TSLP does not affect the proliferation and survival of CD4+CD25- or CD4+CD25+ thymocytes in vitro. A. Lack of proliferation of thymocytes in the absence or presence of TSLP. Total thymocytes from 4–6 weeks old mice were pre-labeled with CSFE, and then cultured with or without TSLP (100 ng/ml) for two days. Thymocytes were analyzed for CD4, CD8, CD25 and CFSE by FACS. Relative CFSE levels on CD25- and CD25+ SP thymocytes (CD4+ SP and CD8+ SP) were measured. No significant proliferation was detected in these thymocytes under the culture conditions. B. TSLP does not affect apoptosis of thymocytes. Total adult thymocytes were cultured with or without TSLP for 2 days. Annexin V+ cells in the CD4+CD25- and CD4+CD25+ populations are shown by FACS analysis. Similar results were obtained in three independent experiments.