CD4(+)CD25(+) Cells Are Essential for Maintaining Immune Tolerance in Chickens Inoculated with Bovine Serum Albumin at the Late Stage of Embryonic Development

In this study, the role of chicken CD4(+)CD25(+) cells during induced immunotolerance was tested. Properties of chicken CD4(+)CD25(+) cells sorted by flow cytometry were analyzed. Results showed that chicken CD4(+)CD25(+) cells express IL-10, TGF-β highly and suppress proliferation of CD4(+)CD25(−) cells in vitro. To induce immunotolerance, embryos were inoculated with bovine serum albumin (BSA) via an intravascular route on embryo incubation day 20 (EID20), and after hatching chicks experienced BSA immunization four times at 7-day intervals. Serum anti-BSA antibodies and CD4(+)CD25(+) cell ratio was analyzed. Results showed that humoral tolerance was obtained and the CD4(+)CD25(+) cell percentage in peripheral blood lymphocytes increased along with this progress. Injection of anti-chicken CD25 antibody via an intravascular route on EID16 is applied to block CD4(+)CD25(+) cells, and the CD4(+)CD25(+) cell ratio decreased significantly up to 35 d post-hatch. Based on the above, injections of anti-chicken CD25 antibody on EID16 and BSA on EID20 were carried out sequentially, and tolerance level was contrasted to the BSA-injection group. Data revealed the anti-BSA antibodies increased significantly in the CD4(+)CD25(+) cell-blocked groups indicating that immune tolerance level was weakened. In conclusion, chicken CD4(+)CD25(+) cells are essential in maintaining induced immune tolerance.