Abstract
Thymic CD4(+)CD25(+) cells have regulatory-T-cell-like properties in chickens. This study examined the ontogeny of CD4(+)CD25(+) cells in the thymus and in peripheral compartments in chickens. CD4(+)CD25(+) cells started to appear in the thymus at day 15 of incubation (E15), although at low percentages. Expressed as a percentage of CD4(+) cells, CD4(+)CD25(+) cells increased (P<0.01) from 1.7% at E20 to 7.3% at 0 d post-hatch (D0). CD4(+)CD25(+) cells did not appear in the spleen or cecal tonsils of embryos. Expressed as a percentage of CD4(+) cells, CD4(+)CD25(+) cells increased (P<0.01) from 0% at D0 to 27% at D1 in cecal tonsils and from 0% at D0 to 11% at D1 in the spleen. Expressed as a percentage of all mononuclear cells, cecal tonsils at D1 had approximately 3.5-fold higher percentage of CD4(+)CD25(+) cells than the spleen at D1. CD4(+)CD25(+) cells from cecal tonsils of chicks at D1 were suppressive. CD4(+)CD25(+) cells from D0 thymus, when injected back into MHC-compatible chicks, migrated to cecal tonsils and lungs and were detected until 10 d post-injection. CD4(+)CD25(+) cells from cecal tonsils had a higher (P = 0.01) relative amount of CCR9 mRNA than CD4(+)CD25(+) cells from the thymus. It could be concluded that in chickens CD4(+)CD25(+) cells migrate from the thymus immediately post-hatch and preferentially colonize the gut associated lymphoid tissues. CD4(+)CD25(+) cells' preferential migration to cecal tonsils is likely directed through the CCR9 pathway in chickens.