Coxsackievirus B3 (CV-B3), a Group B Enterovirus (EV-B), is a major cause of human myocarditis. In some cases, CV-B infections can progress to chronic cardiomyopathies and sudden cardiac death in both infants and young adults (< 40 years). To infect cardiomyocytes, CV-B3 must first cross the microvascular endothelium, the primary barrier.

While CV-B3 is known to infect endomyocardial microvascular endothelial cells and modulate inflammation, its impact on endothelial permeability and the underlying mechanisms remains unclear.

We investigated the effects of CV-B3 infection on endothelial permeability using a cardiotropic CVB3/28 strain (MOI 5) in human endothelial cell lines. Viral RNA and infectious particles were quantified by qRT-PCR and plaque assays, respectively, while vascular permeability was assessed via FITC-Dextran in Boyden chambers.

CV-B3 infection resulted in significantly higher viral RNA and infectious particles levels in human cardiac microvascular endothelial cells (HCMEC) compared to human coronary artery endothelial cells (HCAEC) and non-cardiac lines (HMEC-1, HUVEC) (P<0.01). Productive infection in HCMEC and HCAEC significantly increased vascular permeability versus mock-infected cells (P<0.05). To explore the mechanisms, we examined VE-cadherin, a key regulator of endothelial barrier integrity. While VE-cadherin mRNA and protein levels (qRT-PCR, Western blot) remained unchanged at 24hours post-infection (pi), confocal immunofluorescence revealed significant VE-cadherin internalization in infected HCMEC and HCAEC at 24h pi. Remarkably, these in vitro findings were corroborated in heart tissue sections from an adult patient who died of acute EV-B myocarditis. Hematoxylin and eosin staining (HES) of the heart tissue confirmed acute viral myocarditis, characterized by perivascular inflammatory cell infiltrates and disorganized VE-cadherin expression in the presence of viral VP1 capsid protein (co-detection by confocal immunofluorescence).

These findings demonstrate that CV-B3 infection increases cardiac endothelial cell permeability through VE-cadherin internalization. This process may involve VEGF-mediated signalling pathways, providing new insights into how CV-B3 disrupts endothelial barrier function, facilitating viral dissemination and cardiac tissue damage during myocarditis.