An approach to identifying antibodies to the spike (S) protein of severe acute respiratory disease coronavirus 2 (SARS-CoV-2) from patients exposed to the virus has been developed by a research team from the Icahn School of Medicine at Mount Sinai in New York, New York. The researchers published a preprint report of their results on the medRxiv preprint server on March 18, 2020.

“Here we describe a serological method to detect seroconversion upon SARS-CoV-2 infection,” the researchers wrote in their report.

The approach was based on serological enzyme-linked immunosorbent assays (ELISAs) used to detect reactivity to the S protein from SARS-CoV-2. Recombinant antigens were developed based on either the full-length S protein or just the receptor binding domain (RBD) of the protein. These antigens were produced in expression systems using either mammalian or insect cells and without the need to handle live virus.

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Reactions to the recombinant antigens were tested in 59 serum or plasma samples from human participants, including 4 samples from 3 patients with coronavirus disease 2019 (COVID-19). The remaining samples were used as negative controls to measure background reactivity in the population. Reactivity was assessed by the binding of antibodies to the recombinant antigens.

The researchers found that samples from patients with COVID-19 showed strong reactivity to both the full-length S protein and the RBD, with somewhat stronger reactivity to the full-length protein than to the RBD. Across comparisons, negative controls demonstrated overall significantly lower reactivity than did samples from patients with COVID-19 (P <.001 for each comparison).

Additionally, samples from patients with COVID-19 had been collected at times ranging from 2 to 20 days following the onset of symptoms, and all were reactive in both full-length protein and RBD assays.

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In their report, the researchers concluded that patients recuperating from COVID19 “could be screened for strong antibody responses using the assays described here.” They suggested that the approach and reagents that were developed for this study could be used for screening health care workers, testing convalescent serum, in vaccine development, and in other applications.

Editor’s note: This article is a preprint and has not been peer-reviewed. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.

Reference Amanat F, Nguyen THO, Chromikova V, et al. A serological assay to detect SARS-CoV-2 seroconversion in humans [published online ahead of peer-review on March 18, 2020]. medRxiv. doi: 10.1101/2020.03.17.20037713