Androgen withdrawal increases UEA⁺ thymic epithelial cell proliferation. Six-week-old male mice were treated with 2 mg of BrdU i.p. on day 1 and 0.08% BrdU p.o. continuously for 7 days after castration or sham castration. Data represent 5 experiments with 3 thymi pooled per group for digestion. TEC populations were enumerated by flow cytometry, with medullary TEC defined as CD45⁻ UEA⁺, cortical TEC as CD45⁻ Ly51⁺, and a double-negative population of CD45⁻ UEA⁻ Ly51⁻. Representative flow cytometry plots are shown for gating of CD45 negative population (A) and discrimination of medullary and cortical populations within the CD45⁻ population (B). BrdU-negative populations were defined using a noncastrated control group that underwent TEC preparation and were stained with BrdU antibody but did not receive exogenous BrdU. (C) Graph represents the mean frequency of BrdU + populations with standard error bars.