Clinical studies reveal changes in blood eosinophil counts and eosinophil cationic proteins that may serve as risk factors for human coronary heart diseases. Here we report an increase of blood or heart eosinophil counts in humans and mice after myocardial infarction (MI), mostly in the infarct region. Genetic or inducible depletion of eosinophils exacerbates cardiac dysfunction, cell death, and fibrosis post-MI, with concurrent acute increase of heart and chronic increase of splenic neutrophils and monocytes. Mechanistic studies reveal roles of eosinophil IL4 and cationic protein mEar1 in blocking H2O2- and hypoxia-induced mouse and human cardiomyocyte death, TGF-β-induced cardiac fibroblast Smad2/3 activation, and TNF-α-induced neutrophil adhesion on the heart endothelial cell monolayer. In vitro-cultured eosinophils from WT mice or recombinant mEar1 protein, but not eosinophils from IL4-deficient mice, effectively correct exacerbated cardiac dysfunctions in eosinophil-deficient ∆dblGATA mice. This study establishes a cardioprotective role of eosinophils in post-MI hearts.

Interleukin-18 (IL18) participates in atherogenesis through several putative mechanisms1,2. Interruption of IL18 action reduces atherosclerosis in mice3,4. This study shows that the absence of IL18 receptor (IL18r) does not affect atherosclerosis in apolipoprotein E-deficient (Apoe−/−) mice, nor does it affect IL18 cell surface binding or signaling. IL18 antibody-mediated immunoprecipitation identified an interaction between IL18 and Na-Cl co-transporter (NCC), a 12-transmembrane-domain ion transporter protein preferentially expressed in the kidney5. Yet, we find NCC expression and colocalization with IL18r in atherosclerotic lesions and both molecules form a complex. IL18 also binds to the cell surface and induces cell signaling and down-stream cytokine expression in NCC-transfected COS-7 cells that do not express IL18r. In Apoe−/− mice, combined deficiency of IL18r and NCC, but not single deficiency, protects mice from atherosclerosis. Peritoneal macrophages from Apoe−/− mice or those lacking IL18r or NCC respond to IL18 binding or IL18 induction of cell signaling and cytokine and chemokine production, but those with combined deficiency of IL18r and NCC do not. This study identifies NCC as an IL18-binding protein that coordinates with IL18r in cell signaling, inflammatory molecule expression, and experimental atherogenesis.