Temporal overexpression of IL-22 and Reg3γ differentially impacts the severity of experimental autoimmune encephalomyelitis.

IL-22 is an alpha-helical cytokine which belongs to the IL-10 family of cytokines. IL-22 is produced by RORγt+ innate and adaptive lymphocytes, including ILC3, γδ T, iNKT, Th17 and Th22 cells and some granulocytes. IL-22 receptor is expressed primarily by non-haematopoietic cells. IL-22 is critical for barrier immunity at the mucosal surfaces in the steady state and during infection. Although IL-22 knockout mice were previously shown to develop experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS), how temporal IL-22 manipulation in adult mice would affect EAE course has not been studied previously. In this study, we overexpressed IL-22 via hydrodynamic gene delivery or blocked it via neutralizing antibodies in C57BL/6 mice to explore the therapeutic impact of IL-22 modulation on the EAE course. IL-22 overexpression significantly decreased EAE scores and demyelination, and reduced infiltration of IFN-γ+IL-17A+Th17 cells into the central nervous system (CNS). The neutralization of IL-22 did not alter the EAE pathology significantly. We show that IL-22-mediated protection is independent of Reg3γ, an epithelial cell-derived antimicrobial peptide induced by IL-22. Thus, overexpression of Reg3γ significantly exacerbated EAE scores, demyelination and infiltration of IFN-γ+IL-17A+ and IL-17A+GM-CSF+Th17 cells to CNS. We also show that Reg3γ may inhibit IL-2-mediated STAT5 signalling and impair expansion of Treg cells in vivo and in vitro. Finally, Reg3γ overexpression dramatically impacted intestinal microbiota during EAE. Our results provide novel insight into the role of IL-22 and IL-22-induced antimicrobial peptide Reg3γ in the pathogenesis of CNS inflammation in a murine model of MS.

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

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 subsequent Th17 cell activation. METHODS: Peripheral blood mononuclear cells (PBMCs) were purified using Ficoll-Paque from healthy donors. Monocytes were 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 and costimulatory molecules, production of cytokine subunits IL-23p19, IL-12p40, IL-12p35 and cytokine IL-23 via flow cytometry or real-time qPCR or ELISA. Finally, the phosphorylation of signaling molecules after curdlan stimulation was assessed using phospho-flow assays. RESULTS: IL-15 exposure suppressed IL-23 production by DCs. As a result, IL-15-exposed DCs suppressed IL-17 production by 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 by human DCs exposed to IL-15 compared with controls. These results may explain why IL-15-exposed DCs produce less IL-23 after 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 DCs against Th17 cell polarization, which suggests that IL-15 availability may affect CD4+ T cell-mediated protective immunity to fungal infections.