IL-33 expands cardiac ILC2 cells and reduces ISO-induced cardiac fibrosis. (A) BALB/cByJ mice were subcutaneously administered saline or ISO followed by saline or IL-33 on days 3, 5, and 7. The heart tissues were harvested on day 10 after the last ISO injection. Flow cytometry analysis for the CD45+Lin-Thy1.2+ ILC2 cells in the cardiac tissues on day 10 after the last ISO injection. (B) Frequency of ILC2 among CD45+ cells. (C) Number of ILC2s per heart. (D) Picrosirius red staining and quantification of cardiac fibrosis area. Data are pooled from two independent experiments and expressed as the means ± SD (n = 5-10 per group). Scale bar = 100 µm. *P < 0.05, **P <0.01, ***P <0.001, ****P <0.0001; ns, not significant by one-way ANOVA followed by the Bonferroni multiple comparison post-hoc test. All values are means ± SD. Each dot indicates a biological replicate. (E) Gating strategy for each leukocyte population and the comparison of each condition. (F) ST2+ cell gating for the gated leukocyte population. (G) Proportion of ST2-positive leukocytes. (H) Mean fluorescence intensity (MFI) of ST2 on the surface of ILC (Lineage- Thy1.2+), DC (CD11c+), macrophages (F4/80+), B cells (CD19+), and eosinophils (CD11b+ SiglecF+).