T-lymphopoiesis is inhibited at an early stage in thymocyte maturation in TSLP transgenic mice. (A) The top row shows plots that were generated by gating on viable cells. The normal distribution of thymocytes is altered in TG mice compared with LM controls. In LM controls (upper left), the DP thymocytes constitute the majority of the cells in thymus, whereas in TG mice (upper right), the majority of cells are in the CD4 and CD8 single-positive populations. The plot for DN thymocytes was generated by gating on viable CD4/CD8 DN cells. Each DN thymocyte subpopulation (I-IV) is present in the LM controls (lower left). There is a maturation arrest at the DN II stage of thymocytes development in TG mice (lower right). Note: These plots represent experiments performed on mice killed at 5 weeks of age. (B) Total numbers of thymocytes from TG and LM thymus. Compared to the LM controls, *TG mice have significantly fewer DN thymocytes (i; P = .004); DP thymocytes (ii; P = .002); CD4 single-single positive cell (iii; P = .002); and CD8 single-positive cells (iv; P = .004). The results are presented as the average number of thymocytes ± SEM (n = 6 and n = 7 for TG and LM mice, respectively).