Reduced proportion of regulatory CD4⁺ T cells and development of autoimmune disorders in reconstituted lymphopenic NOD mice. (A) A total of 5 × 10² to 5 × 10⁶ CD4⁺ T cells from C57BL/6 and NOD mice was transferred into C57BL/6 CD3ϵ^−/− and NOD Cα^−/− mice, respectively. The number of initially injected CD4⁺ T cells expanding strongly in response to lymphopenia was evaluated by dividing the total number of CD4⁺ T cells injected into mice by the frequency of CD4⁺ T cells, as determined in limiting dilution analyses (1/214 for C57BL/6 mice, and 1/25 for NOD mice). The numbers obtained were plotted against the frequency of Foxp3⁺ cells among the CD4⁺ T cells recovered 1 month after transfer. (B) A total of 5 × 10³ or 5 × 10⁴ CD4⁺ T cells from C57BL/6 mice and from NOD mice was transferred into C57BL/6 CD3ϵ^−/− mice and NOD Cα^−/− mice, respectively. One month after transfer, mice were killed and paraffin-embedded sections of various organs were stained with hematoxylin and eosin. The presence of mononuclear cell infiltrates in the indicated organs is recorded. Results are expressed as the number of infiltrated organs among the total number of organs examined.