Dendritic Cells Mediate the Dual Effects of IFN alpha/beta in HCV Immunity

Hepatitis C virus (HCV) infects an estimated 170 million people and is responsible for considerable morbidity and mortality worldwide. Successful resolution of infection is achieved naturally in approximately 30% of infected individuals and correlates with a strong T cell response. Furthermore, treatment with interferon (IFN)a achieves sustained virologic response in approximately 50% of chronically infected individuals. Conventional dendritic cells (cDCs), as the most potent antigen presenting cells, and plasmacytoid DCs (pDCs), as the principal IFNa/|3 producing cells, serve as potential targets for both immune evasion and therapeutic strategies. In order to evaluate the effects of HCV on DC function, we compared phenotypic and functional characteristics of DCs from chronically infected patients to DCs from healthy donors. Our results suggest that despite non-specific decreases in total numbers, DC phenotypic and functional integrity is maintained. Consequently, we propose that other factors associated with HCV immunity may act on DCs to regulate pathogenesis and immunity. In light of the important roles of IFNa/p and CD4+ T cells in the clinical response to HCV, we focused on the interplay of these factors with DCs during CD8+ T cell priming. Using a human in vitro cross-presentation system, we found that IFNa/p acts on immature DCs (iDCs) to inhibit CD8+ T cell activation by cross-presentation. Further analysis revealed that ST ATIdependent inhibition of CD40-induced IL-12 was responsible for this block. In contrast, a switch from STAT1 to STAT4 signaling enabled an immune enhancing effect of IFNa/p on mature DCs (mDCs) that potentiated CD8+ T cell activation. In order to evaluate this latter effect in vivo, we monitored the ability of pDC IFNa/p production to substitute for CD4+ T cells in CD8+ T cell priming. The results revealed that pDC activation overcomes the need for CD4 \u27help\u27 in priming CD8+ T cell responses in an IFNa/p receptor-dependent manner. Importantly, IFNa/p produced by non-pDCs did not provide similar priming signals. These results provide support for HCV immunotherapy trials and offer a unique mechanism to account for the dual effects of IFNa/p in pathogenesis and immunity

Plasmacytoid dendritic cells initiate a complex chemokine and cytokine network and are a viable drug target in chronic HCV patients

Plasmacytoid dendritic cells (pDCs) are the professional type I interferon (IFN)-producing cells, and upon activation they traffic to lymph organs, where they bridge innate and adaptive immunity. Using multianalyte profiling (MAP), we have mapped the key chemokines and cytokines produced in response to pDC activation, taking into consideration the role of autocrine IFN, as well as paracrine effects on other innate cells (e.g., monocytes and conventional DCs). Interestingly, we identify four distinct cytokine/chemokine loops initiated by Toll-like receptor engagement. Finally, we applied this analytic approach to the study of pDC activity in chronic hepatitis C patients. Based on the activation state of pDCs in fresh blood, the lack of agonistic activity of infectious virions, the production of a broad array of cytokines/chemokines once stimulated, and the direct effects of pDCs on other PBMCs, we conclude that the pDCs from hepatitis C virus (HCV)-infected individuals are fully functional and are, indeed, a viable drug target. In sum, this study provides insight into the use of MAP technology for characterizing cytokine networks, and highlights how a rare cell type integrates the activation of other inflammatory cells. Furthermore, this work will help evaluate the therapeutic application of pDC agonists in diseases such as chronic HCV infection

Expansion of intestinal Prevotella copri correlates with enhanced susceptibility to arthritis

Rheumatoid arthritis (RA) is a prevalent systemic autoimmune disease, caused by a combination of genetic and environmental factors. Animal models suggest a role for intestinal bacteria in supporting the systemic immune response required for joint inflammation. Here we performed 16S sequencing on 114 stool samples from rheumatoid arthritis patients and controls, and shotgun sequencing on a subset of 44 such samples. We identified the presence of Prevotella copri as strongly correlated with disease in new-onset untreated rheumatoid arthritis (NORA) patients. Increases in Prevotella abundance correlated with a reduction in Bacteroides and a loss of reportedly beneficial microbes in NORA subjects. We also identified unique Prevotella genes that correlated with disease. Further, colonization of mice revealed the ability of P. copri to dominate the intestinal microbiota and resulted in an increased sensitivity to chemically induced colitis. This work identifies a potential role for P. copri in the pathogenesis of RA. DOI: http://dx.doi.org/10.7554/eLife.01202.00

Dietary L-Tryptophan Consumption Determines the Number of Colonic Regulatory T cells and Susceptibility to Colitis via GPR15

Environmental factors are the major contributor to the onset of immunological disorders such as ulcerative colitis. However, their identities remain unclear. Here, we discover that the amount of consumed L-Tryptophan (L-Trp), a ubiquitous dietary component, determines the transcription level of the colonic T cell homing receptor, GPR15, hence affecting the number of colonic FOXP3+ regulatory T (Treg) cells and local immune homeostasis. Ingested L-Trp is converted by host IDO1/2 enzymes, but not by gut microbiota, to compounds that induce GPR15 transcription preferentially in Treg cells via the aryl hydrocarbon receptor. Consequently, two weeks of dietary L-Trp supplementation nearly double the colonic GPR15+ Treg cells via GPR15-mediated homing and substantially reduce the future risk of colitis. In addition, humans consume 3–4 times less L-Trp per kilogram of body weight and have fewer colonic GPR15+ Treg cells than mice. Thus, we uncover a microbiota-independent mechanism linking dietary L-Trp and colonic Treg cells, that may have therapeutic potential

A two-step induction of indoleamine 2,3 dioxygenase (IDO) activity during dendritic-cell maturation

Prostaglandins, a family of lipidic molecules released during inflammation, display immunomodulatory properties in several models. One use includes exposure of monocyte-derived dendritic cells (DCs) to a cocktail of cytokines that contains prostaglandin E2 (PGE2) for purposes of maturation; such cells are currently being used for cancer immunotherapy trials. Our analysis of the transcription profile of DCs matured in the presence of tumor necrosis factor α (TNFα) and PGE2 revealed a strong up-regulation of indoleamine 2-3 dioxygenase (IDO), an enzyme involved in tryptophan catabolism and implicated in both maternal and T-cell tolerance. Using quantitative assays to monitor levels of IDO mRNA, protein expression, and enzyme activity, we report that PGE2 induces mRNA expression of IDO; however, a second signal through TNF receptor (TNF-R) or a Toll-like receptor (TLR) is necessary to activate the enzyme. Interestingly, use of TNFα, lipopolysaccharide, or Staphylococcus aureus Cowan I strain (SAC) alone does not induce IDO. The effect of PGE2 is mediated by activation of adenylate cyclase via the Gs-protein-coupled receptor E prostanoid-2 (EP2). A better understanding of these regulatory mechanisms and the crosstalk between TNF-R/TLR and EP2 signaling pathways will provide insight into the regulation of T-cell activation by DCs and may help to improve existing immunotherapy protocols

Live attenuated yellow fever 17D infects human DCs and allows for presentation of endogenous and recombinant T cell epitopes.

International audienceThe yellow fever (YF) 17D vaccine is one of the most successful live attenuated vaccines available. A single immunization induces both long-lasting neutralizing antibody and YF-specific T cell responses. Surprisingly, the mechanism for this robust immunity has not been addressed. In light of several recent reports suggesting flavivirus interaction with dendritic cells (DCs), we investigated the mechanism of YF17D interaction with DCs and the importance of this interaction in generating T cell immunity. Our results show that YF17D can infect immature and mature human DCs. Viral entry is Ca(2+) dependent, but it is independent of DC-SIGN as well as multiple integrins expressed on the DC surface. Similar to infection of cell lines, YF infection of immature DCs is cytopathic. Although infection itself does not induce DC maturation in vitro, TNF-alpha-induced maturation protects DCs from YF-induced cytopathogenicity. Furthermore, we show that DCs infected with YF17D or YF17D carrying a recombinant epitope can process and present antigens for CD8(+) T cell stimulation. These findings offer insight into the immunologic mechanisms associated with the highly capable YF17D vaccine that may guide effective vaccine design

Dendritic-cell maturation alters intracellular signaling networks, enabling differential effects of IFN-alpha/beta on antigen cross-presentation.

International audienceThe broad and often contrasting effects of type I interferons (IFNs) in innate and adaptive immunity are belied by the signaling via a single receptor, IFN-alpha receptor (IFNAR). Here, we show that IFN-alpha/beta induces opposing effects on the immunologic outcome of antigen cross-presentation depending on dendritic cell (DC) maturation status. Despite equivalent IFNAR expression, immature conventional DCs (cDCs) activate STAT1 in response to IFN-alpha/beta, whereas exposure of mature DCs to IFN-alpha/beta results in signaling via STAT4. Microarray analysis revealed numerous transcriptional changes resulting from the altered signaling. Importantly, STAT1 signaling resulted in significant inhibition of CD40L-induced IL-12 production, accounting for the inhibition of CD8+ T-cell activation. These data provide evidence for a molecular switch in signaling pathways concomitant with DC maturation that offers a novel mechanism by which DCs modulate the integration of signals from the surrounding environment