Vaccination with a high dose of OVA-CTLA-4-pcDNA3.1 prevented the OVA-induced reduction of percentages of CD25+ Foxp3+ Treg cells in the spleen. (A) Representative results of percentages of CD25+ Foxp3+ Treg cells in spleens from mice in the control group (a), the model group (b), the pcDNA3.1 group (c), the OVA-pcDNA3.1 group (d), the OVA-CTLA-4-pcDNA3.1(L) group (e), and the OVA-CTLA-4-pcDNA3.1(H) group (f). (B) The percentages of CD25+ Foxp3+ Treg cells were significantly increased in mice from the OVA-CTLA-4-pcDNA3.1(H) group. The values represented means ± the standard deviations (n = 5). Values with different letters showed significant differences (P < 0.05).