| Summary: | Summary: We find that cardiac group 2 innate lymphoid cells (ILC2s) are essential for the development of IL-33-induced eosinophilic pericarditis. We show a pathogenic role for ILC2s in cardiac inflammation, in which ILC2s activated by IL-33 drive the development of eosinophilic pericarditis in collaboration with cardiac fibroblasts. ILCs, not T and B cells, are required for the development of pericarditis. ILC2s transferred to the heart of Rag2−/−Il2rg−/− mice restore their susceptibility to eosinophil infiltration. Moreover, ILC2s direct cardiac fibroblasts to produce eotaxin-1. We also find that eosinophils reside in the mediastinal cavity and that eosinophils transferred to the mediastinal cavity of eosinophil-deficient ΔdblGATA1 mice following IL-33 treatment migrate to the heart. Thus, the serous cavities may serve as a reservoir of cardiac-infiltrating eosinophils. In humans, patients with pericarditis show higher amounts of ILCs in pericardial fluid than do healthy controls and patients with other cardiac diseases. We demonstrate that ILCs play a critical role in pericarditis. : Choi et al. show a pathogenic role for innate lymphoid cells (ILCs) in IL-33-induced eosinophilic pericarditis. ILCs are required for the development of pericarditis, and group 2 ILCs (ILC2s) promote the expression of eotaxin by cardiac fibroblasts. In humans, ILCs are found higher in the pericardial fluid of patients with pericarditis compared to others. Keywords: Innate lymphoid cells, group 2 innate lymphoid cells, IL-33, pericarditis, cardiac inflammation, eosinophils, mediastinum, serosal cavity
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