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Background: Recent studies have shown that heat shock protein (HSP) 70 may serve as a ''damage signal'' to the immune system and could be the endogenous ligand for Toll-like receptor (TLR) 4 mediating synthesis of inflammatory cytokines. Aims: To explore the relationship between circulating HSP70 levels and activation of monocyte TLR4 and myocardial damage after AMI. Methods and results: This study examined circulating HSP70 and monocyte TLR4 levels in 52 patients with AMI and 20 controls, and analyzed ex vivo inflammatory cytokine productions using HSP70-stimulated monocytes. Circulating HSP70 levels were higher in AMI patients on day 1 after onset than in controls and remained elevated in AMI patients 14 days after onset. HSP70 levels were positively correlated with monocyte TLR4, plasma interleukin-6 and tumor necrosis factor-a levels in AMI patients. HSP70 levels 14 days after onset were higher in AMI patients with heart failure (n = 15) than in those without heart failure. In our in vitro study, HSP70-stimulated monocytes resulted in dose-dependent TLR4 expression and release of inflammatory cytokines. TLR4 antibody inhibited inflammatory cytokines release. Conclusions: Elevated circulating levels of HSP70 may be involved in TLR4 signal-mediated immune response and the progression of heart failure after AMI.

Several reports suggest that a chronic inflammatory process plays a key role in coronary artery plaque instability and subsequent occlusive thrombosis. In a previous study, we found that TLR4 (Toll-like receptor 4) mediates the synthesis of cytokines in circulating monocytes of patients with AMI (acute myocardial infarction); however, it remains unclear whether TLRs are expressed at the site of the ruptured plaque in these patients. The aim of the present study was to determine whether TLR2 and TLR4 are expressed at the site of ruptured plaques in patients with AMI and to compare this with systemic levels. The study included 62 patients with AMI, 20 patients with SA (stable angina) and 32 subjects with a normal coronary angiogram (control). Local samples from the site of the ruptured plaque were taken from patients with AMI using aspiration catheterization. Systemic blood samples from the aorta were taken from patients with AMI and SA and controls. Systemic levels of TLR2 and TLR4 were higher in patients with AMI than in patients with SA and controls. In patients with AMI, local TLR4 levels were higher than systemic levels. There was no significant difference in TLR2 levels between local and systemic samples. TLR4 immunostaining was positive in infiltrating macrophages in ruptured plaque material. Cardiac events were observed in 16 patients with AMI at the time of the 6-month follow-up study. Local and systemic levels of TLR4 were higher in patients with AMI with cardiac events than in those without. These results indicate an increase in monocytic TLR4 expression not only in the systemic circulation, but also at the site of plaque rupture. In conclusion, expression of both systemic and local plaque TLR4 may be one of the mechanisms responsible for the pathogenesis of AMI.

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Inflammatory process plays a fundamental role in ischemic coronary artery disease (CAD) in terms of both the etiology of atherosclerosis and the pathophysiology of CAD. In particular, chronic inflammation plays a key role in coronary artery plaque instability and subsequent occlusive thrombosis. It is therefore important to clarify the mechanism underlying the activation of the immune response in the pathogenesis of CAD. Currently 10 toll-like receptors (TLRs) have been reported in mammalian species, and these appear to recognize distinct pathogen-associated molecular patterns controlling innate immune responses. In recent studies, signaling of two forms of human TLR (TLR2 and TLR4) has been shown to be involved in the pathogenesis of CAD, establishing a key link between the progression of coronary atherosclerosis and immune response to both foreign pathogens and endogenously generated inflammatory ligands. A better understanding of TLR signal may provide a novel therapeutic agent for the treatment of CAD. This review summarizes the relationship between the pathogenesis of ischemic coronary artery disease and the human TLR system.

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