Enzyme-Linked Immunosorbent Assay for the Human Glial Fibrillary Acidic Protein Using a Mouse Monoclonal Antibody

Two enzyme-linked immunosorbent assays (ELISAs) have been developed for the quantification of soluble human glial fibrillary acidic protein (GFAP). The specificity of the assays for GFAP is ensured by the use of a monoclonal antibody directed against a GFAP-specific antigenic determinant. One ELISA is a four-layer system working in the concentration range 5-600 ng GFAP/ml. The other ELISA is a five-layer system and includes a biotin/avidin binding reaction. The latter assay has a working range of 0.5-60 ng GFAP/ml. The assays may be used for quantification of GFAP in CSFs, amniotic fluids, and extracts or homogenates of normal and pathological brain material. GFAP in serum could not be quantified because of unidentified interference. CSFs from 18 nonneurological subjects were found to contain 2-14 ng GFAP/ml (mean 4.1 ng/ml), whereas amniotic fluids from 50 normal pregnant women contained up to 24 ng GFAP/ml (mean 12.4 ng/ml). GFAP concentrations in CSFs from 32 multiple sclerosis patients were found not to be elevated compared to the control group.     

Polymerization of τ into Filaments in the Presence of Heparin: The Minimal Sequence Required for τ - τ Interaction

Abstract: Paired helical filaments isolated from the brains of patients with Alzheimer's disease are composed of a major protein component, the microtubule-associated protein termed τ, together with other nonprotein components, including heparan, a glycosaminoglycan, the more extensively sulfated form of which is heparin. As some of these nonprotein components may modulate the assembly of τ into filamentous structures, we have analyzed the ability of the whole τ protein or some of its fragments to self-assemble in the presence of heparin. Different τ fragments, all of them containing some sequences of the tubulin-binding motif, can assemble in vitro into filaments. We have also found formation of polymers with the 18-residue-long peptide corresponding to the third tubulin-binding motif of τ. This suggests that the ability of τ for self-assembly could be localized in a short sequence of amino acids present in the tubulin-binding repeats of the τ molecule.     

单克隆抗体酶联免疫吸附法检测尿标本中人巨细胞病毒抗原

本文运用抗人巨细胞病毒(HCMV)包膜20KD或/和130KD结构蛋白的单克隆抗体分别建立了4类酶联免疫吸附试验(ELISA)夹心法,共对44人份临床尿标本进行HCMV抗原检测。方法的敏感度可高达10.3—32.8ng HCMV抗原/ml尿,与尿标本中的HSV-Ⅰ、HSV-Ⅱ和EBV抗原无交叉反应,重复性良好,与病毒分离比较,敏感性和特异性在71—83％和88—100％之间;与核酸杂交比较,敏感性和特异性也可分别高达60—100％和83.3—100％。混合使用多种单克隆抗体作为包被抗体会得到较好的技术参数。上述结果提示运用单克隆抗体ELISA将有助于一般临床实验室对HCMV感染的快速诊断。     

Enzyme-Linked Immunosorbent Assay for Detection of Chitooligosaccharides

In order to detect chitooligosaccharides (COS), an enzyme-linked immunosorbent assay (ELISA) was developed. A chitooligosaccharide mixture (COSM) conjugated to bovine serum albumin was used to immunize rabbits to produce an anti-COS polyclonal antibody. By use of specific antibody and COSM-horseradish peroxidase conjugate, we established a competitive direct ELISA (cdELISA) the detection limit of which was about 0.1 μg/ml. In the cdELISA, the cross-reactivities of the specific antibody toward glucosamine, chitobiose, chitotriose, chitotetraose, chitopentaose, and chitohexaose were 0.27, 27, 75, 75, 144, and 100%, respectively, and those toward N-acetylchitobiose, N-acetylchitotriose, N-acetylchitotetraose, N-acetylchitopentaose, and N-acetylchitohexaose were 1.58, 0.005, 1.08, 0.05, and 0.40%, respectively.     

Detection of Proteins in Normal and Alzheimer's Disease Cerebrospinal Fluid with a Sensitive Sandwich Enzyme-Linked Immunosorbent Assay

Abstract— Alzheimer's disease is a progressive degenerative dementia characterized by the abundant presence of neurofibrillary tangles in neurons. This study was designed to test whether the microtubule-associated protein, a major component of neurofibrillary tangles, could be detected in CSF. Additionally, we investigated whether CSF levels were abnormal in Alzheimer's disease as compared with a large group of control patients. We developed a sensitive sandwich enzyme-linked immunosorbent assay using AT120, a monoclonal antibody directed to human, as a capturing antibody. With this technique, the detection limit for was less than 5 pg/ml of CSF. Using ATS, which recognizes abnormally phosphorylated ser-ines 199–202 in, the detection limit was below 20 pg/ml of CSF. However, with AT8, we found no immunoreactiv-ity in CSF, suggesting that only a small fraction of CSF contains the abnormally phosphorylated AT8 epitope. Our results indicate that CSF levels are significantly increased in Alzheimer's disease. Also, CSF levels in a large group of patients with a diversity of neurological diseases showed overlap with CSF levels in Alzheimer's disease.     

Developmental Changes in τ Phosphorylation: Fetal τ Is Transiently Phosphorylated in a Manner Similar to Paired Helical Filament-τ Characteristic of Alzheimer's Disease

Rat and human fetal brain τ were probed with a panel of monoclonal antibodies (tau-1, AT8, 8D8, RT97, SMI31, SMI34) that distinguish between paired helical filament (PHF)-τ of Alzheimer's disease and normal adult brain τ. These antibodies discriminate between normal and PHF-τ because their epitopes are phosphorylated in PHF-τ. Although only one molecular isoform of τ was shown to be expressed in fetal brain, two fetal τ species could be distinguished on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the slower migrating species was recognized by all of the PHF-τ-specific antibodies. Moreover, this immunoreactivity was shown to be phosphorylation dependent. Our observations suggest that the abnormal phosphorylation of τ in Alzheimer's disease may be the result of reactivation of pathways governing the phosphorylation of τ in the developing brain.     

用酶联免疫吸附法检测蛋白质的聚合

许多蛋白质二聚化或多聚化在调节其功能方面发挥重要作用,研究蛋白质的聚合有助于阐明相关的生物学过程. 本文使用酶联免疫吸附法,对分子量11 kD的马传染性贫血病毒核壳蛋白（nucleocapsid protein 11 kD, NCp11）的聚合进行检测. 首先利用亲和层析分别纯化了NCp11以及N 端或C 端融合有FLAG标签的NCp11. 然后将NCp11包被于聚苯乙烯96孔板底,加入带FLAG标签的NCp11与之聚合,再依次加入抗FLAG抗体、辣根过氧化物酶标记的二抗及底物,反应终止后于450 nm波长下读取吸收值. 结果表明,酶联免疫吸附法适用于NCp11聚合的检测,可对聚合的特异性、剂量依赖效应和影响因素等进行定量评价. 利用该方法不仅能检测蛋白质的聚合,而且具有灵敏度高、特异性好、通量高、成本低和快速简便等优点,有望获得广泛应用.     

β-Amyloid Protein Precursor and τ mRNA Levels Versus β-Amyloid Plaque and Neurofibrillary Tangles in the Aged Human Brain

Abstract: To learn whether or not the levels of β-amyloid protein precursor (APP) and τ mRNAs are related to the formation of β-amyloid and neurofibrillary tangles, we quantified these mRNA levels in three cortical regions of 38 aged human brains, which were examined immunocyto-chemically for β-amyloid and tangles. Marked individual variabilities were noted in APP and τ mRNA levels among elderly individuals. The mean APP mRNA level was slightly reduced in the β-amyloid plaque (++) group, but not in the plaque (+) group, compared to the plaque (−) group. Some brains in the plaque (−) group showed increased APP expression, the extent of which was not seen in the plaque (+)or(++) group. The differences in the mean τ mRNA levels were not statistically significant among the tangle (−), (+), and (++) groups. These results show that β-protein and τ deposition do not accompany increased expression of the APP and τ genes, respectively, and thus suggest that factors other than gene expression may be at work in the progression of β-amyloid and/or tangle formation in the aged human brain.     

The State of Phosphorylation of Normal Adult Brain τ, Fetal τ, and τ from Alzheimer Paired Helical Filaments at Amino Acid Residue Ser262

Abstract: Antibody Ab262 was raised against a synthetic τ peptide (SKIGSTENLK, amino acids 258–267 of τ, termed Ser²⁶² peptide). The antibody was more reactive with Ser²⁶² peptide and unphosphorylated τ than a related phosphopeptide [SKIGS(P)TENLK, termed P-Ser²⁶² peptide] and τ phosphorylated by a partially purified kinase, glycogen synthase kinase (GSK) 3β. Ab262 reacted poorly with a peptide having the sequence DRVQSKIGSLD (amino acids 348–358). Treatment of P-Ser²⁶² peptide or GSK 3β phosphorylated τ with alkaline phosphatase increased Ab262 immunoreactivity, indicating that Ab262 is a reagent useful for studying τ phosphorylation at the Ser²⁶² residue. The Ab262 immunoreactivity was detected in τ from normal brains and Alzheimer paired helical filament (PHF-τ) and in PHFs. Alkaline phosphatase treatment had no effect on the Ab262 immunoreactivity of normal τ and PHF-τ but altered the Tau-1 and PHF-1 immunoreactivities. τ proteins from rat brains at 3 and 8 h postmortem exhibited 5 and 19%, respectively, more Ab262 immunoreactivity than τ from fresh tissues. In comparison, rat τ at 8 h postmortem was 40% more immunoreactive with Tau-1. The results suggest that Ser²⁶² is not a major phosphorylation site in vivo. Moreover, there is little or no difference between PHF-τ and normal τ in the extent of phosphorylation at Ser²⁶².     

The τ Protein in Human Cerebrospinal Fluid in Alzheimer's Disease Consists of Proteolytically Derived Fragments

Abstract: Previous studies have shown that the levels of the microtubule-associated protein τ in the CSF of patients with Alzheimer's disease (AD) are elevated compared with age-matched controls. In spite of these findings, the nature of τ in CSF has not been well documented. In the present study, τ was immunoprecipitated from CSF of patients with AD or acute stroke, as well as normal elderly controls, followed by immunoblot analysis. In all cases, CSF τ consisted primarily of a band migrating at 26–28 kDa. In AD and stroke patients, several smaller τ fragments were also detected. No intact τ was detected in any of the CSF samples examined. Further immunoprecipitation studies showed that the majority of the τ fragments contained the amino terminus of the molecule. Treatment of CSF τ with alkaline phosphatase did not alter the electrophoretic properties of the fragments. These studies clearly demonstrate that CSF τ is truncated rather than intact.     

τ Self-Association: Stabilization with a Chemical Cross-Linker and Modulation by Phosphorylation and Oxidation State

Abstract: τ is a major component of paired helical filaments found in the neurofibrillary tangles of Alzheimer's diseased brain. However, the mechanism or mechanisms responsible for the association of τ to form these aggregates remains unknown. In this study, the role of intermolecular disulfide bonds in the formation of higher order oligomers of bovine τ and the human recombinant τ isoform T3 was examined using the chemical cross-linking agent disuccinimidylsuberate (DSS). In addition, the role of phosphorylation and oxidation state on the in vitro self-association of τ was studied using this experimental model. Stabilization of τ-τ interactions with DSS indicated that intermolecular disulfide bonds probably play a predominant role in dimer formation, but the formation of higher order oligomers of τ cannot be attributed to these bonds alone. τ-τ interactions were significantly decreased either by blocking Cys residues or by exposing the τ to a reducing (nitrogen and dithiothreitol), instead of an oxidizing, environment. τ self-association was also significantly decreased by prior phosphorylation with calcium/calmodulin-dependent protein kinase II. Phosphorylation by cyclic AMP-dependent protein kinase or dephosphorylation by alkaline phosphatase did not alter τ self-assembly. These data suggest a role for several factors that may modulate τ self-association in vivo.     

Okadaic Acid Induces Hyperphosphorylation of τ Independently of Mitogen-Activated Protein Kinase Activation

Abstract: Hyperphosphorylation of the microtubule-associated protein τ is a characteristic of Alzheimer brain tissue. Recent in vitro data suggest that mitogen-activated protein kinase (MAPK), a proline-directed protein kinase, phosphorylates the sites on τ common to Alzheimer's disease. Using an okadaic acid-induced τ hyperphosphorylation model, we have tested the requirement for MAPK activity, using a specific inhibitor {PD098059 [2-(2'-amino-3'-methoxyphenyl)oxanaphthalen-4-one]} of the MAPK activator Mek1. Mobility shift, phosphoepitope analysis, and direct measurement of kinase activity indicated that the Mek1 inhibitor dose-dependently blocked basal and okadaic acid-induced MAPK activation. Despite a block of MAPK activation by this inhibitor, robust τ hyperphosphorylation was observed in response to okadaic acid. In addition, activation of MAPK by phorbol 12-myristate 13-acetate did not result in τ phosphorylation, indicating that in primary cultures of cortical neurons elevated MAPK activity is not sufficient to induce τ hyperphosphorylation.     

τ Protein Kinase II Is Involved in the Regulation of the Normal Phosphorylation State of τ Protein

Abstract: To study the phosphorylation state of τ in vivo, we have prepared antisera by immunizing rabbits with synthetic phosphopeptides containing phosphoamino acids at specific sites that are potential targets for τ protein kinase II. Immunoblot experiments using these antisera demonstrated that τ in microtubule-associated proteins is phosphorylated at Ser¹⁴⁴ and at Ser³¹⁵. Almost all τ variants separated on two-dimensional gel electrophoresis were phosphorylated at Ser¹⁴⁴ and nearly one-half of them at Ser³¹⁵. Phosphorylation at Ser¹⁴⁴ and at Thr¹⁴⁷ of τ isolated from heat-stable brain extracts was shown to be developmentally regulated, with the highest level of phosphorylation found at postnatal week 1. In vitro phosphorylation of τ by τ protein kinase I, a kinase responsible for abnormal phosphorylation of τ found in paired helical filaments of patients with Alzheimer's disease, was enhanced by prior phosphorylation of τ by τ protein kinase II. Thus, we suggest that τ protein kinase II is indirectly involved, at least in part, in the regulation of the phosphorylation state of τ in neuronal cells.     

Stress-Activated Protein Kinase/c-Jun N-Terminal Kinase Phosphorylates τ Protein

Abstract: A proportion of the neuronal microtubule-associated protein (MAP) τ is highly phosphorylated in foetal and adult brain, whereas the majority of τ in the neurofibrillary tangles of Alzheimer's patients is hyperphosphorylated; many of the phosphorylation sites are serines or threonines followed by prolines. Several kinases phosphorylate τ at such sites in vitro. We have now shown that purified recombinant stress-activated protein kinase/c-Jun N-terminal kinase, a proline-directed kinase of the MAP kinase extended family, phosphorylates recombinant τ in vitro on threonine and serine residues. Western blots using antibodies to phosphorylation-dependent τ epitopes demonstrated that phosphorylation occurs in both of the main phosphorylated regions of τ protein. Unlike glycogen synthase kinase-3, the c-Jun N-terminal kinase readily phosphorylates Thr²⁰⁵ and Ser⁴²², which are more highly phosphorylated in Alzheimer τ than in foetal or adult τ. Glycogen synthase kinase-3 may preferentially phosphorylate the sites found physiologically, in foetal and to a smaller extent in adult τ, whereas stress-activated/c-Jun N-terminal kinase and/or other members of the extended MAP kinase family may be responsible for pathological proline-directed phosphorylations. Inflammatory processes in Alzheimer brain might therefore contribute directly to the pathological formation of the hyperphosphorylated τ found in neurofibrillary tangles.     

Tau 2: A Probe for a Ser Conformation in the Amino Terminus of τ

We have determined the epitope for Tau 2, a monoclonal antibody that intensely stained tangles, plaque neurites, and curly fibers in the tissue section, and strongly labeled bovine tau, but only very weakly labeled human tau on the blot. The epitope has been localized to Ala95 through Ala108 of bovine tau. Ser101 is critical for Tau 2 reactivities; the replacement of Ser by Pro, which is found in rat, mouse, and human tau, brings about very weak Tau 2 reactivities. The strong Tau 2 staining of tangles and its effective absorption with a synthetic Ser peptide (Ala95 through Ala108) suggest that the tau in paired helical filaments takes a Ser conformation, rather than a Pro conformation, in its amino-terminal portion.     

Amino Acid Residues 226–240 of τ Which Encompass the First Lys-Ser-Pro Site of τ, Are Partially Phosphorylated in Alzheimer Paired Helical Filament-τ

Abstract: A synthetic peptide corresponding to residues 226–240 (E9 peptide) of human τ, which contains an Lys-Ser-Pro motif, was used to raise a polyclonal antibody. The antibody, E9, was 10-fold less reactive with phospho-E9 peptide than with native E9 peptide. E9 antibody was used to study the extent of phosphorylation in a modified form of τ (PHF-τ) that is found in Alzheimer's disease brain and is incorporated into paired helical filaments (PHFs). E9 immunolabeled Alzheimer's disease neurofibrillary tangles and abnormal neurites in brain sections intensely, with increased immunoreactivity detected after pretreatment of sections with phosphatase. On immunoblots and ELISA, E9 reacted with PHF-τ and recombinant human τ but not with the high and middle molecular weight neurofilament proteins. Phosphatase treatment of PHF-τ improved the E9 immunoreactivity by 30–50%. Dephosphorylated high but not middle molecular weight neurofilament protein became reactive with E9. These results indicate that <50% of the PHF-T is phosphorylated in the subregion corresponding to residues 226–240 of τ and suggest that the phosphorylation of this region may not be essential for PHF formation.     

Phosphorylation of τ Protein by Casein Kinase-1 Converts It to an Abnormal Alzheimer-Like State

Abstract: The microtubule-associated protein τ is abnormally hyperphosphorylated in Alzheimer's disease. Both proline-dependent protein kinases (PDPKs) and non-PDPKs are involved in this hyperphosphorylation of τ. Several PDPKs can phosphorylate τ in vitro and induce Alzheimer-like epitopes to many phosphorylation-dependent antibodies. A similar induction has not been reported with non-PDPKs. In this study we have evaluated six non-PDPKs [cyclic AMP-dependent (A-kinase), calcium/phospholipid-dependent (C-kinase), casein kinase-1 (CK-1), casein kinase-2 (CK-2), calcium/calmodulin-dependent protein kinase II, and calcium/calmodulin-dependent protein kinase from rat cerebellum] for their abilities to induce Alzheimer-like epitopes on τ. Such epitopes were induced by A-kinase, C-kinase, CK-1, and CK-2, but the degree of induction achieved by CK-1 was much greater than with the other kinases. These results suggest that CK-1 may play an important role in the conversion of τ from the normal to the abnormal phosphorylation state in Alzheimer's disease.     

Brain Levels of Microtubule-Associated Protein τ Are Elevated in Alzheimer''s Disease: A Radioimmuno-Slot-Blot Assay for Nanograms of the Protein

The microtubule-associated protein tau, which stimulates the assembly of alpha-beta tubulin heterodimers into microtubules, is abnormally phosphorylated in Alzheimer's disease (AD) brain and is the major component of paired helical filaments. In the present study, the levels of tau and abnormally phosphorylated tau were determined in brain homogenates of AD and age-matched control cases. A radioimmuno-slot-blot assay was developed, using a primary monoclonal antibody, Tau-1, and a secondary antibody, antimouse 125I-immunoglobulin G. To assay the abnormally phosphorylated tau, the blots were treated with alkaline phosphatase before immunolabeling. The levels of total tau were about eightfold higher in AD (7.3 +/- 2.7 ng/micrograms of protein) than in control cases (0.9 +/- 0.2 ng/micrograms), and this increase was in the form of the abnormally phosphorylated protein. These studies indicate that the abnormal phosphorylation--not a decrease in the level of tau--is a likely cause of neurofibrillary degeneration in AD.