Regulatory T cell properties of thymic CD4+CD25+ cells in ducks

Thymic CD4+CD25+ cells from ducks were characterized for mammalian T regulatory cells’ suppressive and cytokine production properties. The cross reactivity of anti-chicken CD25 monoclonal antibody with duck CD25 was confirmed by evaluating Concanavalin-A-stimulated CD25 upregulation in splenocytes. CD4+CD25+ cells were detectable in the thymus, spleen, cecal tonsil, and lung (airsacs), but not in the bursa. Duck CD4+CD25+ cells had approximately nine-fold higher IL-10 mRNA, 12-fold higher TGF-β, 16-fold higher CTLA-4, and nine-fold higher LAG-3 mRNA amounts than thymic CD4+CD25− cells. Thymic CD4+CD25+ cells had no detectable levels of IL-2 mRNA. Duck CD4+CD25+ cells had a three-fold higher IL-10 mRNA amount than chicken CD4+CD25+ cells. Duck CD4+CD25+ cells were anergic in vitro. Duck CD4+CD25+ cells suppressed naive cell proliferation at effector: responder cell ratios above 0.5:1 in both contact-dependent and -independent pathways. It could be concluded that thymic CD4+CD25+ cells in ducks are most likely the counterpart of mammalian T regulatory cells.