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Toraño A, Moreno I, Infantes JA, Domínguez M. Description of a non-competitive ELISA based on time course analysis of ligand binding at saturation, and a direct method for calculating the affinity of monoclonal antibodies. J Immunol Methods 2024; 534:113756. [PMID: 39265885 DOI: 10.1016/j.jim.2024.113756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2024] [Revised: 09/06/2024] [Accepted: 09/09/2024] [Indexed: 09/14/2024]
Abstract
We present a time-course saturation ELISA for measuring the equilibrium constant of the monoclonal antibody (mAb) SIM 28 against horse radish peroxidase (HRP). The curves of HRP binding to a series of fixed mAb dilutions were plotted to completion, and the Kt (= Ks) value (time to occupy 50 % of the mAb paratopes) was determined for each mAb dilution and HRP concentration. Analysis of the kinetic mechanism of the reaction by Lineweaver-Burk and Hanes plots showed that the slope and y-intercept were affected, indicating that mAb ligand saturation follows non-competitive inhibition kinetics in this assay format. In this kinetics, the inhibition constant Ki (= Kd) is the time required to double the slope or halve the Vmax of the Lineweaver-Burk plot. The Kt values of the time courses were doubled (2 x Kt) and normalized by dividing by the total reaction time to obtain a unitless factor which, when multiplied by the concentration of HRP, gives the Ki. The affinity constant of mAb SIM 28 was determined from ELISA data (n = 16) by three methods: i) doubling of Kt, ii) Beatty equation (Kaff = (n-1)/2 (n [HRP']t - [HRP]t), and iii) SPR (Biacore) analysis. The calculated affinities (mean ± 95 % confidence limits) were i) 4.6 ± 0.67 × 10-9 M, ii) Kaff = 0.23 ± 0.03 × 109 M-1 (Kd = 4.8 ± 0.81 × 10-9 M), and iii) 4.3 ± 0.57 × 10-9 M, respectively. The similar results obtained with the three different techniques indicate that this time-course saturation ELISA, combined with the double Kt method, is a repeatable and direct approach to mAb affinity determination.
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Affiliation(s)
- Alfredo Toraño
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - Inmaculada Moreno
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain.
| | - José Antonio Infantes
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - Mercedes Domínguez
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
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Toraño A, Moreno I, Infantes JA, Domínguez M. Development of a competitive inhibition kinetic ELISA to determine the inhibition constant (K i) of monoclonal antibodies. J Immunol Methods 2021; 493:113042. [PMID: 33757841 DOI: 10.1016/j.jim.2021.113042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 03/15/2021] [Accepted: 03/16/2021] [Indexed: 10/21/2022]
Abstract
Antibody-antigen interactions are mediated by the same molecular recognition mechanisms as those of an enzyme and its substrate. On this basis, we developed a competitive inhibition kinetic ELISA to measure monoclonal antibody (mAb) inhibition constants. Serially diluted samples of ligand (mAb) and inhibitor (soluble antigen) were incubated to equilibrium in ELISA plates coated with a fixed concentration of antigen (receptor). Plates were washed, and bound mAb measured with antiglobulin-peroxidase. Initial velocity data of receptor-bound mAb at various ligand and inhibitor concentrations were analyzed with enzyme linear competitive inhibition methods by non-linear regression (NLR), linear transformations (Cornish-Bowden, Lineweaver-Burk, Hanes-Woolf, Dixon, Cortés [1/i0.5 vs. Vi/Vmax], Ascenzi [Ks/Vmax/Ks,0/Vmax vs. [I]]) and NLR IC50 plots, to derive mAb inhibition constants (Ki). We obtained similar mAb Ki and Kd values by ELISA and surface plasmon resonance, which confirmed the accuracy of the ELISA method. This competitive inhibition ELISA is a simple (it requires no labeling or prior knowledge of antibody concentration), sensitive (it detects Ki values in the low nanomolar range by conventional colorimetry), and reproducible method with which to calculate mAb inhibition constants.
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Affiliation(s)
- Alfredo Toraño
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain.
| | - Inmaculada Moreno
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
| | - José Antonio Infantes
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
| | - Mercedes Domínguez
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain
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Halkjær L, Troldborg A, Pedersen H, Jensen L, Hansen AG, Hansen TK, Bjerre M, Østergaard JA, Thiel S. Complement Receptor 2 Based Immunoassay Measuring Activation of the Complement System at C3-Level in Plasma Samples From Mice and Humans. Front Immunol 2020; 11:774. [PMID: 32431705 PMCID: PMC7214740 DOI: 10.3389/fimmu.2020.00774] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Accepted: 04/06/2020] [Indexed: 12/15/2022] Open
Abstract
We aimed at establishing a sensitive and robust assay for estimation of systemic complement activation at complement component C3 level in mouse and human plasma samples. In order to capture the activation products iC3b and C3dg in a specific and physiological relevant manner we utilized a construct consisting of the iC3b/C3dg-binding site of human complement receptor 2 (CR2) attached to an Fc-part of mouse IgG. This construct binds C3dg and iC3b from both mice and humans. We purified the CR2-IgG construct from mouse B myeloma cell line supernatants, J558L-CR2-IgG, by protein G affinity chromatography. The CR2-IgG construct was used for capturing C3 fragments in microtiter wells and an anti-mouse or an anti-human-C3 antibody was used for detection of bound C3 fragments. Initially we tested the specificity of the assays with the use of purified C3 fragments. Further, with the use of the CR2-based assay, we measured an up to three-fold higher signal in activated mouse serum as compared to non-activated mouse serum, whereas activated serum from a C3 knock-out mouse gave no signal. We tested in vivo generated samples from a mouse experiment; complement activation was induced by injecting cobra venom factor or heat aggregated IgG into C57bl6 mice, followed by withdrawal of EDTA blood samples at different time points and measurement of iC3b/C3dg. We observed a clear time-dependent distinction in signals between samples with expected high and low complement activation. Furthermore, with the use of the assay for human C3 fragments, we observed that patients with systemic lupus erythematosus (SLE) (n = 144) had significantly higher iC3b/C3dg levels as compared to healthy individuals (n = 144) (p < 0.0001). We present two functional immunoassays, that are able to measure systemic levels of the C3-activation products iC3b and C3dg in mice and humans. To our knowledge, these are the first assays for complement activation that use a physiological relevant capture construct such as CR2. These assays will be a relevant tool when investigating mouse models and human diseases involving the complement system.
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Affiliation(s)
- Lene Halkjær
- Department of Biomedicine, Faculty of Health, Aarhus University, Aarhus, Denmark.,Department of Clinical Medicine, Faculty of Health, Aarhus University, Aarhus, Denmark.,Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Anne Troldborg
- Department of Biomedicine, Faculty of Health, Aarhus University, Aarhus, Denmark.,Department of Clinical Medicine, Faculty of Health, Aarhus University, Aarhus, Denmark.,Department of Rheumatology, Aarhus University Hospital, Aarhus, Denmark
| | - Henrik Pedersen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Lisbeth Jensen
- Department of Biomedicine, Faculty of Health, Aarhus University, Aarhus, Denmark
| | | | | | - Mette Bjerre
- Department of Clinical Medicine, Faculty of Health, Aarhus University, Aarhus, Denmark
| | - Jakob Appel Østergaard
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark.,Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus, Denmark
| | - Steffen Thiel
- Department of Biomedicine, Faculty of Health, Aarhus University, Aarhus, Denmark
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Moreno I, Domínguez M, Toraño A. A kinetic ELISA to determine the immunoreactive fraction of monoclonal antibodies. J Immunol Methods 2019; 476:112689. [PMID: 31669682 DOI: 10.1016/j.jim.2019.112689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/17/2019] [Accepted: 10/22/2019] [Indexed: 11/29/2022]
Abstract
We developed a two-step ELISA to determine the immunoreactive fraction of monoclonal antibodies in conditions of antigen excess. An antibody aliquot at limiting dilution was incubated in wells coated with increasing amounts of antigen up to concentrations that bind 100% of antibody. At equilibrium, a supernatant aliquot was transferred to a second plate coated with excess of antiglobulin, and the captured antibody was incubated with peroxidase-conjugated anti-IgG. Antibody was quantitated from the enzyme velocity gradient in a kinetic ELISA, and the immunoreactive fraction calculated as (1 - gradienti/gradientT) x 100, where i and T are the gradients for the free and total antibody fractions. For four distinct monoclonal antibodies (anti-diphtheria toxoid, -cholera toxin, -bovine serum albumin (BSA), and -trinitrophenyl-BSA), measurement of inter-assay variability yielded values ranging from 3.1 to 7.4 (% coefficient of variation), which supports method repeatability. This ELISA is simple, precise, and applicable to mono- and polyclonal antibodies.
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Affiliation(s)
- Inmaculada Moreno
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain
| | - Mercedes Domínguez
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain.
| | - Alfredo Toraño
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain
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Domínguez M, Moreno I, Toraño A. Quantitation of monoclonal antibody by capture ELISA based on initial enzyme activity rate. J Immunol Methods 2019; 474:112645. [PMID: 31404550 PMCID: PMC7094287 DOI: 10.1016/j.jim.2019.112645] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Revised: 06/21/2019] [Accepted: 08/08/2019] [Indexed: 11/30/2022]
Abstract
We developed a noncompetitive two-site sandwich ELISA to quantitate monoclonal antibodies in culture supernatant. This assay measures the initial enzyme activity rate during the first minute of the reaction, which ensures linear velocity relative to time and a progress curve slope proportional to analyte concentration. During this period, the enzyme substrate is in large excess relative to the analyte/antibody-enzyme complex, and enzyme catalysis proceeds in steady-state conditions. Analyses of repeatability gave coefficients of variation between 4.4 and 9.7 (interassay) and 4.4 and 6.4 (intra-assay), and analyte detectability ranged from 5.8 to 12 ng/ml. The Z-factor calculated for analyte samples at their end dilution yielded mean values from 0.57 to 0.87, which confirmed assay robustness. This initial velocity-based sandwich ELISA is a simple, sensitive, reproducible method to quantitate bi-epitopic antigens. Antibody quantitation by measuring initial velocity of enzyme product formation Initial rate measurements ensure ELISA velocity proportional to analyte concentration. A mAb isotype-matched standard curve could reduce antiglobulin heterogenous reactivity.
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Affiliation(s)
- Mercedes Domínguez
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain
| | - Inmaculada Moreno
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain.
| | - Alfredo Toraño
- Unidad de Inmunología Microbiana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain
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