Dysregulation of the immune response in TGF-β signalopathies

The transforming growth factor-β (TGF-β) family of cytokines exerts pleiotropic functions during embryonic development, tissue homeostasis and repair as well as within the immune system. Single gene defects in individual component of this signaling machinery cause defined Mendelian diseases associated with aberrant activation of TGF-β signaling, ultimately leading to impaired development, immune responses or both. Gene defects that affect members of the TGF-β cytokine family result in more restricted phenotypes, while those affecting downstream components of the signaling machinery induce broader defects. These rare disorders, also known as TGF-β signalopathies, provide the unique opportunity to improve our understanding of the role and the relevance of the TGF-β signaling in the human immune system. Here, we summarize this elaborate signaling pathway, review the diverse clinical presentations and immunological phenotypes observed in these patients and discuss the phenotypic overlap between humans and mice genetically deficient for individual components of the TGF-β signaling cascade

Trade-Off between Bile Resistance and Nutritional Competence Drives Escherichia coli Diversification in the Mouse Gut

Bacterial diversification is often observed, but underlying mechanisms are difficult to disentangle and remain generally unknown. Moreover, controlled diversification experiments in ecologically relevant environments are lacking. We studied bacterial diversification in the mammalian gut, one of the most complex bacterial environments, where usually hundreds of species and thousands of bacterial strains stably coexist. Herein we show rapid genetic diversification of an Escherichia coli strain upon colonisation of previously germ-free mice. In addition to the previously described mutations in the EnvZ/OmpR operon, we describe the rapid and systematic selection of mutations in the flagellar flhDC operon and in malT, the transcriptional activator of the maltose regulon. Moreover, within each mouse, the three mutant types coexisted at different levels after one month of colonisation. By combining in vivo studies and determination of the fitness advantages of the selected mutations in controlled in vitro experiments, we provide evidence that the selective forces that drive E. coli diversification in the mouse gut are the presence of bile salts and competition for nutrients. Altogether our results indicate that a trade-off between stress resistance and nutritional competence generates sympatric diversification of the gut microbiota. These results illustrate how experimental evolution in natural environments enables identification of both the selective pressures that organisms face in their natural environment and the diversification mechanisms

Mucosal Immunity in Toxoplasma Gondii Infection

Toxoplasma gondii is an intracellular parasite that frequently infects a large spectrum of warm-blooded animals. This parasite induces abortion and establishes both chronic and silent infections, particularly in the brain. Parasite penetration into the host activates a strong anti-parasite immune response. In the present paper, we will discuss the interplay between innate and adaptive immunity that occurs within the infected intestine to clear the parasite and to maintain intestinal homeostasis despite the exacerbation of an inflammatory immune response

Dissecting the Genetic Components of Adaptation of Escherichia coli to the Mouse Gut

While pleiotropic adaptive mutations are thought to be central for evolution, little is known on the downstream molecular effects allowing adaptation to complex ecologically relevant environments. Here we show that Escherichia coli MG1655 adapts rapidly to the intestine of germ-free mice by single point mutations in EnvZ/OmpR two-component signal transduction system, which controls more than 100 genes. The selective advantage conferred by the mutations that modulate EnvZ/OmpR activities was the result of their independent and additive effects on flagellin expression and permeability. These results obtained in vivo thus suggest that global regulators may have evolved to coordinate activities that need to be fine-tuned simultaneously during adaptation to complex environments and that mutations in such regulators permit adjustment of the boundaries of physiological adaptation when switching between two very distinct environments

T84-intestinal epithelial exosomes bear MHC class II/peptide complexes potentiating antigen presentation by dendritic cells: Function of intestinal epithelial exosomes

International audienceBackground and aims: Intestinal epithelial cells release antigen presenting vesicles (exosomes) bearing MHC class II/peptide complexes stimulating specific immune responses in vivo. To further characterize the role of human epithelial exosomes in antigen presentation, their capacity to load antigenic peptides, to bind immune target cells and to induce T cell activation was analyzed in vitro. Methods: The capacity of exosomes derived from the HLA-DR4 expressing, intestinal epithelial cell line T84, to load the HLA-DR4-specific peptide 3H-HSA 64-76 and to activate a HLA-DR4-restricted T cell hybridoma, was tested in the presence or absence of human monocyte-derived dendritic cells (DCs). Interaction of FITC-labeled exosomes with T cells and DCs was analyzed by flow cytometry and confocal microscopy. Results: T84-derived exosomes, enriched in CD9, CD81, CD82 and A33 antigen, were capable of binding specifically HSA 64-76 peptide on HLA-DR4 molecules and of interacting preferentially with DCs. HSA-loaded exosomes were unable to activate the T cell hybridoma directly, but induced a productive T cell activation through DCs. When HSA peptide was bound to exosomal HLA-DR4 molecules instead of in a soluble form, the threshold of peptide presentation by DCs was markedly decreased (x10-3). Conclusions: Exosomes released by intestinal epithelial cells bear exogenous peptides complexed to MHC class II molecules and interact preferentially with DCs, strongly potentiating peptide presentation to T cells. Epithelial exosomes constitute a powerful link between luminal antigens and local immune cells by mediating the transfer of tiny amounts of luminal antigenic information and facilitating immune surveillance at mucosal surfaces

Secretory IgA mediates retrotranscytosis of intact gliadin peptides via the transferrin receptor in celiac disease

Celiac disease (CD) is an enteropathy resulting from an abnormal immune response to gluten-derived peptides in genetically susceptible individuals. This immune response is initiated by intestinal transport of intact peptide 31-49 (p31-49) and 33-mer gliadin peptides through an unknown mechanism. We show that the transferrin receptor CD71 is responsible for apical to basal retrotranscytosis of gliadin peptides, a process during which p31-49 and 33-mer peptides are protected from degradation. In patients with active CD, CD71 is overexpressed in the intestinal epithelium and colocalizes with immunoglobulin (Ig) A. Intestinal transport of intact p31-49 and 33-mer peptides was blocked by polymeric and secretory IgA (SIgA) and by soluble CD71 receptors, pointing to a role of SIgA–gliadin complexes in this abnormal intestinal transport. This retrotranscytosis of SIgA–gliadin complexes may promote the entry of harmful gliadin peptides into the intestinal mucosa, thereby triggering an immune response and perpetuating intestinal inflammation. Our findings strongly implicate CD71 in the pathogenesis of CD

Probiotic VSL#3-induced TGF-β ameliorates food allergy inflammation in a mouse model of peanut sensitization through the induction of regulatory T cells in the gut mucosa.

SCOPE: Among food allergies, peanut allergy is frequently associated with severe anaphylactic reactions. In the need for safe and effective therapeutic strategies, probiotics may be considered on the basis of their immunomodulatory properties. The aim of the present study was to investigate the immunological mediators involved in the effects of probiotic VSL#3 oral supplementation on Th2 inflammation and anaphylaxis in a mouse model of peanut allergy. METHODS AND RESULTS: VSL#3 supplementation to peanut-sensitized mice was effective in ameliorating anaphylaxis and Th2-mediated inflammation, by promoting regulatory responses in the jejunum mucosa and in the mesenteric lymph node, as evaluated by ELISA, real-time PCR, histologic, and immunohistochemical analysis. Probiotic-induced TGF-β mediates its protective effects through the induction of regulatory T cells expressing FOXP3 and/or latency-associated peptide, as proven by in vivo blockade of TGF-β in VSL#3-treated mice with a neutralizing monoclonal antibody one day before challenge. CONCLUSION: TGF-β, induced in the gut by VSL#3 supplementation, is capable of reducing the Th2 inflammation associated with food anaphylaxis in a mouse model of peanut sensitization. TGF-β acts through the induction/maintenance of regulatory T cells expressing FOXP3 and/or latency-associated peptide. Probiotics supplementation may represent an effective and safe strategy for treating food allergies in adult population

Human ALPI deficiency causes inflammatory bowel disease and highlights a key mechanism of gut homeostasis

Herein, we report the first identification of biallelic-inherited mutations in ALPI as a Mendelian cause of inflammatory bowel disease in two unrelated patients. ALPI encodes for intestinal phosphatase alkaline, a brush border metalloenzyme that hydrolyses phosphate from the lipid A moiety of lipopolysaccharides and thereby drastically reduces Toll-like receptor 4 agonist activity. Prediction tools and structural modelling indicate that all mutations affect critical residues or inter-subunit interactions, and heterologous expression in HEK293T cells demonstrated that all ALPI mutations were loss of function. ALPI mutations impaired either stability or catalytic activity of ALPI and rendered it unable to detoxify lipopolysaccharide-dependent signalling. Furthermore, ALPI expression was reduced in patients’ biopsies, and ALPI activity was undetectable in ALPI-deficient patient\u27s stool. Our findings highlight the crucial role of ALPI in regulating host–microbiota interactions and restraining host inflammatory responses. These results indicate that ALPI mutations should be included in screening for monogenic causes of inflammatory bowel diseases and lay the groundwork for ALPI-based treatments in intestinal inflammatory disorders

Human gut symbiont Roseburia hominis promotes and regulates innate immunity

© 2017 Patterson, Mulder, Travis, Lan, Cerf-Bensussan, Gaboriau-Routhiau, Garden, Logan, Delday, Coutts, Monnais, Ferraria, Inoue, Grant and Aminov. Objective: Roseburia hominis is a flagellated gut anaerobic bacterium belonging to the Lachnospiraceae family within the Firmicutes phylum. A significant decrease of R. hominis colonization in the gut of ulcerative colitis patients has recently been demonstrated. In this work, we have investigated the mechanisms of R. hominis-host cross talk using both murine and in vitro models. Design: The complete genome sequence of R. hominis A2-183 was determined. C3H/HeN germ-free mice were mono-colonized with R. hominis, and the host-microbe interaction was studied using histology, transcriptome analyses and FACS. Further investigations were performed in vitro and using the TLR5KO and DSS-colitis murine models. Results: In the bacterium, R. hominis, host gut colonization upregulated genes involved in conjugation/mobilization, metabolism, motility, and chemotaxis. In the host cells, bacterial colonization upregulated genes related to antimicrobial peptides, gut barrier function, toll-like receptors (TLR) signaling, and T cell biology. CD4 + CD25 + FoxP3 + T cell numbers increased in the lamina propria of both mono-associated and conventional mice treated with R. hominis. Treatment with the R. hominis bacterium provided protection against DSS-induced colitis. The role of flagellin in host-bacterium interaction was also investigated. Conclusion: Mono-association of mice with R. hominis bacteria results in specific bidirectional gene expression patterns. A set of genes thought to be important for host colonization are induced in R. hominis, while the host cells respond by strengthening gut barrier function and enhancing Treg population expansion, possibly via TLR5-flagellin signaling. Our data reveal the immunomodulatory properties of R. hominis that could be useful for the control and treatment of gut inflammation

Microbiota Sensing by Mincle-Syk Axis in Dendritic Cells Regulates Interleukin-17 and -22 Production and Promotes Intestinal Barrier Integrity

We are grateful to members of the D.S. laboratory and Dr. E. Fernández-Malavé for discussions and critical reading of the manuscript. We appreciate the support of A. Tomás-Loba, G. Sabio, P. Martín, A. Tsilingiri, A.R. Ramiro, C.L. Abram, C.A. Lowell, J.M. García-Lobo, M. Molina, and M.C. Rodríguez for providing reagents and support. We thank the staff at the Fundación Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC) facilities for technical support. M.M.-L. received a Formación de Personal Universitario (FPU) fellowship (AP2010-5935) from the Spanish Ministerio de Educación. S.I. is funded by grant SAF2015-74561-JIN from the Spanish Ministerio de Ciencia, Innovación, y Universidades (MCIU) and Fondos Europeos de Desarrollo Regional (FEDER). G.D.B and D.M.R. are supported by the Wellcome Trust and the MRC Centre for Medical Mycology at the University of Aberdeen. S.L.L. is supported by the Swiss National Science Foundation (PP00P3_150758). Work in the D.S. laboratory is funded by the CNIC and grant SAF2016-79040-R from MCIU, the Agencia Estatal de Investigación, and FEDER; B2017/BMD-3733 Immunothercan-CM from Comunidad de Madrid; RD16/0015/0018-REEM from FIS-Instituto de Salud Carlos III, MCIU, and FEDER; the Acteria Foundation; the Constantes y Vitales prize (Atresmedia); La Marató de TV3 Foundation (201723); the European Commission (635122-PROCROP H2020), and the European Research Council (ERC-2016-Consolidator Grant 725091). The CNIC is supported by the MCIU and the Pro-CNIC Foundation and is a Severo Ochoa Center of Excellence (SEV-2015-0505).Peer reviewedPublisher PD