Alzheimer's disease cerebrospinal fluid antibodies display selectivity for microglia. Investigations with cell cultures and human cortical biopsies

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.

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.

Cerebrospinal fluid antimicroglial antibodies in Alzheimer disease: A putative marker of an ongoing inflammatory process

Immunocompetent microglia play an important role in the pathogenesis of Alzheimer's disease (AD). Antimicroglial antibodies in the cerebrospinal fluid (CSF) in clinically diagnosed AD patients have been previously recorded. Here, we report the results of the analysis of the CSF from 38 autopsy cases: 7 with definite AD; 14 with mild and 10 with moderate Alzheimer's type pathology; and 7 controls. Antimicroglial antibodies were identified in 70% of patients with definite AD, in 80% of patients with moderate and in 28% of patients with mild Alzheimer's type pathology. CSF antimicroglial antibodies were not observed in any of the control cases. The results show that CSF antimicroglial antibodies are present in the majority of patients with definite AD and also in cases with moderate Alzheimer's type changes. They may also indicate dysregulation of microglial function. Together with previous observations, these findings indicate that compromised immune defense mechanisms play an important role in the pathogenesis of AD.

Frontotemporal dementia—A brief review

Frontotemporal dementia (FTD) is the second most common type of presenile dementia and the forth most common type of senile dementia, but probably the most costly due to its florid symptom characteristics. Clinically, it often presents with changes of personality, restlessness, disinhibition, and impulsiveness and the clinical features can be complicated by neurological signs, such as motor neuron signs, parkinsonism, and gait disturbances. Syndromatically, FTD can be subdivided into a group with predominating behavioural disturbances (frontal variant) and another with predominating language deterioration (temporal variant). Based on the underlying pathological changes, FTD is nosologically divided into disorders such as Pick's disease, frontotemporal lobar degeneration, corticobasal degeneration, progressive supranuclear palsy, and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). The cause in sporadic FTD is most often unknown, but in FTDP-17, one of the hereditary FTDs, there is a causative mutation in the tau gene. The frequency of tau-gene mutations is low in sporadic FTD and present in about 10-40% of hereditary FTD. Other types of hereditary FTD have been described, such as FTD caused by mutations in chromosome 3, chromosome 9, and a FTD syndrome can also be caused by mutations in the presenilin-1 gene. Since there is no curative, treatment of prevailing symptoms is the given alternative. Serotonergic acting drugs have been shown to alleviate behavioural symptoms.

Identification of Aldolase as a Target Antigen in Alzheimer’s Disease

Alzheimer's disease (AD) is the most common human neurodegenerative disease, leading to progressive cognitive decline and eventually death. The prevailing paradigm on the pathogenesis of AD is that abnormally folded proteins accumulate in specific brain areas and lead to neuronal loss via apoptosis. In recent years it has become evident that an inflammatory and possibly autoimmune component exists in AD. Moreover, recent data demonstrate that immunization with amyloid-beta peptide is therapeutically effective in AD. The nature of CNS Ags that are the target of immune attack in AD is unknown. To identify potential autoantigens in AD, we tested sera IgG Abs of AD patients in immunoblots against brain and other tissue lysates. We identified a 42-kDa band in brain lysates that was detected with >50% of 45 AD sera. The band was identified by mass spectrometry to be aldolase A. Western blotting with aldolase using patient sera demonstrated a band of identical size. The Ab reactivity was verified with ELISAs using aldolase. One of 25 elderly control patients and 3 of 30 multiple sclerosis patients showed similar reactivity (p < 0.002). In enzymatic assays, anti-aldolase positive sera were found to inhibit the enzyme's activity, and the presence of the substrate (fructose 1,6-diphosphate) enhanced Ab binding. Immunization of rats and mice with aldolase in complete Freund's adjuvant was not pathogenic. These findings reveal an autoimmune component in AD, point at aldolase as a common autoantigen in this disease, and suggest a new target for potential immune modulation.

Increased intrathecal inflammatory activity in frontotemporal dementia: pathophysiological implications

OBJECTIVE

Immunological mechanisms may be part of the pathophysiological mechanisms in frontotemporal dementia (FTD), but hitherto only vague evidence of such mechanisms has been presented. The aim of this study was to compare the cerebrospinal fluid (CSF) levels of the pro-inflammatory cytokines interleukin (IL)-1beta and tumour necrosis factor (TNF)-alpha, and the anti-inflammatory cytokine transforming growth factor (TGF)-beta in patients with FTD and normal controls. Furthermore, serum levels of TNF-alpha, TGF-beta, and IL-1beta were measured in FTD patients.

METHODS

The CSF levels of IL-1beta, TNFalpha, and TGF-beta were measured using ELISA in 19 patients with FTD and 24 sex and age matched healthy controls.

RESULTS

The CSF levels of TNF-alpha (FTD 0.6 pg/mL (median: lower, upper quartile 0.3, 0.7); controls: 0.0 pg/mL (0.0, 0.0); p = 0.008) and TGF-beta (FTD 266 pg/mL (157, 371), controls: 147 pg/mL (119, 156); p = 0.0001) were significantly increased in FTD patients compared with controls. No correlations were found between CSF and serum levels of the cytokines. In the controls, but not in the FTD patients, a positive correlation was found between the CSF levels of TGF-beta and age (r = 0.42, p < 0.05). No correlation was found between any of the cytokines and degree of brain atrophy or white matter changes. No differences between the groups were found for age, gender, or CSF/serum albumin ratio.

CONCLUSIONS

The results suggest an increased intrathecal production of both pro- and anti-inflammatory cytokines in FTD. As no correlations were found with the albumin ratio, and no correlations between CSF and serum levels of the cytokines were found, these changes in the CSF cannot be explained by a systemic overproduction of cytokines.

Pathophysiological aspects of frontotemporal dementia--emphasis on cytoskeleton proteins and autoimmunity

The aim of this study was to investigate two putative pathophysiological aspects of the common neurodegenerative disorder frontotemporal dementia (FTD). To this end, cerebrospinal fluid (CSF) levels of tau (total tau) and the light subtype of the neurofilament proteins (NFL) were studied in patients with FTD (n=16) and in age-matched controls (n=16). In addition, serum was analysed for IgG and IgM antibodies to the most common gangliosides and sulfatide in FTD patients (n=13) and in age-matched controls (n=20). The CSF-NFL levels were increased in FTD (1606+/-1151 pg/ml, mean+/-S.D.; P<0.001) compared with controls (308+/-203 pg/ml), whereas the CSF-tau levels were normal. In serum, autoantibody IgG-GA1 was significantly increased in FTD (P<0.05) compared with controls. No correlations were found between the effect parameters and demographic variables in any group. The results of this study suggest that cytoskeleton proteins other than tau are also involved in the pathophysiology of FTD and that autoimmunity may be part of the pathophysiological processes in FTD, as it is believed to be in Alzheimer's disease.

Effects of incorporation of immunoglobulin G and complement component C1q on uptake and degradation of Alzheimer's disease amyloid fibrils by microglia

Microglia are macrophage-like immune system cells found in the brain. They are associated with Alzheimer's Disease plaques, which contain fibrillar beta-amyloid (fAbeta) and other components such as complement proteins. We have shown previously that murine microglia bind and internalize fAbeta microaggregates via the type A scavenger receptor, but degradation of internalized fAbeta is significantly slower than normal degradation. In this study, we compared internalization by microglia of fAbeta microaggregates to that of anti-Abeta-antibody-coated fAbeta (IgG-fAbeta) microaggregates and found that the uptake of the latter is increased by about 1.5-fold versus unmodified fAbeta. The endocytic trafficking of IgG-fAbeta is similar to that of fAbeta microaggregates, following an endosomal/lysosomal pathway. We also compared the internalization of fAbeta microaggregates to that of complement protein, C1q-coated fAbeta microaggregates, and found that the levels of uptake are also increased by about 1.5-fold. Rates of degradation of both types of modified fAbeta microaggregates are unchanged compared with unmodified fAbeta microaggregates. We demonstrated by blocking studies that internalization of IgG-fAbeta is mediated by Fc receptors. These data suggest that, in vivo, several different microglial receptors may play a part in internalizing fAbeta, but the involvement of other receptors may not increase the degradation of fAbeta.

Aluminum-induced oxidative events in cell lines: glioma are more responsive than neuroblastoma

Aluminum, a trivalent cation unable to undergo redox reactions, has been linked to many diseases such as dialysis dementia and microcytic anemia without iron deficiency. It has also been implicated in Alzheimer's disease although this is controversial. Because cell death due to oxidative injury is suspected to be a contributory factor in many neurological diseases and aluminum neurotoxicity, glioma (C-6) and neuroblastoma (NBP2) cells were utilized to assess early changes in oxidative parameters consequent to a 48-h exposure to aluminum sulfate. A 500-microM concentration of this salt produced a significant increase in reactive oxygen species (ROS) production and a significant decrease in glutathione (GSH) content in glioma cells. However, the same concentration of the aluminum salt did not lead to any significant changes in the neuroblastoma cells. Mitochondrial respiratory activity in glioma cells was also found to be significantly higher in the aluminum treated cells. As judged by morin-metal complex formation, aluminum can enter glioma cells much more readily than neuroblastoma cells. Thus, it is possible that the cerebral target following an acute exposure to aluminum may be glial rather than neuronal.

Microglial activation induced by factor(s) contained in sera from Alzheimer-related ApoE genotypes

Several factors that increase the likelihood of developing Alzheimer's disease (AD) have already been identified. A correct evaluation of these may contribute to a better understanding of the etiology of the disease. The risk of developing AD definitely increases with (a) age, (b) head injuries, (c) family history of AD or Down syndrome, (d) sex (higher prevalence of AD in women), (e) vascular disease, (f) exposure to environmental toxins, (g) infectious processes, or (h) changes in immune function, and recent advances in molecular genetics have suggested that genetic predisposition (i) can be considered one of the most important risk factors in the development of AD. A significant increase in the number of amyloid plaques in AD patients with an apolipoprotein E4 (ApoE) allele has been observed and the results of several genetic studies indicate that the etiology of this neurodegenerative disease is associated with the presence of the allele E4 of ApoE. A potential source of damage in the AD brain is an altered response triggered by microglial activation, which is associated with amyloid plaques. It has become evident that a dysregulation of cytokine release appears within lesions of many types of brain disorders including infection, trauma, stroke, and neurodegenerative diseases. Many studies have shown that microglia secrete both cytokines and cytotoxins and since reactive microglia appears in nearly every type of brain damage, it is likely that their secreted products ultimately help to determine the rate of damaged brain tissue. In this study, in vitro cell cultures were established to investigate the effect of different concentrations of human sera (2.5% and 10%) with specific ApoE genotypes from Alzheimer's and non-Alzheimer's subjects on ameboid and flat microglial cells obtained from neonatal rat hippocampi. Results show that a modulation in the proliferation and activation of microglial cells was obtained and that AD sera, mainly in the ApoE 3/4 and 4/4 genotype contain factor(s) which are able to induce morphological changes, as measured by an increase in the ameboid cell type. In addition, major histocompatibility complex (MHC) class II antigen expression, as measured by flow cytometric analysis, and interleukin-1beta (IL-1beta) release as measured by enzyme linked immunoadsorbent assay (ELISA), in comparison with control groups and lipopolysaccharide (LPS)-treated cells, clearly demonstrate a direct effect of ApoE 3/4 and 4/4 and/or an indirect effect mediated by the release of IL-1beta on microglia activation. These results strongly suggest that primary in vitro microglial cell cultures can be used as a screening model to test human sera as well as the effect of new potential drugs aimed at down-regulating microglia activation.

Autoantibodies in neurodegenerative diseases: antigen-specific frequencies and intrathecal analysis

The frequency of autoantibodies (AAbs) was surveyed in several neurodegenerative diseases, other neurological diseases, and controls using antigen-specific EIAs for neurofilament heavy subunit, tubulin, glial fibrillary acidic protein, S100 protein, tau, beta-amyloid peptide, myelin basic protein, and heparan sulfate proteoglycan. High frequencies of sera and cerebrospinal fluid tubulin AAbs were found in Alzheimer disease (62% and 69%, respectively), Parkinson disease (27% and 70%), amyotrophic lateral sclerosis (54% and 67%), and in sera from multiple sclerosis (50% and 67%), optic neuritis (85%), Guillain-Barré syndrome (88%), and vascular dementia (52%). High frequencies of neurofilament heavy subunit AAbs were detected in Guillain-Barré syndrome, chronic peripheral neuropathy (88%) and optic neuritis (62%); whereas, some Alzheimer's disease (33%) and vascular dementia (44%) patients had glial fibrillary acidic protein AAbs. Lower frequencies of other AAbs were found in patient groups. AAb results were also compared to functional assessment of blood-brain barrier integrity in Parkinson's disease and Alzheimer's disease. The relevance of these AAbs to pathogenesis and/or course of neurologic diseases merits further study with particular reference to subgrouping and prognosis.

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.

T lymphocyte benzodiazepine binding is reduced in demented patients

Blood cells, especially platelets and lymphocytes, are used in neuropsychiatric research as tools for investigating systemic derangements in neuropsychiatric disorders, and as peripheral models for studying central nervous system biochemistry. In the present work, we determined T lymphocyte peripheral-type benzodiazepine binding: a significant reduction of Bmax values was observed in demented patients as compared with healthy controls, whereas Kd values were similar in the two subjects' groups. A significant negative correlation was found between Bmax values and illness severity. These data, which seem to be related to an impairment of immune response and cell energy metabolism in demented patients, may represent a state-dependent marker in monitoring disease course and treatment efficacy.

Microglial cerebrospinal fluid antibodies. Significance for Alzheimer disease

Hallmark lesions of Alzheimer disease (AD) are filled with reactive immunocompetent microglia, suggesting that immunological aderrations may participate in the pathophysiology of this disorder. If immune-mediated processes are closely linked to neuronal breakdown, it would be or importance to have a reliable means to detect these processes. Cerebrospinal fluid (CSF) antibodies are discussed as such potential sources. The seredipitous use of the developing rat central nervous system (CNS) unexpectedly demonstrated that some AD CSF recognize amoeboid microglial cells. Similarly, AD CSF specifically stains activated microglia and neural macrophages in experimentally induced lesions. A cell-culture technique is described that allows rapid screening of CSF antibodies. Examination of CSF from a diversified dementia population revealed that AD CSF, in contrast to other dementia CSF, displayed remarkable selectivity toward microglial cells. Cortical biopsies from patients suspected to have AD were incubated with the patient's own CSF and that of confirmed AD patients. Both CSF samples recognized microglial cells in the cortical biopsy. AD CSF microglial antibodies appear to be significant in view of the increasing association between microglia and neuro degenerative processes in AD. These findings add further support to the concept that inflammation and similar immune mechanisms may contribute to to AD pathogenesis.