Lamina propria dendritic cells in the physiology and pathology of the gastrointestinal tract

Current Progress and Challenges in the Study of Adjuvants for Oral Vaccines

Over the past 20 years, a variety of potential adjuvants have been studied to enhance the effect of oral vaccines in the intestinal mucosal immune system; however, no licensed adjuvant for clinical application in oral vaccines is available. In this review, we systematically updated the research progress of oral vaccine adjuvants over the past 2 decades, including biogenic adjuvants, non-biogenic adjuvants, and their multi-type composite adjuvant materials, and introduced their immune mechanisms of adjuvanticity, aiming at providing theoretical basis for developing feasible and effective adjuvants for oral vaccines. Based on these insights, we briefly discussed the challenges in the development of oral vaccine adjuvants and prospects for their future development.

Metabolic programming in dendritic cells tailors immune responses and homeostasis

It is being increasingly acknowledged that immune cells depend on certain metabolic traits to perform their functions and that the extracellular environment can influence cell metabolism and vice versa. Dendritic cell (DC) subsets traffic through highly diverse environments from the bone marrow, where they develop, to the various peripheral tissues, where they differentiate and capture antigens, before they migrate to the lymph node to present antigens and prime T cells. It is plausible that DC subsets modulate their stimulatory abilities in response to unique metabolic programming. The metabolic requirements of DCs are just recently being discovered, and subset- and context-specific metabolic phenotypes in DCs are highly intertwined with DC functions. In this review, we present the current knowledge on the intrinsic and extrinsic determinants of DC metabolism, how they regulate DC function with examples from tumor biology and in interaction with the microbiota, and discuss how this can be applied therapeutically.

Mucosal immunity to poliovirus

A cornerstone of the global initiative to eradicate polio is the widespread use of live and inactivated poliovirus vaccines in extensive public health campaigns designed to prevent the development of paralytic disease and interrupt transmission of the virus. Central to these efforts is the goal of inducing mucosal immunity able to limit virus replication in the intestine. Recent clinical trials have evaluated new combined regimens of poliovirus vaccines, and demonstrated clear differences in their ability to restrict virus shedding in stool after oral challenge with live virus. Analyses of mucosal immunity accompanying these trials support a critical role for enteric neutralizing IgA in limiting the magnitude and duration of virus shedding. This review summarizes key findings in vaccine-induced intestinal immunity to poliovirus in infants, older children, and adults. The impact of immunization on development and maintenance of protective immunity to poliovirus and the implications for global eradication are discussed.

Specialized transendothelial dendritic cells mediate thymic T-cell selection against blood-borne macromolecules

T cells undergo rigorous selection in the thymus to ensure self-tolerance and prevent autoimmunity, with this process requiring innocuous self-antigens (Ags) to be presented to thymocytes. Self-Ags are either expressed by thymic stroma cells or transported to the thymus from the periphery by migratory dendritic cells (DCs); meanwhile, small blood-borne peptides can access the thymic parenchyma by diffusing across the vascular lining. Here we describe an additional pathway of thymic Ag acquisition that enables circulating antigenic macromolecules to access both murine and human thymi. This pathway depends on a subset of thymus-resident DCs, distinct from both parenchymal and circulating migratory DCs, that are positioned in immediate proximity to thymic microvessels where they extend cellular processes across the endothelial barrier into the blood stream. Transendothelial positioning of DCs depends on DC-expressed CX3CR1 and its endothelial ligand, CX3CL1, and disrupting this chemokine pathway prevents thymic acquisition of circulating proteins and compromises negative selection of Ag-reactive thymocytes. Thus, transendothelial DCs represent a mechanism by which the thymus can actively acquire blood-borne Ags to induce and maintain central tolerance.

Immunomodulatory Role and Therapeutic Potential of Non-Coding RNAs Mediated by Dendritic Cells in Autoimmune and Immune Tolerance-Related Diseases

Dendritic cells (DCs) are professional antigen-presenting cells that act as a bridge between innate immunity and adaptive immunity. After activation, DCs differentiate into subtypes with different functions, at which point they upregulate co-stimulatory molecules and produce various cytokines and chemokines. Activated DCs also process antigens for presentation to T cells and regulate the differentiation and function of T cells to modulate the immune state of the body. Non-coding RNAs, RNA transcripts that are unable to encode proteins, not only participate in the pathological mechanisms of autoimmune-related diseases but also regulate the function of immune cells in these diseases. Accumulating evidence suggests that dysregulation of non-coding RNAs contributes to DC differentiation, functions, and so on, consequently producing effects in various autoimmune diseases. In this review, we summarize the main non-coding RNAs (miRNAs, lncRNAs, circRNAs) that regulate DCs in pathological mechanisms and have tremendous potential to give rise to novel therapeutic targets and strategies for multiple autoimmune diseases and immune tolerance-related diseases.

Region-specific transcriptomic and functional signatures of mononuclear phagocytes in the epididymis

In the epididymis, prevention of autoimmune responses against spermatozoa and simultaneous protection against pathogens is important for male fertility. We have previously shown that mononuclear phagocytes (MPs) are located either in the epididymal interstitium or in close proximity to the epithelium. In the initial segments (IS), these 'intraepithelial' MPs extend slender luminal-reaching projections between epithelial cells. In this study, we performed an in-depth characterisation of MPs isolated from IS, caput-corpus and cauda epididymis of CX3CR1EGFP+/- mice that express EGFP in these cells. Flow cytometry analysis revealed region-specific subsets of MPs that express combinations of markers traditionally described in 'dendritic cells' or 'macrophages'. RNA sequencing identified distinct transcriptomic signatures in MPs from each region and revealed specific genes involved in inflammatory and anti-inflammatory responses, phagosomal activity and antigen processing and presentation. Functional fluorescent in vivo labelling assays showed that higher percentages of CX3CR1+ MPs that captured and processed antigens were detected in the IS compared to other regions. Confocal microscopy showed that in the IS, caput and corpus, circulatory antigens were internalised and processed by interstitial and intraepithelial MPs. However, in the cauda only interstitial MPs internalised and processed antigens, while intraepithelial MPs did not take up antigens, indicating that all antigens have been captured before they reached the epithelial lining. Cauda MPs may thus confer a stronger protection against blood-borne pathogens compared to proximal regions. By identifying immunoregulatory mechanisms in the epididymis, our study may lead to new therapies for male infertility and epididymitis and identify potential targets for immunocontraception.

Culture-Dependent and Sequencing Methods Revealed the Absence of a Bacterial Community Residing in the Urine of Healthy Cats

A growing number of studies suggest that the lower urinary tract of humans and dogs can harbor a urinary microbiota. Nevertheless, a certain concern has developed that the microbiota reported could be due to unaccounted contamination, especially in low-biomass samples. The aim of this study was to investigate the bacterial community which populates the urine of healthy cats using two approaches: a culture-dependent approach which consisted of the expanded quantitative urine culture (EQUC) techniques capable of identifying live bacteria not growing in standard urine cultures, and a culture-independent approach which consisted of 16S ribosomal RNA next generation sequencing (16S rRNA NGS) capable of identifying bacterial DNA and exploring microbial diversity with high resolution. To avoid confounding factors of possible bacterial contamination, the urine was sampled using ultrasound-guided cystocentesis, and several sample controls and negative controls were analyzed. The urine sampled from the 10 cats included in the study showed no bacterial growth in the EQUC procedure. Although several reads were successfully originated using 16S rRNA NGS, a comparable pattern was observed between urine samples and the negative control, and no taxa were statistically accepted as non-contaminant. Taken together, the results obtained allowed stating that no viable bacteria were present in the urine of healthy cats without lower urinary tract disease and urinary tract infections, and that the bacterial DNA detected was of contaminant origin.

Regulating colonic dendritic cells by commensal glycosylated large surface layer protein A to sustain gut homeostasis against pathogenic inflammation

Microbial interaction with the host through sensing receptors, including SIGNR1, sustains intestinal homeostasis against pathogenic inflammation. The newly discovered commensal Propionibacterium strain, P. UF1, regulates the intestinal immunity against pathogen challenge. However, the molecular events driving intestinal phagocytic cell response, including colonic dendritic cells (DCs), by this bacterium are still elusive. Here, we demonstrate that the glycosylation of bacterial large surface layer protein A (LspA) by protein O-mannosyltransferase 1 (Pmt1) regulates the interaction with SIGNR1, resulting in the control of DC transcriptomic and metabolomic machineries. Programmed DCs promote protective T cell response to intestinal Listeria infection and resist chemically induced colitis in mice. Thus, our findings may highlight a novel molecular mechanism by which commensal surface glycosylation interacting with SIGNR1 directs the intestinal homeostasis to potentially protect the host against proinflammatory signals inducing colonic tissue damage.

Bacillus toyonensis improves immune response in the mice vaccinated with recombinant antigen of bovine herpesvirus type 5

Probiotics modulate the immune response and can increase the effectiveness of vaccines. Bacillus toyonensis is widely used as a probiotic in animal feed. The aim of this study was to assess the effects of B. toyonensis administration on the immune response to an experimental recombinant vaccine against bovine herpesvirus type 5 (BoHV-5) in mice. Mice were vaccinated with BoHV-5 recombinant glycoprotein D and supplemented with the probiotic B. toyonensis in two regimes: one group received the probiotic only during seven days prior to the initial vaccination while the second group was given the probiotic throughout the experimental period of seven weeks. Animals supplemented with probiotic B. toyonensis in two regimes showed an increase in total immunoglobulin (Ig)G, IgG1 and IgG2a levels in serum, in addition to higher titres of antibodies capable of neutralising the BoHV-5 virus than non-supplemented animals (P<0.05). Splenocytes from the supplemented mice had higher mRNA transcription levels of cytokines interleukin (IL)-4 and IL-12. These results show that the use of this probiotic may significantly contribute to the response elicited by recombinant vaccines, especially those that rely on increasing antibody and cell-mediated immune responses for efficacy. Further, the data support an immunomodulatory effect for probiotic B. toyonensis and imply that enhance effect on the immune response against a BoHV-5 recombinant vaccine in mice.

Cross-protective efficacy of dendritic cells targeting conserved influenza virus antigen expressed by Lactobacillus plantarum

Avian influenza virus (AIV) can infect birds and mammals, including humans, and are thus a serious threat to public health. Vaccination is vital for controlling AIV circulation. In this study, we generated a recombinant lactobacillus expressing the NP-M1-DCpep of H9N2 avian influenza virus and evaluated the activation effect of NC8-pSIP409-NP-M1-DCpep on dendritic cells (DCs) in a mouse model. The specific mucosal antibody responses and B and T cell responses in lymphoid tissues were also characterized. Importantly, we confirmed that specific CD8 T cells presented in vitro and antigen-specific cytotoxicity (activated the expression of CD107a) and in vivo antigen-specific cytotoxicity after vaccination. The adoptive transfer of NC8-pSIP409-NP-M1-DCpep-primed CD8+ T cells into NOD-SCID mice resulted in effective protection against mouse-adapted AIV infection. In addition, we observed protection in immunized mice challenged with mouse-adapted H9N2 AIV and H1N1 influenza virus, as evidenced by reductions in the lung virus titers, improvements in lung pathology, and weight loss and complete survival. Our data are promising for the generation of effective, non-traditional influenza vaccines against AIVs.

Dendritic cell migration in health and disease

Dendritic cells (DCs) are potent and versatile antigen-presenting cells, and their ability to migrate is key for the initiation of protective pro-inflammatory as well as tolerogenic immune responses. Recent comprehensive studies have highlighted the importance of DC migration in the maintenance of immune surveillance and tissue homeostasis, and also in the pathogenesis of a range of diseases. In this Review, we summarize the anatomical, cellular and molecular factors that regulate the migration of different DC subsets in health and disease. In particular, we focus on new insights concerning the role of migratory DCs in the pathogenesis of diseases of the skin, intestine, lung, and brain, as well as in autoimmunity and atherosclerosis.

Exploring the role of mononuclear phagocytes in the epididymis

The onslaught of foreign antigens carried by spermatozoa into the epididymis, an organ that has not demonstrated immune privilege, a decade or more after the establishment of central immune tolerance presents a unique biological challenge. Historically, the physical confinement of spermatozoa to the epididymal tubule enforced by a tightly interwoven wall of epithelial cells was considered sufficient enough to prevent cross talk between gametes and the immune system and, ultimately, autoimmune destruction. The discovery of an intricate arrangement of mononuclear phagocytes (MPs) comprising dendritic cells and macrophages in the murine epididymis suggests that we may have underestimated the existence of a sophisticated mucosal immune system in the posttesticular environment. This review consolidates our current knowledge of the physiology of MPs in the steady state epididymis and speculates on possible interactions between auto-antigenic spermatozoa, pathogens and the immune system by drawing on what is known about the immune system in the intestinal mucosa. Ultimately, further investigation will provide valuable information regarding the origins of pathologies arising as a result of autoimmune or inflammatory responses in the epididymis, including epididymitis and infertility.

Regulation of lung immunity and host defense by the intestinal microbiota

Every year in the United States approximately 200,000 people die from pulmonary infections, such as influenza and pneumonia, or from lung disease that is exacerbated by pulmonary infection. In addition, respiratory diseases such as, asthma, affect 300 million people worldwide. Therefore, understanding the mechanistic basis for host defense against infection and regulation of immune processes involved in asthma are crucial for the development of novel therapeutic strategies. The identification, characterization, and manipulation of immune regulatory networks in the lung represents one of the biggest challenges in treatment of lung associated disease. Recent evidence suggests that the gastrointestinal (GI) microbiota plays a key role in immune adaptation and initiation in the GI tract as well as at other distal mucosal sites, such as the lung. This review explores the current research describing the role of the GI microbiota in the regulation of pulmonary immune responses. Specific focus is given to understanding how intestinal “dysbiosis” affects lung health.

Preventive and therapeutic effects of Lactobacillus paracasei B21060-based synbiotic treatment on gut inflammation and barrier integrity in colitic mice

BACKGROUND

Although gut microbiota perturbation is recognized as a main contributing factor to the pathogenesis of inflammatory bowel disease, synbiotic therapies, as prevention or treatment, have remained overlooked.

OBJECTIVE

To verify whether Lactobacillus paracasei B21060-based synbiotic therapy could prevent or repair colon damage in a mouse model of colitis, we performed treatments before and after colitis induction.

METHODS

The experimental study lasted 19 d. Experimental colitis was induced in BALB/c mice by giving them dextran sodium sulfate (DSS, 2.5%) in drinking water (days 7-12) followed by DSS-free water (days 13-19) (DSS group). L. paracasei B21060 (2.5 × 10(7) bacteria/10 g body weight) was orally administered 7 d before DSS [synbiotic as preventive treatment (P-SYN) group] or 2 d after DSS [synbiotic as therapeutic treatment (T-SYN) group] until day 19. Another group was not treated with DSS or synbiotic and was given tap water (control group), for a total of 4 groups.

RESULTS

Compared with the DSS group, both synbiotic-treated groups had significantly less pronounced weight loss and colon damage. Consistently, mRNA levels of chemokine (C-C motif) ligand 5 in the colon were reduced in both P-SYN and T-SYN mice compared with the DSS group (51%, P < 0.05 and 72%, P < 0.001, respectively). In the P-SYN and T-SYN groups, neutrophil elastase transcription was also reduced (51%, P < 0.01 and 59%, P < 0.001, respectively). Accordingly, oxidative/nitrosative stress was lower in P-SYN and T-SYN mice than in the DSS group. In P-SYN and T-SYN mice, colonic gene expression of tumor necrosis factor (47%, P < 0.01 and 61%, P < 0.001, respectively) and prostaglandin-endoperoxide synthase 2 (45%, P < 0.01 and 35%, P < 0.05, respectively) was lower, whereas interleukin 10 mRNA was doubled compared with the DSS group (both P < 0.5). Remarkably, epithelial barrier integrity (zonulin and occludin) and gut protection (β-defensin and mucin expression) were completely restored in P-SYN and T-SYN mice.

CONCLUSIONS

Our data highlight the beneficial effects of this synbiotic formulation in acutely colitic mice, suggesting that it may have therapeutic and possibly preventive efficacy in human colitis.

Efferent intestinal lymph protein responses in nematode-resistant, -resilient and -susceptible lambs under challenge with Trichostrongylus colubriformis

The mechanisms underlying resistance to challenge by gastrointestinal nematode parasites in sheep are complex. Using DIGE, we profiled ovine lymph proteins in lambs with host resistance (R), resilience (Ri) or susceptibility (S) to a daily trickle challenge with the nematode Trichostrongylus colubriformis. Efferent intestinal lymph was collected prior to infection (day 1) and on days 5 and 10 post-infection. Eight proteins identified by LC-MS/MS, showed differences relating to host genotype. Of these, Serpin A3-3 and Serpin A3-7 have not been reported previously in the lymph proteome. Three acute phase proteins showed significant differences relating to interactions between breeding line and parasite challenge, including complement C3β, C3α and haptoglobin (Hp) β. In the R lambs C3α was significantly up regulated (P<0.05) on day 10, while in the Ri lambs Hp β was significantly down regulated (P<0.05). In the S lambs, levels of C3β were up regulated and levels of Hp β down regulated (both P<0.05) on day 10. Hence we demonstrate that acute phase inflammation proteins contribute to differences in the innate immune response of sheep to challenge by T. colubriformis. The findings may lead to the development of new approaches to combat nematode infestations in sheep production systems.

BIOLOGICAL SIGNIFICANCE

Breeding lines of sheep with resistance (R), resilience (Ri) or susceptibility (S) to nematode infections provide an experimental model to examine the biological mechanisms underlying the ability of some sheep to expel worms and remain healthy without the use of an anthelmintic. Using proteomics we identified differences in the expression of acute phase lymph proteins in the R, Ri and S lambs. The results will assist the development of alternative control strategies to manage nematode infections in livestock.

The microbiota and helminths: sharing the same niche in the human host

Human gastrointestinal bacteria often share their environment with parasitic worms, allowing physical and physiological interaction between the two groups. Such associations have the potential to affect host health as well as the bacterial and helminth populations. Although still in its early stages, research on the interaction between the microbiome and parasitic helminths in humans offers the potential to improve health by manipulating the microbiome. Previously, supplementation with various nutritional compounds has been found to increase the abundance of potentially beneficial gut commensal bacteria. Thus, nutritional microbiome manipulation to produce an environment which may decrease malnutrition associated with helminth infection and/or aid host recovery from disease is conceivable. This review discusses the influence of the gut microbiota and helminths on host nutrition and immunity and the subsequent effects on the human host's overall health. It also discusses changes occurring in the microbiota upon helminth infections and the underlying mechanisms leading to these changes. There are still significant knowledge gaps which need to be filled before meaningful progress can be made in translating knowledge from studying the human gut microbiome into therapeutic strategies. Ultimately this review aims to discuss our current knowledge as well as highlight areas requiring further investigation.

The effect of oxidized cholesterol on barrier functions and IL-10 mRNA expression in human intestinal epithelium co-cultured with dendritic cells in the transwell system

The intestinal epithelium is exposed to oxygenated cholesterol products present in foodstuffs. In vitro studies demonstrate the effect of oxysterols on cytokine release by intestinal cells cultured alone. However, physiologically, the response of the intestinal epithelium to external agents occurs in the presence of dendritic cells (DCs). The aim of the study was to analyze the effect of 7-ketocholesterol on the barrier functions and IL-10 mRNA expression of Caco-2 cells in the presence of DCs, and secondly, on IL-10 mRNA expression in DCs. Caco-2 cells were co-cultured with monocyte-derived dendritic cells and induced with 7-ketocholesterol in a transwell system. DCs did not affect the transepithelial electrical resistance (TER) of the Caco-2 cell monolayer, but increased IL-10 mRNA expression in Caco-2 cells. 7-ketocholesterol decreased the TER of Caco-2 cells co-cultured with DCs and diminished IL-10 mRNA expression in Caco-2 cells induced by the presence of DCs. IL-10 mRNA expression fell in DCs co-cultured with Caco-2 cells after treatment with 7-ketocholesterol. Oxidized cholesterols present in gut mucosa may contribute to the decrease of epithelial barrier functions and the inappropriate development of an inflammatory response to food compounds.

Endocytosis of environmental and engineered micro- and nanosized particles

There are many studies with cells to find out how particles interact with them. In contrast to micronsized particles, which are actively taken up by phagocytosis or macropinocytosis, nanosized particles may be taken up by cells through different endocytic pathways or by another, yet to be defined mechanism. There is increasing evidence that it is the nanosized particles, which are a particular risk because of their high content of organic chemicals and their pro-oxidative potential due to the high surface-to-volume ratio of the particles as compared to the bulk material. It is the goal of this article to create an understanding for the interaction of particles with biological systems, with particular consideration of the interaction of nanoparticles (NPs) with lung cells. One is attempting to understand, how NPs interact with cellular membranes, as it is hardly known, how they are taken up by cells, how they are trafficking in cells, and how they interact with subcellular compartments, such as with mitochondria or with the nucleus. Cells tend to defend themselves against any foreign material, which is taken up. In general, they try to eliminate particulate intruders and this is what they usually manage with micronsized particles. However, with NPs it is different. NPs may not be eliminated easily, and, hence may stimulate the cells to react in an unfavorable way. What we can learn is that NPs behave differently than microparticles.

The ABCs (Antibody, B Cells, and Carbohydrate Epitopes) of Cholera Immunity: Considerations for an Improved Vaccine

Cholera, a diarrheal disease, is known for explosive epidemics that can quickly kill thousands. Endemic cholera is a seasonal torment that also has a significant mortality. Not all nations with extensive rural communities can achieve the required infrastructure or behavioral changes to prevent epidemic or endemic cholera. For some communities, a single-dose cholera vaccine that protects those at risk is the most efficacious means to reduce morbidity and mortality. It is clear that our understanding of what a protective cholera immune response is has not progressed at the rate our understanding of the pathogenesis and molecular biology of cholera infection has. This review addresses V. cholerae lipopolysaccharide (LPS)-based immunogens because LPS is the only immunogen proven to induce protective antibody in humans. We discuss the role of anti-LPS antibodies in protection from cholera, the importance and the potential role of B cell subsets in protection that is based on their anatomical location and the intrinsic antigen-receptor specificity of various subsets is introduced.

Mucosal Lactobacillus vectored vaccines

Traditional non-gastrointestinal vaccines can prevent effectively the invasion of pathogens; however, these vaccines are less effective against mucosal infections because there is not a sufficient immune response at the mucosa. Most pathogens invade via a mucosal pathway (oral, intranasal, or vaginal). It is widely accepted that Lactobacillus species play a critical role as commensals in the gastrointestinal (GI) tract. Their ability to survive in the digestive tract, their close association with the intestinal epithelium, their immunomodulatory properties and their safety even when consumed in large amounts make lactobacilli attractive candidates for live vehicles for the delivery of immunogens to the intestinal mucosa. The oral or intranasal administration of Lactobacillus-based vaccines is a promising method to control mucosal infection because these vaccines could induce strong humoral and cellular immune responses both in the blood and at mucosal sites.

Immune heterogeneity in neuroinflammation: dendritic cells in the brain

Dendritic cells (DC) are critical to an integrated immune response and serve as the key link between the innate and adaptive arms of the immune system. Under steady state conditions, brain DC’s act as sentinels, continually sampling their local environment. They share this function with macrophages derived from the same basic hemopoietic (bone marrow-derived) precursor and with parenchymal microglia that arise from a unique non-hemopoietic origin. While multiple cells may serve as antigen presenting cells (APCs), dendritic cells present both foreign and self-proteins to naïve T cells that, in turn, carry out effector functions that serve to protect or destroy. The resulting activation of the adaptive response is a critical step to resolution of injury or infection and is key to survival. In this review we will explore the critical roles that DCs play in the brain’s response to neuroinflammatory disease with emphasis on how the brain’s microenvironment impacts these actions.

Natural alternatives to in-feed antibiotics in pig production: can immunomodulators play a role?

As a result of the European ban of in-feed growth-promoting antibiotics, new strategies are being developed to increase the resistance to disease in farm animals. In pig production, this is of particular importance during the weaning transition when piglets are subjected to major stressful events, making them highly sensitive to digestive disorders. At this time, the development of both innate and adaptive immunity at the mucosal surface is critical in preventing the potential harmful effects of intestinal pathogenic agents. Strategies aiming at stimulating natural host defences through the use of substances able to modulate immune functions have gained increasing interest in animal research, and different bioactive components a priori sharing those properties have been the subject of in vivo nutritional investigations in pig. Among these, yeast derivates (β-glucans and mannans) are able to interact with immune cells, particularly phagocytic cells. However, studies where they have been fed to pigs have shown inconsistent results, suggesting that their ability to target the sensitive immune cells through the oral route is questionable. The plant extracts, which would benefit from a positive image in the public opinion, have also been tested. However, due to a lack of data on the bioactive components of particular plants and the large diversity of species, it has proved difficult to prepare extracts of equivalent potency and thus, the literature on their influence on pig immunity remains inconclusive. In considering piglet immunity and health benefits, the most promising results to date have been obtained with spray-dried animal plasma, whose positive effects would be provided by specific antibodies and non-specific competition of some plasma components with bacteria for intestinal receptors. The major positive effect of spray-dried animal plasma is in reducing the infiltration of gut-associated lymphoid tissue by immune cells, which is likely to be the result of a decreased colonisation by potentially harmful bacteria. This review also highlights the limitations of some of the published in vivo studies on the immunomodulatory activity of certain feed additives. Among those, the lack of standardisation of extracts and the heterogeneity of piglet-rearing conditions (e.g. exposure to pathogens) are likely the most limiting.

Human intestinal dendritic cells decrease cytokine release against Salmonella infection in the presence of Lactobacillus paracasei upon TLR activation

Probiotic bacteria have been shown to modulate immune responses and could have therapeutic effects in allergic and inflammatory disorders. However, little is known about the signalling pathways that are engaged by probiotics. Dendritic cells (DCs) are antigen-presenting cells that are involved in immunity and tolerance. Monocyte-derived dendritic cells (MoDCs) and murine DCs are different from human gut DCs; therefore, in this study, we used human DCs generated from CD34+ progenitor cells (hematopoietic stem cells) harvested from umbilical cord blood; those DCs exhibited surface antigens of dendritic Langerhans cells, similar to the lamina propria DCs in the gut. We report that both a novel probiotic strain isolated from faeces of exclusively breast-fed newborn infants, Lactobacillus paracasei CNCM I-4034, and its cell-free culture supernatant (CFS) decreased pro-inflammatory cytokines and chemokines in human intestinal DCs challenged with Salmonella. Interestingly, the supernatant was as effective as the bacteria in reducing pro-inflammatory cytokine expression. In contrast, the bacterium was a potent inducer of TGF-β2 secretion, whereas the supernatant increased the secretion of TGF-β1 in response to Salmonella. We also showed that both the bacteria and its supernatant enhanced innate immunity through the activation of Toll-like receptor (TLR) signalling. These treatments strongly induced the transcription of the TLR9 gene. In addition, upregulation of the CASP8 and TOLLIP genes was observed. This work demonstrates that L. paracasei CNCM I-4034 enhanced innate immune responses, as evidenced by the activation of TLR signalling and the downregulation of a broad array of pro-inflammatory cytokines. The use of supernatants like the one described in this paper could be an effective and safe alternative to using live bacteria in functional foods.

Late rather than early responses of human dendritic cells highlight selective induction of cytokines, chemokines and growth factors by probiotic bacteria

The probiotic properties of commensal bacteria including lactobacilli and bifidobacteria are likely to be determined at least in part by their effects on dendritic cells. Like traditional immune stimulants such as lipopolysaccharides (LPS), probiotic bacteria promote maturation of cultured human dendritic cells (DC) by inducing elevated expression of MHC-II and co-stimulatory molecules. Different effects have been reported on cytokine induction, especially of major regulatory cytokines such as TNF-α, IL-12 and IL-10. Yet, these previous analyses have failed to reveal consistent differences between such effects of probiotics on the one hand, and of LPS on the other. Selective response markers for probiotics, however, would be important for our understanding of their biological properties and for a rational selection of strains for in vivo studies. In this study, we compared in detail both early and late effects on cultured human DC of 4 different probiotics with those of LPS. At the early stages of stimulation, all stimuli induced qualitatively very similar responses in DC at the level of surface markers and secretion of cytokines and chemokines. A lower immune stimulatory effect was observed by Bifidobacterium animalis BB-12 as compared to lactobacilli. Late responses, on the other hand, tended to diverge. Microarray transcript profiling for 268 cytokines, chemokines, growth factors and their receptors after 2 days of culture revealed various transcripts to be selectively induced by certain probiotics but not LPS. Our data indicate that late rather than early DC responses may be helpful to clarify the divergent biological effects of probiotics on human innate immune responses.

Acid-sensing ion channels contribute to the effect of acidosis on the function of dendritic cells

As an H(+)-gated subgroup of the degenerin/epithelial Na(+) channel family, acid-sensing ion channels (ASICs) were reported to be involved in various physiological and pathological processes in neurons. However, little is known about the role of ASICs in the function of dendritic cells (DCs). In this study, we investigated the expression of ASICs in mouse bone marrow-derived DCs and their possible role in the function of DCs. We found that ASIC1, ASIC2, and ASIC3 are expressed in DCs at the mRNA and protein levels, and extracellular acid can evoke ASIC-like currents in DCs. We also demonstrated that acidosis upregulated the expression of CD11c, MHC class II, CD80, and CD86 and enhanced the Ag-presenting ability of DCs via ASICs. Moreover, the effect of acidosis on DCs can be abolished by the nonsteroidal anti-inflammatory drugs ibuprofen and diclofenac. These results suggest that ASICs are involved in the acidosis-mediated effect on DC function.

A dense network of dendritic cells populates the murine epididymis

One of the most intriguing aspects of male reproductive physiology is the ability to generate spermatogenic cells - which are 'foreign' to the host - without triggering immune activation. After leaving the testis, spermatozoa enter the epididymis where they mature and are stored. In this study, we report a previously unrecognized dense network of dendritic cells (DCs) located at the base of the epididymal epithelium. This network was detected in transgenic mice expressing CD11c-EYFP and CX3CR1-GFP reporters. Epididymal DCs (eDCs) establish intimate interactions with the epithelium and project long dendrites between epithelial cells toward the lumen. We show that isolated eDCs express numerous leukocyte markers described previously in other organs that are in contact with the external environment, and present and cross-present ovalbumin to T cells in vitro. eDCs are, therefore, strategically positioned to regulate the complex interplay between immune tolerance and activation, a balance that is fundamental to male fertility.

The puzzle of intestinal lamina propria dendritic cells and macrophages

A specialized network of immune cells is positioned directly in the mucosa of the intestinal tract. In this Viewpoint, we discuss the nature and function of DC and macrophages occupying the intestinal lamina propria of mice. DC and macrophages share phenotypic traits and functional plasticity, properties that preclude simple classification of the two cell types. Nevertheless, the information available appears to have reached "critical mass" to allow for a clear demarcation between intestinal macrophages and DC.

Intestinal Langerhans cell histiocytosis-like lesion in an adult presented with diverticulitis: a reactive or neoplastic condition?

The involvement of the gut by Langerhans cell histiocytosis (LCH) is very rare in adults; however this is usually observed with a disseminated disease in children. We report a 75-year-old male patient who underwent right hemicolectomy for a complicated intestinal diverticular disease. The surgical specimen revealed LCH-like proliferative lesion associated with diverticulitis. The overall morphological and immunohistochemical findings are indistinguishable from LCH. Systemic scans and subsequently performed bone marrow biopsies were free of disease. Although the HUMARA clonality assay cannot be assessed, the lack of evidence of LCH progression or disease elsewhere in the whole body strongly supported the possibility of an atypical reactive phenomenon probably due to the underlying intestinal diverticular disease. Therefore, it is important to avoid diagnosing such a unifocal Langerhans cell proliferation as LCH in patients with underlying pathologies in the absence of systemic involvement. Therefore, without knowledge of clonal status of a unifocal Langerhans cell proliferation, we recommend using the terminology of LCH-like lesion.

Rotavirus infection activates dendritic cells from Peyer's patches in adult mice

This study used an in vivo mouse model to analyze the response of dendritic cells (DCs) in Peyer's patches (PPs) within the first 48 h of infection with the wild-type murine rotavirus EDIM (EDIM(wt)). After the infection, the absolute number of DCs was increased by 2-fold in the PPs without a modification of their relative percentage of the total cell number. Also, the DCs from PPs of infected mice showed a time-dependent migration to the subepithelial dome (SED) and an increase of the surface activation markers CD40, CD80, and CD86. This response was more evident at 48 h postinfection (p.i.) and depended on viral replication, since DCs from PPs of mice inoculated with UV-treated virus did not show this phenotype. As a result of the activation, the DCs showed an increase in the expression of mRNA for the proinflammatory cytokines interleukin-12/23p40 (IL-12/23p40), tumor necrosis factor alpha (TNF-alpha), and beta interferon (IFN-beta), as well as for the regulatory cytokine IL-10. These results suggest that, a short time after rotavirus infection, the DCs from PPs play a critical role in controlling the infection and, at the same time, avoiding an excessive inflammatory immune response.

The role of the high-affinity IgE receptor, FcepsilonRI, in eosinophilic gastrointestinal diseases

Primary eosinophilic gastrointestinal diseases (EGIDs) are a heterogeneous group of diseases including eosinophilic esophagitis, eosinophilic gastritis, eosinophilic gastroenteritis, eosinophilic enteritis, and eosinophilic colitis. The unifying hallmark and diagnostic marker of EGIDs is an eosinophil-rich inflammatory infiltrate of the GI mucosa, in the absence of known causes for eosinophilia. The etiology of EGIDs is not yet fully understood. The pathogenesis however seems to involve a complex interplay of genetic predisposition, exposure to food- and environmental allergens and IgE-mediated activation of the immune system. Accumulating evidence relates EGIDs to the group of T-helper (Th) 2 mediated immune disorders, like IgE-mediated allergy. In this article we discuss a possible role of IgE-mediated immune-activation via the high affinity receptor for IgE, FcepsilonRI, in the pathogenesis of primary EGIDs. Beyond its defined role in type I allergic reactions, we here hypothesize that activation of tetrameric FcepsilonRI on mast cells and basophils as well as trimeric FcepsilonRI on human eosinophils and antigen presenting cells in the gastrointestinal mucosa is critically involved in the pathology of EGIDs. We also discuss how IgE-independent triggering of FcepsilonRI could be a mechanisms responsible for activation of the immune system in patients with EGID.

Bone marrow chimeras and c-fms conditional ablation (Mafia) mice reveal an essential role for resident myeloid cells in lipopolysaccharide/TLR4-induced corneal inflammation

The mammalian cornea contains an extensive network of resident macrophages and dendritic cells. To determine the role of these cells in LPS-induced corneal inflammation, TLR4(-/-) mice were sublethally irradiated and reconstituted with bone marrow cells from either enhanced GFP (eGFP)(+)/C57BL/6 or eGFP(+)/TLR4(-/-) mice. The corneal epithelium was abraded, LPS was added topically, and cellular infiltration to the corneal stroma and development of corneal haze were examined after 24 h. TLR4(-/-) mice reconstituted with C57BL/6, but not TLR4(-/-) bone marrow cells donor cells were found to cause infiltration of eGFP(+) cells to the cornea, including neutrophils, and also increased corneal haze compared with saline-treated corneas. In a second experimental approach, corneas of transgenic macrophage Fas induced apoptosis (Mafia) mice were stimulated with LPS. These mice express eGFP and a suicide gene under control of the c-fms promoter, and systemic treatment with the FK506 dimerizer (AP20187) causes Fas-mediated apoptosis of monocytic cells. AP20187-treated mice had significantly fewer eGFP(+) cells in the cornea than untreated mice. After stimulation with LPS neutrophil recruitment and development of corneal haze were impaired in AP20187-treated mice compared with untreated controls. Furthermore, LPS induced CXCL1/KC and IL-1alpha production within 4 h in corneas of untreated Mafia mice, which is before cellular infiltration; however, cytokine production was impaired after AP20187 treatment. Together, results from both experimental approaches demonstrate an essential role for resident corneal monocytic lineage cells (macrophages and dendritic cells) in development of corneal inflammation.

Dendritic cell targeting of Bacillus anthracis protective antigen expressed by Lactobacillus acidophilus protects mice from lethal challenge

Efficient vaccines potentiate antibody avidity and increase T cell longevity, which confer protection against microbial lethal challenge. A vaccine strategy was established by using Lactobacillus acidophilus to deliver Bacillus anthracis protective antigen (PA) via specific dendritic cell-targeting peptides to dendritic cells (DCs), which reside in the periphery and mucosal surfaces, thus directing and regulating acquired immunity. The efficiency of oral delivery of L. acidophilus expressing a PA-DCpep fusion was evaluated in mice challenged with lethal B. anthracis Sterne. Vaccination with L. acidophilus expressing PA-DCpep induced robust protective immunity against B. anthracis Sterne compared with mice vaccinated with L. acidophilus expressing PA-control peptide or an empty vector. Additionally, serum anti-PA titers, neutralizing PA antibodies, and the levels of IgA-expressing cells were all comparable with the historical recombinant PA plus aluminum hydroxide vaccine administered s.c. Collectively, development of this strategy for oral delivery of DC-targeted antigens provides a safe and protective vaccine via a bacterial adjuvant that may potentiate mucosal immune responses against deadly pathogens.

Differentiation and heterogeneity in the mononuclear phagocyte system

Cells of the mononuclear phagocyte system (MPS) are found in large numbers in every organ of the body, where they contribute to innate and acquired immunity and homeostasis. This review considers the locations of MPS cells, surface markers that distinguish subsets of monocytes and macrophages, the pathways of MPS differentiation, and the growth factors and transcription factors that guide them. Although the number of MPS sub-populations that can be defined is infinite, the features that unite the MPS remain compelling. Those features clearly include antigen-presenting dendritic cells within the MPS and argue against any basis for separating them from macrophages.

Epithelial-cell recognition of commensal bacteria and maintenance of immune homeostasis in the gut

Mucosal surfaces such as the intestinal tract are continuously exposed to both potential pathogens and beneficial commensal microorganisms. This creates a requirement for a homeostatic balance between tolerance and immunity that represents a unique regulatory challenge to the mucosal immune system. Recent findings suggest that intestinal epithelial cells, although once considered a simple physical barrier, are a crucial cell lineage for maintaining intestinal immune homeostasis. This Review discusses recent findings that identify a cardinal role for epithelial cells in sampling the intestinal microenvironment, discriminating pathogenic and commensal microorganisms and influencing the function of antigen-presenting cells and lymphocytes.

Protective and destructive innate immune responses to enteropathogenic Escherichia coli and related A/E pathogens

Enteropathogenic Escherichia coli, enterohemorrhagic E. coli (O157:H7) and Citrobacter rodentium are classified as attaching and effacing (A/E) pathogens based on their ability to adhere to intestinal epithelium, destroy microvilli and induce pedestal formation at the site of infection. A/E bacterial infections also cause acute diarrheal episodes and intestinal inflammation. The use of model systems has led to an understanding of the innate immune response to A/E pathogens. The innate immune system plays a protective role, initiating a productive antibody response, directly killing bacteria and inducing repair mechanisms following tissue damage caused by infection. However, hyperactivation of the innate immune system can have negative consequences, including exacerbated tissue destruction following neutrophil infiltration. Here we review how innate immune cell types, including neutrophils, macrophages and dendritic cells, orchestrate both protective and destructive responses. Such information is crucial for the development of therapeutics that can mitigate destructive inflammatory responses while accentuating those that are protective.

Role of retinoic acid in gut immune homeostasis

FOXP3⁺ regulatory T cells play a key role in controlling immune pathological reactions and preventing organs from immune damages. In the gut, native T cells express FOXP3 when antigens make T cells active. It is necessary for the retinoic acid and transforming growth factor β(TGF-β) to involve in the procession. The retinoic acid is the metabolite of vitamin A produced by gut-associated dendritic cells, with induction T cells to produce integrin α4β7 and CCR9, which enhance the ability in transferring native T cells into regulatory T cells, and regulatory T cells migrate preferentially to the small intestine. Besides, retinoic acid can make RORγt weak, resulting in the reduction of Th17 and the improvement of regulatory T cell transformation.

Host-bacteria interaction in inflammatory bowel disease

INTRODUCTION/BACKGROUND

Inflammatory bowel disease (IBD) results from complex interactions between: host genome, immune system, mucosa, bacteria, and environment.

SOURCES OF DATA

Review of PubMed database using search terms 'bacteria and inflammatory bowel disease' and 'genetics and inflammatory bowel disease'. PubMed 'related reference' feature and references from retrieved articles were examined.

AREAS OF AGREEMENT

IBD results from interaction between the microbiota of the gut and the immune system. Key gene defects associated with IBD are involved in bacterial recognition and processing. The environment at least modifies and may determine pathogenesis.

AREAS OF CONTROVERSY

It has been disputed whether the primary defect in IBD is immunological or bacterial, and which bacteria are key. GROWING POINTS/AREAS FOR RESEARCH: 'M cells', the specialized epithelial cells that overlie Peyer's patches, are a major interface between gut bacteria and the immune system. Improved understanding is needed of the bacteria involved in IBD pathogenesis, their genotypes and phenotypes, their portal of entry and their mechanism for escaping attack from the immune system. Bacterial ligands involved in bacteria-epithelial adhesion are emerging, and molecular techniques are rapidly increasing our knowledge of the human intestinal microbiota.

Small intestine lamina propria dendritic cells promote de novo generation of Foxp3 T reg cells via retinoic acid

To maintain immune homeostasis, the intestinal immune system has evolved redundant regulatory strategies. In this regard, the gut is home to a large number of regulatory T (T reg) cells, including the Foxp3⁺ T reg cell. Therefore, we hypothesized that the gut environment preferentially supports extrathymic T reg cell development. We show that peripheral conversion of CD4⁺ T cells to T reg cells occurs primarily in gut-associated lymphoid tissue (GALT) after oral exposure to antigen and in a lymphopenic environment. Dendritic cells (DCs) purified from the lamina propria (Lp; LpDCs) of the small intestine were found to promote a high level of T reg cell conversion relative to lymphoid organ–derived DCs. This enhanced conversion by LpDCs was dependent on TGF-β and retinoic acid (RA), which is a vitamin A metabolite highly expressed in GALT. Together, these data demonstrate that the intestinal immune system has evolved a self-contained strategy to promote T reg cell neoconversion.