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. 2021 Dec 22;9(3):e0137621.
doi: 10.1128/spectrum.01376-21. Epub 2021 Dec 22.

Evaluation of Three Quantitative Anti-SARS-CoV-2 Antibody Immunoassays

Sabine Chapuy-Regaud  1   2 , Marcel Miédougé  1 , Florence Abravanel  1   2 , Isabelle Da Silva  1 , Marion Porcheron  1 , Judith Fillaux  3 , Chloé Diméglio  1   2 , Jacques Izopet  1   2
Affiliations

Evaluation of Three Quantitative Anti-SARS-CoV-2 Antibody Immunoassays

Sabine Chapuy-Regaud et al. Microbiol Spectr. .

Abstract

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019 and caused a dramatic pandemic. Serological assays are used to check for immunization and assess herd immunity. We evaluated commercially available assays designed to quantify antibodies directed to the SARS-CoV-2 Spike (S) antigen, either total (Wantaï SARS-CoV-2 Ab ELISA) or IgG (SARS-CoV-2 IgG II Quant on Alinity, Abbott, and Liaison SARS-CoV-2 TrimericS IgG, Diasorin). The specificities of the Wantaï, Alinity, and Liaison assays were evaluated using 100 prepandemic sera and were 98, 99, and 97%, respectively. The sensitivities of all three were around 100% when tested on 35 samples taken 15 to 35 days postinfection. They were less sensitive for 150 sera from late infections (>180 days). Using the first WHO international standard (NIBSC), we showed that the Wantai results were concordant with the NIBSC values, while Liaison and Alinity showed a proportional bias of 1.3 and 7, respectively. The results of the 3 immunoassays were significantly globally pairwise correlated and for late infection sera (P < 0.001). They were correlated for recent infection sera measured with Alinity and Liaison (P < 0.001). However, the Wantai results of recent infections were not correlated with those from Alinity or Liaison. All the immunoassay results were significantly correlated with the neutralizing antibody titers obtained using a live virus neutralization assay with the B1.160 SARS-CoV-2 strain. These assays will be useful once the protective anti-SARS-CoV-2 antibody titer has been determined. IMPORTANCE Standardization and correlation with virus neutralization assays are critical points to compare the performance of serological assays designed to quantify anti-SARS-CoV-2 antibodies in order to identify their optimal use. We have evaluated three serological immunoassays based on the virus spike antigen that detect anti-SARS-CoV-2 antibodies: a microplate assay and two chemiluminescent assays performed with Alinity (Abbott) and Liaison (Diasorin) analysers. We used an in-house live virus neutralization assay and the first WHO international standard to assess the comparison. This study could be useful to determine guidelines on the use of serological results to manage vaccination and treatment with convalescent plasma or monoclonal antibodies.

Keywords: COVID; SARS-CoV-2; binding antibodies; immunoassay; neutralizing antibodies.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

FIG 1
FIG 1
Distribution of the results. (A) Wantaï, (B) Liaison, and (C) Alinity assays according to patient groups. Black lines = median of each group. Red lines = manufacturer’s negative/positive threshold. Zero (0) values in the Liaison negative group (n = 92), the Liaison late infection group (n = 15), the Alinity negative group (n = 14), and the Alinity late infection group (n = 7) are not shown.
FIG 2
FIG 2
ROC curves for Wantaï (black line), Liaison (green line) and Alinity (red line). Gray line: y = x. The AUROCs were: Wantaï: 0.9996 (95% CI: 0.9403 to 0.9787), Liaison: 0.9475 (95% CI: 0.9208 to 0.9742) and Alinity: 0.9475 (95% CI: 0.9208 to 0.9742) indicating their capacity to accurately detect anti-SARS-CoV-2 antibodies.
FIG 3
FIG 3
Quantification of anti-SARS-CoV-2 antibodies relative to the NIBSC international standard. Serial dilutions of the NIBSC 20/136 standard were assayed with the (A) Wantaï, (B) Liaison, and (C) Alinity assay. Neutralizing antibodies (NAb) were also determined with a live method (D). The black line represents the regression line and the dashed lines its 95% CI. The dashed red line represents the y = x line. AU: arbitrary units. BAU: binding antibody unit. The equations were y = 1.073 x − 3.233 (slope 95% CI: 0.8764 to 1.269; y-intercept 95% CI: −41.04 to 34.54) for Wantaï; y = 1.379 x − 9.105 (slope 95% CI: 1.314 to 1.443; y-intercept 95% CI: −22.27 to 4.057) for Liaison; y = 7.015 x - 58.33 (slope 95% CI: 6.501 to 7.529; y-intercept 95% CI: −157.3 to 40.61) for Alinity and y = 0.9504 x + 23.33 (slope 95% CI: 0.711 to 1.19; y-intercept 95% CI: −1.099 to 47.76) for NAb titers.
FIG 4
FIG 4
Correlation between the immunoassay results. Pairwise distribution of the Wantaï, Liaison, and Alinity assays values for all positive results (A to C), recent infections (D to F), and late infections (G to I). When the Spearman rank coefficient (r) indicated a significant correlation, the regression line was drawn. Dashed lines: 95% CI limits.
FIG 5
FIG 5
Immunoassays results and neutralizing antibody titers. Distribution of the Wantaï, Liaison, and Alinity assay values and the NAb titers for all positive results (A to C) The NAb titers were determined in a live virus neutralization assay using the B 1.160 strain. Spearman’s rank coefficients (r) and their P value are indicated. The box extends from the 25th to 75th percentiles and whiskers from minimal to maximal values.
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