Amyloid beta-protein deposition in tissues other than brain in Alzheimer's disease

Alzheimer's disease is the most common cause of progressive intellectual failure in aged humans. The filamentous brain lesions which define the disease occur within neurons (neurofibrillary tangles), in extracellular cerebral deposits (amyloid plaques) and in meningocerebral blood vessels (amyloid angiopathy). They are found in lesser numbers in the brains of virtually all old humans. A protein with a relative molecular mass (Mr) of approximately 4,000, designated amyloid beta-protein or amyloid A4 protein, is the subunit of the vascular and plaque amyloid filaments in individuals with Alzheimer's disease, normal ageing and trisomy 21 (Down's syndrome). The amyloid beta-protein is a small fragment of a membrane-associated glycoprotein, encoded by a gene on human chromosome 21 which is telomeric to a genetic defect that causes at least some cases of familial Alzheimer's disease. Until now, the pathological lesions of the disease have been found only in the brain, although reports of phenotypic abnormalities in non-neural tissues have suggested that Alzheimer's disease may be a widespread, systemic disorder. Here we report the detection of amyloid beta-protein deposits in non-neural tissues and blood vessels of Alzheimer's disease patients, including skin, subcutaneous tissue and intestine. The protein was also present in non-neural tissues in a proportion of aged, normal subjects. Our findings indicate that a principal feature of the disease process is expressed subclinically in tissues other than brain. The occurrence of amyloid beta-protein deposits in multiple tissues suggests that the protein may be produced locally in numerous organs or may, as in other human amyloidoses, be derived from a common circulating precursor. These observations affect the rationale for many experiments analysing the amyloid beta-protein precursor and its messenger RNAs in Alzheimer's disease brain tissue and have major implications for the pathogenesis and treatment of the disease.

Molecular pathology of amyloidogenic proteins and the role of vascular amyloidosis in Alzheimer's disease

Progress in the study of Alzheimer's disease (AD) has been spurred by the recent application of molecular approaches in many laboratories. Attention has centered on the nature of the proteinaceous deposits that accumulate progressively both within and outside of cerebral neurons. Evidence reviewed herein suggests that intraneuronal paired helical filaments are distinct from extracellular amyloid filaments and contain altered forms of the microtubule-associated phosphoprotein, tau. Antibodies to tau detect an extensive neuritic dystrophy in AD cerebral cortex that includes aberrant somatodendritic sprouting, suggesting a role for local growth-promoting molecules in the pathogenesis of AD. Perhaps preceding these neuronal changes, deposits of the beta-amyloid protein (beta AP) occur in a diffuse, nonfibrillar form in AD and Down's syndrome brains in the absence of surrounding neuritic or glial response. Such deposits may represent the earliest structural abnormality yet detected in AD brain. Since the gene encoding the beta AP precursor appears to be distinct from a putative familial AD gene defect also localized to chromosome 21 in some families, changes in transcriptional and posttranslational processing of the precursor in aging and AD are being sought. The central and unresolved question of the origin of the beta AP molecules deposited progressively in brain is reviewed in detail. In concert with other human amyloidoses, growing evidence points to a blood-borne or vascular source for beta AP, although rigorous proof is not at hand. Advances in the molecular analysis of AD brain lesions point to new experimental strategies that should bear directly on unsolved diagnostic and therapeutic issues in the disease.

The beta-amyloid protein precursor of Alzheimer disease has soluble derivatives found in human brain and cerebrospinal fluid

In this study, we use antisera to synthetic beta-amyloid protein precursor (beta APP) peptides to identify, in human brain and cerebrospinal fluid (CSF), soluble approximately 125- and approximately 105-kDa derivatives of the beta APP that lack the carboxyl terminus of the full-length, membrane-associated forms. We show that the soluble approximately 125-kDa beta APP derivative contains the Kunitz protease inhibitor domain, whereas the approximately 105-kDa form does not, and we confirm that these two proteins are soluble beta APP derivatives by purifying each from human CSF and directly sequencing its amino terminus.

Diffuse senile plaques occur commonly in the cerebellum in Alzheimer's disease

Diffuse senile plaques are characterized by the presence of beta protein (beta P), also called A4 protein, in a dispersed form and the apparent lack of associated dystrophic neurites or reactive glial cells. They are the most common type of senile plaque found in the cerebral cortex in Alzheimer's disease (AD), Down's syndrome (DS), and normal aging. Here is reported the frequent presence of diffuse senile plaques in the molecular layer of cerebellar cortex in AD. Typical neuritic plaques were never detected in this location, making the cerebellar molecular cortex a useful site for the study of diffuse plaques because diffuse plaques in the cerebral cortex are intermingled with neuritic plaques. Diffuse cerebellar plaques were detected by modified Bielschowsky silver stain in 47 of 100 cases of clinically and pathologically diagnosed AD and in none of 40 aged demented and nondemented controls. They were immunolabeled by antibodies to purified AD meningeal or cortical beta P, and to a synthetic beta P but not by two antibodies to the carboxyl- and amino-termini of the beta protein precursor (beta PP), which label a subgroup of cerebral cortical plaques. This latter result suggests that the beta P deposited in the cerebellar molecular layer may be derived from a form of the beta PP from which the carboxyl and amino terminal regions of the precursor have already been cleaved. Diffuse cerebellar plaques were not recognized by antibodies to neurofilaments, tau, and PHF, all of which detect dystrophic neurites in cerebral cortical neuritic plaques. Also, no association of reactive astrocytes or microglial cells with diffuse cerebellar plaques was observed. Thus, diffuse cerebellar plaques represent multifocal deposits of noncompacted beta P that cause little or no morphologic reaction in their microenvironment.

Amyloid protein in Alzheimer's disease

Progressive deposition of amyloid fibrils in senile plaques and in blood vessels is a pathological hallmark of Alzheimer's disease. The AD amyloid protein, called beta amyloid protein, or A4 protein, is derived from a much larger precursor protein, the gene for which has now been cloned, sequenced, and localized to chromosome 21. This chromosomal location is of great interest because it has long been known that all Down's patients over the age of 40 develop the classical neuropathological lesions of AD. An anonymous DNA marker, which segregates with cases of dominantly inherited AD, has also been found to be located on chromosome 21. It is now known, however, that this marker and the gene encoding the beta amyloid precursor protein are not tightly linked. The beta amyloid precursor protein gene appears to code for a normal cellular product whose function is not yet known. The gene is expressed not only in brain but also in many non-neural tissues. It is highly conserved in evolution. Two closely related alternative transcripts have recently been identified; these contain an insert showing homology to certain members of the Kunitz family of proteinase inhibitors. All evidence accumulated thus far suggests that the beta amyloid precursor protein gene is not abnormal in AD; therefore, recent research has focused on transcriptional, translational, or posttranslational events that may be implicated in the progressive deposition of beta amyloid protein in AD.

Amyloid beta protein enhances the survival of hippocampal neurons in vitro

The beta-amyloid protein is progressively deposited in Alzheimer's disease as vascular amyloid and as the amyloid cores of neuritic plaques. Contrary to its metabolically inert appearance, this peptide may have biological activity. To evaluate this possibility, a peptide ligand homologous to the first 28 residues of the beta-amyloid protein (beta 1-28) was tested in cultures of hippocampal pyramidal neurons for neurotrophic or neurotoxic effects. The beta 1-28 appeared to have neurotrophic activity because it enhanced neuronal survival under the culture conditions examined. This finding may help elucidate the sequence of events leading to plaque formation and neuronal damage in Alzheimer's disease.

Alpha 1-antichymotrypsin is present together with the beta-protein in monkey brain amyloid deposits

The recent finding that the serine protease inhibitor, alpha 1-antichymotrypsin, is tightly associated with the amyloid deposits in brains of normal aged individuals and patients with Alzheimer's disease [Abraham C. R., Selkoe D. J. and Potter H. (1988) Cell 52, 487-501], suggests a role for this inhibitor in the progressive deposition of brain amyloid in humans. We have used immunocytochemistry to detect alpha 1-antichymotrypsin in the amyloid that accumulates in brains of aged monkeys, a naturally occurring animal model of Alzheimer-like neuropathology. In monkeys of increasing age, the earliest alpha 1-antichymotrypsin immunoreactivity was found in cortical perivascular cells, before the appearance of either Thioflavin S-detectable amyloid deposits or beta-protein reactivity in the vessel walls. Subsequently, amyloid deposits appeared in small meningeal blood vessels and cortical neuritic plaques. The oldest monkeys also showed microvascular amyloid in the cortical gray matter. Amyloid was never seen in white matter. The amyloid deposits in meningeal vessels were always positive for both beta-protein and alpha 1-antichymotrypsin, whereas in the cortex, alpha 1-antichymotrypsin immunoreactivity seemed to appear somewhat later than that of beta-protein. These findings demonstrate that two of the brain amyloid components of human senescence and Alzheimer's disease--the beta-protein and the protease inhibitor alpha 1-antichymotrypsin--are also present in the amyloid deposits of normal aged monkey brain. The extended molecular parallels between normal brain aging and Alzheimer's disease suggest that similar biochemical mechanisms may underlie progressive amyloid deposition in both situations.

The deposition of amyloid proteins in the aging mammalian brain: implications for Alzheimer's disease

Dysfunction and loss of neurons and their processes in Alzheimer's disease is accompanied by the progressive accumulation of intraneuronal and extracellular proteinaceous filaments. Currently available evidence indicates that the principal confirmed constituent of the intraneuronal paired helical filaments (PHF) is the microtubule-associated protein, tau. Whether other neuronal proteins contribute to the PHF remains unresolved. The amyloid filaments found in cerebral and meningeal microvessels and in the centers of senile plaques appear so far to be protein chemically and immunochemically distinct from the intraneuronal PHF. The native precursor of the beta-amyloid protein comprising these amyloid filaments has now been identified and characterized in brain, non-neural tissues and cDNA-transfected cells of several species, including humans. It occurs as a heterogeneous group of approximately 105-135 kD membrane-associated proteins. cDNA-transfected cells reproduce certain beta-amyloid precursor fragment patterns observed in human brain tissue, including a favored and stable 11 kd fragment containing the carboxyl terminus and presumably the beta-amyloid region. Circulating forms of the precursor have been specifically detected in human cerebrospinal fluid. Understanding the processing of the beta-amyloid precursor protein and the origin of beta-amyloid deposits should provide insights into a potentially seminal feature of cortical degeneration in Alzheimer's disease.

Protein chemical and immunocytochemical studies of meningovascular beta-amyloid protein in Alzheimer's disease and normal aging

As a comparison to previous analyses of purified amyloid plaque cores from Alzheimer's disease (AD) brain, we performed protein chemical and immunocytochemical studies on amyloid filaments extracted from meningeal blood vessels of patients with Alzheimer's disease. Results were compared with those obtained from identically prepared fractions of aged normals without cerebral amyloid angiopathy or other microscopic findings of AD. The amyloid isolation method of Glenner and Wong was modified, including an extraction with sodium dodecyl sulfate (SDS). Gel electrophoresis of purified amyloid from AD meninges yielded bands centered at 4.2 kDa. Sequencing of the HPLC-purified amyloid protein from AD meninges confirmed the published beta-protein sequence for residues 1-30 and 35-40, with the exception of glutamic acid rather than glutamine at position 11. N-terminal heterogeneity was not prominent. No sequence beyond residue 40 was obtained. Proteins of similar but not identical mol. wt. were present in HPLC-purified fractions of normal meninges; neither the beta-protein sequence nor any other interpretable sequence was detected in such fractions. Two antisera raised against the purified AD meningovascular amyloid protein identified the 4.2 kDa band on Western blots of AD preparations; no protein band in this region was labeled in control preparations. The 4.2 kDa band in AD meningeal preparations was also lableled by an antiserum to synthetic beta-peptide but not by an antiserum to the carboxyl terminus of the beta-protein precursor. Both the AD meningovascular amyloid antisera selectively labeled amyloid in cortical and meningeal vessels and plaque cores; tangles, plaque neurites, and cells of normal CNS and numerous non-neural tissues were unstained. The antisera also labeled the occasional deposits of vascular amyloid and less frequent plaque core amyloid found in some aged individuals without AD. We conclude that (1) the meningovascular amyloid beta-protein of AD, whose sequence has been confirmed and extended to residue 40, was not immunocytochemically detectable in neurofibrillary tangles; (2) beta-protein could not be detected in meningeal preparations from aged controls who lack light microscopically visible meningovascular amyloid; and (3) the vascular and plaque core amyloid present in aged normals is antigenically cross-reactive with AD meningovascular amyloid.

Neurofibrillary tangles and senile plaques in aged bears

In aged human beings and in individuals with age-associated degenerative disorders, particularly Alzheimer's disease (AD), neurons develop cytoskeletal abnormalities, including neurofibrillary tangles (NFT) and senile plaques (SP). Senile plaques occur in several nonhuman species; however, NFT, with ultrastructural or immunocytochemical similarities to those occurring in humans, have not been identified in other mammals. In this study of five aged bears (Ursus, 20-30 years of age), we identified cytoskeletal abnormalities similar to those occurring in humans. An aged Asiatic brown bear had NFT, composed of straight 10-16-nm filaments, that were immunoreactive with antibodies directed against: phosphorylated epitopes of neurofilaments (NF); tau; A68 (a protein enriched in AD); and an antigen associated with paired helical filaments (PHF). An aged polar bear had numerous SP; neurites of these plaques were immunoreactive with antibodies against phosphorylated epitopes of NF, but NFT were not identified. These results indicate that nonprimate species develop age-related cytoskeletal abnormalities similar to those occurring in humans. Investigations of the comparative pathology of aged mammals may be useful in elucidating the pathogeneses of these abnormalities.

Antisera to an amino-terminal peptide detect the amyloid protein precursor of Alzheimer's disease and recognize senile plaques

The cerebral amyloid deposited in Alzheimer's disease (AD) contains a 4.2 kDa beta amyloid polypeptide (beta AP) that is derived from a larger beta amyloid protein precursor (beta APP). Three beta APP mRNAs encoding proteins of 695, 751, and 770 amino acids have previously been identified. In each of these, there is a single membrane-spanning domain close to the carboxyl-terminus of the beta APP, and the 42 amino acid beta AP sequence extends from within the membrane-spanning domain into the large extracellular region of the beta APP. We raised rabbit antisera to a peptide corresponding to amino acids 45-62 near the amino-terminus of the beta APP. We show that these antisera detect the beta APP by demonstrating that they (i) label a set of approximately 120 kDa membrane-associated proteins in human brain previously detected by antisera to the carboxyl-terminus of beta APP and (ii) label a set of approximately 120 kDa membrane-associated proteins that are selectively overexpressed in cells transfected with a full length beta APP expression construct. The beta APP45-62 antisera specifically stain senile plaques in AD brains. This finding, along with the previous demonstration that antisera to the carboxyl-terminus of the beta APP label senile plaques, indicates that both near amino-terminal and carboxyl-terminal domains of the beta APP are present in senile plaques and suggests that proteolytic processing of the full length beta APP molecule into insoluble amyloid fibrils occurs in a highly localized fashion at the sites of amyloid deposition in AD brains.

Beta-amyloid precursor protein of Alzheimer disease occurs as 110- to 135-kilodalton membrane-associated proteins in neural and nonneural tissues

Progressive cerebral deposition of extracellular filaments composed of the beta-amyloid protein (beta AP) is a constant feature of Alzheimer disease (AD). Since the gene on chromosome 21 encoding the beta AP precursor (beta APP) is not known to be altered in AD, transcriptional or posttranslational changes may underlie accelerated beta AP deposition. Using two antibodies to the predicted carboxyl terminus of beta APP, we have identified the native beta APP in brain and nonneural human tissues as a 110- to 135-kDa protein complex that is insoluble in buffer and found in various membrane-rich subcellular fractions. These proteins are relatively uniformly distributed in adult brain, abundant in fetal brain, and detected in nonneural tissues that contain beta APP mRNA. Similarly sized proteins occur in rat, cow, and monkey brain and in cultured human HL-60 and HeLa cells; the precise patterns in the 110- to 135-kDa range are heterogeneous among various tissues and cell lines. Confirmation that the immunodetected tissue proteins are forms of beta APP was obtained when mammalian cells transfected with a full-length beta APP cDNA showed selectively augmented expression of 110- to 135-kDa proteins and specific immunocytochemical staining. Unexpectedly, the antibodies to the carboxyl terminus of beta APP labeled amyloid-containing senile plaques in AD brain. We conclude that the highly conserved beta APP molecule occurs in mammalian tissues as a heterogeneous group of membrane-associated proteins of approximately 120 kDa. Detection of the nonamyloidogenic carboxyl terminus within plaques suggests that proteolytic processing of the beta APP into insoluble filaments occurs locally in cortical regions that develop beta-amyloid deposits with age.

Clinically diagnosed Alzheimer's disease: autopsy results in 150 cases

One hundred fifty autopsy brains from patients with clinically diagnosed Alzheimer's disease (AD) were examined pathologically. The brains were received consecutively over a 3-year period from numerous sources as part of a research program in which one brain half was frozen for biochemical studies and the other half was fixed in formalin. One hundred thirty-one (87%) of the 150 cases fulfilled histological criteria for AD, with or without additional findings, such as Parkinson's disease or stroke. At least a minimal degree of amyloid angiopathy was found in every brain showing histopathological abnormalities of AD. Twenty-three (18%) of the 131 AD brains had Lewy bodies in neurons of the substantia nigra. Thirteen of the 19 non-AD cases were diagnosed as other neurodegenerative disorders. In only 2 cases was no histological correlate for the patient's dementia found. We conclude that (1) the many physicians who diagnosed these cases did so highly accurately; (2) degenerative changes in the substantia nigra were more common in patients with AD than has been reported for the general aged population; (3) amyloid angiopathy was a constant accompaniment of AD, although its severity varied widely; (4) vascular dementia was rarely clinically misdiagnosed as AD; (5) neuropathological findings were insufficient to account for the clinical syndrome of dementia in less than 2% of cases; (6) the histological criteria established by the National Institutes of Health/American Association of Retired Persons Workshop on the Diagnosis of Alzheimer's Disease worked well in assessing this large series.

The monoclonal antibody, Alz 50, recognizes tau proteins in Alzheimer's disease brain

The monoclonal antibody, Alz 50, is known to label many dystrophic neurites and neurofibrillary tangles in Alzheimer's disease (AD) brain. Using immunoprecipitation and immunoblotting, we have compared Alz 50 to monoclonal antibodies directed at two known components of neurofibrillary tangles, tau and ubiquitin, in order to characterize further the antigens recognized by Alz 50 in AD brain. Alz 50 labeled purified tau proteins in a highly similar fashion to two well-characterized tau monoclonal antibodies. Alz 50 precipitated proteins at the molecular weight of 50-70 kDa from AD but not normal brain; these proteins were reactive with the tau antibodies. In addition, Alz 50 precipitated proteins migrating principally around 160-180 kDa from AD but not normal brain; the relationship of the latter proteins to tau remains unclear. None of these proteins reacted with a ubiquitin antibody. We hypothesize that the proteins recognized by Alz 50 at much higher levers in AD than normal brain include modified and aggregated forms of tau.

Immunochemical identification of the serine protease inhibitor alpha 1-antichymotrypsin in the brain amyloid deposits of Alzheimer's disease

Two approaches--molecular cloning and immunochemical analysis--have identified one of the components of Alzheimer's disease amyloid deposits as the serine protease inhibitor alpha 1-antichymotrypsin. An antiserum against isolated Alzheimer amyloid deposits detected immunoreactivity in normal liver. The antiserum was then used to screen a liver cDNA expression library, yielding three related clones. DNA sequence analysis showed that these clones code for alpha 1-antichymotrypsin. Antisera against purified alpha 1-antichymotrypsin stained Alzheimer amyloid deposits, both in situ and after detergent extraction from brain. The anti-amyloid antiserum recognizes at least two distinct epitopes in alpha 1-antichymotrypsin, further supporting the presence of this protein in Alzheimer amyloid deposits. In addition to being produced in the liver and released into the serum, alpha 1-antichymotrypsin is expressed in Alzheimer brain, particularly in areas that develop amyloid lesions. Models by which alpha 1-antichymotrypsin could contribute to the development of Alzheimer amyloid deposits are discussed.

Accumulation of phosphorylated neurofilaments in anterior horn motoneurons of amyotrophic lateral sclerosis patients

Perikaryal collections of intermediate filaments have been described in the anterior horn motoneurons of patients with amyotrophic lateral sclerosis (ALS), but these inclusions have generally been considered rare and mainly associated with the familial form of ALS. Using the monoclonal antibody NF2F11, which recognizes phosphorylated neurofilament epitopes, we showed that focal collections of neurofilaments in anterior horn motoneurons were a characteristic finding in sporadic as well as in familial ALS; they were present in seven of nine ALS patients, but in none of nine control spinal cords. These neurofilamentous collections are not cross-reactive with antibodies directed against paired helical filaments and the microtubule associated protein tau. In addition, diffuse staining for phosphorylated neurofilament epitopes in chromatolytic anterior horn perikarya was significantly more frequent in ALS patients than in controls.

Tau epitopes are incorporated into a range of lesions in Alzheimer's disease

The neuronal microtubule-associated phosphoprotein, tau, has been identified as a major antigenic component of paired helical filaments in Alzheimer's disease (AD). The extent and distribution of altered tau antigens in AD brain, other than those found in neurofibrillary tangles (NFT) and senile plaque (SP) neurites, has not been widely discussed. We have examined tau immunoreactivity in AD using the monoclonal antibody (MAb), 5E2, raised against human fetal tau. Four types of abnormalities were recognized by MAb 5E2, each having some counterpart in Bielschowsky silver impregnations: 1) NFT; 2) thickened neurites in SP; 3) diffuse perikaryal staining seen in some neurons apparently lacking NFT; and 4) a dispersed network of randomly oriented thickened neurites not clustered into discrete plaques but found in NFT- and SP-rich cerebral cortex. These four alterations could also be recognized using three different polyclonal antibodies which had strong tau immunoreactivity but were optimally shown by MAb 5E2. Our findings demonstrate the complexity of altered tau-immunoreactive neuronal elements and emphasize the widespread abnormality of microtubule-associated proteins in AD cortex.

Gene dosage of the amyloid beta precursor protein in Alzheimer's disease

The progressive deposition in the human brain of amyloid filaments composed of the amyloid beta protein is a principal feature of Alzheimer's disease (AD). Densitometric analysis of Southern blots probed with a complementary DNA for the amyloid protein has been carried out to determine the relative dosage of this gene in genomic DNA of 14 patients with AD, 12 aged normal subjects, and 10 patients with trisomy 21 (Down syndrome). Whereas patients in the last group showed the expected 1.5-fold increase in dosage of this gene, none of the patients with AD had a gene dosage higher than that of the normal controls. These results do not support the hypothesis that the genetic defect in AD involves duplication of a segment of chromosome 21 containing the amyloid gene. Alternative mechanisms for the brain-specific increase in amyloid protein deposition in AD should be considered.

Synthetic peptide homologous to beta protein from Alzheimer disease forms amyloid-like fibrils in vitro

Progressive amyloid deposition in senile plaques and cortical blood vessels may play a central role in the pathogenesis of Alzheimer disease. We have used x-ray diffraction and electron microscopy to study the molecular organization and morphology of macromolecular assemblies formed by three synthetic peptides homologous to beta protein of brain amyloid: beta-(1-28), residues 1-28 of the beta protein; [Ala16]beta-(1-28), beta-(1-28) with alanine substituted for lysine at position 16; and beta-(18-28), residues 18-28 of the beta protein. beta-(1-28) readily formed fibrils in vitro that were similar in ultrastructure to the in vivo amyloid and aggregated into large bundles resembling those of senile plaque cores. X-ray patterns from partially dried, oriented pellets showed a cross-beta-conformation. A series of small-angle, equatorial maxima were consistent with a tubular fibril having a mean diameter of 86 A and a wall composed of pairs of cross-beta-pleated sheets. The data may also be consistent with pairs of cross-beta-sheets that are centered 71-A apart. [Ala16]beta-(1-28) formed beta-pleated sheet assemblies that were dissimilar to in vivo fibrils. The width of the 10-A spacing indicated stacks of about six sheets. Thus, substitution of the uncharged alanine for the positively charged lysine in the beta-strand region enhances the packing of the sheets and dramatically alters the type of macromolecular aggregate formed. beta-(18-28) formed assemblies that had even a greater number of stacked sheets, approximately equal to 24 per diffracting domain as indicated by the sharp intersheet reflection. Our findings on these homologous synthetic assemblies help to define the specific sequence that is required to form Alzheimer-type amyloid fibrils, thus providing an in vitro model of age-related cerebral amyloidogenesis.

Tau antisera recognize neurofibrillary tangles in a range of neurodegenerative disorders

Neurofibrillary tangles occur in a number of apparently distinct neurodegenerative diseases and in normal aging of the human brain. Antibodies raised against Alzheimer's disease paired helical filaments immunolabel the tangles seen in all other tangle-associated disorders examined to date. The neuronal microtubule-associated protein, tau, has recently been identified as an antigenic component of neurofibrillary tangles and senile plaque neurites in Alzheimer's disease. Three different polyclonal antibodies with strong tau immunoreactivity are examined in this study. These antibodies were found to immunostain tangles in normal aged brain and in brains affected by a range of neurodegenerative disorders, including Down's syndrome, Alzheimer's disease plus Parkinson's disease, progressive supranuclear palsy, and the parkinsonism-dementia complex of Guam, as well as Pick bodies in Pick's disease. The findings further illustrate the relative nonspecificity of neurofibrillary lesions in neurodegenerative disorders.

Recognition of Alzheimer paired helical filaments by monoclonal neurofilament antibodies is due to crossreaction with tau protein

Neurofibrillary tangles and senile plaques are the principal pathological features of Alzheimer disease. Neurofibrillary tangles and the neurites of senile plaques contain paired helical filaments (PHF) that consist of two 10-nm filaments twisted into a double helix. The precursor proteins of PHF are not fully known. To identify these precursors, numerous immunochemical studies have been carried out during the past decade. Two apparently conflicting results have been reported. (i) Some, but not all, monoclonal antibodies to neurofilaments stained neurofibrillary tangles. (ii) Polyclonal antibodies prepared to PHF purified in NaDodSO4 because of their unusual insolubility did not recognize normal proteins, including neurofilaments, on electrophoretic transfer blots of human brain homogenates. These results have been confirmed in several laboratories, including by the use of electron microscopic labeling. Recently, we reported that polyclonal PHF antibodies include antibodies to tau proteins, a family of heat-stable microtubule-associated phosphoproteins, and that antibodies to tau stain Alzheimer neurofibrillary tangles. Those monoclonal neurofilament antibodies that recognize tangles are reported to be directed against phosphorylated epitopes. These facts prompted us to reexamine certain neurofilament monoclonal antibodies that stain neurofibrillary tangles. All monoclonal neurofilament antibodies that stain tangles that we examined, including those initially reported, reacted with tau proteins. Our results suggest that these antibodies react with phosphorylated tau proteins in PHF, not neurofilament proteins, highlighting the problem of using antibodies to phosphorylated protein epitopes in immunochemical studies. Independent evidence for the presence of neurofilament proteins in human paired helical filaments is now required.