Mitigated thymic involution in TGFβRII^lox/lox::Foxn1 Cre mice. (A) Thymic cellularity in prepubescent, adolescent, and adult mice either deficient (▵) or proficient (●) for TGF-β signaling in TECs. Each symbol denotes the average of 2 or more mice of the respective genotype of the same litter at the indicated age. A logarithmic regression curve was calculated for TGFβRII^lox/lox::Foxn1-Cre (broken line) and TGFβRII^lox/lox (solid line). Using a paired t test, a significant difference in thymic cellularity between the 2 mouse strains is represented by the horizontal bar in the upper part of the graph. (B) Ratio of thymic cellularity between TGFβRII^lox/lox::Foxn1-Cre and TGFβRII^lox/lox littermates displayed for 5 separate age groups; n denotes the number of litters per age group analyzed (with ≥ 2 animals per litter and genotype). The broken horizontal line represents the values of TGFβRII^lox/lox mice normalized to 1. The white line in each bar represents the mean, the bar represents the 25th percentile, and the whiskers represent the 75th percentile. P values were calculated using a paired t test. (C) Total thymic cellularity of 2dGuo-depleted thymic grafts from E12.5 TGFβRII^lox/lox::Hoxa3Cre (□, n = 6) and TGFβRII^lox/lox (■, n = 10) embryos grafted into syngeneic nu/nu mice and analyzed 12 weeks later (P value obtained using a nonparametric U test). This experiment was independently performed 4 times with similar results. Error bars represent SD.