A 3′ enhancer in the IL-4 gene regulates cytokine production by Th2 cells and mast cells

Differentiation of naive T cells into mature Th2 cells is associated with the appearance of a complex pattern of DNase I hypersensitive (DH) sites within the IL-4/IL-13 cytokine gene cluster. We show here that targeted deletion of an inducible DH site, V-A, and the adjacent conserved DH site V (CNS-2) selectively compromises IL-4 gene transcription by differentiated Th2 cells and mast cells. In mast cells, the deletion abrogates IL-4 mRNA induction, an effect mimicked by deletion of the transcription factor NFAT1 (NFATc2), which binds DH site VA. In T cells, the deletion impairs a process of response maturation, defined by progressive increases in IL-4 levels as Th2 differentiation proceeds. These results identify an essential enhancer which regulates IL-4 gene expression in two important cell lineages in vivo.