Androgen withdrawal leads to enhanced thymic activity with increased thymic TREC, splenic subsets, and splenic TREC. Mice were killed at 8 days, 1 month, and 3 months after castration, and thymic (A) and splenic TREC (B) was enumerated by real-time PCR (6-12 mice/group). (A) By 1 week after castration, thymic TREC was increased (P < .02) and persisted for 3 months compared with sham-castrated control mice. (B) One month after androgen withdrawal, enhanced thymic activity was reflected in increased splenic TREC (P < .03). Splenic subsets demonstrated increased CD4⁺ (C) and CD8⁺ (D) subsets 1 month after androgen withdrawal compared with control mice (6-12 mice/group). Persistent increase in CD4⁺ splenocytes was seen at 3 months after castration as well.