Expression of Toll-like receptor 4 is associated with enteroviral replication in human myocarditis

Previous studies have demonstrated that inflammatory cytokine expression associated with enteroviral (EV) infection may play an important role in human myocarditis. However, the mechanism of the host immune response against viral pathogens has not been fully understood. The aim of the present study was to determine whether Toll-like receptor 4 (TLR4) and EV RNA are present in human myocarditis. Endomyocardial biopsy samples were obtained from 44 patients with myocarditis and five controls. Levels of plus- and minus-strand EV RNAs and TLR4 mRNA were measured by real-time reverse transcriptase–PCR. Immunohistochemical analysis was performed to identify the cellular source of TLR4 and the EV capsid protein VP1. EV RNA was present in 21 patients with myocarditis and these patients were defined as having either active viral replication ( n =15) or latent viral persistence ( n =6). Neither strand of EV RNA was detected in controls. TLR4 mRNA expression levels were higher in myocarditis patients than in controls (TLR4/glyceraldehyde-3-phosphate dehydrogenase ratio 1.48±0.17 compared with 0.08±0.06, P r =0.66, P r =0.48, P