Identification of Pathogenic Cardiac CD11c⁺ Macrophages in Nod1-Mediated Acute Coronary Arteritis

Objective - Nod1 is an intracellular pattern recognition receptor for bacterial peptidoglycan fragments. We previously reported that a synthetic Nod1 ligand, FK565, induced acute coronary arteritis in mice similar to that of Kawasaki disease. However, the molecular mechanisms underlying this characteristic inflammation have remained elusive. Approach and Results - We found that CD11c⁺MHC class II⁺ cells accumulated in the heart of FK565-treated mice before arteritis development. Morphological features and gene expression signatures of the cardiac CD11c⁺MHC class II⁺ cells suggested that this population is closely related to macrophages, and thus, we designated them cardiac CD11c⁺ macrophages. Nod1 in nonhematopoietic cells, rather than hematopoietic cells, was required for the increase of cardiac CD11c⁺ macrophages and arteritis development. Among nonhematopoietic cells, cardiac endothelial cells produced a large amount of chemokines in response to FK565. Endothelial cell-specific blockade of Nod1 signaling suppressed FK565-induced expression of these chemokines, accumulation of cardiac CD11c⁺ macrophages, and subsequent coronary arteritis development. We also found that CCR2⁺Ly6C^hi inflammatory monocytes in peripheral blood supplied precursors of cardiac CD11c⁺ macrophages. CCR2-deficient mice or pertussis toxin-treated mice exhibited decreased numbers of cardiac CD11c⁺ macrophages and reduced arteritis. Conclusions - These results suggest that Ly6C^hi monocytes are recruited to FK565-activated endothelial cells to generate cardiac CD11c⁺ macrophages, which play a pivotal role in the pathogenesis of acute coronary arteritis.