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International audience; Education of our intestinal immune system early in life strongly influences adult health. This education strongly relies on series of events that must occur in well-defined time windows. From initial colonization by maternal-derived microbiota during delivery to dietary changes from mother's milk to solid foods at weaning, these early-life events have indeed long-standing consequences on our immunity, facilitating tolerance to environmental exposures or, on the contrary, increasing the risk of developing noncommunicable diseases such as allergies, asthma, obesity, and inflammatory bowel diseases. In this review, we provide an outline of the recent advances in our understanding of these events and how they are mechanistically related to intestinal immunity development and education. First, we review the susceptibility of neonates to infections and inflammatory diseases, related to their immune system and microbiota changes. Then, we highlight the maternal factors involved in protection and education of the mucosal immune system of the offspring, the role of the microbiota, and the nature of neonatal immune system until weaning. We also present how the development of some immune responses is intertwined in temporal and spatial windows of opportunity. Finally, we discuss pending questions regarding the neonate particular immune status and the activation of the intestinal immune system at weaning.

International audience; Initially intended for nutrient uptake, phagocytosis represents a central mechanism of debris removal and host defense against invading pathogens through the entire animal kingdom. In vertebrates and also many invertebrates, macrophages (MFs) and MF-like cells (e.g., coelomocytes and hemocytes) are professional phagocytic cells that seed tissues to maintain homeostasis through pathogen killing, efferocytosis and tissue shaping, repair, and remodeling. Some MF functions are common to all species and tissues, whereas others are specific to their homing tissue. Indeed, shaped by their microenvironment, MFs become adapted to perform particular functions, highlighting their great plasticity and giving rise to high population diversity. Interestingly, the gut displays several anatomic and functional compartments with large pools of strikingly diversified MF populations. This review focuses on recent advances on intestinal MFs in several species, which have allowed to infer their specificity and functions.

Food allergens are innocuous proteins that promote tolerogenic adaptive immune responses in healthy individuals yet in other individuals induce an allergic adaptive immune response characterized by the presence of antigen-specific immunoglobulin E and type-2 immune cells. The cellular and molecular processes that determine a tolerogenic versus non-tolerogenic immune response to dietary antigens are not fully elucidated. Recently, there have been advances in the identification of roles for microbial communities and anatomical sites of dietary antigen exposure and presentation that have provided new insights into the key regulatory steps in the tolerogenic versus non-tolerogenic decision-making processes. Herein, we will review and discuss recent findings in cellular and molecular processes underlying food sensitization and tolerance, immunological processes underlying severity of food-induced anaphylaxis, and insights obtained from immunotherapy trials.

Vaccines targeting mucosal tissues offer promise in providing both mucosal and systemic immunity to pathogens. Many current efforts are aimed at delivering immunostimulatory antigens in the form of macrovesicles and particulates, including nanoparticles and engineered plant-derived proteins, as well as live attenuated vectors, to organized lymphoid tissues, such as Peyer’s patches. These efforts target M cells, a specialized gateway cells to mucosal lumen and luminal antigen uptake within the follicle-associated epithelium, in an attempt to overcome the considerable barriers to antigen transit through the mucosal barrier. However, recent findings suggest novel paths for antigen uptake across these barriers (e.g., transepithelial dendrites of myeloid cells, goblet cells, and FcRn-dependent epithelial transport) that offer opportunities for new vaccine approaches. This chapter will first describe the basic components of mucosal barriers, followed by a discussion of what is known about antigen uptake across the villus epithelium. It will conclude with thoughts about how these mechanisms may be used by currently available vaccines and potentially exploited to develop novel vaccination strategies to generate or enhance mucosal immunity.

During Salmonella Typhimurium infection, intestinal CX3CR1+ cells can either extend transepithelial cellular processes to sample luminal bacteria or, very early after infection, migrate into the intestinal lumen to capture bacteria. However, until now, the biological relevance of the intraluminal migration of CX3CR1+ cells remained to be determined. We addressed this by using a combination of mouse strains differing in their ability to carry out CX3CR1-mediated sampling and intraluminal migration. We observed that the number of S. Typhimurium traversing the epithelium did not differ between sampling-competent/migration-competent C57BL/6 and sampling-deficient/migration-competent BALB/c mice. In contrast, in sampling-deficient/migration-deficient CX3CR1−/− mice the numbers of S. Typhimurium penetrating the epithelium were significantly higher. However, in these mice the number of invading S. Typhimurium was significantly reduced after the adoptive transfer of CX3CR1+ cells directly into the intestinal lumen, consistent with intraluminal CX3CR1+ cells preventing S. Typhimurium from infecting the host. This interpretation was also supported by a higher bacterial fecal load in CX3CR1+/gfp compared with CX3CR1gfp/gfp mice following oral infection. Furthermore, by using real-time in vivo imaging we observed that CX3CR1+ cells migrated into the lumen moving through paracellular channels within the epithelium. Also, we reported that the absence of CX3CR1-mediated sampling did not affect Ab responses to a noninvasive S. Typhimurium strain that specifically targeted the CX3CR1-mediated entry route. These data showed that the rapidly deployed CX3CR1+ cell–based mechanism of immune exclusion is a defense mechanism against pathogens that complements the mucous and secretory IgA Ab–mediated system in the protection of intestinal mucosal surface.

Mucosal dendritic cells (DCs) constantly survey the luminal microenvironment which contains commensal microbiota and potentially harmful organisms regulating pathogen recognition and adaptive as well as innate defense activation. Distinct mechanisms are beginning to emerge by which intestinal antigen sampling and handling is achieved ensuring specificity and contributing to redundancy in pathogen detection. Distinct DC subsets are associated with these mechanisms and regulate specific innate or adaptive immune responses to help distinguish between commensal microbiota, pathogens and self antigens. Understanding DC biology in the mucosal immune system may contribute to the unraveling of infection routes of intestinal pathogens and may aid in developing novel vaccines and therapeutic strategies for the treatment of infectious and inflammatory diseases.

The specific role of most of these newly discovered DC subsets in antigen sampling and presentation is unknown and it remains therefore unclear whether they work synergistically, as alternatives or have distinct functions in the recognition of the intestinal microbiota. The focus of effort in this field will be to understand how these diverse DC subsets cooperate in regulating the complex homeostasis and host defense in the different intestinal immune compartments. The intestinal lamina propria contains a DC network that serves as a newly discovered gateway for the uptake and transport of the intestinal microbiota. Specialized vesicular structures at the end of transepithelial dendrites serve as 'luminal sensors' for the mucosal immune system. Characterization of the surface components of these luminal sensors may aid in developing strategies to prevent bacterial and viral pathogen entry. We propose that the lamina propria and M cell-dependent antigen sampling systems are associated with specific DC subsets. The discovery of functionally defined subsets of dendritic cells associated with distinct mechanisms responsible for the uptake of antigens across the intestinal barrier opens the path for strategies for targeting them specifically in the development of vaccines or treatment approaches for inflammatory bowel diseases. For these exciting possibilities to progress into practical applications, it needs to be established whether distinct DCs subsets are associated with multiple pathways or if their function is linked to specific innate or adaptive immune responses. Defining DC function in the intestine will be pivotal in finally progressing our understanding on how the mucosal immune system makes the distinction between commensal microbiota, pathogens and self antigens.

The active transcytosis of many different polypeptides (either presented free or adsorbed on latex nanoparticles), found in the respiratory mucosa of the upper nasal concha, has previously been shown to be proportional to the total volume of the lymphoid aggregates present in the tissue. By combining the use of fluorescent nanoparticles, flux measurements, confocal and scanning electron microscopy and conventional histology, it is shown in this paper that: (i) the areas of epithelium overlying lymphoid aggregates are the only transporting polypeptides; (ii) the respiratory epithelium in these areas consists mainly of non-ciliated microvillar cells, with numerous ciliated cells and rare mucous goblet cells at the periphery of the area only; (iii) non-ciliated microvillar cells are distinguishable in cells with well developed finger-like microvilli and cells with an irregularly pleated apical membrane, similar to that of intestinal and bronchial antigen-sampling M-cells; (iv) groups of polypeptide-coated nanospheres are found bound to this latter type of cells, demonstrating that these are the transporting cells, detected at the first stage of the transcytotic cycle.

Accumulating evidence points toward active uptake by mucosal antigen sampling cells as the mechanism for rectal HIV acquisition. Organized lymphoid tissue in the intestine consists of lymphoid follicles with an epithelium containing M cells specialized for uptake and transport of microorganisms, bringing them into contact with lymphoid cells. M cells have been found in the human colon and rectum, and adherence and uptake of HIV by M cells in mouse and rabbit Peyer’s patches has been demonstrated in vitro. In an in vivo mouse model of viral acquisition, reovirus is actively taken up by M cells into rectal lymphoid tissue containing CD4 lymphocytes and macrophages, which are targets and replication sites for HIV. Immunization strategies for prevention of HIV transmission should include a mucosal component to prevent initial entry, since elimination from cellular sanctuaries remains an elusive goal.

all prescribedmedications. Demographic, dietary and clinical information, PCDAI, Harvey Bradshaw (HB) and Lewis score (LS) were collected at 0, 12 and 52 weeks. CE’s were evaluated by an experienced reader blinded to patient clinical information and timing. Results: Sixteen patients were screened; 10 enrolled; and 9 completed the initial 12 week trial; receiving 85% of estimated caloric needs prior to, and 101%, on the SCD. HB significantly decreased from 3.3 +2.0 to 0.6 +1.3 (p=0.007) as did PCDAI (21.1 +5.9 to 7.8 +7.1; p=0.011). LS declined significantly from 2153+732 to 960+433 (p=0.012). Seven patients continued the SCD to 52weekswith HB (0.1 +0.4) and PCDAI (5.4 +5.5) remaining improved (p=0.016 and 0.027 compared to baseline) withmean LS at 1046 +372 and 2 patients showing sustained mucosal healing. Conclusions: Clinical and mucosal improvements were seen in childrenwith CD using the SCD over 12 and 52weeks. Additionally, CE can monitor mucosal improvement in treatment trials for pediatric CD. Further studies are critically needed to understand the mechanisms underlying SCD’s effectiveness in children with CD.

We have demonstrated that direct antigen sampling of bacteria by intestinal dendritic cells (DCs) is accompanied by a rapid migration of CD11c+CX3CR1+MHCII+CD8alpha; CD11b-DCs into the intestinal lumen upon exposure to non-invasive δSPI1-Salmonella. Importantly, intraluminal DCs internalized Salmonella but were not able to cross the epithelium to return into tissue, thus showing that these DCs do not function as antigen-presenting cells and participate in the conventional regulation of immune responses to intestinal pathogens. Here we show that the presence of the chemokine receptor CX3CR1, that plays a vital role in DC-mediated antigen sampling and clearance in the gut, is also instrumental for the transepithelial migration of DCs. The latter observation, along with the notion that CX3CR1-deficient mice displayed higher susceptibility to Salmonella infection compared to wild type mice raises the possibility that Salmonella-induced migration of bacteria-capturing DCs into the lumen may be an important mechanism of mucosal defence and clearance. © 2010 Landes Bioscience.

The aim of this paper is to investigate the antigen sampling component of the deterministic version of the dendritic cell algorithm (dDCA). To achieve this, a model is presented, and used to produce synthetic data for two temporal correlation problems. The model itself is designed to simulate a system stochastically switching between a normal and an anomalous state over time. By investigating five parameter values for the dDCA’s maximum migration threshold, and benchmarking alongside a minimised version of the dDCA, the effect of sampling using a multi-agent population is explored. Potential sources of error in the dDCA outputs are identified, and related to the duration of the anomalous state in the input data.

Background: M (microfold or membranous) cells are specialised epithelial cells responsible for antigen sampling at the interface of mucosal surfaces and the environment. Their high transcytotic ability make M cells an attractive target for mucosally delivered vaccines and therapeutics. Objective: This brief review discusses the current state of M cell-targeted mucosal delivery systems and the potential of such delivery systems for the development of new vaccines and therapeutics against mucosal infectious and inflammatory diseases. Scope: A variety of synthetic microparticles/nanoparticles have been developed and tested as vehicles for M cell-targeted mucosal drug and vaccine delivery. β1 integrins, pathogen recognition receptors, specific carbohydrate residues and other M cell surface antigens have been exploited as potential targets for the delivery of mucosal vaccines and therapeutics. Conclusion: Despite a considerable body of literature, much work still needs to be done before an effective M cell-tar...

M cells are located in the epithelia overlying mucosa-associated lymphoid tissues such as Peyer's patches where they function as the antigen sampling cells of the mucosal immune system. Paradoxically, some pathogens exploit M cells as a route of invasion. Here we review our current knowledge of intestinal M cells with particular emphasis on the mechanisms underlying bacterial infection of these atypical epithelial cells.

The lung is a fragile network of thin-walled alveoli littered with immune cells that are required to carry out the critical, but normal functions, of gas exchange and antigen sampling. In the adult human, this occurs over the expansive surface area of some 70 m2. The almost constant and direct contact of lung epithelium with the outside environment means that the respiratory tract must maintain a delicate, and tightly regulated balance, to avert almost certain disaster. This is especially true during eradication of a pathogen infection. The fact that lung infection only occasionally goes wrong resulting in a catastrophic outcome suggests that sophisticated mechanisms are in play to keep this process in check.

It has been suggested that the specific transcytosis of polypeptides, demonstrated in rabbit nasal mucosa (upper concha), is involved in antigen sampling at the airway entry. To test this hypothesis, unidirectional transepithelial fluxes of carbocalcitonin (CCT Mw=3362) from the mucosal to the submucosal side, and vice versa, were measured by radioimmunoassay every 30min for 120min and, from the difference, net absorption was determined in the upper concha and septum mucosae. The exposed mucosae were examined by quantitative histology; isolated scattered lymphoid cells/mm2 and volumes of lymphoid infiltrates and aggregates were quantified. CCT absorption was observed in the mucosae of the upper concha and septum provided that aggregates were present, being proportional to aggregate volume. No relationship was noted with isolated scattered lymphoid cells and infiltrates. Passive permeability was unaffected by lymphoid tissue. On this basis, the antigen sampling hypothesis seems to be at least partially substantiated.

The mucosal immune system defends the host against pathogens, most of which invade through mucosal surfaces. Antigen sampling in the mucosal immune system in the intestine occurs constantly in specialized inductive sites known as gut associated lymphoreticular tissue or GALT. Antigen-primed cells then migrate to effector sites in the gut lamina propria and epithelium as well as to other mucosal tissues. A variety of strategies are being pursued to develop effective oral vaccines that will protect mucosal surfaces. Some approaches involve recently identified mucosal adjuvants, the best known of which is cholera toxin. One approach is illustrated in which antigen and adjuvant are incorporated in the inner water phase of a water-in-oil-in-water or multiple emulsion, thus protecting antigen and delivering it into GALT.

▪ Abstract Epithelial barriers on mucosal surfaces at different sites in the body differ dramatically in their cellular organization, and antigen sampling strategies at diverse mucosal sites are adapted accordingly. In stratified and pseudostratified epithelia, dendritic cells migrate to the outer limit of the epithelium, where they sample antigens for subsequent presentation in local or distant organized lymphoid tissues. In simple epithelia, specialized epithelial M cells (a phenotype that occurs only in the epithelium over organized lymphoid follicles) deliver samples of foreign material by transepithelial transport from the lumen to organized lymphoid tissues within the mucosa. Certain pathogens exploit the M cell transport process to cross the epithelial barrier and invade the mucosa. Here we review the features of M cells that determine antigen and pathogen adherence and transport into mucosal lymphoid tissues.

Antigen sampling and antigen presentation by DCs is regionally segregated in the allergic lung.

In rabbit nasal mucosa, polypeptides and polypeptide-coated nanospheres are actively transported from lumen to blood by M-cells present in specialized transport areas of the epithelium. The largest transport is shown here to occur when some molecules of the polypeptides coating the nanospheres, after adsorption, are bound to the specific anti-polypeptide IgG, e.g. when insulin is bound to the anti-insulin IgG. The transport kinetics of nanospheres coated by insulin bound to its antibody, as a function of bead concentration or of the antibody/insulin coating ratio, have been analyzed. On this basis it was possible to assess the maximal transport capacity of the epithelium and to calculate the percentage of M-cells involved.