Molecular in situ localization techniques in diagnosis and pathogenicity studies of enteroviral heart disease

Enteroviruses, including coxsackieviruses of group B (CVB), are considered to be the most common agents of viral myocarditis. As demonstrated by in situ hybridization for the detection of viral RNA in endomyocardial biopsies and autopsy hearts, such infections are also detectable in patients with 'idiopathic' dilated cardiomyopathy, indicating the possibility of myocardial enterovirus persistence. Persistent enterovirus infection of the human heart is supported by the recent discovery in various murine models of chronic myocarditis, demonstrating that CVB3, typically a cytolytic virus, is capable of evading immunological surveillance in a host-dependent manner.

In order to investigate mechanisms underlying acute and persistent enterovirus infection in the myocardium, diverse tissues from CVB3 infected immunocompetent mice were processed in in situ hybridization for the detection of viral RNA. In addition, virus-host interactions were analyzed at the subcellular level in the myocardium in the course of the infection by means of an electron microscopic in situ hybridization assay.

A close spatial and temporal relationship between viral replication and inflammatory lesions was observed during the acute as well as persistent phase of myocardial infection. A multiorgan study revealed that, in addition to heart muscle cells, lymphoid cells of spleen and lymph nodes are persistently infected. The results obtained at the ultrastructural level demonstrate that loss of host cell integrity is a direct consequence of acute viral replication and confirm that chronic myocarditis may be associated with persistent heart muscle infection.

Viral replication plays a central role in the pathogenesis of acute and chronic myocarditis. Immune cells are important targets of the infection and provide a non-cardiac viral reservoir.