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Li D, Cho YK. High specificity of widely used phospho-tau antibodies validated using a quantitative whole-cell based assay. J Neurochem 2019; 152:122-135. [PMID: 31325178 DOI: 10.1111/jnc.14830] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2019] [Revised: 06/25/2019] [Accepted: 07/11/2019] [Indexed: 02/04/2023]
Abstract
Antibodies raised against defined phosphorylation sites of the microtubule-associated protein tau are widely used in scientific research and being applied in clinical assays. However, recent studies have revealed an alarming degree of non-specific binding found in these antibodies. In order to quantify and compare the specificity phospho-tau antibodies and other post-translational modification site-specific antibodies in general, a measure of specificity is urgently needed. Here, we report a robust flow cytometry assay using human embryonic kidney cells that enables the determination of a specificity parameter termed Φ, which measures the fraction of non-specific signal in antibody binding. We validate our assay using anti-tau antibodies with known specificity profiles, and apply it to measure the specificity of seven widely used phospho-tau antibodies (AT270, AT8, AT100, AT180, PHF-6, TG-3, and PHF-1) among others. We successfully determined the Φ values for all antibodies except AT100, which did not show detectable binding in our assay. Our results show that antibodies AT8, AT180, PHF-6, TG-3, and PHF-1 have Φ values near 1, which indicates no detectable non-specific binding. AT270 showed Φ value around 0.8, meaning that approximately 20% of the binding signal originates from non-specific binding. Further analyses using immunocytochemistry and western blotting confirmed the presence of non-specific binding of AT270 to non-tau proteins found in human embryonic kidney cells and the mouse hippocampus. We anticipate that the quantitative approach and parameter introduced here will be widely adopted as a standard for reporting the specificity for phospho-tau antibodies, and potentially for post-translational modification targeting antibodies in general. Cover Image for this issue: doi: 10.1111/jnc.14727.
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Affiliation(s)
- Dan Li
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA
| | - Yong Ku Cho
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA.,Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, USA.,Institute for Systems Genomics, University of Connecticut, Storrs, Connecticut, USA.,Connecticut Institute for the Brain and Cognitive Sciences, University of Connecticut, Storrs, Connecticut, USA
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2
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Li D, Cho YK. High specificity of widely used phospho-tau antibodies validated using a quantitative whole-cell based assay. J Neurochem 2019. [PMID: 31325178 DOI: 10.1111/jnc.14727] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Antibodies raised against defined phosphorylation sites of the microtubule-associated protein tau are widely used in scientific research and being applied in clinical assays. However, recent studies have revealed an alarming degree of non-specific binding found in these antibodies. In order to quantify and compare the specificity phospho-tau antibodies and other post-translational modification site-specific antibodies in general, a measure of specificity is urgently needed. Here, we report a robust flow cytometry assay using human embryonic kidney cells that enables the determination of a specificity parameter termed Φ, which measures the fraction of non-specific signal in antibody binding. We validate our assay using anti-tau antibodies with known specificity profiles, and apply it to measure the specificity of seven widely used phospho-tau antibodies (AT270, AT8, AT100, AT180, PHF-6, TG-3, and PHF-1) among others. We successfully determined the Φ values for all antibodies except AT100, which did not show detectable binding in our assay. Our results show that antibodies AT8, AT180, PHF-6, TG-3, and PHF-1 have Φ values near 1, which indicates no detectable non-specific binding. AT270 showed Φ value around 0.8, meaning that approximately 20% of the binding signal originates from non-specific binding. Further analyses using immunocytochemistry and western blotting confirmed the presence of non-specific binding of AT270 to non-tau proteins found in human embryonic kidney cells and the mouse hippocampus. We anticipate that the quantitative approach and parameter introduced here will be widely adopted as a standard for reporting the specificity for phospho-tau antibodies, and potentially for post-translational modification targeting antibodies in general. Cover Image for this issue: doi: 10.1111/jnc.14727.
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Affiliation(s)
- Dan Li
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA
| | - Yong Ku Cho
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA.,Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, USA.,Institute for Systems Genomics, University of Connecticut, Storrs, Connecticut, USA.,Connecticut Institute for the Brain and Cognitive Sciences, University of Connecticut, Storrs, Connecticut, USA
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Kogot JM, Pennington JM, Sarkes DA, Kingery DA, Pellegrino PM, Stratis-Cullum DN. Screening and characterization of anti-SEB peptides using a bacterial display library and microfluidic magnetic sorting. J Mol Recognit 2015; 27:739-45. [PMID: 25319622 PMCID: PMC4274986 DOI: 10.1002/jmr.2400] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Revised: 04/22/2014] [Accepted: 05/27/2014] [Indexed: 11/06/2022]
Abstract
Bacterial peptide display libraries enable the rapid and efficient selection of peptides that have high affinity and selectivity toward their targets. Using a 15-mer random library on the outer surface of Escherichia coli (E.coli), high-affinity peptides were selected against a staphylococcal enterotoxin B (SEB) protein after four rounds of biopanning. On-cell screening analysis of affinity and specificity were measured by flow cytometry and directly compared to the synthetic peptide, off-cell, using peptide-ELISA. DNA sequencing of the positive clones after four rounds of microfluidic magnetic sorting (MMS) revealed a common consensus sequence of (S/T)CH(Y/F)W for the SEB-binding peptides R338, R418, and R445. The consensus sequence in these bacterial display peptides has similar amino acid characteristics with SEB peptide sequences isolated from phage display. The Kd measured by peptide-ELISA off-cell was 2.4 nM for R418 and 3.0 nM for R445. The bacterial peptide display methodology using the semiautomated MMS resulted in the discovery of selective peptides with affinity for a food safety and defense threat. Published 2014. This article is a U.S. Government work and is in the public domain in the USA. Journal of Molecular Recognition published by John Wiley & Sons, Ltd.
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Affiliation(s)
- Joshua M Kogot
- US Army Research Laboratory; Sensors and Electron Devices, Adelphi, MD, USA
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Elliott SE, Parchim NF, Liu C, Xia Y, Kellems RE, Soffici AR, Daugherty PS. Characterization of antibody specificities associated with preeclampsia. Hypertension 2014; 63:1086-93. [PMID: 24446060 DOI: 10.1161/hypertensionaha.113.02362] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The presence of maternal autoantibodies has been previously associated with preeclampsia, although the composition of the antibody repertoire in preeclampsia has not been well characterized. Given this, we applied a bacterial display peptide library to identify peptides that preferentially react with plasma antibodies from patients with preeclampsia (n=15) versus healthy-outcome pregnancies (n=18). Screening using fluorescence-activated cell sorting identified 38 peptides that preferentially bind to antibodies from individuals with preeclampsia. These preeclampsia-specific peptides possessed similar motifs of R(G)/S(G)/-WW(G)/S, RWW(G)/S, or WGWGXX(R)/K distinct from the angiotensin II type 1 receptor epitope AFHYESQ. Seven library-isolated peptides and a cell surface-displayed angiotensin II type 1 receptor epitope were used to construct a diagnostic algorithm with a training set of 18 new preeclamptic and 22 healthy-outcome samples from geographically distinct cohorts. Cross-validation within the training group resulted in averaged areas underneath a receiver operating characteristic curve of 0.78 and 0.72 with and without the known receptor epitope, respectively. In a small validation set (12 preeclamptic; 8 healthy), the algorithm consisting only of library-isolated peptides correctly classified 10 preeclamptic and 6 healthy samples using a predefined cutoff that achieved 61% sensitivity (95% confidence interval, 36%-83%) at 95% specificity (95% confidence interval, 77%-100%) in training set (n=40) cross-validation. Our results indicate that antibodies with specificities other than anti-angiotensin II type 1 receptor are prevalent in preeclampsia patients and may be useful as diagnostic biomarkers.
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Affiliation(s)
- Serra E Elliott
- Engineering II, Room 3357, University of California, Santa Barbara, CA 93106-5080.
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Spatola BN, Murray JA, Kagnoff M, Kaukinen K, Daugherty PS. Antibody repertoire profiling using bacterial display identifies reactivity signatures of celiac disease. Anal Chem 2013; 85:1215-22. [PMID: 23234559 PMCID: PMC3903178 DOI: 10.1021/ac303201d] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A general strategy to identify serum antibody specificities associated with a given disease state and peptide reagents for their detection was developed using bacterial display peptide libraries and multiparameter flow cytometry (MPFC). Using sera from patients with celiac disease (CD) (n = 45) or healthy subjects (n = 40), bacterial display libraries were screened for peptides that react specifically with antibodies from CD patients and not with those from healthy patients. The libraries were screened for peptides that simultaneously cross-react with CD patient antibodies present in two separate patient groups labeled with spectrally distinct fluorophores but do not react with unlabeled non-CD antibodies, thus affording a quantitative separation. A panel of six unique peptide sequences yielded 85% sensitivity and 91% specificity (AUC = 0.91) on a set of 60 samples not used for discovery, using leave-one-out cross-validation. Individual peptides were dissimilar with known CD-specific antigens tissue transglutaminase (tTG) and deamidated gliadin, and the classifier accuracy was independent of anti-tTG antibody titer. These results demonstrate that bacterial display/MPFC provides a highly effective tool for the unbiased discovery of disease-associated antibody specificities and peptide reagents for their detection that may have broad utility for diagnostic development.
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Affiliation(s)
- Bradley N. Spatola
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Joseph A. Murray
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota 55905, United States
| | - Martin Kagnoff
- Laboratory of Mucosal Immunology, Department of Medicine, University of California, San Diego, La Jolla, California 92093, United States
- Department of Pediatrics, University of California, San Diego, La Jolla, California 92093, United States
| | - Katri Kaukinen
- Department of Gastroenterology and Alimentary Tract Surgery, Tampere University Hospital, Tampere, Finland
- Medical School, University of Tampere, Tampere, Finland
| | - Patrick S. Daugherty
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
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Site-specific targeting of antibody activity in vivo mediated by disease-associated proteases. J Control Release 2012; 161:804-12. [PMID: 22634092 DOI: 10.1016/j.jconrel.2012.05.035] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Revised: 05/12/2012] [Accepted: 05/17/2012] [Indexed: 01/19/2023]
Abstract
As a general strategy to selectively target antibody activity in vivo, a molecular architecture was designed to render binding activity dependent upon proteases in disease tissues. A protease-activated antibody (pro-antibody) targeting vascular cell adhesion molecule 1 (VCAM-1), a marker of atherosclerotic plaques, was constructed by tethering a binding site-masking peptide to the antibody via a matrix metalloprotease (MMP) susceptible linker. Pro-antibody activation in vitro by MMP-1 yielded a 200-fold increase in binding affinity and restored anti-VCAM-1 binding in tissue sections from ApoE⁻/⁻ mice ex vivo. The pro-antibody was efficiently activated by native proteases in aorta tissue extracts from ApoE⁻/⁻, but not from normal mice, and accumulated in aortic plaques in vivo with enhanced selectivity when compared to the unmodified antibody. Pro-antibody accumulation in aortic plaques was MMP-dependent, and significantly inhibited by a broad-spectrum MMP inhibitor. These results demonstrate that the activity of disease-associated proteases can be exploited to site-specifically target antibody activity in vivo.
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Abstract
Peptides are increasingly used as therapeutic and diagnostic agents. The combination of bacterial cell-surface display peptide libraries with magnetic- and fluorescence-activated cell sorting technologies provides an efficient and highly effective methodology to identify and engineer peptides for a growing number of molecular recognition applications. Here, detailed protocols for both the generation and screening of bacterial display peptide libraries are presented. The methods described enable the discovery and evolutionary optimization of protein-binding peptides, cell-specific peptides, and enzyme substrates for diverse biotechnology applications.
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Affiliation(s)
- Jennifer A Getz
- Department of Chemical Engineering, Institute for Collaborative Biotechnologies, University of California, Santa Barbara, California, USA
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