tetano
Editor, Senior Moderator
Microbiol Spectr
. 2021 Nov 17;e0113121.
doi: 10.1128/Spectrum.01131-21. Online ahead of print.
A Highly Sensitive and Specific SARS-CoV-2 Spike- and Nucleoprotein-Based Fluorescent Multiplex Immunoassay (FMIA) to Measure IgG, IgA, and IgM Class Antibodies
Anna Solastie[SUP] 1 [/SUP], Camilla Virta[SUP] 1 [/SUP], Anu Haveri[SUP] 1 [/SUP], Nina Ekström[SUP] 1 [/SUP], Anu Kantele[SUP] 2 [/SUP], Simo Miettinen[SUP] 3 [/SUP], Johanna Lempainen[SUP] 4 5 [/SUP], Pinja Jalkanen[SUP] 6 [/SUP], Laura Kakkola[SUP] 6 [/SUP], Timothée Dub[SUP] 7 [/SUP], Ilkka Julkunen[SUP] 6 8 [/SUP], Merit Melin[SUP] 1 [/SUP]
Affiliations
Abstract
Validation and standardization of accurate serological assays are crucial for the surveillance of the coronavirus disease 2019 (COVID-19) pandemic and population immunity. We describe the analytical and clinical performance of an in-house fluorescent multiplex immunoassay (FMIA) for simultaneous quantification of antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein and spike glycoprotein. Furthermore, we calibrated IgG-FMIA against World Health Organization (WHO) International Standard and compared FMIA results to an in-house enzyme immunoassay (EIA) and a microneutralization test (MNT). We also compared the MNT results of two laboratories. IgG-FMIA displayed 100% specificity and sensitivity for samples collected 13 to 150 days post-onset of symptoms (DPO). For IgA- and IgM-FMIA, 100% specificity and sensitivity were obtained for a shorter time window (13 to 36 and 13 to 28 DPO for IgA- and IgM-FMIA, respectively). FMIA and EIA results displayed moderate to strong correlation, but FMIA was overall more specific and sensitive. IgG-FMIA identified 100% of samples with neutralizing antibodies (NAbs). Anti-spike IgG concentrations correlated strongly (ρ = 0.77 to 0.84, P < 2.2 × 10[SUP]-16[/SUP]) with NAb titers, and the two laboratories' NAb titers displayed a very strong correlation (ρ = 0.95, P < 2.2 × 10[SUP]-16[/SUP]). Our results indicate good correlation and concordance of antibody concentrations measured with different types of in-house SARS-CoV-2 antibody assays. Calibration against the WHO international standard did not, however, improve the comparability of FMIA and EIA results. IMPORTANCE SARS-CoV-2 serological assays with excellent clinical performance are essential for reliable estimation of the persistence of immunity after infection or vaccination. In this paper we present a thoroughly validated SARS-CoV-2 serological assay with excellent clinical performance and good comparability to neutralizing antibody titers. Neutralization tests are still considered the gold standard for SARS-CoV-2 serological assays, but our assay can identify samples with neutralizing antibodies with 100% sensitivity and 96% specificity without the need for laborious and slow biosafety level 3 (BSL-3) facility-requiring analyses.
Keywords: COVID-19; SARS-CoV-2; WHO international standard; antibody; immunoassay; microneutralization; neutralizing antibodies; nucleoprotein; receptor-binding domain; spike glycoprotein.
. 2021 Nov 17;e0113121.
doi: 10.1128/Spectrum.01131-21. Online ahead of print.
A Highly Sensitive and Specific SARS-CoV-2 Spike- and Nucleoprotein-Based Fluorescent Multiplex Immunoassay (FMIA) to Measure IgG, IgA, and IgM Class Antibodies
Anna Solastie[SUP] 1 [/SUP], Camilla Virta[SUP] 1 [/SUP], Anu Haveri[SUP] 1 [/SUP], Nina Ekström[SUP] 1 [/SUP], Anu Kantele[SUP] 2 [/SUP], Simo Miettinen[SUP] 3 [/SUP], Johanna Lempainen[SUP] 4 5 [/SUP], Pinja Jalkanen[SUP] 6 [/SUP], Laura Kakkola[SUP] 6 [/SUP], Timothée Dub[SUP] 7 [/SUP], Ilkka Julkunen[SUP] 6 8 [/SUP], Merit Melin[SUP] 1 [/SUP]
Affiliations
- PMID: 34787485
- DOI: 10.1128/Spectrum.01131-21
Abstract
Validation and standardization of accurate serological assays are crucial for the surveillance of the coronavirus disease 2019 (COVID-19) pandemic and population immunity. We describe the analytical and clinical performance of an in-house fluorescent multiplex immunoassay (FMIA) for simultaneous quantification of antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein and spike glycoprotein. Furthermore, we calibrated IgG-FMIA against World Health Organization (WHO) International Standard and compared FMIA results to an in-house enzyme immunoassay (EIA) and a microneutralization test (MNT). We also compared the MNT results of two laboratories. IgG-FMIA displayed 100% specificity and sensitivity for samples collected 13 to 150 days post-onset of symptoms (DPO). For IgA- and IgM-FMIA, 100% specificity and sensitivity were obtained for a shorter time window (13 to 36 and 13 to 28 DPO for IgA- and IgM-FMIA, respectively). FMIA and EIA results displayed moderate to strong correlation, but FMIA was overall more specific and sensitive. IgG-FMIA identified 100% of samples with neutralizing antibodies (NAbs). Anti-spike IgG concentrations correlated strongly (ρ = 0.77 to 0.84, P < 2.2 × 10[SUP]-16[/SUP]) with NAb titers, and the two laboratories' NAb titers displayed a very strong correlation (ρ = 0.95, P < 2.2 × 10[SUP]-16[/SUP]). Our results indicate good correlation and concordance of antibody concentrations measured with different types of in-house SARS-CoV-2 antibody assays. Calibration against the WHO international standard did not, however, improve the comparability of FMIA and EIA results. IMPORTANCE SARS-CoV-2 serological assays with excellent clinical performance are essential for reliable estimation of the persistence of immunity after infection or vaccination. In this paper we present a thoroughly validated SARS-CoV-2 serological assay with excellent clinical performance and good comparability to neutralizing antibody titers. Neutralization tests are still considered the gold standard for SARS-CoV-2 serological assays, but our assay can identify samples with neutralizing antibodies with 100% sensitivity and 96% specificity without the need for laborious and slow biosafety level 3 (BSL-3) facility-requiring analyses.
Keywords: COVID-19; SARS-CoV-2; WHO international standard; antibody; immunoassay; microneutralization; neutralizing antibodies; nucleoprotein; receptor-binding domain; spike glycoprotein.