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. 2021 Dec 16;219(2):e20211381. doi: 10.1084/jem.20211381

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© 2021 Hoste et al.

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Figure 2. — Widespread B cell activation and convalescent antibody repertoire but absence of immune complex mediated complement activation. (A) Violin plots of anti–SARS-CoV-2–specific serological assays, quantified as relative OD versus the calibrator for anti-spike 1 (S1) IgA and IgG, and anti-nucleocapsid (NCP) IgG for MIS-C (red) and adults with severe COVID-19 (orange). Area in gray depicts insufficient serological response. Dashed lines show median and quartiles. (B) Fold increase of serology during hospitalization, calculated as ratio of OD values of second and first time point of sampling of patients with MIS-C and severe COVID-19. Significance determined by Mann–Whitney U tests (and Dunn’s test for multiple testing), indicated by *, P < 0.05; **, P < 0.01; ***, P < 0.001; and ****, P < 0.0001. (C) UMAP representation of B lymphocytes (within PBMCs) of 9 MIS-C patients, 9 adults with severe COVID-19, and 20 age-matched HCs. (D) Signature marker expression characterizing B lymphocyte clusters. Legend depicting fluorescence intensity. (E) Density plot of UMAP panels stratified by condition or HC group. (F) Boxplots representing median and ranges of normalized B lymphocyte cluster proportions versus the median of corresponding HCs (Log2 fold change). Significance determined by multiple Mann–Whitney U tests and corrected for multiple testing (FDR of 5%) both within disease and age-matched HCs (in red and orange for MIS-C and severe COVID-19, respectively) or between MIS-C and severe COVID-19 (in black, right), indicated as *, q < 0.05; **, q < 0.01; ***, q < 0.001; and ****, q < 0.0001. (G) MFI of CD86 on B lymphocytes (CD3⁻CD20⁺; left) and specific B cell subsets (right): naive (IgD⁺CD27⁻), unswitched memory (IgD⁺CD27⁺), switched memory (IgD⁻CD27⁺), and DN (IgD⁻CD27⁻) B cells. (H and I) Violin plots representing values of CICs bound by C1q (H) and (I) concentrations of cleaved complement factor 4 (C4a) and soluble membrane attack complex (sC5b9) in plasma. Dashed lines show median and quartiles. Significance determined by Mann–Whitney U tests (and Dunn’s test for multiple testing), indicated by ****, P < 0.0001. (J) Dot plots displaying concentrations of C4a and sC5b9 in relation to CIC-C1q in patients with MIS-C. Dashed lines represent simple linear regression with 95% CIs. R² displays goodness-of-fit, and statistical analysis to test if slope differs from 0 (P < 0.05) is shown. Values for individual patients are displayed with MIS-C (red), severe adult COVID-19 (orange), and age-matched HCs (blue). Distinct symbols depict patients with severe MIS-C with (inverted triangle) or without treatment (triangle) and moderate disease (circle).