Systemic application of mesenchymal stromal cells (MSCs) in inflammatory cardiomyopathy exerts cardiobeneficial effects. The mode of action is unclear since a sufficient and long-acting cardiac homing of MSCs is unlikely. We therefore investigated the regulation of the immune response in coxsackievirus B3 (CVB3)-induced acute myocarditis after intravenous application of MSCs. Wildtype mice were infected with CVB3 and treated with either PBS, human MSCs or human cardiac fibroblasts intravenously 1 day after infection. Seven days after infection, MSCs could be detected in the spleen, heart, pancreas, liver, lung and kidney, whereby the highest presence was observed in the lung. MSCs increased significantly the myocardial expression of HGF and decreased the expression of the proinflammatory cytokines TNFα, IL1β and IL6 as well as the severity of myocarditis and ameliorated the left ventricular dysfunction measured by conductance catheter. MSCs upregulated the production of IFNγ in CD4+ and CD8+ cells, the number of IL10-producing regulatory T cells and the apoptosis rate of T cells in the spleen. An increased number of CD4+CD25+FoxP3 could be found in the spleen as well as in the circulation. In contrast, application of human cardiac fibroblasts had no effect on the severity of myocarditis and the systemic immune response observed after MSCs-administration. In conclusion, modulation of the immune response in extracardiac organs is associated with cardiobeneficial effects in experimental inflammatory cardiomyopathy after systemic application of MSCs.

NOD2 is an important mediator in the viral uptake and inflammatory response during the pathogenesis of CVB3 myocarditis.

Increased levels of interleukin-6 (IL-6) have been observed in patients with acute myocarditis and are associated with poor prognosis. This study was designed to examine whether treatment with anti-IL-6 receptor antibody improves cardiac dysfunction and left ventricular (LV) remodeling in experimental Coxsackie virus B3 (CVB3)-induced myocarditis. C57BL6/J mice were subjected to acute CVB3 infection. One day after viral infection mice were treated with a single injection of an anti-IL-6 receptor antibody (MR16-1, tocilizumab) or control IgG. Seven days after viral infection, LV function was examined by conductance catheter technique, cardiac remodeling assessed by estimation of titin phosphorylation, cardiac fibrosis, and inflammatory and antiviral response by immunohistochemistry, RT-PCR and cell culture experiments. Compared to controls, infected mice displayed an impaired systolic and diastolic LV function associated with an increase in cardiac inflammation, fibrosis and impaired titin phosphorylation. IL-6 receptor blockade led to a shift of the immune response to a Th1 direction and significant reduction of viral load. In addition, cardiac immune response, extracellular matrix regulation and titin function improved, resulting in a preserved LV function. IL-6 receptor blockade exerts cardiac beneficial effects by antiviral and immunomodulatory actions after induction of an acute murine CVB3 virus myocarditis.

Mesenchymal stromal cell (MSC) application in Coxsackievirus B3 (CVB3)‐induced myocarditis reduces myocardial inflammation and fibrosis, exerts prominent extra‐cardiac immunomodulation, and improves heart function. Although the abovementioned findings demonstrate the benefit of MSC application, the mechanism of the MSC immunomodulatory effects leading to a final cardioprotective outcome in viral myocarditis remains poorly understood. Monocytes are known to be a trigger of myocardial tissue inflammation. The present study aims at investigating the direct effect of MSC on the mobilization and trafficking of monocytes to the heart in CVB3‐induced myocarditis. One day post CVB3 infection, C57BL/6 mice were intravenously injected with 1 x 106 MSC and sacrificed 6 days later for molecular biology and flow cytometry analysis. MSC application reduced the severity of myocarditis, and heart and blood pro‐inflammatory Ly6Chigh and Ly6Cmiddle monocytes, while those were retained in the spleen. Anti‐inflammatory Ly6Clow monocytes increased in the blood, heart, and spleen of MSC‐treated CVB3 mice. CVB3 infection induced splenic myelopoiesis, while MSC application slightly diminished the spleen myelopoietic activity in CVB3 mice. Left ventricular (LV) mRNA expression of the chemokines monocyte chemotactic protein‐1 (MCP)−1, MCP‐3, CCL5, the adhesion molecules intercellular adhesion molecule‐1, vascular cell adhesion molecule‐1, the pro‐inflammatory cytokines interleukin‐6, interleukin‐12, tumor necrosis factor‐α, the pro‐fibrotic transforming growth factorβ1, and circulating MCP‐1 and MCP‐3 levels decreased in CVB3 MSC mice, while LV stromal cell‐derived factor‐1α RNA expression and systemic levels of fractalkine were increased in CVB3 MSC mice. MSC application in CVB3‐induced myocarditis modulates monocytes trafficking to the heart and could be a promising strategy for the resolution of cardiac inflammation and prevention of the disease progression. Stem Cells Translational Medicine 2017;6:1249–1261