Interleukin-17A Serves a Priming Role in Autoimmunity by Recruiting IL-1ß-Producing Myeloid Cells that Promote Pathogenic T Cells.

Interleukin-17A (IL-17A) is a major mediator of tissue inflammation in many autoimmune diseases. Anti-IL-17A is an effective treatment for psoriasis and is showing promise in clinical trials in multiple sclerosis. In this study, we find that IL-17A-defective mice or mice treated with anti-IL-17A at induction of experimental autoimmune encephalomyelitis (EAE) are resistant to disease and have defective priming of IL-17-secreting γδ T (γδT17) cells and Th17 cells. However, T cells from Il17a-/- mice induce EAE in wild-type mice following in vitro culture with autoantigen, IL-1ß, and IL-23. Furthermore, treatment with IL-1ß or IL-17A at induction of EAE restores disease in Il17a-/- mice. Importantly, mobilization of IL-1ß-producing neutrophils and inflammatory monocytes and activation of γδT17 cells is reduced in Il17a-/- mice. Our findings demonstrate that a key function of IL-17A in central nervous system (CNS) autoimmunity is to recruit IL-1ß-secreting myeloid cells that prime pathogenic γδT17 and Th17 cells.

Loss of the molecular clock in myeloid cells exacerbates T cell-mediated CNS autoimmune disease.

The transcription factor BMAL1 is a core component of the molecular clock, regulating biological pathways that drive 24 h (circadian) rhythms in behaviour and physiology. The molecular clock has a profound influence on innate immune function, and circadian disruption is linked with increased incidence of multiple sclerosis (MS). However, the mechanisms underlying this association are unknown. Here we show that BMAL1 and time-of-day regulate the accumulation and activation of various immune cells in a CNS autoimmune disease model, experimental autoimmune encephalomyelitis (EAE). In myeloid cells, BMAL1 maintains anti-inflammatory responses and reduces T cell polarization. Loss of myeloid BMAL1 or midday immunizations to induce EAE create an inflammatory environment in the CNS through expansion and infiltration of IL-1ß-secreting CD11b+Ly6Chi monocytes, resulting in increased pathogenic IL-17+/IFN-γ+ T cells. These findings demonstrate the importance of the molecular clock in modulating innate and adaptive immune crosstalk under autoimmune conditions.

An Emerging Role for SNARE Proteins in Dendritic Cell Function.

Dendritic cells (DCs) provide an essential link between innate and adaptive immunity. At the site of infection, antigens recognized by DCs via pattern-recognition receptors, such as Toll-like receptors (TLRs), initiate a specific immune response. Depending on the nature of the antigen, DCs secrete distinct cytokines with which they orchestrate homeostasis and pathogen clearance. Dysregulation of this process can lead to unnecessary inflammation, which can result in a plethora of inflammatory diseases. Therefore, the secretion of cytokines from DCs is tightly regulated and this regulation is facilitated by highly conserved trafficking protein families. These proteins control the transport of vesicles from the Golgi complex to the cell surface and between organelles. In this review, we will discuss the role of soluble n-ethylmaleimide-sensitive factor attachment protein receptor proteins (SNAREs) in DCs, both as facilitators of secretion and as useful tools to determine the pathways of secretion through their definite locations within the cells and inherent specificity in opposing binding partners on vesicles and target membranes. The role of SNAREs in DC function may present an opportunity to explore these proteins as novel targets in inflammatory disease.

Soluble factors from colonic epithelial cells contribute to gut homeostasis by modulating macrophage phenotype.

Intestinal macrophages originate from inflammatory blood monocytes which migrate to the intestine, where they differentiate into anti-inflammatory macrophages through a number of transitional stages. These macrophages typically remain hypo-responsive to commensal bacteria and food Ags in the intestine, yet also retain the ability to react to invading pathogens. In this study we examined the role of epithelial cells in inducing this intestinal macrophage phenotype. Using an in vitro system we showed that, in two-dimensional culture, epithelial cell-derived factors from a murine cell line, CMT-93, are sufficient to induce phenotypic changes in macrophages. Exposure of monocyte-derived macrophages, J774A.1, to soluble factors derived from epithelial cells, induced an altered phenotype similar to that of intestinal macrophages with decreased production of IL-12p40, IL-6 and IL-23 and expression of MHC ІІ and CD80 following TLR ligation. Furthermore, these conditioned macrophages showed enhanced phagocytic activity in parallel with low respiratory burst and NO production, similar to the response seen in intestinal macrophages. Our findings suggest a role for colonic epithelial cells in modulation of macrophage phenotype for maintenance of gut homeostasis. Further understanding of the cell interactions that maintain homeostasis in the gut could reveal novel therapeutic strategies to restore the balance in disease.

Conjugated linoleic acid suppresses dendritic cell activation and subsequent Th17 responses.

PUFAs (polyunsaturated fatty acids) can modify immune responses, so they may have potential therapeutic effects in inflammatory disorders. We previously demonstrated that the cis-9, trans-11 isomer of the PUFA conjugated linoleic acid (CLA) can modulate dendritic cell (DC) cytokine production. Since DCs play a central role in initiating inflammation by directing T helper (Th) cell differentiation, here we examined the effects of CLA on DC maturation and migration and the subsequent generation of Th cell responses. We examined the effect of CLA in vitro on the function of lipopolysaccharide (LPS)-activated bone marrow-derived DCs and ex vivo using cells from mice with high levels of CLA in their diet. We report that CLA inhibits DC migration and modulates TLR-induced production of key cytokines involved in Th cell differentiation both in vitro and in vivo. These changes were accompanied by a significant decrease in expression of MHCII, CD80 and CD86 on the DC surface. Exposure of DCs to CLA suppressed their ability to promote differentiation of naïve T cells into Th1 and/or Th17 cells in vitro and following their adoptive transfer in vivo. Furthermore, in a murine model of endotoxic shock, treatment with CLA suppressed LPS-induced induction of circulating IFN-γ, IL-12p40 and IL-1ß. This is the first study to demonstrate that exposure of antigen-presenting cells to CLA can modulate the subsequent Th cell response, and the findings may explain some of the beneficial effects of c9, t11-CLA in inflammatory diseases mediated by Th1 and Th17 cells.

A role for syntaxin 3 in the secretion of IL-6 from dendritic cells following activation of toll-like receptors.

The role of dendritic cells (DCs) in directing the immune response is due in part to their capacity to produce a range of cytokines. Importantly, DCs are a source of cytokines, which can promote T cell survival and T helper cell differentiation. While it has become evident that soluble-N-ethylmaleimide-sensitive-factor accessory-protein receptors (SNAREs) are involved in membrane fusion and ultimately cytokine release, little is known about which members of this family facilitate the secretion of specific cytokines from DCs. We profiled mRNA of 18 SNARE proteins in DCs in response to activation with a panel of three Toll-like receptors (TLR) ligands and show differential expression of SNAREs in response to their stimulus and subsequent secretion patterns. Of interest, STX3 mRNA was up-regulated in response to TLR4 and TLR7 activation but not TLR2 activation. This correlated with secretion of IL-6 and MIP-1α. Abolishment of STX3 from DCs by RNAi resulted in the attenuation of IL-6 levels and to some extent MIP-1α levels. Analysis of subcellular location of STX3 by confocal microscopy showed translocation of STX3 to the cell membrane only in DCs secreting IL-6 or MIP-1α, indicating a role for STX3 in trafficking of these immune mediators. Given the role of IL-6 in Th17 differentiation, these findings suggest the potential of STX3 as therapeutic target in inflammatory disease.

Syntaxin-4 is essential for IgE secretion by plasma cells.

The humoral immune system provides a crucial first defense against the invasion of microbial pathogens via the secretion of antigen specific immunoglobulins (Ig). The secretion of Ig is carried out by terminally differentiated B-lymphocytes called plasma cells. Despite the key role of plasma cells in the immune response, the mechanisms by which they constitutively traffic large volumes of Ig out of the cell is poorly understood. The involvement of Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins in the regulation of protein trafficking from cells has been well documented. Syntaxin-4, a member of the Qa SNARE syntaxin family has been implicated in fusion events at the plasma membrane in a number of cells in the immune system. In this work we show that knock-down of syntaxin-4 in the multiple myeloma U266 human plasma cell line results in a loss of IgE secretion and accumulation of IgE within the cells. Furthermore, we show that IgE co-localises with syntaxin-4 in U266 plasma cells suggesting direct involvement in secretion at the plasma membrane. This study demonstrates that syntaxin-4 plays a critical role in the secretion of IgE from plasma cells and sheds some light on the mechanisms by which these cells constitutively traffic vesicles to the surface for secretion. An understanding of this machinery may be beneficial in identifying potential therapeutic targets in multiple myeloma and autoimmune disease where over-production of Ig leads to severe pathology in patients.