Human small intestinal epithelial cells constitutively express the key elements for antigen processing and the production of exosomes

The renaissance of oral tolerance: merging tradition and new insights

Oral tolerance is the process by which feeding of soluble proteins induces antigen-specific systemic immune unresponsiveness. Oral tolerance is thought to have a central role in suppressing immune responses to 'harmless' food antigens, and its failure can lead to development of pathologies such as food allergies or coeliac disease. However, on the basis of long-standing experimental observations, the relevance of oral tolerance in human health has achieved new prominence recently following the discovery that oral administration of peanut proteins prevents the development of peanut allergy in at-risk human infants. In this Review, we summarize the new mechanistic insights into three key processes necessary for the induction of tolerance to oral antigens: antigen uptake and transport across the small intestinal epithelial barrier to the underlying immune cells; the processing, transport and presentation of fed antigen by different populations of antigen-presenting cells; and the development of immunosuppressive T cell populations that mediate antigen-specific tolerance. In addition, we consider how related but distinct processes maintain tolerance to bacterial antigens in the large intestine. Finally, we outline the molecular mechanisms and functional consequences of failure of oral tolerance and how these may be modulated to enhance clinical outcomes and prevent disease.

Generation of Devil Facial Tumour Cells Co-Expressing MHC With CD80, CD86 or 41BBL to Enhance Tumour Immunogenicity

The major histocompatibility complex (MHC) molecules play an integral role in the adaptive immune response to transmissible cancers through tumour antigen presentation and recognition of allogeneic MHC molecules. The transmissible devil facial tumours 1 and 2 (DFT1 and DFT2) modulate MHC-I antigen presentation to evade host immune responses and facilitate transmission of tumours cells to new Tasmanian devil (Sarcophilus harrisii) hosts. To enhance T-cell-driven tumour immunogenicity for vaccination and immunotherapy, DFT1 and DFT2 cells were co-transfected with (i) NLRC5 for MHC-I expression or CIITA for MHC-I and MHC-II expression, and (ii) a co-stimulatory molecule, either CD80, CD86 or 41BBL. The co-transfected DFT cells presented enhanced expression of MHC-I and/or MHC-II. As few devil-specific monoclonal antibodies exist, we used recombinant CTLA4 and 41BB fused to a fluorescent protein to confirm expression of cell surface CD80, CD86 and 41BBL. The capacity for these cells to induce T-cell responses including PD1 and IFNG expression was evaluated in in vitro co-culture assays with captive devil peripheral blood mononuclear cells (PBMCs). Although PBMC viability had increased, there was no evidence of enhanced T-cell activation. This system can be used to identify additional factors required to promote activation of naïve devil T-cells in vitro.

Assessing Cellular and Transcriptional Diversity of Ileal Mucosa Among Treatment-Naïve and Treated Crohn's Disease

BACKGROUND

Crohn's disease is a lifelong disease characterized by chronic inflammation of the gastrointestinal tract. Defining the cellular and transcriptional composition of the mucosa at different stages of disease progression is needed for personalized therapy in Crohn's.

METHODS

Ileal biopsies were obtained from (1) control subjects (n = 6), (2) treatment-naïve patients (n = 7), and (3) established (n = 14) Crohn's patients along with remission (n = 3) and refractory (n = 11) treatment groups. The biopsies processed using 10x Genomics single cell 5' yielded 139 906 cells. Gene expression count matrices of all samples were analyzed by reciprocal principal component integration, followed by clustering analysis. Manual annotations of the clusters were performed using canonical gene markers. Cell type proportions, differential expression analysis, and gene ontology enrichment were carried out for each cell type.

RESULTS

We identified 3 cellular compartments with 9 epithelial, 1 stromal, and 5 immune cell subtypes. We observed differences in the cellular composition between control, treatment-naïve, and established groups, with the significant changes in the epithelial subtypes of the treatment-naïve patients, including microfold, tuft, goblet, enterocyte,s and BEST4+ cells. Surprisingly, fewer changes in the composition of the immune compartment were observed; however, gene expression in the epithelial and immune compartment was different between Crohn's phenotypes, indicating changes in cellular activity.

CONCLUSIONS

Our study identified cellular and transcriptional signatures associated with treatment-naïve Crohn's disease that collectively point to dysfunction of the intestinal barrier with an increase in inflammatory cellular activity. Our analysis also highlights the heterogeneity among patients within the same disease phenotype, shining a new light on personalized treatment responses and strategies.

Extracellular Vesicles: The Next Generation Theranostic Nanomedicine for Inflammatory Bowel Disease

The recent rapid development in the field of extracellular vesicles (EVs) based nanotechnology has provided unprecedented opportunities for nanomedicine platforms. As natural nanocarriers, EVs such as exosomes, exosome-like nanoparticles and outer membrane vesicles (OMVs), have unique structure/composition/morphology characteristics, and show excellent physical and chemical/biochemical properties, making them a new generation of theranostic nanomedicine. Here, we reviewed the characteristics of EVs from the perspective of their formation and biological function in inflammatory bowel disease (IBD). Moreover, EVs can crucially participate in the interaction and communication of intestinal epithelial cells (IECs)-immune cells-gut microbiota to regulate immune response, intestinal inflammation and intestinal homeostasis. Interestingly, based on current representative examples in the field of exosomes and exosome-like nanoparticles for IBD treatment, it is shown that plant, milk, and cells-derived exosomes and exosome-like nanoparticles can exert a therapeutic effect through their components, such as proteins, nucleic acid, and lipids. Moreover, several drug loading methods and target modification of exosomes are used to improve their therapeutic capability. We also discussed the application of exosomes and exosome-like nanoparticles in the treatment of IBD. In this review, we aim to better and more clearly clarify the underlying mechanisms of the EVs in the pathogenesis of IBD, and provide directions of exosomes and exosome-like nanoparticles mediated for IBD treatment.

Mesenchymal Stromal/Stem Cells-Derived Exosomes as an Antimicrobial Weapon for Orodental Infections

The oral cavity as the second most various microbial community in the body contains a broad spectrum of microorganisms which are known as the oral microbiome. The oral microbiome includes different types of microbes such as bacteria, fungi, viruses, and protozoa. Numerous factors can affect the equilibrium of the oral microbiome community which can eventually lead to orodental infectious diseases. Periodontitis, dental caries, oral leukoplakia, oral squamous cell carcinoma are some multifactorial infectious diseases in the oral cavity. In defending against infection, the immune system has an essential role. Depending on the speed and specificity of the reaction, immunity is divided into two different types which are named the innate and the adaptive responses but also there is much interaction between them. In these responses, different types of immune cells are present and recent evidence demonstrates that these cell types both within the innate and adaptive immune systems are capable of secreting some extracellular vesicles named exosomes which are involved in the response to infection. Exosomes are 30-150 nm lipid bilayer vesicles that consist of variant molecules, including proteins, lipids, and genetic materials and they have been associated with cell-to-cell communications. However, some kinds of exosomes can be effective on the pathogenicity of various microorganisms and promoting infections, and some other ones have antimicrobial and anti-infective functions in microbial diseases. These discrepancies in performance are due to the origin of the exosome. Exosomes can modulate the innate and specific immune responses of host cells by participating in antigen presentation for activation of immune cells and stimulating the release of inflammatory factors and the expression of immune molecules. Also, mesenchymal stromal/stem cells (MSCs)-derived exosomes participate in immunomodulation by different mechanisms. Ease of expansion and immunotherapeutic capabilities of MSCs, develop their applications in hundreds of clinical trials. Recently, it has been shown that cell-free therapies, like exosome therapies, by having more advantages than previous treatment methods are emerging as a promising strategy for the treatment of several diseases, in particular inflammatory conditions. In orodental infectious disease, exosomes can also play an important role by modulating immunoinflammatory responses. Therefore, MSCs-derived exosomes may have potential therapeutic effects to be a choice for controlling and treatment of orodental infectious diseases.

Scavenger receptors in host defense: from functional aspects to mode of action

Scavenger receptors belong to a superfamily of proteins that are structurally heterogeneous and encompass the miscellaneous group of transmembrane proteins and soluble secretory extracellular domain. They are functionally diverse as they are involved in various disorders and biological pathways and their major function in innate immunity and homeostasis. Numerous scavenger receptors have been discovered so far and are apportioned in various classes (A-L). Scavenger receptors are documented as pattern recognition receptors and known to act in coordination with other co-receptors such as Toll-like receptors in generating the immune responses against a repertoire of ligands such as microbial pathogens, non-self, intracellular and modified self-molecules through various diverse mechanisms like adhesion, endocytosis and phagocytosis etc. Unlike, most of the scavenger receptors discussed below have both membrane and soluble forms that participate in scavenging; the role of a potential scavenging receptor Angiotensin-Converting Enzyme-2 has also been discussed whereby only its soluble form might participate in preventing the pathogen entry and replication, unlike its membrane-bound form. This review majorly gives an insight on the functional aspect of scavenger receptors in host defence and describes their mode of action extensively in various immune pathways involved with each receptor type. Video abstract.

An Update on the Role of Extracellular Vesicles in the Pathogenesis of Necrotizing Enterocolitis and Inflammatory Bowel Diseases

Some of the most fundamental influences of microorganisms inhabiting the human intestinal tract are exerted during infant development and impact the maturation of intestinal mucosa and gut immune system. The impact of bacteria on the host gut immune system is partially mediated via released extracellular vesicles (EVs). The heterogeneity in EV content, size, and bacterial species origin can have an impact on intestinal cells, resulting in inflammation and an immune response, or facilitate pathogen entry into the gut wall. In mammals, maintaining the integrity of the gut barrier might also be an evolutionary function of maternal milk EVs. Recently, the usage of EVs has been explored as a novel therapeutic approach in several pathological conditions, including necrotizing enterocolitis (NEC) and inflammatory bowel disease (IBD). In this review, we attempt to summarize the current knowledge of EV biology, followed by a discussion of the role that EVs play in gut maturation and the pathogenesis of NEC and IBD.

Extracellular vesicles: General features and usefulness in diagnosis and therapeutic management of colorectal cancer

In the world, among all type of cancers, colorectal cancer (CRC) is the third most commonly diagnosed in males and the second in females. In most of cases, (RP1) patients’ prognosis limitation with malignant tumors can be attributed to delayed diagnosis of the disease. Identification of patients with early-stage disease leads to more effective therapeutic interventions. Therefore, new screening methods and further innovative treatment approaches are mandatory as they may lead to an increase in progression-free and overall survival rates. For the last decade, the interest in extracellular vesicles (EVs) research has exponentially increased as EVs generation appears to be a universal feature of every cell that is strongly involved in many mechanisms of cell-cell communication either in physiological or pathological situations. EVs can cargo biomolecules, such as lipids, proteins, nucleic acids and generate transmission signal through the intercellular transfer of their content. By this mechanism, tumor cells can recruit and modify the adjacent and systemic microenvironment to support further invasion and dissemination. This review intends to cover the most recent literature on the role of EVs production in colorectal normal and cancer tissues. Specific attention is paid to the use of EVs for early CRC diagnosis, follow-up, and prognosis as EVs have come into the spotlight of research as a high potential source of ‘liquid biopsies’. The use of EVs as new targets or nanovectors as drug delivery systems for CRC therapy is also summarized.

Exosomes in Intestinal Inflammation

Exosomes are 30–150 nm sized vesicles released by a variety of cells, and are found in most physiological compartments (feces, blood, urine, saliva, breast milk). They can contain different cargo, including nucleic acids, proteins and lipids. In Inflammatory Bowel Disease (IBD), a distinct exosome profile can be detected in blood and fecal samples. In addition, circulating exosomes can carry targets on their surface for monoclonal antibodies used as IBD therapy. This review aims to understand the exosome profile in humans and other mammals, the cargo contained in them, the effect of exosomes on the gut, and the application of exosomes in IBD therapy.

Cell-to-Cell Communication by Host-Released Extracellular Vesicles in the Gut: Implications in Health and Disease

Communication between cells is crucial to preserve body homeostasis and health. Tightly controlled intercellular dialog is particularly relevant in the gut, where cells of the intestinal mucosa are constantly exposed to millions of microbes that have great impact on intestinal homeostasis by controlling barrier and immune functions. Recent knowledge involves extracellular vesicles (EVs) as mediators of such communication by transferring messenger bioactive molecules including proteins, lipids, and miRNAs between cells and tissues. The specific functions of EVs principally depend on the internal cargo, which upon delivery to target cells trigger signal events that modulate cellular functions. The vesicular cargo is greatly influenced by genetic, pathological, and environmental factors. This finding provides the basis for investigating potential clinical applications of EVs as therapeutic targets or diagnostic biomarkers. Here, we review current knowledge on the biogenesis and cargo composition of EVs in general terms. We then focus the attention to EVs released by cells of the intestinal mucosa and their impact on intestinal homeostasis in health and disease. We specifically highlight their role on epithelial barrier integrity, wound healing of epithelial cells, immunity, and microbiota shaping. Microbiota-derived EVs are not reviewed here.

The primacy of gastrointestinal tract antigen-presenting cells in lethal graft-versus-host disease

Allogeneic stem cell transplantation is a cornerstone of curative therapy for high-risk and/or advanced hematological malignancies but remains limited by graft-versus-host disease (GVHD). GVHD is initiated by the interaction between recipient antigen-presenting cells (APCs) and donor T cells, culminating in T-cell differentiation along pathogenic type-1 and type-17 paradigms at the expense of tolerogenic regulatory T-cell patterns. Type-1 and type-17 T cells secrete cytokines (eg, granulocyte-macrophage colony-stimulating factor and interferon-γ) critical to the cytokine storm that amplifies expansion of donor APCs and their alloantigen presentation. It has become increasingly clear that pathogenic donor T-cell differentiation is initiated by both professional recipient APCs (eg, dendritic cells [DCs]) and nonprofessional APCs (eg, epithelial and mesenchymal cells), particularly within the gastrointestinal (GI) tract. In the immediate peritransplantation period, these APCs are profoundly modified by pathogen-associated molecular pattern (PAMP)/damage-associated molecular pattern (DAMP) signals derived from conditioning and intestinal microbiota. Subsequently, donor DCs in the GI tract are activated by DAMP/PAMP signals in the colon that gain access to the lamina propria once the mucosal barrier mucosa is compromised by GVHD. This results in donor DC expansion and alloantigen presentation in the colon and subsequent migration into the mesenteric lymph nodes. Here, new donor T cells are primed, expanded, differentiated, and imprinted with gut-homing integrins permissive of migration into the damaged GI tract, resulting in the lethal feed-forward cascade of GVHD. These new insights into our understanding of the cellular and molecular factors initiating GVHD, both spatially and temporally, give rise to a number of logical therapeutic targets, focusing on the inhibition of APC function in the GI tract.

[Dialogue between intestinal stem cells and CD4+ T lymphocytes orchestrates intestinal stem cell homeostasis]

Dans le cadre d’un partenariat avec médecine/sciences, et pour la troisième année, des étudiants du module d’immunologie virologie et cancer du Master de cancérologie de Lyon présentent une analyse d’articles scientifiques récents faisant état d’observations innovantes et importantes. Ce travail a été encadré par des chercheurs confirmés du département d’immunologie, virologie et inflammation du CRCL. Le master de cancérologie de Lyon (Lyon1-VetAgroSup) accueille chaque année 30 à 40 étudiants en M1 et en M2. Ce master dit « d’excellence » assure aux étudiants de M1 une formation à la cancérologie reposant sur un socle de base commun (biologie cellulaire, moléculaire, immunologie, bio-statistique...). En M2, les étudiants peuvent choisir l’une des trois spécialités suivantes : le Master recherche « Recherche en cancérologie », le Master recherche et professionnel « Technologie haut débit en cancérologie » et enfin le Master recherche et professionnel « Innovations thérapeutiques en cancérologie ». Le Master de cancérologie de Lyon repose sur une forte implication des chercheurs et enseignants-chercheurs du laboratoire d’excellence en développement et cancérologie (LabEx DEVweCAN), ainsi que sur un partenariat solide avec plusieurs instituts dont le MIT (Massachusetts Institute of Technology, Cambridge, États-Unis), l’université d’Harvard (Boston, États-Unis), l’université Johns Hopkins (Baltimore, États-Unis), l’Imperial College of London (Royaume-Uni), les universités de Jiao Tong (République Populaire de Chine) et de Tokyo (Japon), entre autres. Pour plus d’information : http://devwecan.universite-lyon.fr/formation/

Extracellular Vesicles with Possible Roles in Gut Intestinal Tract Homeostasis and IBD

The intestinal tract consists of various types of cells, such as epithelial cells, Paneth cells, macrophages, and lymphocytes, which constitute the intestinal immune system and play a significant role in maintaining intestinal homeostasis by producing antimicrobial materials and controlling the host-commensal balance. Various studies have found that the dysfunction of intestinal homeostasis contributes to the pathogenesis of inflammatory bowel disease (IBD). As a novel mediator, extracellular vesicles (EVs) have been recognized as effective communicators, not only between cells but also between cells and the organism. In recent years, EVs have been regarded as vital characters for dysregulated homeostasis and IBD in either the etiology or the pathology of intestinal inflammation. Here, we review recent studies on EVs associated with intestinal homeostasis and IBD and discuss their source, cargo, and origin, as well as their therapeutic effects on IBD, which mainly include artificial nanoparticles and EVs derived from microorganisms.

Intestinal epithelial cells: at the interface of the microbiota and mucosal immunity

The intestinal epithelium forms a barrier between the microbiota and the rest of the body. In addition, beyond acting as a physical barrier, the function of intestinal epithelial cells (IECs) in sensing and responding to microbial signals is increasingly appreciated and likely has numerous implications for the vast network of immune cells within and below the intestinal epithelium. IECs also respond to factors produced by immune cells, and these can regulate IEC barrier function, proliferation and differentiation, as well as influence the composition of the microbiota. The mechanisms involved in IEC-microbe-immune interactions, however, are not fully characterized. In this review, we explore the ability of IECs to direct intestinal homeostasis by orchestrating communication between intestinal microbes and mucosal innate and adaptive immune cells during physiological and inflammatory conditions. We focus primarily on the most recent findings and call attention to the numerous remaining unknowns regarding the complex crosstalk between IECs, the microbiota and intestinal immune cells.

Microfluidic Technology for Clinical Applications of Exosomes

Exosomes, a type of nanovesicle, are distinct cellular entities specifically capable of carrying various cargos between cells. It has been hypothesized that exosomes, as an enriched source of biomolecules, may serve as biomarkers for various diseases. This review introduces general aspects of exosomes, presents the challenges in exosome research, discusses the potential of exosomes as biomarkers, and describes the contribution of microfluidic technology to enable their isolation and analysis for diagnostic and disease monitoring. Additionally, clinical applications of exosomes for diagnostic purposes are also summarized.

In vivo multivesicular bodies and their exosomes in the absorptive cells of the zebrafish (Danio Rerio) gut

Intercellular communication of gut epithelial cells is critical to gut mucosal homeostasis. Exosomes are important intercellular mediators in communication between cell to cell. Although many literature focus on the immunologic roles in the gut by the exosomes, the biological process of exosomes in the absorptive cells remains unknown. Uncovering the distribution, classification and formation process of multivesicular bodies (MVBs) and their exosomes in the absorptive cells of the zebrafish gut, is urgently needed to establish a platform for immunological research of fish gut exosomes. The expression levels of CD63 and TSG101 were different among the three segments of the gut, and they were enriched at the apex of the mid gut villi. The characteristics of MVBs and their exosomes in the absorptive cells were further revealed by transmission electron microscopy (TEM). Early endosomes (ee) were mainly present in the apical and basal cytoplasm of absorptive cells. Late endosomes (le) were mostly distributed with the supranuclear part of these cells. "Heterogeneous" MVBs were detected underlying the apical membranes of absorptive cells. Many exosomes with some MVB-like structures occurred in the lumen, indicating that the release process was mainly through apical secretion. Various MVBs with exosomes and the endosome-heterogeneous MVB-exosome complex existed widely in the mid gut absorptive cells, concluding that zebrafish as a potential model for in vivo MVBs and their exosomes research. All the results were summarized in a schematic diagram illustrating the morphological characteristics of gut MVBs and their exosomes in zebrafish.

Class II MHC antigen processing in immune tolerance and inflammation

Presentation of peptide antigens by MHC-II proteins is prerequisite to effective CD4 T cell tolerance to self and to recognition of foreign antigens. Antigen uptake and processing pathways as well as expression of the peptide exchange factors HLA-DM and HLA-DO differ among the various professional and non-professional antigen-presenting cells and are modulated by cell developmental state and activation. Recent studies have highlighted the importance of these cell-specific factors in controlling the source and breadth of peptides presented by MHC-II under different conditions. During inflammation, increased presentation of selected self-peptides has implications for maintenance of peripheral tolerance and autoimmunity.

Amnion epithelial cell-derived exosomes induce inflammatory changes in uterine cells

BACKGROUND

Fetal endocrine signals are generally considered to contribute to the timing of birth and the initiation of labor. Fetal tissues under oxidative stress release inflammatory mediators that lead to sterile inflammation within the maternal-fetal interface. Importantly, these inflammatory mediators are packaged into exosomes, bioactive cell-derived extra cellular vesicles that function as vectors and transport them from the fetal side to the uterine tissues where they deposit their cargo into target cells enhancing uterine inflammatory load. This exosome-mediated signaling is a novel mechanism for fetal-maternal communication.

OBJECTIVE

This report tested the hypothesis that oxidative stress can induce fetal amnion cells to produce exosomes, which function as a paracrine intermediary between the fetus and mother and biochemically signal readiness for parturition.

STUDY DESIGN

Primary amnion epithelial cells were grown in normal cell culture (control) or exposed to oxidative stress conditions (induced by cigarette smoke extract). Exosomes were isolated from cell supernatant by sequential ultracentrifugation. Exosomes were quantified and characterized based on size, shape, and biochemical markers. Myometrial, decidual, and placental cells (BeWo) were treated with 2 × 105, 2 × 107, and 2 × 109 control or oxidative stress-derived amnion epithelial cell exosomes for 24 hours. Entry of amnion epithelial cell exosomes into cells was confirmed by confocal microscopy of fluorescent-labeled exosomes. The effect of amnion epithelial cell exosomes on target cell inflammatory status was determined by measuring production of interleukin-6, interleukin-8, interleukin-1β, tumor necrosis factor-α, and prostaglandin E2 by enzyme-linked immunosorbent assay and inflammatory gene transcription factor (nuclear factor-κβ) activation status by immunoblotting for phosphorylated RelA/p65. Localization of NANOG in term human myometrium and decidua obtained from women before labor and during labor was performed using immunohistochemistry. Data were analyzed by Wilcoxon-Mann-Whitney test to compare effects of exosomes from control and oxidative stress-treated amnion epithelial cells on inflammatory status of target cells.

RESULTS

Amnion epithelial cells released ∼125 nm, cup-shaped exosomes with ∼899 and 1211 exosomes released per cell from control and oxidative stress-induced cells, respectively. Amnion epithelial cell exosomes were detected in each target cell type after treatment using confocal microscopy. Treatment with amnion epithelial cell exosomes increased secretion of interleukin-6, interleukin-8, and PGE2 and activation of NF-κβ (each P < .05) in myometrial and decidual cells. Exosome treatments had no effect on interleukin-6 and PGE2 production in BeWo cells. NANOG staining was higher in term labor myometrium and decidua compared to tissues not in labor.

CONCLUSION

In vitro, amnion epithelial cell exosomes lead to an increased inflammatory response in maternal uterine cells whereas placental cells showed refractoriness. Fetal cell exosomes may function to signal parturition by increasing maternal gestational cell inflammation.

The elusive case of human intraepithelial T cells in gut homeostasis and inflammation

The epithelial barrier of the gastrointestinal tract is home to numerous intraepithelial T cells (IETs). IETs are functionally adapted to the mucosal environment and are among the first adaptive immune cells to encounter microbial and dietary antigens. They possess hallmark features of tissue-resident T cells: they are long-lived nonmigratory cells capable of rapidly responding to antigen challenges independent of T cell recruitment from the periphery. Gut-resident T cells have been implicated in the relapsing and remitting course and persisting low-grade inflammation of chronic gastrointestinal diseases, including IBD and coeliac disease. So far, most data IETs have been derived from experimental animal models; however, IETs and the environmental makeup differ between mice and humans. With advances in techniques, the number of human studies has grown exponentially in the past 5 years. Here, we review the literature on the involvement of human IETs in gut homeostasis and inflammation, and how these cells are influenced by the microbiota and dietary antigens. Finally, targeting of IETs in therapeutic interventions is discussed. Broad insight into the function and role of human IETs in gut homeostasis and inflammation is essential to identify future diagnostic, prognostic and therapeutic strategies.

Epithelial MHC Class II Expression and Its Role in Antigen Presentation in the Gastrointestinal and Respiratory Tracts

As the primary barrier between an organism and its environment, epithelial cells are well-positioned to regulate tolerance while preserving immunity against pathogens. Class II major histocompatibility complex molecules (MHC class II) are highly expressed on the surface of epithelial cells (ECs) in both the lung and intestine, although the functional consequences of this expression are not fully understood. Here, we summarize current information regarding the interactions that regulate the expression of EC MHC class II in health and disease. We then evaluate the potential role of EC as non-professional antigen presenting cells. Finally, we explore future areas of study and the potential contribution of epithelial surfaces to gut-lung crosstalk.

Host-Derived Serine Protease Inhibitor 6 Provides Granzyme B-Independent Protection of Intestinal Epithelial Cells in Murine Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a serious complication after allogeneic hematopoietic cell transplantation (allo-HCT) that limits the therapeutic potential of this treatment. Host antigen-presenting cells (APCs) play a vital role in activating donor T cells that subsequently use granzyme B (GzmB) and other cytotoxic molecules to damage host normal tissues. Serine protease inhibitor 6 (Spi6), known as the sole endogenous inhibitor of GzmB, has been implicated in protecting T cells and APCs against GzmB-inflicted damage. In this study we used murine models to examine the previously unknown role of host-derived Spi6 in GVHD pathogenesis. Our results indicated that host Spi6 deficiency exacerbated GVHD as evidenced by significantly increased lethality and clinical and histopathologic scores. Using bone marrow chimera system, we found that Spi6 in nonhematopoietic tissue played a dominant role in protecting against GVHD and was significantly upregulated in intestinal epithelial cells after allo-HCT, whereas Spi6 in hematopoietic APCs surprisingly suppressed alloreactive T cell response. Interestingly, the protective effect of Spi6 and its expression in intestinal epithelial cells appeared to be independent of donor-derived GzmB. We used in silico modeling to explore potential targets of Spi6. Interaction tested in silico demonstrated that Spi6 could inhibit caspase-3 and caspase-8 with the same functional loop that inhibits GzmB but was not capable of forming stable interaction with caspase-1 or granzyme A. Using an in vitro co-culture system, we further identified that donor T cell-derived IFN-γ was important for inducing Spi6 expression in an intestinal epithelial cell line. Altogether, our data indicate that host Spi6 plays a novel, GzmB-independent role in regulating alloreactive T cell response and protecting intestinal epithelial cells. Therefore, enhancing host-derived Spi6 function has the potential to reduce GVHD.

Exosomes, DAMPs and miRNA: Features of Stress Physiology and Immune Homeostasis

Psychological/physical stressors and local tissue damage increase inflammatory proteins in tissues and blood in humans and animals, in the absence of pathogenic disease. Stress-evoked cytokine/chemokine responses, or sterile inflammation, can facilitate host survival and/or negatively affect health, depending on context. Recent evidence supports the hypothesis that systemic stress-evoked sterile inflammation is initiated by the sympathetic nervous system, resulting in the elevation of exosome-associated immunostimulatory endogenous danger/damage associated molecular patterns (DAMPs) and a reduction in immunoinhibitory miRNA, which are carried in the circulation to tissues throughout the body. We propose that sterile inflammation should be considered an elemental feature of the stress response and that circulating exosomes transporting immunomodulatory signals, may play a role fundamental role in immune homeostasis.

Molecular pathways driving disease-specific alterations of intestinal epithelial cells

Due to the fact that chronic inflammation as well as tumorigenesis in the gut is crucially impacted by the fate of intestinal epithelial cells, our article provides a comprehensive overview of the composition, function, regulation and homeostasis of the gut epithelium. In particular, we focus on those aspects which were found to be altered in the context of inflammatory bowel diseases or colorectal cancer and also discuss potential molecular targets for a disease-specific therapeutic intervention.

Urinary Microvesicle-Bound Uromodulin: A Potential Molecular Biomarker in Diabetic Kidney Disease

This study was designed to investigate the changes of urinary microvesicle-bound uromodulin and total urinary uromodulin levels in human urine and the correlations with the severity of diabetic kidney disease (DKD). 31 healthy subjects without diabetes and 100 patients with type 2 diabetes mellitus (T2DM) were included in this study. The patients with T2DM were divided into three groups based on the urinary albumin/creatinine ratio (UACR): normoalbuminuria group (DM, n = 46); microalbuminuria group (DN1, n = 32); and macroalbuminuria group (DN2, n = 22). We use a specific monoclonal antibody AD-1 to capture the urinary microvesicles. Urinary microvesicle-bound uromodulin and total urinary uromodulin levels were determined by enzyme-linked immunosorbent assay (ELISA). Our results showed that the levels of urinary microvesicle-bound uromodulin in DN1 and DN2 groups were significantly higher than those in control group and DM group (P < 0.01). Multiple stepwise linear regression analysis showed that UACR was independent determinant for urinary microvesicle-bound uromodulin (P < 0.05) but not for total urinary uromodulin. These findings suggest that the levels of urinary microvesicle-bound uromodulin are associated with the severity of DKD. The uromodulin in urinary microvesicles may be a specific marker of DKD and potentially may be used to predict the onset and/or monitor the progression of DKD.

CD68/macrosialin: not just a histochemical marker

CD68 is a heavily glycosylated glycoprotein that is highly expressed in macrophages and other mononuclear phagocytes. Traditionally, CD68 is exploited as a valuable cytochemical marker to immunostain monocyte/macrophages in the histochemical analysis of inflamed tissues, tumor tissues, and other immunohistopathological applications. CD68 alone or in combination with other cell markers of tumor-associated macrophages showed a good predictive value as a prognostic marker of survival in cancer patients. Lowression of CD68 was found in the lymphoid cells, non-hematopoietic cells (fibroblasts, endothelial cells, etc), and tumor cells. Cell-specific CD68 expression and differentiated expression levels are determined by the complex interplay between transcription factors, regulatory transcriptional elements, and epigenetic factors. Human CD68 and its mouse ortholog macrosialin belong to the family of LAMP proteins located in the lysosomal membrane and share many structural similarities such as the presence of the LAMP-like domain. Except for a second LAMP-like domain present in LAMPs, CD68/microsialin has a highly glycosylated mucin-like domain involved in ligand binding. CD68 has been shown to bind oxLDL, phosphatidylserine, apoptotic cells and serve as a receptor for malaria sporozoite in liver infection. CD68 is mainly located in the endosomal/lysosomal compartment but can rapidly shuttle to the cell surface. However, the role of CD68 as a scavenger receptor remains to be confirmed. It seems that CD68 is not involved in binding bacterial/viral pathogens, innate, inflammatory or humoral immune responses, although it may potentially be involved in antigen processing/presentation. CD68 could be functionally important in osteoclasts since its deletion leads to reduced bone resorption capacity. The role of CD68 in atherosclerosis is contradictory.

EpCAM-dependent extracellular vesicles from intestinal epithelial cells maintain intestinal tract immune balance

How the intestinal tract develops a tolerance to foreign antigens is still largely unknown. Here we report that extracellular vesicles (EVs) with TGF-β1-dependent immunosuppressive activity are produced by intestinal epithelial cells (IECs) under physiological conditions. Transfer of these EVs into inflammatory bowel disease (IBD) mice induced by dextran sulfate sodium salt decreases IBD severity by inducing regulatory T cells and immunosuppressive dendritic cells. In contrast, decreased endogenous EV production promotes IBD development. IECs produce EVs with increased levels of TGF-β1 upon IBD development in an ERK-dependent manner. Furthermore, these EVs tend to localize in the intestinal tract associated with epithelial cell adhesion molecule (EpCAM). Knockdown of EpCAM in vivo increases the severity of murine IBD, and the protective effect of EVs from IECs with decreased EpCAM on murine IBD is blunted. Therefore, our study indicates that EVs from IECs participate in maintaining the intestinal tract immune balance.

Neisseria gonorrhoeae Modulates Cell Death in Human Endocervical Epithelial Cells through Export of Exosome-Associated cIAP2

Several bacterial pathogens persist and survive in the host by modulating host cell death pathways. We previously demonstrated that Neisseria gonorrhoeae, a Gram-negative pathogen responsible for the sexually transmitted infection gonorrhea, protects against exogenous induction of apoptosis in human cervical epithelial cells. However, induction of cell death by N. gonorrhoeae has also been reported in other cell types. The mechanisms by which N. gonorrhoeae modulates cell death are not clear, although a role for the inhibitor of apoptosis-2 (cIAP2) has been proposed. In this study, we confirmed that N. gonorrhoeae induces production of cIAP2 in human cervical epithelial cells. High levels of intracellular cIAP2 were detected early after N. gonorrhoeae stimulation, which was followed by a marked decrease at 24 h. At this time point, we observed increased levels of extracellular cIAP2 associated with exosomes and an overall increase in production of exosomes. Inhibition of cIAP2 in N. gonorrhoeae-stimulated epithelial cells resulted in increased cell death and interleukin-1β (IL-1β) production. Collectively these results indicate that N. gonorrhoeae stimulation of human endocervical epithelial cells induces the release of cIAP2, an essential regulator of cell death and immune signaling.

Immunotherapeutic potential of extracellular vesicles

Extracellular vesicle or EV is a term that encompasses all classes of secreted lipid membrane vesicles. Despite being scientific novelties, EVs are gaining importance as a mediator of important physiological and pathological intercellular activities possibly through the transfer of their cargo of protein and RNA between cells. In particular, exosomes, the currently best characterized EVs have been notable for their in vitro and in vivo immunomodulatory activities. Exosomes are nanometer-sized endosome-derived vesicles secreted by many cell types and their immunomodulatory potential is independent of their cell source. Besides immune cells such as dendritic cells, macrophages, and T cells, cancer and stem cells also secrete immunologically active exosomes that could influence both physiological and pathological processes. The immunological activities of exosomes affect both innate and adaptive immunity and include antigen presentation, T cell activation, T cell polarization to regulatory T cells, immune suppression, and anti-inflammation. As such, exosomes carry much immunotherapeutic potential as a therapeutic agent and a therapeutic target.

Nuts 'n' guts: transport of food allergens across the intestinal epithelium

The increase in the incidence of food allergy is a growing problem for the western world. This review will focus on the findings from several macromolecular epithelial transport experiments and drug permeability studies to provide a recent comprehension of food allergen intestinal epithelial cell transport and the allergen-epithelial relationship. Specifically, this review will aim to answer whether allergens can permeate the intestinal barrier directly via intestinal epithelial cells, and whether this mode of transport affects downstream immune reactions. By improving our understanding of the interactions which take place during exposure of food allergens with the intestinal epithelium, we can begin to understand whether the epithelial barrier plays a major role in the allergic sensitization process rather than simply restricting the entry of allergens to the underlying lamina propria.

Gut-associated lymphoid tissues for the development of oral vaccines

Oral vaccine has been considered to be a prospective vaccine against many pathogens especially invading across gastrointestinal tracts. One key element of oral vaccine is targeting efficient delivery of antigen to gut-associated lymphoid tissue (GALT), the inductive site in the intestine where antigen-specific immune responses are initiated. Various chemical and biological antigen delivery systems have been developed and some are in clinical trials. In this review, we describe the immunological features of GALT and the current status of antigen delivery system candidates for successful oral vaccine.

Gut microbiota, probiotics and inflammatory bowel disease

The colonization of humans with commensals is critical for our well-being. This tightly regulated symbiotic relationship depends on the flora and an intact mucosal immune system. A disturbance of either compound can cause intestinal inflammation. This review summarizes extrinsic and intrinsic factors contributing to intestinal dysbiosis and inflammatory bowel disease.

Membrane vesicles released by intestinal epithelial cells infected with rotavirus inhibit T-cell function

Rotavirus (RV) predominantly replicates in intestinal epithelial cells (IEC), and "danger signals" released by these cells may modulate viral immunity. We have recently shown that human model IEC (Caco-2 cells) infected with rhesus-RV release a non-inflammatory group of immunomodulators that includes heat shock proteins (HSPs) and TGF-β1. Here we show that both proteins are released in part in association with membrane vesicles (MV) obtained from filtrated Caco-2 supernatants concentrated by ultracentrifugation. These MV express markers of exosomes (CD63 and others), but not of the endoplasmic reticulum (ER) or nuclei. Larger quantities of proteins associated with MV were released by RV-infected cells than by non-infected cells. VP6 co-immunoprecipitated with CD63 present in these MV, and VP6 co-localized with CD63 in RV-infected cells, suggesting that this viral protein is associated with the MV, and that this association occurs intracellularly. CD63 present in MV preparations from stool samples from 36 children with gastroenteritis due or not due to RV were analyzed. VP6 co-immunoprecipitated with CD63 in 3/8 stool samples from RV-infected children, suggesting that these MV are released by RV-infected cells in vivo. Moreover, fractions that contained MV from RV-infected cells induced death and inhibited proliferation of CD4(+) T cells to a greater extent than fractions from non-infected cells. These effects were in part due to TGF-β, because they were reversed by treatment of the T cells with the TGF-β-receptor inhibitor ALK5i. MV from RV-infected and non-infected cells were heterogeneous, with morphologies and typical flotation densities described for exosomes (between 1.10 and 1.18 g/mL), and denser vesicles (>1.24 g/mL). Both types of MV from RV-infected cells were more efficient at inhibiting T-cell function than were those from non-infected cells. We propose that RV infection of IEC releases MV that modulate viral immunity.

Function of the intestinal epithelium and its dysregulation in inflammatory bowel disease

The intestinal epithelium not only acts as a physical barrier to commensal bacteria and foreign antigens but is also actively involved in antigen processing and immune cell regulation. The inflammatory bowel diseases (IBDs) are characterized by inflammation at this mucosal surface with well-recognized defects in barrier and secretory function. In addition to this, defects in intraepithelial lymphocytes, chemokine receptors, and pattern recognition receptors promote an abnormal immune response, with increased differentiation of proinflammatory cells and a dysregulated relationship with professional antigen-presenting cells. This review focuses on recent developments in the structure of the epithelium, including a detailed account of the apical junctional complex in addition to the role of the enterocyte in antigen recognition, uptake, processing, and presentation. Recently described cytokines such as interleukin-22 and interleukin-31 are highlighted as is the dysregulation of chemokines and secretory IgA in IBD. Finally, the effect of the intestinal epithelial cell on T effector cell proliferation and differentiation are examined in the context of IBD with particular focus on T regulatory cells and the two-way interaction between the intestinal epithelial cell and certain immune cell populations.

A33 antigen-deficient mice have defective colonic mucosal repair

BACKGROUND

A33 antigen is a transmembrane protein expressed predominantly in normal intestinal epithelium and most colon cancers and cell lines. The function of A33 antigen is unclear, but indirect evidence indicates a role in cell adhesion, trafficking, and the gut immune response. The aim of this study was to determine the contribution made by A33 antigen in mediating colonic repair following colitis induction in the A33 antigen-deficient mutant mouse.

METHODS

Colitis was induced by treatment with TNBS/ethanol. A33 antigen-deficient or wildtype mice were sacrificed at 0, 3, 7, and 14 days after colitis induction and morphological damage, mucosal proliferation, and inflammatory cell infiltration were quantified. In a subsequent study, following the induction of colitis mice were monitored for 22 days and morbidity and mortality determined.

RESULTS

Mice lacking A33 antigen expression were compromised in their ability to resolve TNBS-induced damage and exhibited distinct crypt pathology. In A33 antigen-deficient mice morphological damage remained unresolved at 14 days postcolitis induction. Increases in colonic cell proliferation were delayed in A33 antigen-deficient mice, and the rate of crypt fission was increased after TNBS treatment. Commensurate with these observations, polymorphonuclear cell infiltration was suppressed in the absence of A33 antigen. Mortality following colitis induction was 20% higher in A33 antigen-deficient mice than in wildtype controls.

CONCLUSIONS

Mice deficient in A33 antigen expression show impaired resolution of hapten-induced mucosal damage, leading to increased mortality, associated with impaired epithelial cell proliferation and a suppressed adaptive immune response. This study suggests a contribution for A33 antigen in the colonic healing response following mucosal damage.

Tumor-derived microvesicles promote regulatory T cell expansion and induce apoptosis in tumor-reactive activated CD8+ T lymphocytes

Sera of patients with cancer contain membraneous microvesicles (MV) able to induce apoptosis of activated T cells by activating the Fas/Fas ligand pathway. However, the cellular origin of MV found in cancer patients' sera varies as do their molecular and cellular profiles. To distinguish tumor-derived MV in cancer patients' sera, we used MAGE 3/6(+) present in tumors and MV. Molecular profiles of MAGE 3/6(+) MV were compared in Western blots or by flow cytometry with those of MV secreted by dendritic cells or activated T cells. These profiles were found to be distinct for each cell type. Only tumor-derived MV were MAGE 3/6(+) and were variably enriched in 42-kDa Fas ligand and MHC class I but not class II molecules. Effects of MV on signaling via the TCR and IL-2R and proliferation or apoptosis of activated primary T cells and T cell subsets were also assessed. Functions of activated CD8(+) and CD4(+) T lymphocytes were differentially modulated by tumor-derived MV. These MV inhibited signaling and proliferation of activated CD8(+) but not CD4(+) T cells and induced apoptosis of CD8(+) T cells, including tumor-reactive, tetramer(+)CD8(+) T cells as detected by flow cytometry for caspase activation and annexin V binding or by DNA fragmentation. Tumor-derived but not dendritic cell-derived MV induced the in vitro expansion of CD4(+)CD25(+)FOXP3(+) T regulatory cells and enhanced their suppressor activity. The data suggest that tumor-derived MV induce immune suppression by promoting T regulatory cell expansion and the demise of antitumor CD8(+) effector T cells, thus contributing to tumor escape.

Essential role of Notch signaling in apoptosis of human pancreatic tumoral cells mediated by exosomal nanoparticles

We previously reported that exosomal nanoparticles secreted by human pancreatic tumoral cell lines decrease tumoral cell proliferation through the mitochondria-dependent apoptotic pathway, because of activation of pro-apoptotic phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and of glucose synthase kinase-3beta (GSK-3beta). Interactions between exosomal nanoparticles and cells are thought to involve membrane lipid rafts. However, the underlying mechanism is unknown. Here, we report that the interaction of exosomal nanoparticles with pancreatic cancer cells led to decreased expression of hairy and enhancer-of-split homolog-1 (Hes-1), the intranuclear target of Notch-1 signaling pathway, and to activation of the apoptotic pathway after a cell cycle arrest in G(0)G(1) phase. Strikingly, the expression level of Notch-1 pathway components was critical, because exosomal nanoparticles decreased the proliferation of cells in which these partners are either weakly represented, in differentiated adenocarcinoma cells, or inhibited, in poorly differentiated carcinoma cells, by blocking presenilin in the gamma-secretase complex that regulates the Notch-1 pathway. Overexpression of Notch-1 intracellular domain resulted in the reversion of the cell proliferation inhibition promoted by exosomal nanoparticles. Blocking presenilin unexpectedly resulted in activation of PTEN and GSK-3beta. Conversely, inhibiting either PTEN or GSK-3beta increased Hes-1 expression and partially counteracted the inhibition of proliferation promoted by exosomal nanoparticles, highlighting reciprocal regulations between Notch signaling and PTEN/GSK-3beta. We concluded that interactions of exosomal nanoparticles with target cells, at lipid rafts where Notch-1 pathway partners are localized, hampered the functioning of the Notch-1 survival pathway and activated the apoptotic pathway, which determines tumoral cell fate.

Multivesicular bodies in intestinal epithelial cells: responsible for MHC class II-restricted antigen processing and origin of exosomes

In normal conditions intestinal epithelial cells (IECs) constitutively stimulate regulatory CD4(+) T cells. However, in Crohn's disease (CD), this major histocompatibility complex (MHC) class II-restricted antigen presentation results in stimulation of proinflammatory CD4(+) T cells. We hypothesized that these alternative functions might be mediated by differential sorting and processing of antigens into distinct MHC II-enriched compartments (MIICs). Accordingly, we analysed the endocytic pathways of lumenally applied ovalbumin (OVA) in IECs of the jejunum and ileum of wild-type (WT) and TNFDeltaARE/WT mice that develop a CD-resembling ileitis. Using quantitative reverse transcription polymerase chain reaction, we found that messenger RNA levels of interferon-gamma, tumour necrosis factor-alpha, interleukin-17 and interleukin-10 were significantly up-regulated in the inflamed ileum of TNFDeltaARE/WT mice, confirming CD-like inflammation. Fluorescence and immunoelectron microscopy revealed the presence of MHC II and invariant chain throughout the late endocytic compartments, with most molecules concentrated in the multivesicular bodies (MVB). OVA was targeted into MVB and, in contrast to other MIICs, accumulated in these structures within 120 min of exposure. The IEC-specific A33 antigen localized to internal vesicles of MVB and A33/class II-bearing exosomes were identified in intercellular spaces. Remarkably, the expression pattern of MHC II/invariant chain molecules and the trafficking of OVA were independent of mucosal inflammation and the specific region in the small intestine. MVB seem to be principally responsible for class II-associated antigen processing in IECs and to constitute the origin of MHC II-loaded exosomes. The distinctive functions of IECs in antigen presentation to CD4(+) T cells might arise as a result of differential processing within the MVB identified here.

HLA-DM negatively regulates HLA-DR4-restricted collagen pathogenic peptide presentation and T cell recognition

Rheumatoid arthritis, an autoimmune disease, is significantly associated with the HLA class II allele HLA-DR4. While the etiology of rheumatoid arthritis remains unknown, type II collagen (CII) is a candidate autoantigen. An immunodominant pathogenic epitope from this autoantigen, CII(261-273), which binds to HLA-DR4 and activates CD4+ T cells, has been identified. The non-classical class II antigen, HLA-DM, is also a key component of class II antigen presentation pathways influencing peptide presentation by HLA-DR molecules expressed on professional antigen-presenting cells (APC). Here, we investigated whether the HLA-DR4-restricted presentation of the pathogenic CII(261-273) epitope was regulated by HLA-DM expression in APC. We show that APC lacking HLA-DM efficiently display the CII(261-273) peptide/epitope to activate CD4+ T cells, and that presentation of this peptide is modulated dependent on the level of HLA-DM expression in APC. Mechanistic studies demonstrated that the CII(261-273) peptide is internalized by APC and edited by HLA-DM molecules in the recycling pathway, inhibiting peptide presentation and T cell recognition. These findings suggest that HLA-DM expression in APC controls class II-mediated CII(261-273) peptide/epitope presentation and regulates CD4+ T cell responses to this self epitope, thus potentially influencing CII-dependent autoimmunity.

Serum-derived exosomes from antigen-fed mice prevent allergic sensitization in a model of allergic asthma

Oral tolerance is an active process that starts with sampling of luminal antigens by the intestinal epithelial cells (IEC), followed by processing and assembly with major histocompatibility complex class II and subsequently a release of tolerogenic exosomes (tolerosomes) from the IEC. We have previously shown that tolerosomes can be isolated from serum shortly after an antigen feed, and will potently transfer antigen-specific tolerance to naive recipients. Here we study the capacity of the tolerosomes to protect against allergic sensitization in a mouse model of allergic asthma. Serum or isolated serum exosomes from tolerized BALB/c donor mice were transferred to syngeneic recipients followed by sensitization and intranasal exposure to ovalbumin (OVA). Blood, bronchoalveolar lavage (BAL) and lymph nodes were sampled 24 hr after the final exposure. The number of eosinophils was counted in BAL fluid and the levels of immunoglobulin E (IgE) and OVA-specific IgE were measured in serum. Mediastinal and coeliac lymph nodes were analysed by flow cytometry. The animals receiving serum from OVA-fed mice displayed significantly lower numbers of airway eosinophils and lower serum levels of total IgE as well as of OVA-specific IgE compared with controls. Moreover, the tolerant animals showed a significantly higher frequency of activated T cells with a regulatory phenotype in both mediastinal and coeliac lymph nodes. The results show that serum or isolated serum exosomes obtained from OVA-fed mice and administered intraperitoneally to naive recipient mice abrogated allergic sensitization in the recipients.

Luminal antigens access late endosomes of intestinal epithelial cells enriched in MHC I and MHC II molecules: in vivo study in Crohn's ileitis

In contrast to healthy conditions, intestinal epithelial cells (IECs) stimulate proinflammatory CD4+ and CD8+ T cells during Crohn's disease (CD). The underlying regulatory mechanisms remain unknown. Here we investigated the epithelial expression of major histocompatibility complex (MHC) I and MHC II and its interference with endocytic pathways, in vivo. During ileoscopy, ovalbumin (OVA) was sprayed onto ileal mucosa of CD patients (ileitis and remission) and controls. The epithelial traffic of OVA and MHC I/II pathways were studied in biopsies using fluorescence and electron microscopy. We found MHC I and MHC II to accumulate within multivesicular late endosomes (MVLE) of IECs. Faint labeling for these molecules was seen in early endosomes and lysosomes. MVLE were entered by OVA 10 min after exposure. Exosomes carrying MHC I, MHC II, and OVA were detected in intercellular spaces of the epithelium. OVA trafficking and labeling patterns for MHC I and MHC II in IECs showed no differences between CD patients and controls. Independent of inflammatory stimuli, MHC I and MHC II pathways intersect MVLE in IECs, which were efficiently targeted by luminal antigens. Similar to MHC II-enriched compartments in professional antigen presenting cells, these MVLE might be critically involved in MHC I- and MHC II-related antigen processing in IECs and the source of epithelial-released exosomes. The access of luminal antigens to MHC I in MVLE might indicate that the presentation of exogenous antigens by IECs must not be restricted to MHC II but might also occur as "cross-presentation" via MHC I to CD8+ T cells.

Human tumor-derived vs dendritic cell-derived exosomes have distinct biologic roles and molecular profiles

Microvesicles (MV) or exosomes are produced and secreted by tumor and normal cells. The molecular profile and functions of tumor-derived vs dendritic cell (DC)-derived MV are distinct. The former express death ligands and mediate apoptosis of activated T cells. The latter promote CD4+ T cell proliferation and may play a role in regulating T cell responses. Serving as intercellular communication networks, tumor-derived MV contribute to tumor escape, while DC-derived MV drive and regulate immune response.

Role of exosomes in immune regulation

Exosomes are small vesicles originating from late endosomes, 30–100 nm in diameter with typical cup-shape morphology. They are reported to bear high levels of a narrow spectrum of molecules involved in immune response and signal transduction. Apart from removing obsolete membrane proteins, some surprising biological functions of exosomes were unveiled recently and their applications in immunotherapy of tumors are currently intensively investigated. Dendritic cell- (DC) and tumor-derived exosomes have considerable anti-tumor effects in experimental studies and several clinical trials. Despite their potential applications in eliciting a “positive” immune response, exosomes might induce some “unwanted” immune responses, such as immune tolerance and immune evasion. Therefore further investigations about the physiological functions of exosomes and the optimal way of exosome application in tumor immunotherapy are necessary. This review presents recent developments in the field of exosome research and focuses on its applications to tumor immunotherapy.

Exosomes biological significance: A concise review

Exosomes were initially thought to be a mechanism for removing unneeded membrane proteins from reticulocytes. Current studies have shown that the process of exosome formation extends to many mammalian cells. This concise review highlights the findings reported at a Workshop on Exosomes. Full knowledge of the contribution of exosomes to intercellular information transmission and the potential medical application of this knowledge will depend on the ingenuity of future investigators and their insight into biological processes.