Two genomic regions promote an enhanced selection of Tregs in NOD. (A) Repopulation thymus organ culture revealed that differences in Treg selection were intrinsic to the developing T cells. DN thymocytes from E15.5 embryos from the two strains were repopulated into deoxyguanosine-treated FTOC lobes from NOD or Bg7 mice. Donor cells could be discriminated by differences in expression of CD45 (NOD, CD45.1; Bg7, CD45.2). Numbers show the percentage of Foxp3+ Tregs per CD4SP. One of two independent experiments is shown. (B) FTOCs from NOD.idd3b/b, NOD.idd3b/n congenic, and NOD, Bg7, and F1 (NODxBg7) mice are shown. Representative dot plots from three to five FTOCs are shown. (C) NOD, Bg7, F1, and F2 FTOCs were cultured for 7 days, and expression of Foxp3+CD25+ Tregs per CD4SP was measured. (D) Logarithm of odds plots for the FTOC/F2 cohorts are shown. Dotted line represents level of significance (P < 0.05). (E) Linkage maps of Chr1 (Left) and Chr11 (Right).