['Syngeneic bone marrow transplantation into the adult tgepsilon26 mouse results in severe wasting disease and colitis. On transplantation, the rudimentary thymus of the adult tgepsilon26 mouse repopulates briefly but quickly regresses in temporal association with the onset of colitis. The aim of this study is to test the hypothesis that treatment of colitis restores thymic capability to generate regulatory T cells (CD4+25+ T(R) cells).', 'Colitis was induced by bone marrow transplantation into adult irradiated tgepsilon26 mice. Colitis was prevented by 3 distinct modalities. CD4+25+ T cells were collected from both the thymus and spleen and studied for regulatory function by an in vitro suppression assay.', 'CD4+25+ T(R) cells do not develop efficiently in the thymus of bone marrow transplanted adult tgepsilon26 mice, which have a developmental arrest affecting thymic epithelium. By contrast, the thymic epithelium of neonatal tgepsilon26 mice supports development of T(R) cells. Consequently, colitis develops only in adult transplanted mice but not in the neonatally transplanted mice. Treatment of colitis prevents destruction of the thymus of adult transplanted tgepsilon26 mice and T(R) cells are produced.'] Is colitis associated with thymic destruction attenuating CD4+25+ regulatory T cells in the periphery?