Frequencies of conventional and regulatory T cells undergoing spontaneous proliferation in lymphopenic NOD mice 1 month after reconstitution. (A) Twenty-five CD4⁺CD25⁻ or CD4⁺CD25⁺ LN T cells from CD45.2 NOD mice and 2 × 10³ CD4⁺ T cells from CD45.1 NOD mice were cotransferred into CD45.1 NOD Cα^−/− recipients. Left: absolute numbers of recovered CD45.2⁺CD4⁺CD8⁻ TCR⁺ cells. Each point represents an individual mouse, and horizontal lines represent the mean number of CD4⁺ T cells recovered from positive mice; right: frequency of positive mice and numbers of CD45.2⁺CD4⁺CD8⁻ TCR⁺ cells recovered from positive mice. Data show means ± SEM from 3 independent experiments. (B) A total of 5 × 10² to 5 × 10⁶ CD4⁺ T cells from CD45.2 NOD mice was labeled with CFSE and transferred into CD45.1 NOD Cα^−/− mice. Proportion of CD45.2⁺ CFSE⁻ CD4⁺ T cells expressing Foxp3. Results are from 2 independent experiments. The gray area represents the mean ± SEM proportion of Foxp3-expressing cells among CD4⁺ T cells from control NOD mice. ***P < .001; **P < .01; *P < .05.