

Alzheimer's disease: a pathogenetic autoimmune disorder caused by herpes simplex in a gene-dependent manner

Herpes simplex is implicated in Alzheimer's disease and viral infection produces Alzheimer's disease like pathology in mice. The virus expresses proteins containing short contiguous amino acid stretches (5–9aa “vatches” = viralmatches) homologous to APOE4, clusterin, PICALM, and complement receptor 1, and to over 100 other gene products relevant to Alzheimer's disease, which are also homologous to proteins expressed by other pathogens implicated in Alzheimer's disease. Such homology, reiterated at the DNA level, suggests that gene association studies have been tracking infection, as well as identifying key genes, demonstrating a role for pathogens as causative agents. Vatches may interfere with the function of their human counterparts, acting as dummy ligands, decoy receptors, or via interactome interference. They are often immunogenic, and antibodies generated in response to infection may target their human counterparts, producing protein knockdown, or generating autoimmune responses that may kill the neurones in which the human homologue resides, a scenario supported by immune activation in Alzheimer's disease. These data may classify Alzheimer's disease as an autoimmune disorder created by pathogen mimicry of key Alzheimer's disease-related proteins. It may well be prevented by vaccination and regular pathogen detection and elimination, and perhaps stemmed by immunosuppression or antibody adsorption-related therapies.

Autoantibodies in patients with Alzheimer's disease: pathogenetic role and potential use as biomarkers of disease progression

Growing evidence suggests that autoantibodies specific to distinct molecular antigens are present in sera or cerebrospinal fluids from patients with Alzheimer's disease (AD). They could have a protective (i.e., anti-β-amyloid) or a pathogenetic role (i.e., anti-GM1 or anti-ATP synthase) but, in any case, they might be considered as useful diagnostic or prognostic markers of the disease. In this review, we briefly summarize the autoantibodies known to be detectable in patients with AD and we discuss their potential role in the pathogenesis of the disease, as well as their potential use as peripheral blood biomarkers.

Autoantibodies to the adenosine triphosphate synthase play a pathogenetic role in Alzheimer's disease

It has become evident that an autoimmune component could play a role in Alzheimer's disease (AD) onset and/or progression. The aim of this study was to identify neuronal antigenic targets specifically recognized by serum autoantibodies and to investigate their cellular effects and their possible pathogenetic role. We identified, by an immunoproteomic approach using mouse brain proteins, the adenosine triphosphate (ATP) synthase β subunit as a new autoantigen in AD. Using an ELISA assay we found that serum anti-ATP synthase autoantibodies were present in 38% of patients with AD, but in no age-matched healthy subjects or in patients with Parkinson's disease or atherosclerosis. Analytical cytology studies, using SH-SY5Y neuroblastoma cell line, showed that ATP synthase autoantibodies were capable of inducing the inhibition of ATP synthesis, alterations of mitochondrial homeostasis and cell death by apoptosis. These findings suggest that autoantibodies specific to ATP synthase can exert a pathogenetic role via a mechanism that brings into play the impairment of the extracellular ATP homeostasis and the alteration of mitochondrial function triggering cell death by apoptosis.

Brain-reactive autoantibodies are nearly ubiquitous in human sera and may be linked to pathology in the context of blood-brain barrier breakdown

Previous studies have reported antibodies bound to cells in postmortem Alzheimer's disease (AD) brains, which are only rarely observed in the brains of healthy, age-matched controls. This implies that brain-reactive autoantibodies exist in the sera of AD individuals and can gain access to the brain interstitium. To investigate this possibility, we determined the prevalence of brain-reactive antibodies in sera from AD patients, patients with other neurodegenerative diseases, age-matched, non-demented controls and healthy younger individuals via immunohistochemistry and western blot analysis. Surprisingly, western analyses revealed that 92% of all human sera tested contain brain-reactive autoantibodies. When sera were used to probe western blots of human, pig, or rat brain membrane proteins, a number of comparably-sized protein targets were detected, suggesting cross-species reactivity. While the presence of brain-reactive autoantibodies was nearly ubiquitous in human sera, some autoantibodies appeared to be associated with age or disease. Furthermore, the intensity of antibody binding to brain tissue elements, especially the surfaces of neurons, correlated more closely to the serum's autoantibody profile than to age or the presence of neurodegenerative disease. However, while the blood-brain barrier (BBB) in control brains remained intact, BBB breakdown was common in AD brains. Results suggest a high prevalence of brain-reactive antibodies in human sera which, in the common context of BBB compromise, leads us to propose that these antibodies may contribute to the initiation and/or pathogenesis of AD and other neurodegenerative diseases.

Circulating Antibodies to IDO/THO Pathway Metabolites in Alzheimer's Disease

In Alzheimer's disease, indoleamine 2,3-dioxygenase and tryptophan hydroxylase are known to induce an overproduction of neurotoxic compounds, such as quinolinic acid and 3-hydroxykynurenine from the former, and 5-hydroxytryptophol and 5-methoxytryptophol from the latter. Other compounds, such as kynurenic acid, serotonin, and melatonin are produced via the same pathways. An improved ELISA method identified circulating antibodies directed against these compounds, linked to proteins, as previously described for other chronic diseases. This describes how only the A isotype of circulating immunoglobulins recognized a pattern of conjugated tryptophan metabolites in the sera of Alzheimer patients. These data indirectly confirmed the involvement of tryptophan derivatives in the pathogenic processes of Alzheimer's disease. Further studies are required to evaluate the relevance of these antibody patterns in monitoring this disease.

Early inflammation and immune response mRNAs in the brain of AD11 anti-NGF mice

We characterized the gene expression profile of brain regions at an early stage of the Alzheimer's like neurodegeneration in the anti-NGF AD11 model. Total RNA was extracted from hippocampus, cortex and basal forebrain of postnatal day 30 (P30) and postnatal day 90 (P90) mice and expression profiles were studied by microarray analysis, followed by qRT-PCR validation of 243 significant candidates. Wide changes in gene expression profiles occur already at P30. As expected, cholinergic system and neurotrophins related genes expression were altered. Interestingly, the most significantly affected clusters of mRNAs are linked to inflammation and immune response, as well as to Wnt signaling. mRNAs encoding for different complement factors show a large differential expression. This is noteworthy, since these complement cascade proteins are involved in CNS synapse elimination, during normal brain developing and in neurodegenerative diseases. This gene expression pattern highlights that an early event in AD11 neurodegeneration is represented, together with neurotrophic deficits and synaptic remodeling, by an inflammatory response and an unbalance in the immunotrophic state of the brain. These might be key events in the pathogenesis and development of AD.

Reproductive age-related changes in the blood brain barrier: expression of IgG and tight junction proteins

We previously demonstrated that there is a significantly greater transfer of intravenously-injected Evan's blue dye into the forebrain of acyclic (reproductive senescent) females compared to young adult females, indicating that blood brain barrier permeability is compromised in the reproductive senescent forebrain. The present study examined brain IgG expression and microvessel tight junction proteins to assess ovarian age-related changes in microvascular permeability, and further compared young and senescent females with age-matched males to distinguish changes attributable to age and reproductive senescence. Blood brain barrier breakdown are often associated with increased extravasation of plasma proteins and high levels of immunoglobulin G (IgG) in brain. In the present study, IgG expression was dramatically increased in the hippocampus and thalamus, but not the hypothalamus of reproductive senescent females compared to young adult females. In males, IgG expression was increased in all these regions in middle-aged animals (aged-matched to senescent females) as compared to young males (age-matched to the young adult females). Furthermore, the proportion of hippocampal microvessels with perivascular IgG immunoreactivity was significantly greater in reproductive senescent females as compared to young adult females, while middle-aged males and young adult males did not differ. The tight junctions between adjacent microvascular endothelial cells regulated by transmembrane proteins such as claudin-5 and occludin play a critical role in maintaining the blood brain barrier integrity. Increased hippocampal IgG expression in senescent females was paralleled by poor junctional localization of the tight junction protein claudin-5 in hippocampal microvessels. However, there was no difference in hippocampal claudin-5 localization between young adult and middle-aged males, indicating that dysregulation of this junctional protein was associated with ovarian aging. Parallel studies in human brain microvessels also revealed age-dependent disruption in claudin-5 distribution in post-menopausal women compared to pre-menopausal women. Collectively, these data support the hypothesis that constitutive loss of barrier integrity in the forebrain during reproductive senescence may be due, in part, to the selective loss of tight junction proteins in endothelial junctions.

Autoimmune pathology accounts for common manifestations in a wide range of neuro-psychiatric disorders: the olfactory and immune system interrelationship

Smell has traditionally been considered a less important sense when compared to sight or hearing, but recent research has unraveled important features inherent to the sense of smell. Once considered just a chemical sensor for sampling the environment, data from animal models and human studies currently imply numerous and complex effects of smell on behavior, mood, and on the immune response. In this review we discuss a possible inter-relationship between olfactory impairment, autoimmunity and neurological/psychiatric symptoms in several diseases affecting the central nervous system (CNS) such as Parkinson, Alzheimer's disease, autism, schizophrenia, multiple sclerosis and neuropsychiatric lupus erythematosus. We suggest that common manifestations are not mere coincidences. Current data from animal models show that neuropsychiatric manifestations are intimately associated with smell impairment, and autoimmune dysregulation, via autoantibodies (anti-NMDAR, anti-ribosomal P) or other mechanisms. From clues of pathological manifestations, we propose a novel approach to the understanding of the interactions between the CNS, the smell and the immune system.