Figure 6.

SARS-CoV-2-specific immune response up to 10 months after infection. Dot plots summarizing the frequencies of IFN-γ-producing cells by ELISPOT assay responding to (A) a set of overlapping peptides of SARS-CoV-2 spike protein and (B) a set of overlapping peptides of SARS-CoV-2 nucleocapsid protein in children (left panel, blue) and adults (right panel, red), at different time points after infection, and compared to unexposed children/adults. (C) Dot plots showing the frequencies of IFN-γ-producing cells responding to SARS-CoV-2 spike and nucleocapsid proteins, at 10 months after symptom onset (T4) comparison of groups of children versus total, mild, and moderate adult cases separately. (D) Immunophenotyping at the single-cell level comparing the frequencies of different memory subsets from T3 versus T4 within the SARS-CoV-2-specific activated CD4⁺ T cells from infected adults. (E) Spearman correlation between frequency of IFN-γ⁺ responder cells and concentrations of anti-spike-S1 IgG serum antibodies measured by multiplex immunoassay (MIA) at T4 in children (upper panel, blue) and adults (lower panel, red). (F) Dot plots comparing the concentrations of anti-spike-S1 IgG serum antibodies at T2 or T3 versus T4 in children and adults. Each dot represents one subject. Bars indicate the median. SFU, spot-forming unit. (A, B) P values related to comparisons with the unexposed controls are listed at the top of the graph, above the corresponding group for comparison. For unpaired comparisons, Mann-Whitney U test (two-group comparisons) (mild adults versus moderate adults, infected children or adults at T4 versus unexposed children or adults) or Kruskal-Wallis rank-sum test with Dunn’s post hoc test for multiple comparisons were used (children versus total adults versus mild adults versus moderate adults; unexposed versus infected children or adults at T1 versus T2 versus T3). Differences between paired data were compared using the Wilcoxon signed-rank test (for comparison of two paired groups) (memory T cell subsets at T3 versus T4; concentrations of anti-spike-S1 IgG serum antibodies at T2 or T3 versus T4) or the Friedman test with Dunn’s multiple comparison tests (infected children or adults at T1 versus T2 versus T3 versus T4). Statistically significant comparisons are indicated, with P values < 0.05 considered significant. Cut-off values for seroprevalence are indicated with vertical dotted lines in (E, F). Correlation coefficients (r_s) were determined with Spearman’s rank correlation. Statistically significant comparisons are indicated. P values < 0.05 were considered significant. T1, first timepoint of sampling for adults median 12.5 days and children median 8 days post-symptom onset; T2, 10-14 days after T1; T3, 4-6 weeks after T1; T4, 10 months ± 13 days after symptom onset.