The immune response following myocardial infarction: a role for T-cell-mediated myocyte damage

Myocardial infarct-sparing effect of adenosine A2A receptor activation is due to its action on CD4+ T lymphocytes

BACKGROUND

We previously used adenosine A2A receptor (A2AR) knockout (KO) mice and bone marrow transplantation to show that the infarct-sparing effect of A2AR activation at reperfusion is primarily due to effects on bone marrow-derived cells. In this study we show that CD4+ but not CD8+ T lymphocytes contribute to myocardial ischemia/reperfusion injury.

METHOD AND RESULTS

After a 45-minute occlusion of the left anterior descending coronary artery and reperfusion, T cells accumulate in the infarct zone within 2 minutes. Addition of 10 microg/kg of the A2AR agonist ATL146e 5 minutes before reperfusion produces a significant reduction in T-cell accumulation and a significant reduction in infarct size (percentage of risk area) measured at 24 hours. In Rag1 KO mice lacking mature lymphocytes, infarct size is significantly smaller than in C57BL/6 mice. Infarct size in Rag1 KO mice is increased to the level of B6 mice by adoptive transfer of 50 million CD4+ T lymphocytes derived from C57BL/6 or A2AR KO but not interferon-gamma KO mice. ATL146e completely blocked the increase in infarct size in Rag1 KO mice reconstituted with B6 but not A2AR KO CD4+ T cells. The number of neutrophils in the reperfused heart at 24 hours after infarction correlated well with the number of lymphocytes and infarct size.

CONCLUSIONS

These results strongly suggest that the infarct-sparing effect of A2AR activation is primarily due to inhibition of CD4+ T-cell accumulation and activation in the reperfused heart.

Inflammation and cardiac remodeling during viral myocarditis

Acute viral myocarditis is the main cause of cardiac failure in young patients and accounts for up to 60% of "idiopathic" dilated cardiomyopathy. The clinical course of viral myocarditis is mostly insidious with limited cardiac inflammation and dysfunction. However, overwhelming inflammation may occur in a subset of patients, leading to fulminant cardiac injury, whereas others develop chronic heart failure due to autoimmune myocarditis. Today, little effective treatment exists for patients, apart from general supportive therapy and antifailure regimens. Urokinase-type plasminogen activator (u-PA) and matrix metalloproteinases (MMP) have been implicated in cardiac inflammation, matrix remodeling, and wound healing after cardiac injury. The present review will assess the mechanism by which these proteinases mediate cardiac dilatation, fibrosis, and dysfunction after cardiac stress or injury, in order to understand how inhibition of proteinases may provide a novel therapeutic tool to prevent cardiac dilatation and failure during viral myocarditis.

Targeting 2A protease by RNA interference attenuates coxsackieviral cytopathogenicity and promotes survival in highly susceptible mice

BACKGROUND

Enteroviridae such as coxsackievirus B3 (CVB3) are important infectious agents involved in viral heart disease, hepatitis, and pancreatitis, but no specific antiviral therapy is available.

METHODS AND RESULTS

The aim of the present study was to evaluate the impact of RNA interference on viral replication, cytopathogenicity, and survival. Small interfering RNA (siRNA) molecules were designed against the viral 2A region (siRNA-2A), which is considered to be highly conserved and essential for both virus maturation and host cytopathogenicity. siRNA-2A exhibited a significant protective effect on cell viability mediated by marked inhibition of CVB3 gene expression and viral replication. In highly susceptible type I interferon receptor-knockout mice, siRNA-2A led to significant reduction of viral tissue titers, attenuated tissue damage, and prolonged survival. Repeated siRNA-2A transfection was associated with a further improvement of survival. Various control siRNA molecules had no protective effect in vitro or in vivo.

CONCLUSIONS

RNA interference directed against the 2A protease encoding genomic region effectively confers intracellular immunity toward CVB3-mediated cell injury and improves survival, suggesting a potential role for RNA interference for future treatment options targeting enteroviral diseases.

Enhanced Expression of the Apoptosis Inducing Ligand TRAIL in Mononuclear Cells After Myocardial Infarction

Tumor necrosis factor (TNF) family proteins including TNF-alpha and Fas (CD95)-ligand have been implicated in the development of acute myocardial infarction (AMI). We studied whether AMI patients displayed up-regulation of another TNF family member, TNF-related-apoptosis-inducing ligand (TRAIL), on peripheral blood mononuclear cells (PBMCs). We compared expression of TRAIL on PBMCs from 26 patients in the acute phase of AMI with that on PBMCs from 16 healthy control subjects using flow cytometry and RT-PCR. In addition, expression of TRAIL protein on PBMCs from patients in the acute phase of AMI was also compared with that from the same patients 7 days later. Furthermore, we compared the expression of TRAIL protein on CD4+, CD8+, CD14+, and CD19+ cells from patients in the acute phase of AMI with that from control subjects using flow cytometry. Finally, expression of the TRAIL receptors (TRAILR)-1 and TRAILR-2 in human cardiomyocytes was examined immunohistochemically. Expression of TRAIL protein was significantly higher in the acute phase of AMI than in control subjects. Expression of TRAIL protein was significantly higher in the acute phase of AMI than 7 days later. TRAIL mRNA expression in the acute phase of AMI was higher than in control subjects. Expression of TRAIL protein on CD4+ and CD14+ cells from AMI patients was significantly higher than that from control subjects. Expression of TRAILR-1 and TRAILR-2 in human cardiomyocytes was confirmed immunohistochemically. TRAIL on infiltrating CD4 and CD146 cells may be involved in the induction of cardiomyocyte apoptosis after AMI.