Abstract: Objective To observe the changes of regulatory B (Breg) cells in mice with viral myocarditis (VMC) induced by coxsackie virus B3 (CVB3), and to explore the role of Breg cells in VMC mice. Methods Balb/c male mice were randomly divided into experimental group and control group. Mice in the experimental group were intraperitoneally infected with CVB3 to establish VMC models, while mice in the control group were treated with phosphate-buffered saline (PBS) intraperitoneally. According to the time after injection of CVB3 or PBS, all mice in the two groups were randomly divided into 1-week and 2-week subgroups. Myocardial histopathological scores were determined in hematoxylin eosin stained sections. Expression of CVB3 mRNA in heart was measured with real-time reverse transcription-polymerase chain reaction (RT-PCR), and the frequency of splenic Breg subsets in CD19⁺ B cells was measured with flow cytometry. Results There were significant differences in the pathological scores and expression of myocardial CVB3 mRNA between the VMC mice and controls. The pathological scores of 1-week experimental subgroup were lower than those of 2-week experimental subgroup, while the expression of myocardial CVB3 mRNA in 1-week experimental subgroup was higher than that in 2-week experimental subgroup (all P<0.05). Compared with controls, the frequency of splenic Breg cells in the VMC mice increased significantly at different time points. Moreover, the frequency of splenic Breg cells in 1-week experimental subgroup was higher than that in the 2-week experimental subgroup (all P<0.05). Conclusion Breg cells increase in mice with CVB3-induced VMC, indicating that Breg cells mayplay an important role in the pathogenesis of CVB3-induced VMC.

Key words: Inflammation, Myocarditis, CD19⁺CD1d^hiCD5⁺ B cells, Enterovirus, Regulatory B cells