Whereas recent research has characterized the mechanism by which dendritic cells (DCs) induce T(H)1/T(H)17 responses, the functional specialization enabling DCs to polarize T(H)2 responses remains undefined. Because IL-4 is essential during T(H)2 responses not only by acting on CD4(+) T cells through the activation of GATA-3 but also by regulating IgE class-switching, epithelial cell permeability, and muscle contractility, we hypothesized that IL-4 could also have a role in the conditioning of DCs during T(H)2 responses.