Kinetics of TEC regeneration following surgical castration of aged mice. (A) Total thymic cellularity and TEC number at various time points after castration or sham-castration of 10-monthold mice. (B) Dot plots of MHC II versus Ly51 expression on TECs (CD45^–EpCAM⁺) from castrated or sham-castrated mice at various time points following surgery. Histograms show Ki67 expression on TECs with numbers showing the frequency of Ki67⁺ TECs. All sham-castrated controls showed similar profiles and proportions to the day 3 control shown. (C) Total thymic and TEC number of castrated or sham-castrated 4-month-old RAG^–/– mice 28 days after surgery. Means and standard errors are shown for all graphs from 5 mice per group, and a Student t test was used to determine statistical significance (*P < .05, **P < .01, ***P < .001).