The intestinal microbiota is vital for shaping the local intestinal environment as well as host immunity and metabolism. At the same time, epidemiological and experimental evidence suggest an important role for parasitic worm infections in maintaining the inflammatory and regulatory balance of the immune system. In line with this, the prevalence of persistent worm infections is inversely correlated with the incidence of immune-associated diseases, prompting the use of controlled parasite infections for therapeutic purposes. Despite this, the impact of parasite infection on the intestinal microbiota, as well as potential downstream effects on the immune system, remain largely unknown. We have assessed the influence of chronic infection with the large-intestinal nematode Trichuris muris, a close relative of the human pathogen Trichuris trichiura, on the composition of the murine intestinal microbiota by 16S ribosomal-RNA gene-based sequencing. Our results demonstrate that persistent T. muris infection dramatically affects the large-intestinal microbiota, most notably with a drop in the diversity of bacterial communities, as well as a marked increase in the relative abundance of the Lactobacillus genus. In parallel, chronic T. muris infection resulted in a significant shift in the balance between regulatory and inflammatory T cells in the intestinal adaptive immune system, in favour of inflammatory cells. Together, these data demonstrate that chronic parasite infection strongly influences the intestinal microbiota and the adaptive immune system. Our results illustrate the complex interactions between these factors in the intestinal tract, and contribute to furthering the understanding of this interplay, which is of crucial importance considering that 500 million people globally are suffering from these infections and their potential use for therapeutic purposes.

RIPK1 regulates cell death and inflammation through kinase-dependent and -independent mechanisms. As a scaffold, RIPK1 inhibits caspase-8-dependent apoptosis and RIPK3/MLKL-dependent necroptosis. As a kinase, RIPK1 paradoxically induces these cell death modalities. The molecular switch between RIPK1 pro-survival and pro-death functions remains poorly understood. We identify phosphorylation of RIPK1 on Ser25 by IKKs as a key mechanism directly inhibiting RIPK1 kinase activity and preventing TNF-mediated RIPK1-dependent cell death. Mimicking Ser25 phosphorylation (S > D mutation) protects cells and mice from the cytotoxic effect of TNF in conditions of IKK inhibition. In line with their roles in IKK activation, TNF-induced Ser25 phosphorylation of RIPK1 is defective in TAK1- or SHARPIN-deficient cells and restoring phosphorylation protects these cells from TNF-induced death. Importantly, mimicking Ser25 phosphorylation compromises the in vivo cell death-dependent immune control of Yersinia infection, a physiological model of TAK1/IKK inhibition, and rescues the cell death-induced multi-organ inflammatory phenotype of the SHARPIN-deficient mice.

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Obesity impairs the relaxant capacity of adipose tissue surrounding the vasculature (PVAT) and has been implicated in resultant obesity-related hypertension and impaired glucose intolerance. Resident immune cells are thought to regulate adipocyte activity. We investigated the role of eosinophils in mediating normal PVAT function. Healthy PVAT elicits an anti-contractile effect, which was lost in mice deficient in eosinophils, mimicking the obese phenotype, and was restored upon eosinophil reconstitution. Ex vivo studies demonstrated that the loss of PVAT function was due to reduced bioavailability of adiponectin and adipocyte-derived nitric oxide, which was restored after eosinophil reconstitution. Mechanistic studies demonstrated that adiponectin and nitric oxide are released after activation of adipocyte-expressed β3 adrenoceptors by catecholamines, and identified eosinophils as a novel source of these mediators. We conclude that adipose tissue eosinophils play a key role in the regulation of normal PVAT anti-contractile function.

A hallmark of parasite infection is the accumulation of innate immune cells, notably granulocytes and mast cells, at the site of infection. While this is typically viewed as a transient response, with the tissue returning to steady state once the infection is cleared, we found that mast cells accumulated in the large-intestinal epithelium following infection with the nematodeTrichuris muris and persisted at this site for several months after worm expulsion. Mast cell accumulation in the epithelium was associated with the induction of type-2 immunity and appeared to be driven by increased maturation of local progenitors in the intestinal lamina propria. Furthermore, we also detected increased local and systemic levels of the mucosal mast cell protease MCPt-1, which correlated highly with the persistent epithelial mast cell population. Finally, the mast cells appeared to have striking consequences on epithelial barrier integrity, by regulation of gut permeability long after worm expulsion. These findings highlight the importance of mast cells not only in the early phases of infection but also at later stages, which has functional implications on the mucosal tissue. Keywords:Acute parasite infection r Large-intestinal epithelium r MCPt-1 r Mucosal mast cell r Trichuris muris Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionThe intestinal epithelium acts as a barrier to invading pathogens, thus being important for host defense and maintenance of homeostasis. Critical for this process is the intestinal immune system, which populates both the lamina propria and the epithelium. Reciprocal interaction between immune cells and the epithelium is of paramount importance as improperly regulated immune responses can result in inflammatory bowel disease (IBD), food allergies, and other immune-associated disorders [1][2][3]. Innate immune cells, including granulocytes and mast cells, are crucial components of this defense as they are often the first to respond to epithelial breach; however, the possible role for granulocytes in maintaining barrier integrity at later stages of immune responses remains unclear.C 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 258Daniel Sorobetea et al. Eur. J. Immunol. 2017. 47: 257-268 The murine-specific parasitic nematode Trichuris muris has been an invaluable tool to study intestinal immunity for nearly 50 years [4]. Once eggs are ingested, Trichuris-larvae hatch and burrow into the large-intestinal epithelium without penetrating the basal lamina, and remain in this niche unless expelled. Acute infections with T. muris are characterized by an early innate inflammatory response, accompanied by the induction of adaptive Th2 immunity and subsequent worm clearance [4]. After expulsion, the host immune system undergoes a complex and coordinated homeostatic event whereby inflammation is resolved and the infected tissue returns to steady state; a process characterized by immune contraction, clearance ...

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Granulomas are organized immune cell aggregates that form in response to chronic infection or antigen persistence. Yersinia pseudotuberculosis (Yp) blocks innate inflammatory signaling and phagocytosis, inducing formation of neutrophil-rich pyogranulomas within lymphoid tissues. Here, we uncover that Yp triggers pyogranuloma formation within the murine intestinal mucosa, a site not known to contain such structures. Mice lacking circulating monocytes fail to form defined pyogranulomas, have defects in neutrophil activation, and succumb to Yp infection. Yersinia lacking the virulence factors that block phagocytosis did not induce pyogranulomas, indicating that intestinal pyogranulomas form in response to Yp disruption of phagocytosis. Notably, mutation of a single anti-phagocytic virulence factor, YopH, restored pyogranuloma formation and control of Yp infection in monocyte-deficient mice, demonstrating that monocytes override YopH-dependent blockade of innate immune defense. This work reveals an unappreciated site of Yersinia intestinal invasion, and defines host and pathogen drivers of intestinal granuloma formation.

Viral triggers at the intestinal mucosa can have multiple global effects on intestinal integrity, causing elevated intestinal barrier strength and relative protection from subsequent inflammatory bowel disease (IBD) induction in various models. As viruses can interfere with the intestinal immune system both directly and indirectly through commensal bacteria, cause-effect relationships are difficult to define. Due to the complexity of putatively causative factors, our understanding of such virus-mediated protection is currently very limited. We here set out to better understand the impact that adult enteric infection with rotavirus (RV) might have on the composition of the intestinal microbiome and on the severity of IBD. We found that RV infection neither induced significant long-lasting microbiota community changes in the small or large intestine nor affected the severity of subsequent dextran sulfate sodium-induced colitis. Hence, adult murine RV infection does not exert lasting effects on intestinal homeostasis.