Development of Automated Assays for Anticardiolipin Antibodies Determination: Addressing Antigen and Standardization Issues
The lack of reliable standardization tools as well as the poorly defined nature of the “Cardiolipin antigen” makes the development of the anticardiolipin antibody (ACA) assays (for anti-IgG and IgM detection) highly challenging. This article describes how several issues have been solved during the development of an automated ACA immunoassays, based on a technology that includes paramagnetic microbeads as solid-phase reagents and chemiluminescence as a signal. The technology is adapted to an automatic immunoanalyzer, called LIAISON, which performs, in an automatic manner, the whole assay, starting from the primary tube of the bleeding to the display of the assay result. Briefly, the magnetic microbeads were coated with an ethanolic solution of cardiolipin (CL) followed by an affinity-purified, cross-linked human β2-glycoprotein I. CL-coated paramagnetic microbeads, after incubation with an ACA-positive sera plus addition of immunogold-protein A, were visualized by SEM, showing the presence of well-defined protein clusters on the microbeads surface as an indication of the successful occurrence of the “antigen” coating. The assay standardization was achieved on the basis of human samples containing various amount of ACA, which were previously classified according to consensus doses. The evaluation of the optimized LIAISON Cardiolipin assays (IgG and IgM) was conducted by using clinically characterized APS sera. The results of the evaluation showed that the LIAISON assays perform at least similar to certain well-established ACA enzyme-linked immunosorbent assay (ELISA) products.
Available from: Ali Dalloul
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ABSTRACT: The pathogenic role of antiphospholipid antibodies (aPL) has been widely established over past years in several experimental models and clinical studies. Accordingly, the detection of aPL by immunoassays (anticardiolipin antibodies; anti-beta2 glycoprotein I antibodies) has become a routine practice in the clinical workup of patients with systemic autoimmune diseases. aPL are mostly assayed using commercial ELISA kits, whose performance has not been found to be sufficiently concordant among the different manufacturers. In the past years, collaborative groups have spent considerable effort to reach some form of standardization but this process is still ongoing. Such lack of standardization has recently become even more crucial, as manufacturers have had to face an increasing demand for fully automated tests for aPL, like those test systems that have been developed for other autoantibodies (e.g., antinuclear antibodies, anti-ENA antibodies). We therefore report our recent experience with two newly developed automated methods for anticardiolipin antibodies testing. In particular, we discuss the results obtained using routine samples, as we believe that these better reflect the "real-life" situation in which those automated methods will operate. We also mention other emerging technologies in the field of aPL detection.
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ABSTRACT: Controls and calibrators in autoimmune assays are typically developed from patient sera. However, the use of sera is accompanied by a number of disadvantages, such as lack of monospecificity, lack of assay comparability, and supply limitations. Ideally, the control reagent would be an antigen-specific human monoclonal antibody preparation that is defined and pure, easy to produce without any supply limitations, and of defined isotype (IgG, IgM, or IgA). The generation of antigen-specific human monoclonal antibodies has been complicated, but recent advances in development of fully human antibodies by means of in vitro antibody gene library selection has opened a way for the isolation of human antibodies to virtually any antigen, including self-antigens. Such antibodies can be converted to any isotype by gene cloning. Here we developed a set of human monoclonal IgA antibodies specific for the cardiolipin-beta2-glycoprotein 1 complex, using the HuCAL technology. We evaluated the IgA variants of those antibodies for their use as standards in IgA anticardiolipin antibody assays and compared these reagents with serum controls. Such recombinant antibodies may ultimately replace patient sera as assay control and calibration reagents.
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