Hyper-IgE syndrome (HIES) is a primary immunodeficiency characterized by recurrent staphylococcal infections and atopic dermatitis associated with elevated serum IgE levels. Although defective differentiation of IL-17-producing CD4(+) T cells (Th17) partly accounts for the susceptibility to staphylococcal skin abscesses and pneumonia, the pathogenesis of atopic manifestations in HIES still remains an enigma. In this study, we examined the differentiation and function of Th1, Th2, regulatory T cells (T(reg) cells), and dendritic cells (DCs) in HIES patients carrying either STAT3 or TYK2 mutations. Although the in vitro differentiation of Th1 and Th2 cells and the number and function of T(reg) cells in the peripheral blood were normal in HIES patients with STAT3 mutations, primary and monocyte-derived DCs showed defective responses to IL-10 and thus failed to become tolerogenic. When treated with IL-10, patient DCs showed impaired up-regulation of inhibitory molecules on their surface, including PD-L1 and ILT-4, compared with control DCs. Moreover, IL-10-treated DCs from patients displayed impaired ability to induce the differentiation of naive CD4(+) T cells to FOXP3(+) induced T(reg) cells (iT(reg) cells). These results suggest that the defective generation of IL-10-induced tolerogenic DCs and iT(reg) cells may contribute to inflammatory changes in HIES.