TSLP signaling in CD4+ T cells programs a pathogenic T helper 2 cell state

Pathogenic T helper 2 (T(H)2) cells, which produce increased amounts of the cytokines interleukin-5 (IL-5) and IL-13, promote allergic disorders, including asthma. Thymic stromal lymphopoietin (TSLP), a cytokine secreted by epithelial and innate immune cells, stimulates such pathogenic T(H)2 cell responses. We found that TSLP signaling in mouse CD4(+) T cells initiated transcriptional changes associated with T(H)2 cell programming. IL-4 signaling amplified and stabilized the genomic response of T cells to TSLP, which increased the frequency of T cells producing IL-4, IL-5, and IL-13. Furthermore, the TSLP-and IL-4-programmed T(H)2 cells had a pathogenic phenotype, producing greater amounts of IL-5 and IL-13 and other proinflammatory cytokines than did T(H)2 cells stimulated with IL-4 alone. TSLP-mediated T(H)2 cell induction involved distinct molecular pathways, including activation of the transcription factor STAT5 through the kinase JAK2 and repression of the transcription factor BCL6. Mice that received wild-type CD4(+) T cells had exacerbated pathogenic T(H)2 cell responses upon exposure to house dust mites compared to mice that received TSLP receptor-deficient CD4(+) T cells. Transient TSLP signaling stably programmed pathogenic potential in memory T(H)2 cells. In human CD4(+) T cells, TSLP and IL-4 promoted the generation of T(H)2 cells that produced greater amounts of IL-5 and IL-13. Compared to healthy controls, asthmatic children showed enhancement of such T cell responses in peripheral blood. Our data support a sequential cytokine model for pathogenic T(H)2 cell differentiation and provide a mechanistic basis for the therapeutic targeting of TSLP signaling in human allergic diseases.