Tolerance to male antigens occurs mainly through peripheral mechanisms. (A) Congenic male 45.1 BM (15 × 10⁶ cells) was transferred into intact (n = 5) or thymectomized female 45.2 B6 mice (n = 5) conditioned with single intravenous injections of 1 × 10⁵ DBY-Tregs. (B) Male 45.2 BM from wild-type mice or from CD3^null mice (15 × 10⁶ cells) was transferred into congenic female 45.1 mice (n = 5 for each group) conditioned with single intravenous injections of 1 × 10⁵ DBY-Tregs. In panels A and B, donor chimerism and percentage of T cells, expressed as a percentage of CD45.1⁺ or CD45.2⁺ cells, were analyzed in PBMCs at various time points after bone marrow transplantation (BMT). FACS stainings depicted at day 60 are shown. Panels A and B are each representative of 2 experiments.