Quantitative Measurement of IgG to Severe Acute Respiratory Syndrome Coronavirus-2 Proteins Using ImmunoCAP.

Abstract

BACKGROUND:

Detailed understanding of the immune response to severe acute respiratory syndrome coronavirus (SARS-CoV)-2, the cause of coronavirus disease 2019 (CO-VID-19) has been hampered by a lack of quantitative antibody assays.

OBJECTIVE:

The objective was to develop a quantitative assay for IgG to SARS-CoV-2 proteins that could be implemented in clinical and research laboratories.

METHODS:

The biotin-streptavidin technique was used to conjugate SARS-CoV-2 spike receptor-binding domain (RBD) or nucleocapsid protein to the solid phase of the ImmunoCAP. Plasma and serum samples from patients hospitalized with COVID-19 (n = 60) and samples from donors banked before the emergence of COVID-19 (n = 109) were used in the assay. SARS-CoV-2 IgG levels were followed longitudinally in a subset of samples and were related to total IgG and IgG to reference antigens using an ImmunoCAP 250 platform.

RESULTS:

At a cutoff of 2.5 μg/mL, the assay demonstrated sensitivity and specificity exceeding 95% for IgG to both SARS-CoV-2 proteins. Among 36 patients evaluated in a post-hospital follow-up clinic, median levels of IgG to spike-RBD and nucleocapsid were 34.7 μg/mL (IQR 18-52) and 24.5 μg/mL (IQR 9-59), respectively. Among 17 patients with longitudinal samples, there was a wide variation in the magnitude of IgG responses, but generally the response to spike-RBD and to nucleocapsid occurred in parallel, with peak levels approaching 100 μg/mL, or 1% of total IgG.

CONCLUSIONS:

We have described a quantitative assay to measure IgG to SARS-CoV-2 that could be used in clinical and research laboratories and implemented at scale. The assay can easily be adapted to measure IgG to mutated COVID-19 proteins, has good performance characteristics, and has a readout in standardized units.

• Authors: Behnam Keshavarz, Joesph R Wiencek, Lisa J Workman, Matthew D Straesser, Lyndsey M Muehling, Glenda Canderan, Fabrizio Drago, Catherine A Bonham, Jeffrey M Sturek, Chintan Ramani, Coleen A McNamara, Judith A Woodfolk, Alexandra Kadl, Thomas A E Platts-Mills, Jeffrey M Wilson
• Journal: International archives of allergy and immunology (Int Arch Allergy Immunol) Vol. 182 Issue 5 Pg. 417-424 ( 2021) ISSN: 1423-0097 [Electronic] Switzerland
• PMID: 33621972 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
• Copyright: © 2021 The Author(s) Published by S. Karger AG, Basel.

Chemical References

• Antibodies, Viral
• Biomarkers
• Immunoglobulin G

Topics

• Antibodies, Viral (blood)
• Biomarkers (blood)
• COVID-19 (diagnosis, immunology, virology)
• COVID-19 Serological Testing (methods)
• Humans
• Immunoglobulin G (blood)
• Longitudinal Studies
• SARS-CoV-2 (immunology)
• Sensitivity and Specificity