Fig. 3: IL-33 production correlates with T cell activation and disease severity in SARS-CoV-2 infected subjects.

a–e Cytokine production measured in the media of cultured PBMCs (a–d) or via intracellular staining of CD14^hiCD16⁻ monocytes from seropositive (purple) and seronegative (green) subjects are shown as scaled values. Two-tailed Mann–Whitney U tests were calculated and the resulting p-value is reported. Values for subjects are shown as dots, the sample distribution is presented as a violin plot and the population median is a black line. f–j Scaled cytokine production versus corresponding CD4 T cell activation (CD4⁺CD69⁺) in PBMC cultures of seropositive individuals are shown. Linear regression curves fitted to these data (blue) alongside R² values are provided. k–m ST2L expression as a percentage of positive cells was measured in the indicated cell populations via flow cytometry in PBMCs from seropositive (purple) and seronegative (green) subjects (n = 40). Two-tailed Mann–Whitney U tests were calculated and resulting p values are reported. Boxplots indicating the mean (black line), 25th and 75th quantiles (edges), and interquartile ranges (whiskers), as well as outliers (dots), are shown. Flow cytometry staining is presented in a dimensional reduction projection (UMAP), showing immune cell clusters (l) and ST2L median fluorescence intensity (MFI) (m). Scaled MFI is indicated on a gradient from low (gray) to high (purple). n–t Single-cell RNA sequencing data from the bronchoalveolar lavage fluid of 3 healthy individuals compared to 9 SARS-CoV-2 infected subjects with different disease severities (3 milds; 6 severe) was retrieved from a public database (GSE145926), grouped into cell clusters (n) and analyzed for the expression of IL-33 (o). Relative expression levels are indicated on a gradient from low (light gray) to high (blue). p IL-33 expression in clusters 23, 27, and 30 presented as a violin plot grouped by disease status. q–t, Key surface (q–r), and lineage-specific (s–t) genes expressed in IL-33 producing cells. Relative expression levels are indicated on a gradient from low (light gray) to high (blue).