3a,c). However, the absolute cell numbers were reduced in both naive and memory/effector T lymphocytes from control and Stat3 knockout cells (Fig. 3d,e). These data suggest that Stat3 plays crucial roles in the maintenance of not only naive but also memory/effector

selleck screening library T cells. Both the per cent population and the absolute cell numbers of the CD4 or CD8 SP population in thymocytes was significantly reduced in T-cell-specific Stat3-deficient mice at the age of 6 months, whereas those of CD4+ CD8+ double-positive cells were unvarying between both groups (Fig. 4a–c). However, the populations of double-positive, CD4 SP and CD8 SP showed negligible differences between control and Stat3 knockout mice at 4 or 8 weeks of age (data not shown). Next, we investigated whether the decrease of SP cells resulted from the enhanced susceptibility to apoptosis. The annexin V-positive population in CD4 or CD8 SP thymocytes was ~ 45% higher in Stat3-deficient mice compared with control mice (Fig. 4d). We further examined the expression

level of pro-survival Bcl-2 and Bcl-xL in SP thymocytes by flow cytometry analyses. Both Bcl-2 and Bcl-xL expression were significantly decreased in both CD4 and CD8 SP thymocytes from Stat3-deficient cells compared with the control mice (Fig. 4e). The expression of Bcl-2 family genes may be important for the survival of CD4 or CD8 SP thymocytes. These results collectively imply that Stat3 contributes the maintenance of SP thymocytes by promoting the expression next of anti-apoptotic Bcl-2 GS-1101 in vivo and Bcl-xL genes. To identify the role of Stat3 in thymic selection, we performed flow cytometry analyses of various T-cell receptor vβ chain in thymocytes or splenocytes. The population of T-cell receptor vβ4, 5, 6, 11 or 13 expressing cells in CD4 or CD8 SP cells in thymus was unvarying in Stat3 knockout mice compared with wild-type littermates (see Supplementary material, Fig. S3a,b), which was also observed in splenic

T cells (Fig. S3a,c). To determine whether the deficiency in T cells in Stat3-deficient mice was attributable to an altered proliferation rate in T lymphocytes, we conducted in vivo BrdU incorporation assays. The proportion of BrdU-stained cells in CD3-positive populations was similar in Stat3-deficient mice and control mice (Fig. 5a). We next performed annexin V analysis and TUNEL assays to determine whether the T-cell deficiency in Stat3-deficient mice was a result of apoptosis. The annexin V-positive population in splenic T cells was ~ 75% higher in Stat3-deficient mice compared with control mice (Fig. 5b). In addition, numbers of TUNEL-positive apoptotic cells among splenic T cells were considerably increased in Stat3-deficient mice (Fig. 5c,d). These data suggest that Stat3 plays a pivotal role in preventing apoptosis in T lymphocytes.