The origin of thymic CD4 CD25 regulatory T cells and their co-stimulatory requirements are determined after elimination of recirculating peripheral CD4 cells

Abstract

Studies on the thymic ontogeny of naturally arising CD4+ CD25+ regulatory T cells (TR cells) are complicated by the contamination of recirculating cells from the periphery (both activated CD4+ T and TR cells). We investigated TR cells in anti-CD4 antibody transgenic (Tg) (GK) mice that continuously deplete peripheral CD4 T cells but not thymocytes so that the generation of thymic TR cells and their developmental requirement can be accurately assessed. We show that in the thymuses of mice that lack peripheral CD4+ cells, TR cells were present but were fewer in number compared with wild-type (WT) mice. Therefore, we show that peripheral TR cells do re-enter the thymus, comprising 20% of TR cel..