T reg cell development in days 4 and 10 neonates. T reg cell frequencies among CD4⁺ cells have been measured in thymi, spleens, and intestines of day 4 (A) and day 10 (B) foxp3^CNS1mut and foxp3^WT mice. Data on day 4 T reg cell frequencies are representative of 6 foxp3^CNS1mut and 10 foxp3^WT mice and two independent experiments. Data on day 10 T reg cell frequencies in thymus and spleen are representative of 10 foxp3^CNS1mut and 13 foxp3^WT males and four independent experiments. Data for day 10 T reg cell frequencies in intestine are representative of six foxp3^CNS1mut and eight foxp3^WT males and two independent experiments. Error bars indicate means ± SEM.