['The mechanisms by which human dendritic cells (DCs) activate a TH1-polarizing or TH2-polarizing program are still partially unclear.', 'Study of the mechanisms responsible for the TH1/TH2-polarizing activity of human circulating myeloid DCs before and after ligation of their Toll-like receptors (TLRs).', 'IL-4 and IFN-gamma production by CD4+ T cells was assessed in cocultures with myeloid DCs before or after TLR triggering. Expression of Jagged-1 and Delta-4 Notch ligands and of GATA-3 and T-box expressed in T cells transcription factors was evaluated by real-time quantitative PCR. Signal transducer and activator of transcription 4 and 6 phosphorylation was assessed by flow cytometry. Knockdown of Jagged-1 or Delta-4 was performed by transfection of DCs with appropriate silencing mRNAs.', 'Myeloid immature DCs constitutively expressed Jagged-1, which induces in CD4+ T cells a TH2 polarization, as shown by Jagged-1 gene silencing. The TH2 polarization associated with high GATA-3/T-box expressed in T cells ratio and was at least partially dependent on the early induction of IL-4. Maturation of DCs by TLR ligation resulted in the reduction of Jagged-1 and upregulation of Delta-4, which was at least in part responsible for the polarization of CD4+ T cells to the TH1 phenotype.'] Do human immature myeloid dendritic cells trigger a TH2-polarizing program via Jagged-1/Notch interaction?