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

Pathogenic T helper 2 (T2) 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 T2 cell responses. We found that TSLP signaling in mouse CD4 T cells initiated transcriptional changes associated with T2 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 T2 cells had a pathogenic phenotype, producing greater amounts of IL-5 and IL-13 and other proinflammatory cytokines than did T2 cells stimulated with IL-4 alone. TSLP-mediated T2 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 T2 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 T2 cells. In human CD4 T cells, TSLP and IL-4 promoted the generation of T2 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 T2 cell differentiation and provide a mechanistic basis for the therapeutic targeting of TSLP signaling in human allergic diseases.