TI - TSLP induced weak STAT1 and STAT5 activation and improved cell survival of naive CD4+ T cells . AB - Because anti-CD3 and anti-CD28 mAbs can induce low levels of TSLPR expression in naive CD4+ T cells , we further examined whether TSLP could induce the signal transduced by the TSLPR complex . Naive CD4+ T cells were activated by anti-CD3 and anti-CD28 mAbs for 4 d and then cultured with medium alone , with IL-2 , IL-4 , IL-7 , TSLP alone , or in the presence of an isotype control or neutralizing mAbs against IL-4 or TSLP . Activation of STAT family molecules in the T cells after 20 min of culture was examined by Western blot analysis . We found that all of the cytokines investigated , IL-2 , IL-4 and IL-7 , induced strong PHOSphorylation of multiple STAT proteins ( Fig 4 C ) . In contrast , TSLP only induced a very weak PHOSphorylation of STAT1 and STAT5 , which was blocked by the TSLP-neutralizing mAb but not by the IL-4-neutralizing mAb or the isotype control , which confirms a recent study . Because STAT5 activation in T cells has been linked with improved cell survival that is uncoupled with cell proliferation , we further examined whether TSLP could improve the survival of naive CD4+ T cells activated by anti-CD3 and anti-CD28 mAbs . Naive CD4+ T cells were cultured with anti-CD3 and anti-CD28 mAbs for 4 d . Cells were washed and then cultured for 8 d with medium alone or with IL-7 , TSLP or TSLP and IL-7 ( Fig 4 , A and B ) . Viable and apoptotic cells were analyzed by propidium iodide ( PI ) and annexin V staining at different time points of culture ( Fig 4 A ) . We found that IL-7 could greatly maintain the survival of activated CD4+ T cells for up to 8 d , whereas TSLP could only marginally improve the survival of activated CD4+ T cells ( Fig 4 , A and B ) .