Monocytes prime autoreactive T cells after myocardial infarction

Abstract

In humans, loss of central tolerance for the cardiac self-antigen α-myosin heavy chain (α-MHC) leads to circulation of cardiac autoreactive T cells and renders the heart susceptible to autoimmune attack after acute myocardial infarction (MI). MI triggers profound tissue damage, releasing danger signals and self-antigen by necrotic cardiomyocytes, which lead to recruitment of inflammatory monocytes. We hypothesized that excessive inflammation by monocytes contributes to the initiation of adaptive immune responses to cardiac self-antigen. Using an experimental model of MI in α-MHC-mCherry reporter mice, which specifically express mCherry in cardiomyocytes, we detected α-MHC antigen in myeloid cells in the heart-draining mediastinal lymph node (MLN) 7 days after MI. To test whether monocytes were required for cardiac self-antigen trafficking to the MLN, we blocked monocyte recruitment with a C-C motif chemokine receptor type 2 (CCR2) antagonist or immune modifying nanoparticles (IMP). Blockade of monocyte recruitment reduced α-MHC antigen detection in the MLN after MI. Intramyocardial injection of the model antigen ovalbumin into OT-II transgenic mice demonstrated the requirement for monocytes in antigen trafficking and T-cell activation in the MLN. Finally, in nonobese diabetic mice, which are prone to postinfarction autoimmunity, blockade of monocyte recruitment reduced α-MHC-specific responses leading to improved tissue repair and ventricular function 28 days after MI. Taken together, these data support a role for monocytes in the onset of pathological cardiac autoimmunity following MI and suggest that therapeutic targeting of monocytes may mitigate postinfarction autoimmunity in humans.NEW & NOTEWORTHY Our study newly identifies a role for inflammatory monocytes in priming an autoimmune T-cell response after myocardial infarction. Select inhibition of monocyte recruitment to the infarct prevents trafficking of cardiac self-antigen and activation of cardiac myosin reactive T cells in the heart-draining lymph node. Therapeutic targeting of inflammatory monocytes may limit autoimmune responses to improve cardiac remodeling and preserve left ventricular function after myocardial infarction.

Keywords: autoimmunity; monocytes; myocardial infarction.

Fig. 1.

Recruitment of Ly6C^hi monocytes to the infarct drives cardiac self-antigen accumulation in lymphoid organs after myocardial infarction (MI). Trafficking of cardiac self-antigen α-myosin heavy chain to the heart-draining mediastinal lymph node (MLN) after MI using Myh6-mCherry reporter mice, which specifically express mCherry in cardiomyocytes, is shown. A and C: total number of CD11b⁺ cells in the MLN (A) and spleen (C) 7 days after MI. B and D: cardiac self-antigen in CD11b⁺ cells in the MLN (B) and spleen (D) 7 days after MI. Myh6-mCherry reporter mice were subjected to MI surgery followed by treatment with vehicle (Veh) or immune modifying nanoparticles (IMP). E, G, and I: total Ly6C^hi monocytes in MLN (E), spleen (G), and heart (I) 7 days after MI. K: total macrophages in heart 7 days after MI. F and H: cardiac self-antigen expression in CD11b⁺ cells in the MLN (F) and spleen (H) 7 days after MI. J and L: cardiac self-antigen expression in Ly6C^hi monocytes (J) and macrophages (L) in the heart 7 days after MI. *P < 0.05, **P < 0.01 by unpaired t-test; n = 3–5 mice/group.

Fig. 2.

C-C motif chemokine receptor type 2 (CCR2)-dependent Ly6C^hi monocyte recruitment to the infarct promotes antigen-specific CD4⁺ T-cell responses after myocardial infarction (MI). OT-II mice were subjected to sham operation or MI surgery and intramyocardially injected with either vehicle (Veh; PBS) or ovalbumin 323–339 (OVA_323–339) peptide. To inhibit monocyte recruitment, mice were treated daily with subcutaneous injections of the CCR2 antagonist, RS504393, or vehicle control. A: flow cytometric analysis of CD8⁺ and OVA_323–339-specific CD4⁺ T cells in the heart 7 days after sham operation or MI surgery. B: flow cytometric analysis of CD69 and CD44 expression on OVA_323–339-specific CD4⁺ T cells in the heart and mediastinal lymph node (MLN) 7 days after sham operation or MI surgery. Alternatively, OT-II mice were subjected to MI surgery and intramyocardial injection of OVA_323–339 peptide followed by treatment with vehicle or immune modifying nanoparticles (IMP). C–E: total OVA_323–339-specific CD4⁺ T cells and CD8⁺ T cells in the MLN (C), spleen (D), and heart (E) 7 days after MI. *P < 0.05 by unpaired t-test; n = 3–5 mice/group.

Fig. 3.

Ly6C^hi monocyte recruitment drives postinfarction autoimmunity and adverse cardiac remodeling after myocardial infarction (MI) in nonobese diabetic (NOD) mice. Prediabetic NOD mice were subjected to MI surgery followed by treatment with vehicle (Veh) or immune modifying nanoparticles (IMP). A: flow cytometric analysis of Ly6C^hi monocytes in the spleen 7 days after MI with quantification of total Ly6C^hi monocytes. B–F: total CD45⁺ cells (B), CD4⁺ T cells (C), and CD8⁺ T cells (D) in the hearts 28 days after MI. interferon-γ (IFN-γ) production by mediastinal lymph node (E) or splenic cells (F) stimulated with mouse myosin for 72 h ex vivo. G: anticardiac myosin IgG titers in sera 28 days after MI. H: infarct and area-at-risk measurements 7 days after MI. I: collagen deposition 28 days after MI. J: echocardiography quantification of percent ejection fraction (%EF), percent fractional shortening (%FS), systolic and diastolic volume, wall thickness, internal diameter, and left ventricular (LV) mass 28 days after MI. *P < 0.05, **P < 0.01 by unpaired t-test; n = 3–5 mice/group.

Fig. 4.

Monocytes prime autoreactive T cells after myocardial infarction (MI). MI causes release of danger signals and self-antigens from dying cardiomyocytes (CM). Ly6C^hi monocytes are then released from the bone marrow (BM) and spleen into the peripheral blood and are recruited to the heart. Within the infarct, Ly6C^hi monocytes produce inflammatory cytokines and phagocytose-damaged tissue and dying CM. In autoimmune-susceptible individuals, including patients with type 1 diabetes (T1D), persistent inflammatory LyC6^hi monocytosis promotes infiltration and activation of antigen-presenting cells with phagocytosed cardiac self-antigen. Migration of mature antigen-presenting cells (dendritic cells) with engulfed cardiac self-antigen to the mediastinal lymph node and spleen leads to priming of cardiac myosin-specific CD4⁺ T cells and a pathological autoimmune response directed against the heart. This culminates in adverse tissue remodeling and progression to heart failure. Targeting monocyte recruitment to the heart using immune modifying nanoparticles (IMP) redirects the majority of Ly6C^hi monocytes to the spleen for their apoptotic removal, while permitting a minority of these cells to infiltrate the infarct, mediate clearance of tissue debris, and differentiate into Ly6C^lo reparative macrophages. This limits inflammation and both the release of cardiac self-antigen and its presentation by antigen-presenting cells in lymphoid organs, leading to improved cardiac repair after MI. α-MHC, α-myosin heavy chain; CCR2, C-C motif chemokine receptor type 2; Mϕ, macrophage.