The absence of TGFβ signaling in TECs results in an increase in mature, single-positive thymocytes. (A) Relative frequency of phenotypically mature (ie, CD3^high) thymocytes in 8-week-old TGFβRII^lox/lox::Foxn1-Cre (□) and TGFβRII^lox/lox (■) mice. (B) Relative frequency of CD3^high SP thymocytes in E12.5 thymic lobes of phenotypically mature thymocytes in TGFβRII^lox/lox::Hoxa3-Cre (□) and TGFβRII^lox/lox (■) embryos grafted under the kidney capsule of syngeneic nude recipients and analyzed 12 weeks later. (C) Relative frequency of CD24^low and (D) absolute numbers of CD24^low () and CD24^high () thymocytes among single-positive, CD3^high thymocytes in TGFβRII^lox/lox::Foxn1-Cre and TGFβRII^lox/lox mice. (E) Thymic export measured by intrathymic FITC injection of 5-week-old mice and quantification of FITC⁺ cells 24 hours later: absolute number of FITC⁺ T cells detected in spleen and lymph nodes ( CD4⁺ T cells, CD8⁺ T cells). One of 3 experiments with similar results shown. P values were obtained using a t test. Error bars represent SD.