Clin Res Cardiol (2022).

Temporal and spatial dynamics of the immune cell repertoire in murine myocardial infarction
L. S. Mitre1, T. Marchini2, C. Bode2, D. Wolf2
1Kardiologie und Angiologie I, Universitätsklinikum Freiburg, Freiburg im Breisgau; 2Klinik für Kardiologie und Angiologie I, Universitäts-Herzzentrum Freiburg - Bad Krozingen GmbH, Freiburg im Breisgau;
Rationale: Ischemic heart failure caused by myocardial infarction (MI) represents a major cause of death globally. The inflammatory response triggered by myocyte necrosis drives adverse ventricular remodeling that ultimately promotes heart failure. The temporal and spatial characteristics of cardiac immune cell infiltration after MI, however, are only partially understood. Here, we describe a systematic screening by flow cytometry and transcriptomic analysis to decipher the immune cell repertoire in murine experimental MI.

Methods and Results: We characterized the dynamics of the immune cell repertoire in murine hearts following myocardial infarction by multi-color flow cytometry using a novel 13-marker panel allowing us to characterize major principal leukocyte lineages with a total of 10 distinct leukocyte populations. Immune cell infiltrates in infarcted and remote areas of the heart were screened at 1, 3, 7, 14 and 28 days after MI induced by a surgical permanent ligation of the descending left coronary artery (LAD), transient ischemic/reperfusion injury (I/R) or sham surgery in C57BL6/J, 10 weeks old male mice. Dynamics of the immune cell repertoire were screened in injured and remote myocardium, as well as in the blood, mediastinal lymph nodes and the spleen. We detected the strongest influx of leukocytes at day 1 and 3 with a constant decline at later stages. Established myocardial scars were depleted of leukocytes, while remote myocardium contained an enhanced fraction of B cells, CD4+ T cells, NK T cells, and DCs. In contrast, macrophages represented the most frequent leukocytes in the healthy heart. In addition, innate immune cells, such as monocytes and NK cells, peaked at intermediate stages but did not remain up regulated in established myocardial scars. TNF, IFN, IL-17, granzyme, and GMCSF and the antigen-regulated activation marker CD40L increased at 28 days after MI, along with a strong up regulation of immune pathways in gene expression profiling. These findings were consistent with the build-up of a relevant immune memory and an enhanced immune response involving antigen-presenting DCs and effector T and B cells. The existence of immune cells in the human myocardium were confirmed in a re-analysis of existing single cell RNA-sequencing data sets.

Conclusion: Our results clarify the immune cell subsets infiltrating the heart following myocardial infarction and throughout the development of ischemic heart failure. Antigen-directed immune responses may hold great therapeutic promise for developing antigen-specific immunomodulatory therapies.