Fig. 4: Serum antibody kinetics of COVID-19 or MIS-C with SARS-CoV-2 proteins.

Serum from children with mild/moderate (M) or severe (S) COVID-19 or MIS-C or hospitalized controls were analyzed for antibody binding to purified proteins by SPR. a,b, Total antibody binding of tenfold-diluted serum is represented in SPR resonance units (RUs; a) and as linear regressions with DPoS (b). Each dot represents a distinct patient and DPoS, color coded by groups: gray, mild/moderate control (n = 9); black, severe control (n = 5); orange, mild/moderate COVID-19 (n = 20); red, severe COVID-19 (n = 15); cyan, mild/moderate MIS-C (n = 8); blue, severe MIS-C (n = 17). a, The mean values for each group are shown. b, Correlations of binding antibodies reported over DPoS and continuously as linear regressions were performed for mild/moderate COVID-19 (orange) versus severe COVID-19 (red) versus severe MIS-C (blue), using linear regression analysis in GraphPad Prism. Associated Pearson’s correlation coefficients and linear regression significance values are colored accordingly. The trend line fits are shown as the center solid lines, with error bands representing 95% confidence intervals (shaded colored areas). c, Antibody–antigen off-rate constants as a surrogate of antibody avidity of post-SARS-CoV-2 infection serum to SARS-CoV-2 proteins were measured using SPR and plotted in the respective color coding for each patient group. Statistical differences among groups were calculated using R. The differences were considered statistically significant with a 95% confidence interval when the P value was less than 0.05 (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001). Antibody binding of all SARS-CoV-2-infected children (COVID-19 or MIS-C) were significantly higher than control samples for different SARS-CoV-2 proteins. Therefore, for clarity of representation, only statistically significant differences between SARS-CoV-2-infected patient groups are shown (COVID-19 versus MIS-C with mild versus severe disease). Detailed statistical data are provided in Supplementary Table 9. All SPR experiments were performed twice, and the researchers performing the assay were blinded to sample identity. In these optimized SPR conditions, the variation for each sample in duplicate SPR runs was <5%.

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