This is a summary, written by members of the CITF Secretariat, of:
Fu, Z.; Rais, Y.; Dara, D.; Jackson, D.; Drabovich A.P. Rational Design and Development of SARS-CoV-2 Serological Diagnostics by Immunoprecipitation-Targeted Proteomics. Analytical Chemistry 2022, Epub September 12; doi: https://doi.org/10.1021/acs.analchem.2c01325
The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.
In the hopes of creating a more accurate and highly informative diagnostic test, CITF-funded investigator Dr. Andrei Drabovich (University of Alberta) and colleagues have designed and evaluated the performance of novel serological assays to measure the presence of SARS-CoV-2 antibodies in blood and saliva. Their study is published in Analytical Chemistry.
The assay combines two techniques: immunoprecipitation to enrich specific SARS-CoV-2 antibodies , and a mass spectrometry-based assay with near-absolute selectivity (the ability to distinguish between very similar antibody molecules). The combined assay called immunoprecipitation selected reaction monitoring (IP-SRM) provided additional scientific knowledge which could not be found with the conventional tests.
- This new assay allowed for sensitive and specific measurements of SARS-CoV-2 protein in serum and enabled differential quantification of anti-SARS-CoV-2 antibody isotypes (IgG, IgA, IgM, IgD, and IgE) in plasma and saliva.
- The assay revealed that a receptor-binding domain (RBD)-IgG1 combination had the highest diagnostic performance.
- Anti-RBD IgG1, IgG3, IgM, and IgA1 levels were significantly elevated in plasma samples from COVID-19 recovered patients.
- IgA1 antibodies were the most abundant antibody isotype in the saliva samples from COVID-19 recovered patients.
Limitations of current serological diagnostics and importance of the current assay
While serological immunoassays that exploit antigen-antibody binding (e.g., ELISAs) are well suited to identify SARS-CoV-2 proteins and anti-SARS-CoV-2 antibodies, they are unable to provide a comprehensive overview of the immune response. Limitations of such tests, which can affect their accuracy, include, among other things, semi-quantitative as opposed to precise quantitative measurements, lack of standardization to enable comparison across assay platforms, potential cross-reactivity with irrelevant targets, and it could be laborious to differentiate between antibody subclasses (i.e., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2).
On the other hand, an analytical technique called mass spectrometry, by which proteins are identified through their unique fragments is an alternative approach to the identification and quantification of SARS-CoV-2 proteins and anti-SARS-CoV-2 antibodies. Mass spectrometry, however, comes with some limitations, including relatively poor sensitivity.
Overall, the authors propose that the combination of immunoenrichment with mass spectrometry provides many advantages over the use of either method alone. Further development of the combined method may enable improvement of existing serological diagnostic tests for SARS-CoV-2, novel mutant strains, and other viruses and bacteria, as well as providing a means for a comprehensive investigation of various antigen-antibody subclass combinations, which assist in understanding the breadth of an individual’s immune response.