Antibodies to cholinergic neurons in Alzheimer's disease

Gangliosides as Biomarkers of Human Brain Diseases: Trends in Discovery and Characterization by High-Performance Mass Spectrometry

Gangliosides are effective biochemical markers of brain pathologies, being also in the focus of research as potential therapeutic targets. Accurate brain ganglioside mapping is an essential requirement for correlating the specificity of their composition with a certain pathological state and establishing a well-defined set of biomarkers. Among all bioanalytical methods conceived for this purpose, mass spectrometry (MS) has developed into one of the most valuable, due to the wealth and consistency of structural information provided. In this context, the present article reviews the achievements of MS in discovery and structural analysis of gangliosides associated with severe brain pathologies. The first part is dedicated to the contributions of MS in the assessment of ganglioside composition and role in the specific neurodegenerative disorders: Alzheimer’s and Parkinson’s diseases. A large subsequent section is devoted to cephalic disorders (CD), with an emphasis on the MS of gangliosides in anencephaly, the most common and severe disease in the CD spectrum. The last part is focused on the major accomplishments of MS-based methods in the discovery of ganglioside species, which are associated with primary and secondary brain tumors and may either facilitate an early diagnosis or represent target molecules for immunotherapy oriented against brain cancers.

Anti-neurofilament antibodies and neurodegeneration: Markers and generators

Neuroaxonal injury and loss result in the release of cytoskeleton components, including neurofilaments, into the cerebrospinal fluid and peripheral blood. Once released, neurofilaments are highly immunogenic, inducing a specific antibody response. Anti-neurofilament antibody levels correlate with the progression of diverse neurological diseases; however, their role both in the pathogenesis of disease and as a tool for monitoring disease progression is not well understood. This study reviews the current literature on anti-neurofilament antibodies. We suggest the testing of anti-neurofilament antibodies be further developed for diagnosis and targeted for treatment.

The Pathogenic Role of Ganglioside Metabolism in Alzheimer's Disease-Cholinergic Neuron-Specific Gangliosides and Neurogenesis

Alzheimer's disease (AD) is the most common type of dementia with clinical symptoms that include deficits in memory, judgment, thinking, and behavior. Gangliosides are present on the outer surface of plasma membranes and are especially abundant in the nervous tissues of vertebrates. Ganglioside metabolism, especially the cholinergic neuron-specific gangliosides, GQ1bα and GT1aα, is altered in mouse model of AD and patients with AD. Thus, alterations in ganglioside metabolism may participate in several events related to the pathogenesis of AD. Increased expressions of GT1aα may reflect cholinergic neurogenesis. Most changes in ganglioside metabolism occur in the specific brain areas and their lipid rafts. Targeting ganglioside metabolism in lipid rafts may represent an underexploited opportunity to design novel therapeutic strategies for AD.

Antibodies against gangliosides in patients with dementia

BACKGROUND

Increasing evidence suggests that gangliosides act as important mediators in both de- and remyelination. The scope of the present research was to investigate the presence of immunoglobulin (Ig) M antibodies against GM1, GD1b, and GQ1b gangliosides in the sera of patients with dementia and the possible connection with clinical parameters of the disease.

METHOD

This research topic demonstrates the investigation of 103 patients with dementia and 60 healthy individuals using enzyme-linked immunosorbent assay for the presence of 3 antiganglioside antibodies in their sera.

RESULTS

The authors report a positive connection between IgM anti-GM1 and the age (P = .005) and the severity of dementia (P = .005). Most of the patients who revealed increased IgM anti-GD1b levels had Alzheimer's disease (AD; P = .002).

CONCLUSION

This study indicates that elevated IgM anti-GM1 may be connected with the neurodegeneration in older patients with severe dementia and that AD may also be associated with increased IgM anti-GD1b levels.

New immunological approaches in treating and diagnosing CNS diseases

The immune system evolved to launch effective and specific responses against pathogens. A key feature of this defense mechanism is its ability to differentiate between self and nonself. However, in autoimmune diseases, the host's immune system fails to discriminate self versus foreign. The CNS is further protected by the blood-brain barrier. In spite of its 'immune privilege,' the brain is not protected from autoimmunity; perhaps paradoxically xenoantibodies can be used to treat neurological diseases. We describe patents covering treatment methods for CNS diseases with suspected or demonstrated autoimmune etiology. These include multiple sclerosis and, Alzheimer's and Parkinson's disease. The goal is to less invasively, yet efficiently, treat neurological diseases. Although autoimmune responses are often detrimental, recent studies have begun to harness, boost and induce immune responses as a mechanism of treatment. The patents discussed herein highlight new treatments for Alzheimer's and Parkinson's disease, multiple sclerosis, and seizure disorders.

Anti-Chol-1 antigen, GQ1bα, antibodies are associated with Alzheimer's disease

The interaction of amyloid β-proteins (Aβ) with membrane gangliosides has been reported to be an early event in Aβ fibril formation in Alzheimer’s disease (AD). Neuronal degeneration in AD has been postulated to be associated with the presence of anti-ganglioside antibodies in patient sera. Using an enzyme-linked immunosorbent assay (ELISA) and high-performance thin-layer chromatography (HPTLC) immunostaining, sera from 27 individuals (10 with AD, 6 with vascular dementia (VD), and 11 non-demented age-matched pathological controls) were examined in order to detect anti-glycosphingolipid (GSL) antibodies, including anti-cholinergic-specific antigen (Chol-1α; GQ1bα) antibodies. All sera had natural antibodies against ganglio-N-tetraosyl gangliosides (brain-type gangliosides). However, sera of demented patients with AD and VD had significantly higher titers of anti-GSL antibodies than those in age-matched pathological controls. Although most serum antibodies, including anti- GM1, -GT1b, -GQ1b, -GQ1bα, were of the IgM type, the presence of the IgG type antibodies was also significantly elevated in the sera of demented patients with AD. Anti-GT1b antibodies of the IgG type were elevated in AD (90%, 9 of 10 cases) and VD (100%), respectively. Most surprisingly, anti-GQ1bα antibodies (IgM) were found in 90% (9/10) and 100% (6/6) in the sera of patients with AD and VD, respectively. Since GQ1bα is present in the cerebral cortex and hippocampus, the presence of anti-GQ1bα antibodies may play an important role in disrupting cholinergic synaptic transmission and may participate in the pathogenesis of dementia. We conclude that elevated anti-GSL antibody titers may be useful as an aid for clinical diagnosis of those dementias.

The pathological roles of ganglioside metabolism in Alzheimer's disease: effects of gangliosides on neurogenesis

Conversion of the soluble, nontoxic amyloid β-protein (Aβ) into an aggregated, toxic form rich in β-sheets is a key step in the onset of Alzheimer's disease (AD). It has been suggested that Aβ induces changes in neuronal membrane fluidity as a result of its interactions with membrane components such as cholesterol, phospholipids, and gangliosides. Gangliosides are known to bind Aβ. A complex of GM1 and Aβ, termed “GAβ”, has been identified in AD brains. Abnormal ganglioside metabolism also may occur in AD brains. We have reported an increase of Chol-1α antigens, GQ1bα and GT1aα, in the brain of transgenic mouse AD model. GQ1bα and GT1aα exhibit high affinities to Aβs. The presence of Chol-1α gangliosides represents evidence for genesis of cholinergic neurons in AD brains. We evaluated the effects of GM1 and Aβ1–40 on mouse neuroepithelial cells. Treatment of these cells simultaneously with GM1 and Aβ1–40 caused a significant reduction of cell number, suggesting that Aβ1–40 and GM1 cooperatively exert a cytotoxic effect on neuroepithelial cells. An understanding of the mechanism on the interaction of GM1 and Aβs in AD may contribute to the development of new neuroregenerative therapies for this disorder.

Ganglioside metabolism in a transgenic mouse model of Alzheimer's disease: expression of Chol-1α antigens in the brain

The accumulation of Aβ (amyloid β-protein) is one of the major pathological hallmarks in AD (Alzheimer's disease). Gangliosides, sialic acid-containing glycosphingolipids enriched in the nervous system and frequently used as biomarkers associated with the biochemical pathology of neurological disorders, have been suggested to be involved in the initial aggregation of Aβ. In the present study, we have examined ganglioside metabolism in the brain of a double-Tg (transgenic) mouse model of AD that co-expresses mouse/human chimaeric APP (amyloid precursor protein) with the Swedish mutation and human presenilin-1 with a deletion of exon 9. Although accumulation of Aβ was confirmed in the double-Tg mouse brains and sera, no statistically significant change was detected in the concentration and composition of major ganglio-N-tetraosyl-series gangliosides in the double-Tg brain. Most interestingly, Chol-1α antigens (cholinergic neuron-specific gangliosides), such as GT1aα and GQ1bα, which are minor species in the brain, were found to be increased in the double-Tg mouse brain. We interpret that the occurrence of these gangliosides may represent evidence for generation of cholinergic neurons in the AD brain, as a result of compensatory neurogenesis activated by the presence of Aβ.

Role of ganglioside metabolism in the pathogenesis of Alzheimer's disease--a review

Gangliosides are expressed in the outer leaflet of the plasma membrane of the cells of all vertebrates and are particularly abundant in the nervous system. Ganglioside metabolism is closely associated with the pathology of Alzheimer's disease (AD). AD, the most common form of dementia, is a progressive degenerative disease of the brain characterized clinically by progressive loss of memory and cognitive function and eventually death. Neuropathologically, AD is characterized by amyloid deposits or "senile plaques," which consist mainly of aggregated variants of amyloid beta-protein (Abeta). Abeta undergoes a conformational transition from random coil to ordered structure rich in beta-sheets, especially after addition of lipid vesicles containing GM1 ganglioside. In AD brain, a complex of GM1 and Abeta, termed "GAbeta," has been found to accumulate. In recent years, Abeta and GM1 have been identified in microdomains or lipid rafts. The functional roles of these microdomains in cellular processes are now beginning to unfold. Several articles also have documented the involvement of these microdomains in the pathogenesis of certain neurodegenerative diseases, such as AD. A pivotal neuroprotective role of gangliosides has been reported in in vivo and in vitro models of neuronal injury, Parkinsonism, and related diseases. Here we describe the possible involvement of gangliosides in the development of AD and the therapeutic potentials of gangliosides in this disorder.

Add Alzheimer’s disease to the list of autoimmune diseases

A sole pathological event leading to Alzheimer's disease (AD) remains undiscovered in spite of decades of costly research. In fact, it is more probable that the causes of AD are the result of a myriad of intertwining pathologies. However, hope remains that a single awry event could lead to the many pathological events observed in AD brain tissues thereby creating the presentation of simultaneous pathologies. Age-related vascular diseases, which include an impaired blood-brain barrier (BBB), are a common denominator associated with various degrees of dementia, including AD. Recently, a key finding not only demonstrated the anomalous presence of immunoglobulin (Ig) detection in the brain parenchyma of AD tissues but, most importantly, specific neurons that showed degenerative, apoptotic features contained these vascular-derived antibodies. In addition, subsequent studies detected classical complement components, C1q and C5b-9, in these Ig-positive neurons, which also were spatially more associated with reactive microglia over the Ig-negative neurons. Thus, it is possible that the mere presence of anti-neuronal autoantibodies in the serum, whose importance had been previously dismissed, may be without pathological consequence until there is a BBB dysfunction to allow the deleterious effects of these autoantibodies access on their targets. Hence, these observations suggest autoimmunity-induced cell death in AD.

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

The catastrophic loss of cerebral neurons in Alzheimer's disease (AD) is not fully understood. Since serum proteins are known to extravasate into the brain parenchyma in AD due to blood-brain barrier (BBB) dysfunction, this study was designed to explore the possibility that neuronal cell death may be the consequence of the anomalous presence of serum proteins in the brain. As compared to age-matched, non-demented 'control' brain tissues, highly significant increases of immunoglobulins (Igs) were detected in parenchyma, which were associated with vessels in the AD brain tissues. Also, there were dramatic increases of +Ig-neurons in areas with greater parenchymal Ig reactivity. The Ig labeling extended throughout the cell, which showed neurodegenerative apoptotic features that were not observed in -Ig-neurons. Thus, the presence of +Ig-neurons in AD brains implies a critical link between the faulty BBB and neuronal death through an autoimmune mechanism.

Importance of immunological and inflammatory processes in the pathogenesis and therapy of Alzheimer's disease

The contribution of autoimmune processes or inflammatory components in the etiology and pathogenesis of Alzheimer's disease (AD) has been suspected for many years. The presence of antigen-presenting, HLA-DR-positive and other immunoregulatory cells, components of complement, inflammatory cytokines and acute phase reactants have been established in tissue of AD neuropathology. Although these data do not confirm the immune response as a primary cause of AD, they indicate involvement of immune processes at least as a secondary or tertiary reaction to the preexisting pathogen and point out its driving-force role in AD pathogenesis. These processes may contribute to systemic immune response. Thus, experimental and clinical studies indicate impairments in both humoral and cellular immunity in an animal model of AD as well as in AD patients. On the other hand, anti-inflammatory drugs applied for the treatment of some chronic inflammatory diseases have been shown to reduce risk of AD in these patients. Therefore, it seems that anti-inflammatory drugs and other substances which can control the activity of immunocompetent cells and the level of endogenous immune response can be valuable in the treatment of AD patients.

Anti-brain spectrin immunoreactivity in Alzheimer's disease: degradation of spectrin in an animal model of cholinergic degeneration

In a previous work, we described the existence of anti-brain spectrin auto antibodies in Alzheimer's disease (AD) patients (J. Neuroimmunol. 68 (1996) 39-44). In this report, we further support our previous observations, showing that sera from 9 out of 18 AD patients, but none of 14 control subjects, immunoreacted with spectrin synthesized by PC12 cells. In addition, degradation of brain spectrin was found to be greatly enhanced in the frontal cortex of rats subjected to an animal model of cholinergic degeneration. Our data suggest that spectrin degradation and generation of anti-spectrin auto antibodies may be related to the cholinergic degeneration encountered in AD.

Experimental immune-mediated damage of septal cholinergic neurons

Degeneration of cholinergic neurons in the medial septum and the diagonal band of Broca is a frequent neuropathological feature of Alzheimer's disease. To determine whether an immune process can injure these basal forebrain cholinergic neurons, we serially immunized guinea pigs with septal cholinergic hybrid cells (SN-56). Following immunization, a relatively selective damage of septal cholinergic neurons, reduction in septal choline acetyltransferase (ChAT) activity and decrease in acetylcholine release in hippocampus were detected. Serum IgG from guinea pigs immunized with SN-56 cells and stereotactically injected into the medial septal region of rats produced a loss of ChAT activity in the medial septum, frontal cortex and hippocampus, together with impairment of learning and long term spatial memory. These data suggest that relatively selective damage to septal cholinergic neurons can be caused by an immune-mediated process in experimental animals.

Immunocytochemical detection of anti-hippocampal antibodies in Alzheimer's disease and normal cerebrospinal fluid

Immunocytochemical staining was performed to investigate the presence of anti-hippocampal antibodies in cerebrospinal fluid (CSF) from patients with probable Alzheimer's disease (AD) (n = 19), aged normal controls (n = 9), and young normal controls (n = 10). Marked staining of neurons in the granule cell layer of the dentate gyrus and in pyramidal neurons in CA1-3 of the rat hippocampus was observed in 5 AD CSF samples (26%), 1 aged control sample (11%), and 1 young control sample (10%). These differences were not statistically significant. One of the immunoreactive AD CSF specimens also contained high concentrations of C5b-9, the membrane attack complex. The infrequent occurrence of anti-hippocampal antibodies in AD CSF, and the detection of similar immunoreactivity in control CSF specimens, suggest that these antibodies are unlikely to play a role in the neurodegenerative process in most individuals with AD. However, elevated C5b-9 concentration in an AD CSF specimen with marked immunoreactivity to hippocampal neurons suggests the possibility that anti-neuronal antibodies may contribute to complement activation in some AD patients.

Antibodies to human brain spectrin in Alzheimer's disease

We investigated the existence of antibodies in sera of Alzheimer's disease patients which immunoreact with specific antigens from crude human brain extracts. We found that 49% of patients, per only 5% of control subjects, had increased levels of antibodies to a 240 kDa protein. On the basis of immunological criteria and internal amino acid sequencing, this antigen was identified as brain spectrin, a cytoskeletal protein which appears to be implicated in synaptic plasticity. Our data raises the possibility that anti-spectrin antibodies could be implicated in Alzheimer's disease pathogenesis.

Circulating autoantibodies to a 240 kD fetal brain protein

Antibodies (IgG and IgM) recognizing a 240 kD antigen of the cat fetal brain were found in sera of healthy people and in sera (IgG) obtained at uncomplicated delivery from the umbilical cord of the newborn infant. The method applied was immunoblotting. Using the same method, the 240 kD antigen could not be detected in the adult brain or other fetal tissues. It seems that the antigen is specific for the fetal brain. The role of the antigen and the origin of generation and significance of function of the antibodies in the circulation are the objects of our further studies.

Antibodies to different isoforms of the heavy neurofilament protein (NF-H) in normal aging and Alzheimer's disease

Sera of normal controls and of patients with neurological diseases contain antineurofilament antibodies. Recent studies suggest that biochemically and immunologically distinct subclasses of neurofilaments occur in different types of neurons. Alzheimer's disease (AD), the major cause of dementia, is associated with a marked degeneration of brain cholinergic neurons. In the present work we characterized the repertoire and age dependence of antineurofilament antibodies in normal sera and examined whether the degeneration of cholinergic neurons in AD is associated with serum antibodies directed specifically against the neurofilaments of mammalian cholinergic neurons. This was performed by immunoblot assays utilizing neurofilaments from the purely cholinergic bovine ventral root neurons and from the chemically heterogeneous bovine dorsal root neurons. Antibodies to the heavy neurofilament protein NF-H were detected in normal control sera. Their levels were significantly higher in older (aged 70-79) than in younger (aged 40-59) subjects. These antibodies bound similarly to bovine ventral root and dorsal root NF-H and their NF-H specificity was unchanged during aging. In contrast, the levels of IgG in AD sera that are directed against ventral root cholinergic NF-H were higher than those directed against the chemically heterogeneous dorsal root NF-H. Immunoblot experiments utilizing dephosphorylated ventral root and dorsal root NF-H and chymotryptic fragments of these molecules revealed that AD sera contain a repertoire of antimamalian NF-H IgG. A subpopulation of these antibodies binds to phosphorylated epitopes that are specifically enriched in ventral root cholinergic NF-H and that are located on the carboxy terminal domain of this molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

The immunopathology of Alzheimer's disease and some related disorders

Current evidence clearly indicates that elements of the immune system are involved in the pathogenesis of the principal lesions characterizing Alzheimer's disease (AD). Findings are in accord with features associated with both the innate and adaptive immune mechanisms involved in a predominantly local inflammatory response within the parenchyma. Many of the features are unique to AD, presumably related to the unusual properties of beta amyloid protein. Remarkably, the brain holds the capacity to produce almost all the immune system mediators which largely seem to be generated by glia comprising both astrocytes and microglia. While a variety of humoral mediators including classical acute phase proteins (and serpins) are increased and released, the complement seems most intrinsically involved. The cellular response is elaborated by microglia which seem the main immunocompetent cells partaking in the response. These appear to function as pluripotent macrophages expressing both classes of MHC antigens. Further characterization of this interesting response to cerebral amyloidosis will be challenging.

Decreased density of forebrain cholinergic neurons in experimental autoimmune dementia

Sera of Alzheimer's disease and Down's syndrome patients contain antibodies which bind specifically to the high molecular weight neurofilament protein of Torpedo cholinergic neurons. We have recently shown that prolonged immunization of rats with this antigen results in the accumulation of IgG in neurons in the septum and hippocampus of the immunized rats and in cognitive impairments. This animal model is termed experimental autoimmune dementia. In the present study we examined whether the anti-cholinergic high molecular weight neurofilament subunit immune response of the experimental autoimmune dementia rats affects forebrain cholinergic neurons. This was performed immunohistochemically utilizing a monoclonal antibody to nerve growth factor receptor, a specific marker of cholinergic neurons in the forebrain. The results obtained revealed significant decreases in the density of cholinergic neurons in the medial septal nucleus and diagonal band of the experimental autoimmune dementia rats. These decreases are specific to the anti-cholinergic high molecular weight neurofilament subunit immune response of the experimental autoimmune dementia rats and are not observed in control rats which were immunized with chemically heterogeneous high molecular weight neurofilament subunit. The decrease in density of forebrain cholinergic neurons in experimental autoimmune dementia rats may mimic pathogenic processes in Alzheimer's disease and supports a role for anti-cholinergic high molecular weight neurofilament subunit antibodies in the degeneration of cholinergic neurons in the disease.

Disintegration of the spatial organization of behavior in experimental autoimmune dementia

Experimental autoimmune dementia is a rat model designed to examine the potential role of anti-cholinergic neurons antibodies in neuronal degeneration in dementia and Alzheimer's disease. We have previously shown that sera of patients with Alzheimer's disease contain antibodies which bind specifically to the high molecular weight neurofilament protein of the purely cholinergic electromotor neurons of Torpedo. Production of such antibodies in experimental autoimmune dementia rats by prolonged immunization with the Torpedo cholinergic high molecular weight neurofilament subunit results in accumulation of antibodies in the septum and hippocampus of the immunized rats, in a marked decrease in the density of forebrain cholinergic neurons, and in memory deficits. In the present study we characterized the open-field behavior of experimental autoimmune dementia rats, and examined whether, like in dementia, the spatiotemporal organization of their behavior is impaired. The results obtained revealed that experimental autoimmune dementia rats travel shorter distances; explore a smaller part of the open-field; and perform less round-trips to the key location--the home base--in reference to which their behavior is normally organized. The shrinkage of the explored space and the reduced number of round trips are independent of the amount of locomotion and represent a deterioration in the organization of behavior in time and space. These behavioral changes are specific to the anti-cholinergic immune response of experimental autoimmune dementia rats as they are not observed in rats which were immunized with chemically heterogeneous high molecular weight neurofilament subunit.(ABSTRACT TRUNCATED AT 250 WORDS)

Brainstem auditory evoked potentials in experimental autoimmune dementia

Cognitive dysfunction may be induced in rats by immunization with cholinergic neuronal antigens and is associated with degeneration of nuclei in the septum and hippocampus and white matter tracts in the forebrain. Such rats are a putative model of Alzheimer's disease named experimental autoimmune dementia (EAD). The aim of the present study was to investigate brainstem auditory evoked potentials (BAEP) in EAD rats in order to define the extent of white matter tract involvement in this model. Clear reproducible evoked potentials were obtained and the normal range of BAEP in rats was established in adjuvant immunized controls. Measurements of inter peak latencies (IPL) I-IV in 9 EAD rats revealed that they were not significantly prolonged (3.00 +/- 0.22 ms, mean +/- S.E.M.) compared to 9 controls (2.80 +/- 0.08 ms), (P > 0.2, Student's t-test). The lack of significant change in IPL I-IV is compatible with preliminary histological findings and indicates that brainstem structures are generally unaffected in EAD.

Characteristics of Epstein-Barr virus transformed B cell lines from patients with Alzheimer's disease and age-matched controls

The characteristics of B cell lines isolated from patients with Alzheimer's disease (AD) and age-matched controls were investigated after having been transformed by Epstein-Barr virus (EBV). After isolation of mononuclear blood cells and in vivo or in vitro EBV infection, 35 and 21 lymphoblastoid cell lines (LCLs) were generated from 19 patients with AD (mean age 79.4 years) and 21 age-matched controls (mean age 80.0 years), respectively. B lymphocytes from AD patients were immortalised more easily than those from controls; the percentage of in vitro EBV infected LCLs (B95-LCLs) obtained in the AD group was significantly higher (76.2% versus 33.3% in the control group) and the mean time required for establishment was significantly lower (20.2 and 21.9 days versus 26.7 and 60.9 days in the control group). The EBV receptor and surface immunoglobulin (Ig) analyses showed no difference between the two groups. The expression of Epstein-Barr early antigens (EA) and viral capsid antigens (VCAs) revealed a tendency to higher viral replication in LCLs from AD patients; however, VCA expression remained limited to a small number of cells and did not affect overall cell growth. Finally, qualitative and quantitative differences were observed in the pattern of Ig production. Whereas spontaneously established LCLs from AD patients were generally monoclonal (80% of LCLs versus 33% in the control group), B95-LCLs were all polyclonal and secreted more IgM and IgA than those from controls; the mean IgM level was significantly higher in B95-LCLs from the AD group. These results suggest that B cells derived from AD patients seemed to be less differentiated than cells from age-matched controls.

Characterization of an experimental autoimmune dementia model in the rat

Alzheimer's disease (AD) and other age-related cognitive deficits are associated with autoimmune phenomena. We recently showed that AD sera contain IgG that binds specifically to the heavy molecular weight neurofilament protein (NF-H) of Torpedo cholinergic neurons. We presently examined the behavioral effects of the induction of such antibodies in rats by prolonged immunization with Torpedo cholinergic NF-H. Immunohistochemical studies revealed the accumulation of IgG in the septum and hippocampus and in white matter tracts of these rats. T-maze alternation and discrimination tests revealed that immunization impaired the short-term working memory of the rats but had no effect on their reference memory. This impairment in short-term memory was reversed by treatment with the acetylcholinesterase inhibitor physostigmine. This animal model, termed experimental autoimmune dementia (EAD), may replicate immunologically induced pathogenic processes in AD.

Monoclonal antibodies to the heavy neurofilament subunit (NF-H) of Torpedo cholinergic neurons

Previous studies from our laboratory suggest that Alzheimer's disease sera contain a repertoire of antibodies to the heavy neurofilament subunit (NF-H) and that a subpopulation of these antibodies bind specifically to epitopes highly enriched in NF-H isolated from the purely cholinergic electromotor neurons of Torpedo. In the present study, we prepared and characterized monoclonal antibodies (MAbs) that bind to epitopes specifically enriched in Torpedo cholinergic neurons. This was performed by a differential enzyme-linked immunosorbent assay (ELISA) in which MAbs were selected that bind to epitopes much more abundant in the NF-H protein of Torpedo cholinergic neurons than in NF-H from the chemically heterogeneous Torpedo spinal cord. This yielded four MAbs, three of which (TC4, TC8, and TC21) were found to be specific to NF-H and one (TC15) that reacts with both NF-H and the medium-size neurofilament subunit NF-M. Dephosphorylation abolishes the binding of MAbs TC4 and TC15 to Torpedo cholinergic NF-H, partially reduces that of MAb TC21 and has no effect on the binding of MAb TC8. This suggests that the antigenic sites specific to Torpedo cholinergic NF-H contain phosphorylated as well as non phosphorylated epitopes. All the MAbs cross-react with rat brain NF-H.

Induction of cognitive deficits by immunization with cholinergic cell bodies: the influence of age and integrity of the blood-brain barrier

We have recently shown that prolonged immunization of young rats for one year with cholinergic cell bodies (perikarya, PK) purified from Torpedo electric lobe results in the accumulation of IgG in specific brain areas such as the hippocampus and induces behavioral deficits in spatial orientation and short term memory /1, 7/. We presently studied the rate of development of the cognitive deficit in older (12 months old) Sprague Dawley rats which were immunized for periods of up to one year with either Torpedo cholinergic PK or adjuvant (controls). T-maze alternation and Morris swim maze tests revealed a small deficit in the performance of the PK immunized rats after 6 months whereas significant deficits were observed after 12 months of immunization. These results suggest that the duration of immunization is a more significant factor than the age of the animals in the development of the behavioral deficit. In order to examine whether permeability of the blood-brain barrier to IgG influences the rate of development of the cognitive deficit, we disrupted the blood-brain barrier of PK immunized rats by hypercapnia. This treatment repeated weekly for 2 months was found not to accelerate the rate of appearance of deficits in performance of the rats in the T-maze alternation and Morris swim test. These results suggest that penetration of IgG via the blood-brain barrier does not determine the rate of appearance of the cognitive deficits.

Animal models of age-related dementia: neurobehavioral dysfunctions in autoimmune mice

The development of strategies for treatment of Alzheimer's disease and other age-associated dementias is an important goal of research in the neurosciences. It is suggested that advances in understanding of the etiology of those disorders would provide the most obvious avenues to development of preventative treatments. Research findings from both clinical investigations and studies of animal models are presented which suggest a neuroimmunologic component in age-associated dementia. Clinical studies suggest an association between dementia and brain-reactive autoantibodies in subsets of patients with Alzheimer's disease. Studies of mice suggest that: 1) when compared with normal genotypes, mutant mice with accelerated autoimmunity show learning and memory impairments at earlier chronological ages; 2) the learning and memory deficits of autoimmune and normal mice are qualitatively similar; 3) the behavioral deficits of normal aged and autoimmune mice are sensitive to similar pharmacologic interventions. Overall, these findings suggest that intervention strategies targeting the immune system might be useful in the treatment or prevention of aging-associated dementia. Autoimmune mice would be useful as models for the development and testing of such immune-based interventions.

Immunization with cholinergic cell bodies induces histopathological changes in rat brains

We have previously shown that sera from patients with Alzheimer's disease (AD) contain antibodies to the cell bodies (perikarya; PK) of purely cholinergic Torpedo neurons, and that repeated immunization of rats with this neuronal preparation for over a year induces learning and memory impairments. In the present study, we examined the brain morphology of cholinergic PK immunized rats relative to controls. Immunohistochemical studies of the brains of these rats revealed the accumulation of IgG in specific areas, such as, the hippocampus. Parallel histochemical studies demonstrated significant changes in the hippocampus, and in white matter areas. They included large vacuoles and necrotic nuclei in the granular layer of the dentate gyrus, tangle-like appearance in some pyramidal neurons of the hippocampus, and vacuolar degeneration accompanied by oligodendroglia hypertrophy in white matter tracts, such as, the corpus callosum and fimbria. In contrast, immunization with Torpedo cholinergic nerve terminals, that has no cognitive effects on the rat, also did not induce brain morphological changes. These findings suggest that the learning and memory deficits induced by immunizing rats with cholinergic PK are related to the observed brain morphological changes, and support the hypothesis that the antibodies to cholinergic neurons found in the sera of AD patients may play a role in neuronal degeneration in this disease.

Cholinergic modulation of aged-like retention deficits in young autoimmune mice

Separate age groups of autoimmune NZB/BINJ and non-autoimmune C57BL/BNNia mice were compared for habituation of locomotor activity and its retention over four separate testing sessions spaced at 24-hr intervals. A decline in locomotion (distance in cm) or in the time spent in the center zone as a function of sessions was taken to indicate retention for habituation to stimuli within the test apparatus. The time spent in the center zone decreased as a function of sessions in young and mature C57BL/6NNia mice but failed to show reliable between-session decreases in old (24-26-months) C57BL/6NNia mice. When compared with the old C57BL/6NNia mice, young NZB/BINJ mice showed similar impairments. Habituation of locomotion was present in all age groups of C57BL/6NNia mice, but absent in NZB/BINJ mice regardless of age. The retention impairments of 2-4 month old NZB/BINJ mice were attenuated when i.p. injections of 0.04-0.16 mg physostigmine/kg were given just following each habituation session. The effectiveness of physostigmine was substantially reduced when injections were delayed by 20 min or longer following each habituation session. The time-dependent reversal of the aged-like retention deficits by the cholinesterase inhibitor, physostigmine, suggests that cholinergic modulation of memory storage processes may be impaired in NZB/BINJ mice.

Antibodies to viral antigens, xenoantigens, and autoantigens in Alzheimer's disease

Sera from 19 patients with Alzheimer's disease (AD) and 21 control subjects were studied by immunofluorescence and enzyme immunoassay for antibody activity against various viruses and 12 self- and non-self-antigens. Total IgG mean level was significantly higher in the AD group; the IgG level was above 15 g/L in 52.8% of AD patients versus 14.3% of control subjects. Antiviral antibody titers showed no significant differences except for antibodies to herpes simplex virus-1, which were increased in control group. In contrast, autoantibodies were more frequently found in AD patients, and the prevalence of antibodies to spectrin, peroxidase, and thyroglobulin was significantly increased. Thus, in our series, autoimmune but not antiviral responses were heightened in at least 42% of AD patients (versus 9% of the control group) suggesting the existence of two subpopulations in the AD group.

Antibodies in serum of patients with Alzheimer's disease cause immunolysis of cholinergic nerve terminals from the rat cerebral cortex

A blind study showing that serum from patients with Alzheimer's disease causes immunolysis of mammalian brain synaptosomes is reported. Control, aged-matched, sera were largely without effect. The immunolysis was directed mainly against cholinergic synaptosomes. The data support the hypothesis that autoimmune mechanisms may operate in the pathogenesis of Alzheimer's disease.

Immune system response in Alzheimer's disease

Involvement of the immune system in the pathogenesis of Alzheimer's disease was demonstrated in two ways: by the attachment of complement proteins to diseased tissue, and by the activation of cells associated with the immune system. Alzheimer brain tissue was stained immunohistochemically by antibodies to components of the classical, but not the alternative, complement pathway. Antibodies to C1q, C3d, and C4d stained senile plaques, dystrophic neurites, neuropil threads and some tangled neurons. Antibodies to a neoantigenic site on the C5b-9 membrane attack complex stained dystrophic neurites and many tangled neurons, but not senile plaques. Antibodies to Factor P and fraction Bb of Factor B, which are specific for the alternative complement pathway, did not stain Alzheimer brain tissue. The cellular immune response was evaluated by the presence of reactive microglia and by the infiltration of small numbers of T-cells into diseased brain tissue. Reactive microglia were identified by antibodies to HLA-DR, a class II major histocompatibility complex glycoprotein, and by enhanced staining with antibodies to leukocyte common antigen and the Fc gamma RI and Fc gamma RII receptors. T-cells were identified by antibodies to leukocyte common antigen, as well as the CD4 and CD8 surface proteins. Double immunostaining with antibodies to GFAP and MHC class I or class II antigens established that astrocytes, which are GFAP positive, do not express MHC antigens in Alzheimer's disease. Endothelial cells express MHC class I antigens while reactive microglia and some leukocytes express class II antigen.