Myocarditis elicits dendritic cell and monocyte infiltration in the heart and self-antigen presentation by conventional type 2 dendritic cells

Autoimmune myocarditis often leads to dilated cardiomyopathy (DCM). Although T cell reactivity to cardiac self-antigen is common in the disease, it is unknown which antigen presenting cell (ARC) triggers autoimmunity. Experimental autoimmune myocarditis (EAM) was induced by immunizing mice with alpha-myosin loaded bone marrow APCs cultured in GM-CSF. APCs found in such cultures include conventional type 2 CD11b(+) cDCs (GM-cDC2s) and monocyte-derived cells (GM-MCs). However, only alpha-myosin loaded GM-cDC2s could induce EAM. We also studied antigen presenting capacity of endogenous type 1 CD24(+) cDCs (cDC1s), cDC2s, and MCs for alpha-myosin-specific TCR-transgenic TCR-M CD4(+) T cells. After EAM induction, all cardiac APCs significantly increased and cDCs migrated to the heart-draining mediastinal lymph node (LN). Primarily cDC2s presented alpha-myosin to TCR-M cells and induced Th1/Th17 differentiation. Loss of IRF4 in lrf4(fl)(/)(fl).Cd11 cCre mice reduced MHCII expression on GM-cDC2s in vitro and cDC2 migration in vivo. However, partly defective cDC2 functions in lrf4(fl)(/)(fl).Cd11 cCre mice did not suppress EAM. MCs were the largest APC subset in the inflamed heart and produced pro-inflammatory cytokines. Targeting APC populations could be exploited in the design of new therapies for cardiac autoimmunity