Hyper-IgE syndrome (HIES) is a primary immunodeficiency characterized by atopic dermatitis associated with extremely high serum IgE levels and susceptibility to staphylococcal skin abscesses and pneumonia. Recent studies have identified dominant negative mutations in the signal transducer and activator of transcription 3 gene (STAT3) as a major molecular cause of classical hyper-IgE syndrome, but the molecular mechanisms underlying this syndrome remain unclear. We recently showed that the impaired development of interleukin 17 (IL-17)-producing T helper cells (Th17 cells) due to defective IL-6 and IL-23 signaling in T cells, and the impaired generation of induced regulatory T (iT(reg) ) cells from defective IL-10 signaling in dendritic cells, may account for the immunological abnormalities of hyper-IgE syndrome. These findings open up possibilities for exploring new approaches to the treatment of HIES patients.