A novel intramyocardial coxsackievirus B3 injection model of viral myocarditis in C57BL/6J mice with reduced pancreatic involvement

Conventional coxsackievirus B3 (CVB3)-induced murine models of viral myocarditis (VMC) are limited by the relative resistance of C57BL/6J mice to CVB3 infection and the prominent pancreatic involvement associated with conventional intraperitoneal inoculation. In this study, a cardiac-targeted CVB3-induced VMC model was established by intramyocardial injection in C57BL/6J mice. Age-dependent susceptibility and the temporal progression of cardiac injury were first evaluated to define experimental conditions. Among the age groups examined, 4-week-old mice exhibited the most pronounced myocardial pathological changes, with peak cardiac injury observed 7 days post-infection. Under these conditions, intramyocardial and intraperitoneal CVB3 inoculation were compared with respect to myocardial histopathology, cardiac function, inflammatory cytokine expression, myocardial injury biomarkers, viral protein (VP1) expression, and pancreatic involvement. Compared with intraperitoneal inoculation, intramyocardial CVB3 administration induced significantly enhanced myocardial inflammatory responses, greater cardiac dysfunction, and higher serum levels of cTn‑T, CK‑MB. Cardiac inflammatory cytokines and VP1 expression were also markedly increased in the intramyocardial group. In contrast, conventional intraperitoneal inoculation produced substantial pancreatic involvement, whereas intramyocardial inoculation markedly reduced pancreatic pathological changes and viral RNA levels while preserving robust myocardial injury. In conclusion, we established a cardiac-targeted CVB3-induced viral myocarditis model in C57BL/6J mice that provides reproducible myocardial inflammation with markedly reduced pancreatic involvement. This model provides a reproducible experimental platform for investigating myocardial inflammatory mechanisms and therapeutic strategies in acute CVB3-induced viral myocarditis while minimizing pancreatic confounding associated with conventional intraperitoneal infection.