Regulatory T cell properties of thymic CD4+CD25+ cells in turkeys.

Thymic CD4+CD25+ cells from turkeys were analyzed for T regulatory cell suppressive properties and cytokine production profile. Thymocytes treated with concanavalin-A and interleukin-2 upregulated CD25 at 72 h of culture. The mean CD4+CD25+ cell percentage in the blood was 1.1%, in the thymus was 2.7%, in the spleen was 9.6%, in the lung was 18.6%, in cecal tonsils was 9.2%, and in bone marrow was 14.9%. The CD4+CD25+ cells were not detectable in the bursa. Turkey thymic CD4+CD25+ cells had approximately 158-fold higher interleukin-10 mRNA, 7-fold higher transforming growth factor β, 24-fold higher cytotoxic T lymphocyte antigen 4, and 11-fold higher lymphocyte-activation gene 3 mRNA amounts than thymic CD4+CD25- cells. Thymic CD4+CD25+ cells had no detectable levels of interleukin-2 mRNA. Turkey CD4+CD25+ cells suppressed naïve cell proliferation in vitro. It could be concluded that thymic CD4+CD25+ cells in turkeys are likely the counterpart of mammalian T regulatory cells.