AUTHOR=Drouot Laurent , Hantz Sébastien , Jouen Fabienne , Velay Aurélie , Lamia Bouchra , Veber Benoit , Sibilia Jean , Lotellier Marlène , Candon Sophie , Alain Sophie , Fafi-Kremer Samira , Boyer Olivier 

TITLE=Evaluation of Humoral Immunity to SARS-CoV-2: Diagnostic Value of a New Multiplex Addressable Laser Bead Immunoassay

JOURNAL=Frontiers in Microbiology

VOLUME=Volume 11 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.603931

DOI=10.3389/fmicb.2020.603931

ISSN=1664-302X

ABSTRACT=Despite efforts to develop anti-SARS-CoV-2 antibody (Ab) immunoassays, reliable serological methods are still needed. We developed a multiplex addressable laser bead immunoassay (ALBIA) to detect and quantify anti-Spike S1 and nucleocapsid N Abs.
Recombinant S1 and N proteins were bound to fluorescent beads (ALBIA-IgG-S1/N). Abs were revealed using class-specific anti-human Ig Abs. The performances of the test were analyzed on 575 serum samples including 192 from SARS-CoV-2 PCR-confirmed patients, 13 from seasonal coronaviruses, 70 from different inflammatory/autoimmune diseases and 300 from healthy donors. Anti-S1 IgM were detected by monoplex ALBIA-IgM-S1. Comparison with chemiluminescent assays (CLIA) or enzyme-linked immunosorbent assays (ELISA) was performed using commercial tests.
Multiplex ALBIA-IgG-S1/N was effective in detecting and quantifying anti-SARS-CoV-2 IgG Abs. Two weeks after first symptoms, sensitivity and specificity were 97.7% and 98.0% (anti-S1), and 100% and 98.7% (anti-N), respectively. Agreement with commercial tests was good to excellent, with a higher sensitivity of ALBIA. ALBIA-IgG-S1/N was positive in 53% of patients up to day 7, and in 75% between days 7 and 13. For ALBIA-IgM-S1, sensitivity and specificity were 74.4% and 98.7%, respectively. Patients in intensive care unit had higher IgG Ab levels (Mann-Whitney test, p<0.05).
ALBIA provides a robust method for exploring humoral immunity to SARS-CoV-2. Serology should be performed after two weeks following first symptoms, when all Covid-19 patients had at least one anti-S1 or anti-N IgG Ab, illustrating the interest of a multiplex test. The humoral response appeared highly variable, and patients requiring intensive care had higher IgG levels.