Evaluation of a New Spike (S)-Protein-Based Commercial Immunoassay for the Detection of Anti-SARS-CoV-2 IgG

Kirsten Alexandra Eberhardt^{1

2}, Felix Dewald^{3

4}, Eva Heger³, Lutz Gieselmann³, Kanika Vanshylla^{3

4}, Maike Wirtz³, Franziska Kleipass³, Wibke Johannis⁵, Philipp Schommers^{3

6

7}, Henning Gruell^{3

7}, Karl August Brensing⁸, Roman-Ulrich Müller^{4

9

10}, Max Augustin⁶, Clara Lehmann^{4

6

7}, Manuel Koch^{4

11}, Florian Klein^{3

4

7}, Veronica Di Cristanziano^{3

4}

Affiliations

¹ Department of Tropical Medicine, Bernhard Nocht Institute for Tropical Medicine & I. Department of Medicine, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany.
² Institute for Transfusion Medicine, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany.
³ Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50935 Cologne, Germany.
⁴ Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany.
⁵ Institute for Clinical Chemistry, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany.
⁶ Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany.
⁷ German Center for Infection Research (DZIF), Partner Site Bonn-Cologne, 50931 Cologne, Germany.
⁸ Nierenzentrum Bonn, Godesberger Allee 26, 53175 Bonn, Germany.
⁹ Department II of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany.
¹⁰ Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, CECAD, University of Cologne, 50931 Cologne, Germany.
¹¹ Institute for Experimental Dentistry and Oral Musculoskeletal Biology, and Center for Biochemistry, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany.

PMID: 33807490
PMCID: PMC8067155
DOI: 10.3390/microorganisms9040733

Evaluation of a New Spike (S)-Protein-Based Commercial Immunoassay for the Detection of Anti-SARS-CoV-2 IgG

Kirsten Alexandra Eberhardt et al. Microorganisms. 2021.

. 2021 Mar 31;9(4):733.

doi: 10.3390/microorganisms9040733.

Authors

Affiliations

¹ Department of Tropical Medicine, Bernhard Nocht Institute for Tropical Medicine & I. Department of Medicine, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany.
² Institute for Transfusion Medicine, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany.
³ Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50935 Cologne, Germany.
⁴ Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany.
⁵ Institute for Clinical Chemistry, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany.
⁶ Department I of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany.
⁷ German Center for Infection Research (DZIF), Partner Site Bonn-Cologne, 50931 Cologne, Germany.
⁸ Nierenzentrum Bonn, Godesberger Allee 26, 53175 Bonn, Germany.
⁹ Department II of Internal Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50937 Cologne, Germany.
¹⁰ Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, CECAD, University of Cologne, 50931 Cologne, Germany.
¹¹ Institute for Experimental Dentistry and Oral Musculoskeletal Biology, and Center for Biochemistry, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany.

PMID: 33807490
PMCID: PMC8067155
DOI: 10.3390/microorganisms9040733

Abstract

Background: The investigation of the antibody response to SARS-CoV-2 represents a key aspect in facing the COVID-19 pandemic. In the present study, we compared the new Immundiagnostik IDK® anti-SARS-CoV-2 S1 IgG assay with four widely-used commercial serological assays for the detection of antibodies targeting S (spike) and NC (nucleocapsid) proteins. Methods: Serum samples were taken from an unbiased group of convalescent patients and from a negative control group. Sample were simultaneously analyzed by the new Immundiagnostik IDK^® anti-SARS-CoV-2 S1 IgG assay, by the DiaSorin LIAISON^® SARS-CoV-2 S1/S2 IgG assay, and by the Euroimmun anti-SARS-CoV-2 S1 IgG ELISA. Antibodies binding NC were detected by the Abbott SARS-CoV-2 IgG assay and by the pan-immunoglobulin immunoassay Roche Elecsys^® anti-SARS-CoV-2. Moreover, we investigated samples of a group of COVID-19 convalescent subjects that were primarily tested S1 IgG non-reactive. Samples were also tested by live virus and pseudovirus neutralization tests. Results: Overall, the IDK® anti-SARS-CoV-2 S1 IgG assay showed the highest sensitivity among the evaluated spike (S) protein-based assays. Additionally, the Immundiagnostik assay correlated well with serum-neutralizing activity. Conclusions: The novel IDK^® anti-SARS-CoV-2 S1 IgG assay showed high sensitivity and specificity, representing a valid option for use in the routine diagnostic.

Keywords: COVID-19; antibody; coronavirus; humoral response; neutralization; non-responder; pandemic; protection; sensitivity; titer.

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Conflict of interest statement

The University of Cologne (Medical Faculty) receives royalties for the co-development of the IDK^® anti-SARS-CoV-2 IgG ELISA and IDK^® anti-SARS-CoV-2 IgM ELISA kits. Immundiagnostik had no role in the design of this study; in the collection, analyses, or interpretation of data; in the writing of the manuscript except for the Supplement Figure S1, or in the decision to publish the results.

Figures

**Figure 1**
(A) Schematic drawing of the SARS-CoV-2 virus. Spike (S) and nucleocapsid (NC) proteins are highlighted. (B) Schematic drawing of the trimeric S-protein. (C) The domain structure of the S-protein is shown, and the three regions that were tested are depicted. All three versions contain the receptor binding domain (RBD). SP, signal peptide; NTD, N-terminal domain; S1, spike protein subunit 1; S2, spike protein subunit 2; FP, fusion peptide; HR1, heptad repeat 1 domain; HR2, heptad repeat 2 domain; TM, transmembrane domain; FD, foldon motif.

**Figure 2**
(A) Antibody values of five commercially available immunoassays targeting the S (spike) (blue) or the NC (nucleocapsid) protein (yellow) and virus neutralizing assays (grey) displayed against the weeks after infection for each individual from group A. Dashed horizontal lines display cutoff values of individual serological assays. Results of the virus neutralizing immunoassay are categorized into <1:10, 1:10, and ≥1:50. (B) The sensitivity in % achieved by assays against the S-protein (blue), the NC antigen (yellow), the combination of assays targeting the different proteins (red), and the virus neutralizing (VN) test (grey) for group A. LVN, live virus neutralization assay; PVN, pseudovirus neutralization assay; ID100, 100% inhibitory dilution; ID50, 50% inhibitory dose.

**Figure 3**
(A) Correlation between five commercial anti-SARS-CoV-2 serological assays and a pseudovirus neutralizing antibody titer for group A. R represents the Spearman rank correlation coefficient ρ. (B) Correlation between five commercial anti-SARS-CoV-2 serological assays and live virus neutralizing antibody titer for group A. Horizontal lines represent cutoff values for individual commercial tests. Kendall’s τ and Cohen’s κ are displayed for each test combination. LVN, live virus neutralization assay; PVN, pseudovirus neutralization assay; ID100, 100% inhibitory dilution; ID50, 50% inhibitory dose.

**Figure 4**
(A) Antibody values of five commercially available immunoassays targeting the S (spike) (blue) or the NC (nucleocapsid) protein (yellow) and virus neutralizing assays (grey) displayed against the weeks after infection for each individual from group B. Dashed horizontal lines display cutoff values of individual serological assays. Results of the virus neutralizing immunoassay are categorized into <1:10, 1:10, and ≥1:50. (B) The sensitivity in % achieved by assays against the S-protein (blue), the NC antigen (yellow), the combination of assays targeting the different proteins (red), and the VN test (grey) for group B. LVN, live virus neutralization assay; PVN, pseudovirus neutralization assay; ID100, 100% inhibitory dilution; ID50, 50% inhibitory dose.

**Figure 5**
(A) Correlation between five commercial anti-SARS-CoV-2 serological assays and the pseudovirus neutralizing antibody titer for group B. R represents the Spearman rank correlation coefficient ρ. (B) Correlation between five commercial anti-SARS-CoV-2 serological assays and live virus neutralizing antibody titer for group B. Horizontal lines represent cutoff values for individual commercial tests. Kendall’s τ and Cohen’s κ are displayed for each test combination. LVN, live virus neutralization assay; PVN, pseudovirus neutralization assay; ID100, 100% inhibitory dilution; ID50, 50% inhibitory dose.

**Figure 6**
The specificity achieved by assays against the S (spike) protein (blue), the NC (nucleocapsid) antigen (yellow), and the combination of assays targeting the different proteins (red) for group C.

See this image and copyright information in PMC

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Evaluation of a New Spike (S)-Protein-Based Commercial Immunoassay for the Detection of Anti-SARS-CoV-2 IgG

Affiliations

Evaluation of a New Spike (S)-Protein-Based Commercial Immunoassay for the Detection of Anti-SARS-CoV-2 IgG

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

References

Grants and funding

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Full Text Sources

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Miscellaneous