Antibody response in children with multisystem inflammatory syndrome related to COVID-19 (MIS-C) compared to children with uncomplicated COVID-19

Abstract

Objectives: To comprehensively analyze the quality of the antibody response between children with Multisystem inflammatory syndrome (MIS-C) and age-matched controls at one month after SARS-CoV-2 exposure, and infected in the same time-period.

Methods: Serum from 20 MIS-C children at admission, and 14 control children were analyzed. Antigen specific antibody isotypes and subclasses directed against various antigens of SARS-CoV-2 as well as against human common coronavirus (HCoVs) and commensal or pathogenic microorganisms were assessed by a bead-based multiplexed serological assay and by ELISA. The functionality of these antibodies was also assessed using a plaque reduction neutralization test, a RBD-specific avidity assay, a complement deposition assay and an antibody-dependent neutrophil phagocytosis (ADNP) assay.

Results: Children with MIS-C developed a stronger IgA antibody response in comparison to children with uncomplicated COVID-19, while IgG and IgM responses are largely similar in both groups. We found a typical class-switched antibody profile with high level of IgG and IgA titers and a measurable low IgM due to relatively recent SARS-CoV-2 infection (one month). SARS-CoV-2-specific IgG antibodies of MIS-C children had higher functional properties (higher neutralization activity, avidity and complement binding) as compared to children with uncomplicated COVID-19. There was no difference in the response to common endemic coronaviruses between both groups. However, MIS-C children had a moderate increase against mucosal commensal and pathogenic strains, reflecting a potential association between a disruption of the mucosal barrier with the disease.

Conclusion: Even if it is still unclear why some children develop a MIS-C, we show here that MIS-C children produce higher titers of IgA antibodies, and IgG antibodies with higher functionality, which could reflect the local gastro-intestinal mucosal inflammation potentially induced by a sustained SARS-CoV-2 gut infection leading to continuous release of SARS-CoV-2 antigens.

Keywords: MIS-C multisystem inflammatory syndrome in children; SARS-CoV-2; antibody response; commensals; common coronavirus; functional antibody.

Figure 1

Binding antibody response against SARS-CoV-2 in MIS-C and control children. (A) IgM (left panel), IgG (middle panel) and IgA (right panel) antibody levels against SARS-CoV-2 receptor binding domain (RBD), S1 and S2 domain of the spike protein, trimerized full length spike (triS) and nucleocapsid protein (N) as well as a tetanus toxoid (TT) in MIS-C (red dots) and control children (blue dots). Levels of IgG (B) and IgA (C) antibody subclasses against the same antigens. Antibody levels, measured using a bead-based multiplex platform, are expressed as median fluorescence intensity (MFI) and were log10 transformed. Results have been duplicated and mean and standard deviations are represented. * 0.01<p≤0.05, ** 0.001<p≤0.01, *** 0.0001<p≤0.001.

Figure 2

Functional IgG antibody response against SARS-CoV-2 in MIS-C and control children. (A) SARS-CoV-2 specific neutralizing antibodies determined by plaque reduction neutralization assay. (B) Avidity of IgG antibodies against SARS-CoV-2 receptor binding domain (RBD). Antibody dependent complement deposition (ADCD) (C) and antibody dependent neutrophil phagocytosis (ADCP) (D) directed against SARS-CoV-2 RBD, S1 and S2 domain of the spike protein, trimerized full length spike (triS) and nucleocapsid protein (N) as well as a tetanus toxoid (TT) in MIS-C (red dots) and control children (blue dots). Results of antibody neutralization titer, complement binding and phagoscores were log10 transformed. Results have been duplicated, means and standard deviations are represented for (A, C, D) and geometric means and geometric standard deviations for (D). * 0.01<p≤0.05, ** 0.001<p≤0.01, *** 0.0001<p≤0.001.

Figure 3

Binding antibody response against human common cold coronaviruses in MIS-C and control children. IgG (A) and IgA (B) antibody levels against trimerized full length spike (triS) as well as S1 and S2 domain of the spike protein of OC43, HKU1, and NL63 (trimerized spike only) human common cold coronaviruses as well as a tetanus toxoid (TT) in MIS-C (red dots) and control children (blue dots). Antibody levels, measured using a bead-based multiplex platform, are expressed as median fluorescence intensity (MFI) and were log10 transformed. Results have been duplicated and the mean and standard deviations are represented.

Figure 4

Binding antibody response against commensal and pathogenic microbes in MIS-C and control children. IgG (A) and IgA (B) antibody levels against total extract (TotExt), surfactome/secretome (SurSec) and flagellin (FliC) from Escherichia coli, flagellin from Bacillus subtilis (Fla Bs) and Pseudomonas aeruginosa (Fla Pa), zymosan from Saccharomyces cerevisiae (Zym Sc), heat killed and sonicated Candida albicans (hkCa), as well as total extract (TotExt), surfactome/secretome (SurSec) and beta hemolysin (βH) from Staphylococcus aureus in MIS-C (red dots) and control children (blue dots). Antibody levels, measured using a bead-based multiplex platform, are expressed as median fluorescence intensity (MFI) and were log10 transformed. Results have been duplicated and the mean and standard deviations are represented. * 0.01<p≤0.05.

Figure 5

Antigen RBD dosage in serum measured by ELISA and correlations with antibody responses. Concentration of circulating RBD from SARS-CoV-2 (A) in MIS-C (red dots) and control children (blue dots) expressed in pg/ml. Means and standard deviations were represented. Correlation matrices (B) between the antigen RBD measured by ELISA and the measured isotypes and subclasses directed against SARS-CoV-2 receptor binding domain (RBD), S1 and S2 domain of the spike protein, trimerized full length spike (triS) and nucleocapsid protein (N), results were expressed with a color gradient for r coefficient and with stars for p values. Correlation dot plots (C) between the isotype, from left to right, IgG, IgA and IgM and the RBD antigen concentration in serum were represented in in MIS-C (red dots) and control children (blue dots). The regression line and the 95% confidence intervals dotted lines were represented on each graph with the calculated r and p values. **** 0.0001≤p.