- Research article
- Open Access
Ultra-sensitive detection of prion protein fibrils by flow cytometry in blood from cattle affected with bovine spongiform encephalopathy
© Trieschmann et al; licensee BioMed Central Ltd. 2005
- Received: 03 May 2005
- Accepted: 04 October 2005
- Published: 04 October 2005
The definite diagnosis of prion diseases such as Creutzfeldt-Jakob disease (CJD) in humans or bovine spongiform encephalopathy (BSE) in cattle currently relies on the post mortem detection of the pathological form of the prion protein (PrPSc) in brain tissue. Infectivity studies indicate that PrPSc may also be present in body fluids, even at presymptomatic stages of the disease, albeit at concentrations well below the detection limits of currently available analytical methods.
We developed a highly sensitive method for detecting prion protein aggregates that takes advantage of kinetic differences between seeded and unseeded polymerization of prion protein monomers. Detection of the aggregates was carried out by flow cytometry. In the presence of prion seeds, the association of labelled recombinant PrP monomers in plasma and serum proceeds much more efficiently than in the absence of seeds. In a diagnostic model system, synthetic PrP aggregates were detected down to a concentration of approximately 10-8 nM [0.24 fg/ml]. A specific signal was detected in six out of six available serum samples from BSE-positive cattle.
We have developed a method based on seed-dependent PrP fibril formation that shows promising results in differentiating a small number of BSE-positive serum samples from healthy controls. This method may provide the basis for an ante mortem diagnostic test for prion diseases.
- Prion Protein
- Prion Disease
- Bovine Spongiform Encephalopathy
- Chronic Wasting Disease
A group of fatal transmissible neurodegenerative diseases, including Creutzfeld-Jakob disease (CJD), bovine spongiform encephalopathy (BSE), chronic wasting disease (CWD) and scrapie, is caused by an unusual infectious agent that has been termed prion . Prions consist of an aberrant isoform (PrPSc) of the normal cellular prion protein (PrPC). PrPC is a cell surface glycoprotein expressed in neurons  and other cell types [3, 4]. The precise physiological function of the cellular prion protein is not known yet. PrPSc differs from PrPC in its higher content of β-sheet structure [5, 6], its partial resistance to protease digestion , and its tendency to form large aggregates . PrPSc propagates by converting the cellular prion protein to the PrPSc conformation . PrPSc aggregates accumulate predominantly in the central nervous system (CNS), and definitive diagnosis of prion diseases currently relies on the post mortem detection of PrPSc in CNS tissue by immunohistochemistry, Western blotting, or ELISA . Transmission studies indicate that prions may also be present in blood, potentially allowing for ante mortem diagnosis, but the sensitivity of the currently available analytical methods is insufficient for the detection of the extremely low prion titers that can be expected in body fluids .
Here, we report the development of a method based on kinetic differences between seeded and unseeded aggregation of prion protein that allows the detection of PrP aggregates in blood down to attomolar concentrations by flow cytometry.
Detection of synthetic prion protein aggregates in serum or plasma
Kinetic differences between seeded and spontaneous polymerization of peptide monomers can be used for the detection of amyloid β-protein aggregates in the cerebrospinal fluid of Alzheimer's disease patients . Here, we extend the principle of seeded polymerization to the detection of prion protein aggregates.
Analysis of serum from clinical-stage, BSE-positive cattle
We have developed a method based on seed-dependent PrP fibril formation that shows promising results in differentiating a small number of BSE-positive serum samples from healthy controls. More samples need to be tested in order to validate its potential as an ante mortem diagnostic test for BSE and other prion diseases.
Serum samples from six confirmed cases of BSE in cattle and four control animals were obtained from BFAV, Insel Riems, Germany. Control plasma was obtained from a blood bank.
Labeling of prion protein
Preparation of fibrils from recombinant prion protein
25 μM of unlabeled bovine prion protein in PBS containing 0.2 % SDS was incubated for 10 min at room temperature, followed by a twentyfold dilution with PBS. For fibril formation, the diluted reaction mixture was incubated for 48 h at room temperature .
PrP fibril formation in serum or plasma
Recombinant FITC-labeled bovine prion protein was incubated in 150 μl serum or plasma at a concentration of 5 or 10 nM for 5–10 min. at 20°C, shaking at 550 rpm in an Eppendorf thermomixer, followed by an increase of the temperature to 37°C h at constant shaking speed. The incubation was continued for 20 h. Samples were then analyzed by flow cytometry.
Analysis of the samples was carried out on a FACSVantage flow cytometer (BD Biosciences) at room temperature, measurement time was 30 sec per sample.
This work was kindly supported by grant No. 0312711A from the BMBF (Bundesministerium für Bildung und Forschung) in the context of the German National TSE Research Platform. The authors gratefully acknowledge the help of the TSE Research Platform, Munich, and the BFAV Riems, Germany, with respect to the kind gift of biological material in the context of this study.
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