Background— Coxsackievirus B3 infection is an excellent model of human myocarditis and dilated cardiomyopathy. Cardiac injury is caused either by a direct cytopathic effect of the virus or through immune-mediated mechanisms. Regulatory T cells (Tregs) play an important role in the negative modulation of host immune responses and set the threshold of autoimmune activation. This study was designed to test the protective effects of Tregs and to determine the underlying mechanisms.

Methods and Results— Carboxyfluorescein diacetate succinimidyl ester–labeled Tregs or naïve CD4⁺ T cells were injected intravenously once every 2 weeks 3 times into mice. The mice were then challenged with intraperitoneal coxsackievirus B3 immediately after the last cell transfer. Transfer of Tregs showed higher survival rates than transfer of CD4⁺ T cells (P=0.0136) but not compared with the PBS injection group (P=0.0589). Interestingly, Tregs also significantly decreased virus titers and inflammatory scores in the heart. Transforming growth factor-β and phosphorylated AKT were upregulated in Tregs-transferred mice and coxsackie-adenovirus receptor expression was decreased in the heart compared with control groups. Transforming growth factor-β decreased coxsackie-adenovirus receptor expression and inhibited coxsackievirus B3 infection in HL-1 cells and neonatal cardiac myocytes. Splenocytes collected from Treg-, CD4⁺ T-cell–, and PBS-treated mice proliferated equally when stimulated with heat-inactivated virus, whereas in the Treg group, the proliferation rate was reduced significantly when stimulated with noninfected heart tissue homogenate.

Conclusions— Adoptive transfer of Tregs protected mice from coxsackievirus B3–induced myocarditis through the transforming growth factor β–coxsackie-adenovirus receptor pathway and thus suppresses the immune response to cardiac tissue, maintaining the antiviral immune response.