Résumé
The λ interferons (IFN-λs), also known as IL-28 and IL-29, are coexpressed with IFN-β after Toll-like–receptor (TLR) stimulation in human monocyte–derived dendritic cells (DCs). IFN-λ shares with type I IFNs an intracellular signaling pathway that drives the expression of a common set of genes. However, IFN-λ signaling is initiated through a membrane receptor system distinct from that of type I IFNs. Because IFNs produced by DCs in response to TLR stimulation are critical in the differentiation and maturation of DCs, we sought to investigate whether IFN-λ exhibits specific effects on DC differentiation. In this work, we show that DCs acquire IFN-λ responsiveness through the expression of the specific IFN-λ receptor chain during their differentiation from monocytes. IFN-λ–treated DCs express high levels of major histocompatibility complex class I (MHC class I) and MHC class II but low levels of costimulatory molecules. However, they express CCR7 and acquire the ability to migrate to lymph nodes when intravenously injected into SCID/Bg mice. In mixed lymphocyte reaction (MLR) cultures, IFN-λ–treated DCs specifically induced IL-2–dependent proliferation of a CD4+CD25+Foxp3+ T-cell subset with contact-dependent suppressive activity on T-cell proliferation initiated by fully mature DCs. IFN-λs are thus able to generate tolerogenic DCs, an activity that could thwart IFN-β functions.