The role of thymic stromal lymphopoietin in CD8+ T cell homeostasis.

Thymic stromal lymphopoietin (TSLP) is a cytokine produced by stromal cells, epithelial cells, and basophils that acts on dendritic cells, mast cells, and CD4(+) T cells. The receptor for TSLP contains a TSLP-specific receptor chain (TSLPR) and the IL-7R alpha-chain. Although IL-7 critically controls the expansion and survival of naive and memory CD8(+) T cells, an action for TSLP on CD8(+) T cells has not been reported. We now demonstrate that CD8(+) T cells express TSLPR and that TSLP activates both STAT5 and Akt and induces Bcl-2 in these cells. Correspondingly, TSLP increases CD8(+) T cell survival in vitro as well as in wild-type and T-depleted mice in vivo, without altering the homeostatic proliferation of these cells. Moreover, TSLP can maintain CD8(+) T cells even in the absence of IL-7. Thus, our data reveal that TSLP contributes to CD8(+) T cell homeostasis in both normal and lymphopenic conditions.