CD4 and viral myocarditis: As shown in Fig. 7A, adoptive transfer substantially raised CD4+Foxp3+ Treg frequency from 0.48–6.71%, about 14-fold higher than that of control mice; meanwhile, a 6-fold higher frequency was also achieved in CD4+IL10+ T cells, suggesting that female-derived M-MDSCs exerted their protection against viral myocarditis mainly via promoting regulatory and IL-10-secreting T cell production.