Assessment of S1-, S2-, and NCP-Specific IgM, IgA, and IgG Antibody Kinetics in Acute SARS-CoV-2 Infection by a Microarray and Twelve Other Immunoassays

Abstract

In this study, we comprehensively analyzed multispecific antibody kinetics of different immunoglobulins in hospitalized patients with acute severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Three hundred fifty-four blood samples longitudinally obtained from 81 IgG-seroconverting progressed coronavirus disease 2019 (CoVID-19) patients were quantified for spike 1 (S1), S2, and nucleocapsid protein (NCP)-specific IgM, IgA, IgG, and total Ig antibodies using a microarray, 11 different enzyme-linked immunosorbent assays (ELISAs)/chemiluminescence immunoassays (CLIAs), and 1 rapid test by seven manufacturers. The assays' specificity was assessed in 130 non-CoVID-19 pneumonia patients. Using the microarray, NCP-specific IgA and IgG antibodies continuously displayed higher detection rates during acute CoVID-19 than S1- and S2-specific ones. S1-specific IgG antibodies, however, reached higher peak values. Until the 26th day post-symptom onset, all patients developed IgG responses against S1, S2, and NCP. Although detection rates by ELISAs/CLIAs generally resembled those of the microarray, corresponding to the target antigen, sensitivities and specificities varied among all tests. Notably, patients with more severe CoVID-19 displayed higher IgG and IgA levels, but this difference was mainly observed with S1-specific immunoassays. In patients with high SARS-CoV-2 levels in the lower respiratory tract, we observed high detection rates of IgG and total Ig immunoassays with a particular rise of S1-specific IgG antibodies when viral concentrations in the tracheal aspirate subsequently declined over time. In summary, our study demonstrates that differences in sensitivity among commercial immunoassays during acute SARS-CoV-2 infection are only partly related to the target antigen. Importantly, our data indicate that NCP-specific IgA and IgG antibodies are detected earlier, while higher S1-specific IgA antibody levels occur in severely ill patients.

Keywords: ELISA; IgA; SARS; SARS-CoV-2; antibodies; coronavirus; immunoassay; microarray.

FIG 1

Comparison of the assays’ specificity in 130 hospitalized patients with pneumonia without SARS-CoV-2 infection. The assays’ specificity is given as true-negativity rate, counting borderline results as negative.

FIG 2

Detection rates by a commercial microarray (Viramed) in 354 blood samples longitudinally obtained from 81 hospitalized IgG-seroconverting patients with acute SARS-CoV-2 infection, grouped by a 2-day interval (one sample per patient per interval step). (A) S1-, S2-, and NCP-specific IgM antibodies; (B) S1-, S2-, and NCP-specific IgA antibodies; (C) S1-, S2-, and NCP-specific IgG antibodies.

FIG 3

(A) Cumulative microarray (Viramed) detection rates of IgG antibodies in 354 blood samples longitudinally obtained from 81 hospitalized patients with acute SARS-CoV-2 infection, grouped by a 2-day interval (one sample per patient per interval step). (B) Percentage of hospitalized patients with acute SARS-CoV-2 infection with detectable IgG responses (microarray, Viramed) against no, one, two, or all three target antigens (S1, S2, and NCP).

FIG 4

Detection rates by 10 commercial immunoassays (6 ELISAs, 3 CLIAs, one rapid test; all with a specificity >80%) in the 354 blood samples from 81 hospitalized IgG-seroconverting patients with acute SARS-CoV-2 infection, grouped by a 2-day interval (one sample per patient per interval step). (A) IgM ELISAs; (B) IgA ELISA; (C) IgG ELISAs/CLIAs; (D) total Ig ELISAs/CLIAs and rapid tests. Borderline results were counted as negative.

FIG 5

Dynamics of median SARS-CoV-2 RNA concentration in tracheal aspirate samples (black line) and median antibody levels in 20 patients with critical CoVID-19 disease (of whom 9 patients deceased). Kinetics of SARS-CoV-2 S1-, S2-, and NCP-specific IgM (A), IgA (B), and IgG (C) antibodies as quantified by the microarray. Antibody levels as assessed by the anti-SARS-CoV-2 IgM and IgA (D), total Ig (E), and IgG ELISAs/CLIAs (F). Error bars indicate the interquartile range.

FIG 6

PCR and immunoassay results from 12 SARS-CoV-2-infected patients of the whole cohort who developed pneumonia and then displayed a negative PCR result from a nasopharyngeal swab (results from the initial day the nasopharyngeal swab tested negative; median, 20th day post-symptom onset; range, days 9 to 31). (A) Virus concentration by quantitative PCR in nasopharyngeal swab and tracheal aspirate samples; (B) microarray results (detection rates); (C) ELISA/CLIA results (detection rates); (D) results from the rapid test (detection rate).

FIG 7

Longitudinal median levels of IgA, IgG, and total Ig antibodies directed against S1 (A) and NCP (B) among the hospitalized patients with mild (n = 3) or moderate (n = 37) disease severity and patients who displayed severe (n = 11) or critical (n = 11) courses of CoVID-19 or deceased (n = 19).