IL-15 negatively regulates curdlan-induced IL-23 production by human monocyte-derived dendritic cells and subsequent Th17 response

Abstract

OBJECTIVE: In this study, we aimed to assess the effects of long- and short-term IL-15 cytokine exposure of human monocyte-derived curdlan-matured dendritic cells (DCs) on the production of Th17 cell-polarizing cytokine IL-23 and subsequentTh17 cell activation.METHODS: Peripheral blood mononuclear cells (PBMCs) were purified using Ficoll-Paque from healthy donors. Monocyteswere magnetically selected using CD14 Miltenyi beads and differentiated into DCs with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4 for five days in the presence or absence of IL-15 (100ng/ml) for long-term exposure experiments. Then, DCs were matured with peptidoglycan (PGN), or curdlan for 24 hours. For short-term exposure experiments,IL-15 was added only during maturation of DCs. Then, DCs were characterized concerning the expression of MHC II andcostimulatory molecules, production of cytokine subunits IL-23p19, IL-12p40, IL-12p35 and cytokine IL-23 via flow cytometryor real-time qPCR or ELISA. Finally, the phosphorylation of signaling molecules after curdlan stimulation was assessed usingphospho-flow assays.RESULTS: IL-15 exposure suppressed IL-23 production by DCs. As a result, IL-15-exposed DCs suppressed IL-17 productionby allogeneic T cells. Importantly, we observed a reduction in the surface Dectin-1 receptor levels by IL-15-exposed DCs.In line with these observations, curdlan stimulation resulted in reduced phosphorylation of ERK1/2, NF-kB p65 and AKT byhuman DCs exposed to IL-15 compared with controls. These results may explain why IL-15-exposed DCs produce less IL-23after maturation with curdlan, which is a ligand of Dectin-1.CONCLUSION: Short- or long-term exposure to IL-15 of human DCs during their differentiation or maturation programs DCsagainst Th17 cell polarization, which suggests that IL-15 availability may affect CD4+ T cell-mediated protective immunity tofungal infections.