AIMS: Myelomonocytic cells are critical in injury and healing post-myocardial infarction (MI). Mechanisms of regulation, however, are incompletely understood. The aim of the study was to elucidate the role of interferon gamma (IFN-γ) in the orchestrated inflammatory response in a murine model of MI.
METHODS AND RESULTS: MI was induced in 8- to 12-week-old male mice (C57BL/6 background) by permanent ligation of the left anterior descending (LAD) coronary artery. Lysozyme M (LysM)+ cell-depleted LysMiDTR transgenic mice displayed a reduced influx of CD45.2+/CD3-/CD11b+/Gr-1high neutrophils into infarcted myocardium 1 day post-MI compared with infarcted controls, paralleled by decreased cardiac mRNA levels of IFN-γ and tumour necrosis factor alpha (TNF-α). Mortality after MI was significantly increased in LysM+ cell-depleted mice within 28 days post-MI. To more specifically address the role of neutrophils, we depleted C57BL/6 mice with a monoclonal anti-Gr-1 antibody and found increased mortality, deteriorated cardiac function as well as decreased cardiac IFN-γ mRNA expression early after MI. Ccl2, Cxcl1, Cx3cl1, and Il12b mRNA were reduced 3 days after MI, as was the amount of CD11b+/Ly-6G-/Ly-6Chigh inflammatory monocytes. LAD-ligated Cramp-/- mice lacking cathelicidin important in neutrophil-dependent monocyte chemotaxis as well as IFNγ-/- and TNFα-/- mice phenocopied Gr-1+ cell-depleted mice, supporting a regulatory role of IFN-γ impacting on both the sequence of inflammatory cell invasion and cardiac outcome early after MI. The use of conditional IFN-γ receptor deficient mice indicated a direct effect of IFN-γ on LysM+ cells in cardiac injury post-MI. Using IFN-γ reporter mice and flow cytometry, we identified cardiac lymphoid cells (CD4+ and CD8+ T cells and natural killer cells) as primary source of this cytokine in the cardiac inflammatory response post-MI.
CONCLUSION: IFN-γ directs a sequential chemotactic cellular immune response and determines survival and cardiac function post-MI.