Stat6 is necessary and sufficient for IL-4's role in Th2 differentiation and cell expansion

IL-4 plays a critical role in the differentiation of TCR-stimulated naive C D4 T cells to the Th2 phenotype. In response to IL-4, the IL-4R activates a set of phosphotyrosine binding domain-containing proteins, including insul in receptor substrate 1/2, Shc, and IL-4R interacting protein, as well as S tat6. Stat6 has been shown to be required for Th2 differentiation. To deter mine the roles of the phosphotyrosine binding adaptors in Th2 differentiati on, we prepared a retrovirus containing a mutant of the human (h)IL-4R alph a -chain, Y497F, which is unable to recruit these adaptors. The mutant hIL- 4R alpha, as well as the wild-type (WT) hIL-4R alpha, was introduced into n aive CD4 T cells. Upon hIL-4 stimulation, Y497F worked as well as the WT hI L-4R alpha in driving Th2 differentiation, as measured by Gata3 up-regulati on and IL-4 production. Furthermore, IL-4-driven cell expansion was also no rmal in the cells infected with Y497F, although cells infected with Y497F w ere not capable of phosphorylating insulin receptor substrate 2. These resu lts suggest that the signal pathway mediated by Y497 is dispensable for bot h IL-4-driven Th2 differentiation and cell expansion. Both WT and Y497F hIL -4R alpha lose the ability to drive Th2 differentiation and cell expansion in Stat6-knockout CD4 T cells. A constitutively activated form of Stat6 int roduced into CD4 T cells resulted in both Th2 differentiation and enhanced cell expansion. Thus, activated Stat6 is necessary and sufficient to mediat e both IL-4-driven Th2 differentiation and cell expansion in CD4 T cells.