Role of IL-31 in dendritic cells

IL-31 is a recently identified cytokine which is mainly produced by activated T cells. The activity of IL-31 is mediated through a heterodimeric receptor complex (IL-31R) composed of the oncostatin M receptor beta-subunit (OSMR ) and IL-31Ralpha (IL-31RA) The biological function of IL-31 was mainly analysed in skin diseases such as atopic dermatitis, in which a correlation of IL-31 with the severity of the diseases was observed. Moreover, IL- 31/IL-31R interactions were reported to negatively regulate type 2 inflammation in the lung. Based on these studies and on receptor expression analyses, IL-31 was so far thought to preferentially mediate interactions between T cells and epithelial cells. In this study we show for the first time that dendritic cells are a potential target of IL-31, too. Stimulation of dendritic cells with IFN-gamma results in significantly enhanced IL-31R expression. As a consequence, dendritic cells become sensitive for IL-31. IL-31 treated dendritic cells provide so far unknown signals to T cells which promote the generation of IL-17 producing Th17 cells and IFN-gamma producing Th1 cells. Simultaneously, the production of typical Th2 cytokines IL-4, IL-5 and IL-13 seems to be suppressed. To confirm our preliminary observations, the current project will mainly address three topics: 1) Characterise the expression of the IL-31R complex on dendritic cells 2) Investigate IL-31 expression in T cells 3) Analyse effects of IL-31 on dendritic cells for T cell activation. Since Th2 cells are the main source of IL-31, our data suggest a so far unknown negative feedback loop for Th2 responses, induced by IL-31/IL-31R interactions on dendritic cells. The current project will also contribute to a better understanding of mechanisms underlying the development and differentiation of Th17 cells. This is of particular interest, since the identification of Th17 cells as a new subset of CD4 + T cells has helped to clarify many unresolved questions regarding the regulation and deregulation of immune responses.

Interleukin-31 (IL-31) is a T cell-derived cytokine that signals via a hetero-dimeric receptor, composed of IL-31RA and OSMRB. Although several studies aimed at the investigation of IL-31 mediated effects, the biological functions of this cytokine are at present not well understood. IL-31 expression correlates with the expression of IL-4 and IL-13 and is associated with atopic dermatitis in humans. This indicates that IL-31 is involved in Th2-mediated skin-inflammation. However, recent in vivo experiments employing IL-31RA-/- mice show that IL-31RA signalling limits the magnitude of Th2 responses in the lung and in the intestine.On the basis of these findings we raised the issue whether dendritic cells, the main activators of Th cell responses, express the IL-31 receptor complex and govern immune responses triggered by IL-31. In the current study we report that primary human CD1c+ as well as monocyte-derived dendritic cells significantly up-regulate the IL-31 receptor upon stimulation with IFN-gamma. EMSA studies and siRNA based silencing assays revealed STAT1 as the main transcription factor, involved in the upregulation of IL-31RA. This indicates that IFN-gamma/STAT1 signalling renders dendritic cells responsive to IL-31. As IL-31 is one of the latest additions to the list of T-cell-derived cytokines, we next investigated the expression of IL-31 in human CD4+Th cells in more detail. First studies showed that Th2 cells might be regarded as a main source of IL-31, because it is mainly produced in response to stimulation by IL-4. However, besides Th2 cells, the development of Th9 cells also requires IL-4 as a polarizing cytokine. Thus, we further aimed to investigate IL-31 production in human Th9 cells compared to Th2 cells. We found that, although Th9 cells were able to release IL-31 during the first weeks of in vitro polarization, no IL-31 was detected in Th9 cultures after a final re-stimulation in the absence of polarizing cytokines. We further show that TGF-?, which is required to obtain Th9 cells in vitro, potently inhibits the release of IL-31 from Th2 cells in a dose-dependent way, whereas IL-33, a cytokine associated with Th2-mediated inflammation, synergizes with IL-4 in inducing IL-31 secretion. To analyze the molecular mechanisms underlying the induction of IL-31, electrophoretic mobility shift assays, reporter gene assays and siRNA-based silencing experiments were carried out. We show that STAT6 and NF-?B are central players in mediating IL-31 expression induced by IL-4/IL-33. In addition, we identified a novel NF-?B-binding element within the Il31 promoter that mediates the enhancing effects of IL-33 on IL-4/STAT6-induced IL-31 expression in human Th2 cells.Taken together, this study provides novel insights in the molecular regulation of IL-31 and its cognate receptor and describes human DCs as novel target for IL-31 activation. In addition, we show that the pro-allergic cytokine IL-4 is crucial for the expression of IL-31, whereas TGF-? significantly suppresses IL-31 expression and counter-regulates the effects of IL-4 and IL-33.