TSLP specifically enhances FoxP3 expression in CD4+CD8- thymocytes. A: TSLP induced expression of FoxP3 in SP4, but not DP, DN and SP8 thymocytes. Purified adult thymocyte subsets were cultured with TSLP and analyzed for FoxP3 expression by RT-PCR. Relative expression of FoxP3 is shown.B: TSLP induced expression of FoxP3 in both CD4+CD8-CD25- and CD4+CD8-CD25+ SP4 thymocytes. Purified thymocytes were cultured and analyzed as above. No FoxP3 gene expression is detectable with or without TSLP in CD4-CD8+CD25+ or CD4-CD8+CD25- SP8 thymocytes.