IL-4/IL-13 Signaling Inhibits the Potential of Early Thymic Progenitors To Commit to the T Cell Lineage.

Early thymic progenitors (ETPs) are endowed with diverse potencies and can give rise to myeloid and lymphoid lineage progenitors. How the thymic environment guides ETP commitment and maturation toward a specific lineage remains obscure. We have previously shown that ETPs expressing the heteroreceptor (HR) comprising IL-4Rα and IL-13Rα1 give rise to myeloid cells but not T cells. In this article, we show that signaling through the HR inhibits ETP maturation to the T cell lineage but enacts commitment toward the myeloid cells. Indeed, HR ETPs, but not HR ETPs, exhibit activated STAT6 transcription factor, which parallels with downregulation of Notch1, a critical factor for T cell development. Meanwhile, the myeloid-specific transcription factor C/EBPα, usually under the control of Notch1, is upregulated. Furthermore, in vivo inhibition of STAT6 phosphorylation restores Notch1 expression in HR ETPs, which regain T lineage potential. In addition, upon stimulation with IL-4 or IL-13, HR ETPs expressing virally transduced HR also exhibit STAT6 phosphorylation and downregulation of Notch1, leading to inhibition of lymphoid, but not myeloid, lineage potential. These observations indicate that environmental cytokines play a role in conditioning ETP lineage choice, which would impact T cell development.