OBJECTIVE To investigate whether CD4(+)CD25(+) regulatory T (Treg) cells play a role in the development of anterior chamber-associated immune deviation (ACAID). METHODS The dynamic changes in the frequency of CD4(+)CD25(+) T cells, CD4(+)CD25(+) FoxP3(+) T cells and CD4(+)CD25(+) PD-1(+) T cells from spleens of mice with ACAID were analyzed by flow cytometry. Foxp3 mRNA expression in purified CD4(+)CD25(+) T cells was analyzed using real-time PCR. The suppressive effect of purified CD4(+)CD25(+) T cells on the proliferation of CD4(+)CD25(-) T cells was evaluated by [(3)H] thymidine incorporation. A blocking experiment was performed to further address the role of CD4(+)CD25(+) T cells in ACAID. The expression of IL-10 in purified CD4(+)CD25(+) T cells was evaluated by ELISA. RESULTS Increased frequencies of CD4(+)CD25(+) T cells, CD4(+)CD25(+) FoxP3(+) T cells and CD4(+)CD25(+) PD-1(+) T cells were observed in ACAID. The CD4(+)CD25(+) T cells from mice with ACAID showed enhanced suppressive effect on the proliferation of CD4(+)CD25(-) T cells. Treatment of BALB/c mice with anti-CD25 antibody after injection of OVA into the anterior chamber significantly inhibited the induction of ACAID. Furthermore, purified CD4(+)CD25(+) T cells from ACAID mice secreted IL-10. CONCLUSIONS Our results demonstrate that Treg cells are induced in the mice undergoing ACAID. These Treg cells may play a role in the development of ACAID.