Exosomes from bronchoalveolar fluid of tolerized mice prevent allergic reaction

Methods of analysis of dendritic cell-derived exosome-shuttle microRNA and its horizontal propagation between dendritic cells

Exosomes are extremely small (<100 nm) membrane vesicles, generated in the endocytic compartment that are released to the extracellular milieu by living cells. Although the biological function of exosomes in vivo remains unclear, they seem to function as mechanisms of cell-to-cell communication for horizontal transfer of proteins, antigens, prions, morphogens, mRNA, and noncoding regulatory RNAs, including microRNAs (miRNAs) (also known as exosome-shuttle miRNAs). Dendritic cells (DCs), the most potent professional antigen-presenting leukocytes of the immune system, release relatively high levels of exosomes and also interact with free exosomes present in the extracellular space. Therefore, DCs constitute a good model for the analysis of exosome-shuttle miRNAs and their horizontal propagation between cells. This chapter provides basic protocols for purification of exosomes released by mouse bone marrow-derived DCs, analysis of their miRNA content, and assessment of the function of exosome-shuttle miRNAs, once they are transferred to target/acceptor DCs.

Adrenergic regulation of IgE involves modulation of CD23 and ADAM10 expression on exosomes

Soluble CD23 plays a role in the positive regulation of an IgE response. Engagement of the β2 adrenergic receptor (β2AR) on a B cell is known to enhance the level of both soluble CD23 and IgE, although the mechanism by which this occurs is not completely understood. In this study, we report that, in comparison with a CD40 ligand/IL-4-primed murine B cell alone, β2AR engagement on a primed B cell increased gene expression of a disintegrin and metalloproteinase (ADAM)10, which is the primary sheddase of CD23, as well as protein expression of both CD23 and ADAM10, in a protein kinase A- and p38 MAPK-dependent manner, and promoted the localization of these proteins to exosomes as early as 2 d after priming, as determined by both Western blot and flow cytometry and confirmed by electron microscopy. In comparison with isolated exosomes released from primed B cells alone, the transfer of exosomes released from β2AR agonist-exposed primed B cells to cultures of recipient primed B cells resulted in an increase in the level of IgE produced per cell, without affecting the number of cells producing IgE, as determined by ELISPOT. These effects still occurred when a β2AR antagonist was added along with the transfer to block residual agonist, and they failed to occur when exosomes were isolated from β2AR-deficient B cells. These findings suggest that the mechanism responsible for mediating the β2AR-induced increase in IgE involves a shuttling of the β2AR-induced increase in CD23 and ADAM10 proteins to exosomes that subsequently mediate an increase in IgE.

The spectrum of olive pollen allergens. From structures to diagnosis and treatment

Olive tree is one of the main allergy sources in Mediterranean countries. The identification of the allergenic repertoire from olive pollen has been essential for the development of rational strategies of standardization, diagnosis, and immunotherapy, all of them focused to increase the life quality of the patients. From its complex allergogram, twelve allergens - Ole e 1 to Ole e 12 - have been identified and characterized to date. Most of them have been cloned and produced as recombinant forms, whose availability have allowed analyzing their three-dimensional structures, mapping their T-cell and B-cell epitopes, and determining the precise allergenic profile of patients for a subsequent patient-tailored immunotherapy. Protein mutant, hypoallergenic derivatives, or recombinant fragments have been also useful experimental tools to analyze the immune recognition of allergens. To test these molecules before using them for clinic purposes, a mouse model of allergic sensitizations has been used. This model has been helpful for assaying different prophylactic approaches based on tolerance induction by intranasal administration of allergens or hypoallergens, used as free or integrated in different delivery systems, and their findings suggest a promising utilization as nasal vaccines. Exosomes - nanovesicles isolated from bronchoalveolar lavage fluid of tolerogenic mice - have shown immunomodulatory properties, being able to protect mice against sensitization to Ole e 1.

Transfer of extracellular vesicles during immune cell-cell interactions

The transfer of molecules between cells during cognate immune cell interactions has been reported, and recently a novel mechanism of transfer of proteins and genetic material such as small RNA between T cells and antigen-presenting cells (APCs) has been described, involving exchange of extracellular vesicles (EVs) during the formation of the immunological synapse (IS). EVs, a term that encompasses exosomes and microvesicles, has been implicated in cell-cell communication during immune responses associated with tumors, pathogens, allergies, and autoimmune diseases. This review focuses on EV transfer as a mechanism for the exchange of molecules during immune cell-cell interactions.

Antigen-specific, antibody-coated, exosome-like nanovesicles deliver suppressor T-cell microRNA-150 to effector T cells to inhibit contact sensitivity

BACKGROUND

T-cell tolerance of allergic cutaneous contact sensitivity (CS) induced in mice by high doses of reactive hapten is mediated by suppressor cells that release antigen-specific suppressive nanovesicles.

OBJECTIVE

We sought to determine the mechanism or mechanisms of immune suppression mediated by the nanovesicles.

METHODS

T-cell tolerance was induced by means of intravenous injection of hapten conjugated to self-antigens of syngeneic erythrocytes and subsequent contact immunization with the same hapten. Lymph node and spleen cells from tolerized or control donors were harvested and cultured to produce a supernatant containing suppressive nanovesicles that were isolated from the tolerized mice for testing in active and adoptive cell-transfer models of CS.

RESULTS

Tolerance was shown due to exosome-like nanovesicles in the supernatants of CD8(+) suppressor T cells that were not regulatory T cells. Antigen specificity of the suppressive nanovesicles was conferred by a surface coat of antibody light chains or possibly whole antibody, allowing targeted delivery of selected inhibitory microRNA (miRNA)-150 to CS effector T cells. Nanovesicles also inhibited CS in actively sensitized mice after systemic injection at the peak of the responses. The role of antibody and miRNA-150 was established by tolerizing either panimmunoglobulin-deficient JH(-/-) or miRNA-150(-/-) mice that produced nonsuppressive nanovesicles. These nanovesicles could be made suppressive by adding antigen-specific antibody light chains or miRNA-150, respectively.

CONCLUSIONS

This is the first example of T-cell regulation through systemic transit of exosome-like nanovesicles delivering a chosen inhibitory miRNA to target effector T cells in an antigen-specific manner by a surface coating of antibody light chains.

Extracellular vesicles: exosomes, microvesicles, and friends

Cells release into the extracellular environment diverse types of membrane vesicles of endosomal and plasma membrane origin called exosomes and microvesicles, respectively. These extracellular vesicles (EVs) represent an important mode of intercellular communication by serving as vehicles for transfer between cells of membrane and cytosolic proteins, lipids, and RNA. Deficiencies in our knowledge of the molecular mechanisms for EV formation and lack of methods to interfere with the packaging of cargo or with vesicle release, however, still hamper identification of their physiological relevance in vivo. In this review, we focus on the characterization of EVs and on currently proposed mechanisms for their formation, targeting, and function.

Exosomes as intercellular signaling organelles involved in health and disease: basic science and clinical applications

Cell to cell communication is essential for the coordination and proper organization of different cell types in multicellular systems. Cells exchange information through a multitude of mechanisms such as secreted growth factors and chemokines, small molecules (peptides, ions, bioactive lipids and nucleotides), cell-cell contact and the secretion of extracellular matrix components. Over the last few years, however, a considerable amount of experimental evidence has demonstrated the occurrence of a sophisticated method of cell communication based on the release of specialized membranous nano-sized vesicles termed exosomes. Exosome biogenesis involves the endosomal compartment, the multivesicular bodies (MVB), which contain internal vesicles packed with an extraordinary set of molecules including enzymes, cytokines, nucleic acids and different bioactive compounds. In response to stimuli, MVB fuse with the plasma membrane and vesicles are released in the extracellular space where they can interact with neighboring cells and directly induce a signaling pathway or affect the cellular phenotype through the transfer of new receptors or even genetic material. This review will focus on exosomes as intercellular signaling organelles involved in a number of physiological as well as pathological processes and their potential use in clinical diagnostics and therapeutics.

Identification and analysis of circulating exosomal microRNA in human body fluids

Exosomes are 40-100 nm sized vesicles released from cells when multivesicular bodies fuse with the plasma membrane. These vesicles take part in cell-to-cell communication by binding and signalling through membrane receptors on cells or by transferring proteins, RNA, and lipids into the cells. Exosomal RNA in body fluids, such as plasma and urine, has been associated with malignancies, making the exosomal RNA a potential biomarker for early detection of these diseases. This has increased the interest in the field of extracellular RNA and in particular, the interest in exosomal RNA.In this chapter, a well-established exosome isolation method is described, as well as how to characterize the isolated vesicles by electron microscopy. Furthermore, two types of RNA isolation methods are described with a focus on isolating RNA from body fluids, which can be more viscous than cell culture media.

Plasma-derived MHC class II+ exosomes from tumor-bearing mice suppress tumor antigen-specific immune responses

Tumor-specific immunosuppression is frequently observed in tumor-bearing hosts. Exosomes are nano-sized, endosomal-derived membrane vesicles secreted by most tumor and hematopoietic cells and have been shown to actively participate in immune regulation. We previously demonstrated that antigen-specific immunosuppressive exosomes could be isolated from the blood plasma of antigen-immunized mice. Here, we demonstrate that plasma-derived exosomes isolated from mice bearing OVA-expressing tumors were able to suppress OVA-specific immune responses in a mouse delayed-type hypersensitivity model. Enrichment of tumor-derived exosomes in the plasma of mice bearing subcutaneous melanoma was not detected using an exosome-tagging approach. Instead, depletion of MHC class II(+) vesicles from plasma-derived exosomes or using plasma-derived exosomes isolated from MHC class II-deficient mice resulted in significant abrogation of the suppressive effect. These results demonstrate that circulating host-derived, MHC class II(+) exosomes in tumor-bearing hosts are able to suppress the immune response specific to tumor antigens.

Exosomal RNA as biomarkers and the therapeutic potential of exosome vectors

INTRODUCTION

Exosomes are nano-sized (40 - 100 nm), extracellular vesicles, of endosomal origin. They are released by cells and found in many body fluids, including plasma. Exosomes contain proteins, microRNAs (miRNAs), and messenger RNAs (mRNAs) that can be transferred between cells. The discovery that exosomes contain RNA, and that this encapsulated RNA could potentially be transferred over distances in vivo, reinforced the importance of exosomes in cell-to-cell communication.

AREAS COVERED

The existence of exosomes, as a naturally occurring delivery system of RNA, enables their use as both biomarkers and vectors in gene therapy. This review provides an overview of studies reporting that exosomal miRNA and mRNA in plasma can serve as a diagnostic marker in various types of cancers. In addition, the recent finding that exosomes can be used as vectors for delivery of small interfering RNA (siRNA) in mice, with therapeutic effects, is also reviewed.

EXPERT OPINION

The data reviewed here suggest that exosomal RNA has the potential to play an important role in the diagnosis, prognosis, and treatment of diseases in the future.

Immunosuppressive exosomes: a new approach for treating arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease and one of the leading causes of disability in the USA. Although certain biological therapies, including protein and antibodies targeting inflammatory factors such as the tumor necrosis factor, are effective in reducing symptoms of RA, these treatments do not reverse disease. Also, although novel gene therapy approaches have shown promise in preclinical and clinical studies to treat RA, it is still unclear whether gene therapy can be readily and safely applied to treat the large number of RA patients. Recently, nanosized, endocytic-derived membrane vesicles “exosomes” were demonstrated to function in cell-to-cell communication and to possess potent immunoregulatory properties. In particular, immunosuppressive DC-derived exosomes and blood plasma- or serum-derived exosomes have shown potent therapeutic effects in animal models of inflammatory and autoimmune disease including RA. This paper discusses the current knowledge on the production, efficacy, mechanism of action, and potential therapeutic use of immunosuppressive exosomes for arthritis therapy.

Exosomes as extrapulmonary signaling conveyors for nanoparticle-induced systemic immune activation

Evaluation of systemic biosafety of nanomaterials urgently demands a comprehensive understanding of the mechanisms of the undesirable interference and systemic signaling that arises between man-made nanomaterials and biological systems. It is shown that exosomes may act as signal conveyors for nanoparticle-induced systemic immune responses. Exosomes are extracellularly secreted membrane vesicles which act as Trojan horses for the dissemination and intercellular communication of natural nanosized particles (like viruses). Upon exposure to magnetic iron oxide nanoparticles (MIONs), it is possible to dose-dependently generate a significant number of exosomes in the alveolar region of BALB/c mice. These exosomes are quickly eliminated from alveoli into systemic circulation and largely transfer their signals to the immune system. Maturation of dendritic cells and activation of splenic T cells are significantly induced by these exosomes. Furthermore, exosome-induced T-cell activation is more efficient toward sensitized T cells and in ovalbumin (OVA)-sensitized mice than in the unsensitized counterparts. Activation of systemic T cells reveals a T helper 1 polarization and aggravated inflammation, which poses potential hazards to the deterioration of allergic diseases in OVA-sensitized mice. The studies suggest that exosomes may act as conveyors for extrapulmonary signal transduction in nanoparticle-induced immune systemic responses, which are the key in vivo processes of manufactured nanoparticles executing either biomedical functions or toxic responses.

Isolation and characterization of RNA-containing exosomes

The field of exosome research is rapidly expanding, with a dramatic increase in publications in recent years. These small vesicles (30-100 nm) of endocytic origin were first proposed to function as a way for reticulocytes to eradicate the transferrin receptor while maturing into erythrocytes, and were later named exosomes. Exosomes are formed by inward budding of late endosomes, producing multivesicular bodies (MVBs), and are released into the environment by fusion of the MVBs with the plasma membrane. Since the first discovery of exosomes, a wide range of cells have been shown to release these vesicles. Exosomes have also been detected in several biological fluids, including plasma, nasal lavage fluid, saliva and breast milk. Furthermore, it has been demonstrated that the content and function of exosomes depends on the originating cell and the conditions under which they are produced. A variety of functions have been demonstrated for exosomes, such as induction of tolerance against allergen, eradication of established tumors in mice, inhibition and activation of natural killer cells, promotion of differentiation into T regulatory cells, stimulation of T cell proliferation and induction of T cell apoptosis. Year 2007 we demonstrated that exosomes released from mast cells contain messenger RNA (mRNA) and microRNA (miRNA), and that the RNA can be shuttled from one cell to another via exosomes. In the recipient cells, the mRNA shuttled by exosomes was shown to be translated into protein, suggesting a regulatory function of the transferred RNA. Further, we have also shown that exosomes derived from cells grown under oxidative stress can induce tolerance against further stress in recipient cells and thus suggest a biological function of the exosomal shuttle RNA. Cell culture media and biological fluids contain a mixture of vesicles and shed fragments. A high quality isolation method for exosomes, followed by characterization and identification of the exosomes and their content, is therefore crucial to distinguish exosomes from other vesicles and particles. Here, we present a method for the isolation of exosomes from both cell culture medium and body fluids. This isolation method is based on repeated centrifugation and filtration steps, followed by a final ultracentrifugation step in which the exosomes are pelleted. Important methods to identify the exosomes and characterize the exosomal morphology and protein content are highlighted, including electron microscopy, flow cytometry and Western blot. The purification of the total exosomal RNA is based on spin column chromatography and the exosomal RNA yield and size distribution is analyzed using a Bioanalyzer.

Microvesicles and viral infection

Cells secrete various membrane-enclosed microvesicles from their cell surface (shedding microvesicles) and from internal, endosome-derived membranes (exosomes). Intriguingly, these vesicles have many characteristics in common with enveloped viruses, including biophysical properties, biogenesis, and uptake by cells. Recent discoveries describing the microvesicle-mediated intercellular transfer of functional cellular proteins, RNAs, and mRNAs have revealed additional similarities between viruses and cellular microvesicles. Apparent differences include the complexity of viral entry, temporally regulated viral expression, and self-replication proceeding to infection of new cells. Interestingly, many virally infected cells secrete microvesicles that differ in content from their virion counterparts but may contain various viral proteins and RNAs. For the most part, these particles have not been analyzed for their content or functions during viral infection. However, early studies of microvesicles (L-particles) secreted from herpes simplex virus-infected cells provided the first evidence of microvesicle-mediated intercellular communication. In the case of Epstein-Barr virus, recent evidence suggests that this tumorigenic herpesvirus also utilizes exosomes as a mechanism of cell-to-cell communication through the transfer of signaling competent proteins and functional microRNAs to uninfected cells. This review focuses on aspects of the biology of microvesicles with an emphasis on their potential contributions to viral infection and pathogenesis.

Tumor-derived exosomes confer antigen-specific immunosuppression in a murine delayed-type hypersensitivity model

Exosomes are endosome-derived small membrane vesicles that are secreted by most cell types including tumor cells. Tumor-derived exosomes usually contain tumor antigens and have been used as a source of tumor antigens to stimulate anti-tumor immune responses. However, many reports also suggest that tumor-derived exosomes can facilitate tumor immune evasion through different mechanisms, most of which are antigen-independent. In the present study we used a mouse model of delayed-type hypersensitivity (DTH) and demonstrated that local administration of tumor-derived exosomes carrying the model antigen chicken ovalbumin (OVA) resulted in the suppression of DTH response in an antigen-specific manner. Analysis of exosome trafficking demonstrated that following local injection, tumor-derived exosomes were internalized by CD11c+ cells and transported to the draining LN. Exosome-mediated DTH suppression is associated with increased mRNA levels of TGF-β1 and IL-4 in the draining LN. The tumor-derived exosomes examined were also found to inhibit DC maturation. Taken together, our results suggest a role for tumor-derived exosomes in inducing tumor antigen-specific immunosuppression, possibly by modulating the function of APCs.

Extracellular heat shock proteins, cellular export vesicles, and the Stress Observation System: a form of communication during injury, infection, and cell damage. It is never known how far a controversial finding will go! Dedicated to Ferruccio Ritossa

Heat shock proteins (hsp) have been found to play a fundamental role in the recovery from multiple stress conditions and to offer protection from subsequent insults. The function of hsp during stress goes beyond their intracellular localization and chaperone role as they have been detected outside cells activating signaling pathways. Extracellular hsp are likely to act as indicators of the stress conditions, priming other cells, particularly of the immune system, to avoid the propagation of the insult. Some extracellular hsp, for instance Hsp70, are associated with export vesicles, displaying a robust activation of macrophages. We have coined the term Stress Observation System (SOS) for the mechanism for sensing extracellular hsp, which we propose is a form of cellular communication during stress conditions. An enigmatic and still poorly understood process is the mechanism for the release of hsp, which do not contain any consensus secretory signal. The export of hsp appears to be a very complex phenomenon encompassing different alternative pathways. Moreover, extracellular hsp may not come in a single flavor, but rather in a variety of physical conditions. This review addresses some of our current knowledge about the release and function of extracellular hsp, in particular those associated with vesicles.

Exosomes: immune properties and potential clinical implementations

To communicate, cells are known to release in their environment proteins which bind to receptors on surrounding cells. But cells also secrete more complex structures, called membrane vesicles, composed of a lipid bilayer with inserted transmembrane proteins, enclosing an internal content of hydrophilic components. Exosomes represent a specific subclass of such secreted membrane vesicles, which, despite having been described more than 20 years ago by two groups studying reticulocyte maturation, have only recently received attention from the scientific community. This renewed interest originated first from the description of exosome secretion by antigen-presenting cells, suggesting a potential role in immune responses, and very recently by the identification of the presence of RNA (both messenger and microRNA) in exosomes, suggesting a potential transfer of genetic information between cells. In this review, we will describe the conclusions of 20 years of studies on the immune properties of exosomes and the most recent advances on their roles and potential uses as markers or as therapeutic tools during pathologies, especially in cancer.

RNA-containing exosomes in human nasal secretions

BACKGROUND

Exosomes are nanovesicles of endocytic origin released by cells and present in human body fluids such as plasma, breast milk, and bronchoalveolar lavage fluid. These vesicles take part in communication between cells. Recently, it was shown that exosomes contain both mRNA and microRNA. This RNA can be shuttled between cells (exosomal shuttle RNA), which is a new route of communication between cells. The aim of this study was to determine whether nasal secretions harbor exosomes and furthermore, whether these exosomes contain RNA.

METHODS

Human nasal lavage fluid (NLF) underwent centrifugation and filtration to discard cells and debris, followed by a final ultracentrifugation at 120,000 × g to pellet the exosomes. Exosomes were detected using electron microscopy (EM), flow cytometry, and Western blot. RNA was extracted and analyzed using a Bioanalyzer.

RESULTS

Exosomes were visualized as 40-80 nm, CD63(+) vesicles using EM. Flow cytometry of exosomes using anti-major histocompatibility complex class II beads revealed exosomes positive for the tetraspanins CD9, CD63, and CD81. Western blot confirmed the presence of exosomal protein and absence of proteins from the endoplasmic reticulum (ER), because the exosomes were positive for Tsg101, but negative for the ER marker, calnexin. Bioanalyzer analysis revealed that, these exosomes contain RNA.

CONCLUSION

This study shows for the first time that NLF contains exosomes and that these exosomes contain RNA. Further characterization of the exosomal RNA and proteins may provide important information about communication in the nose and potentially provide a source of biomarkers for upper airway diseases.

Extracellular vesicles are key intercellular mediators in the development of immune dysfunction to allergens in the airways

BACKGROUND

Previous evidence indicates that inhalation of lipopolysaccharide (LPS)-containing with allergens induced mixed Th1 and Th17 cell responses in the airways. Extracellular vesicles (EVs) are nanometer-sized spherical, lipid-bilayered structures and are recently in the public eye as an intercellular communicator in immune responses.

OBJECTIVE

To evaluate the role of EVs secreted by LPS inhalation in the development of airway immune dysfunction in response to allergens.

METHODS

Extracellular vesicles in bronchoalveolar lavage fluids of BALB/c mice were isolated and characterized 24 h after applications to the airway of 10 μg of LPS for 3 days. To evaluate the role of LPS-induced EVs on the development of airway immune dysfunction, in vivo and in vitro experiments were performed using the isolated LPS-induced EVs.

RESULTS

The inhalation of LPS enhanced EVs release into the BAL fluid, when compared to the application of PBS. Airway sensitization with allergens and LPS-induced EVs resulted in a mixed Th1 and Th17 cell responses, although that with allergens and PBS-induced EVs induced immune tolerance. In addition, LPS-induced EVs enhanced the production of Th1- and Th17-polarizing cytokines (IL-12p70 and IL-6, respectively) by lung dendritic cells. Moreover, the immune responses induced by the LPS-induced EVs were blocked by denaturation of the EV-bearing proteins.

CONCLUSION

These data suggest that EVs (especially, the protein components) secreted by LPS inhalation are a key intercellular communicator in the development of airway immune dysfunction to inhaled LPS-containing allergens.

Nanostructural and transcriptomic analyses of human saliva derived exosomes

BACKGROUND

Exosomes, derived from endocytic membrane vesicles are thought to participate in cell-cell communication and protein and RNA delivery. They are ubiquitous in most body fluids (breast milk, saliva, blood, urine, malignant ascites, amniotic, bronchoalveolar lavage, and synovial fluids). In particular, exosomes secreted in human saliva contain proteins and nucleic acids that could be exploited for diagnostic purposes. To investigate this potential use, we isolated exosomes from human saliva and characterized their structural and transcriptome contents.

METHODOLOGY

Exosomes were purified by differential ultracentrifugation and identified by immunoelectron microscopy (EM), flow cytometry, and Western blot with CD63 and Alix antibodies. We then described the morphology, shape, size distribution, and density using atomic force microscopy (AFM). Microarray analysis revealed that 509 mRNA core transcripts are relatively stable and present in the exosomes. Exosomal mRNA stability was determined by detergent lysis with RNase A treatment. In vitro, fluorescently labeled saliva exosomes could communicate with human keratinocytes, transferring their genetic information to human oral keratinocytes to alter gene expression at a new location.

CONCLUSION

Our findings are consistent with the hypothesis that exosomes shuttle RNA between cells and that the RNAs present in the exosomes may be a possible resource for disease diagnostics.

Membrane vesicles as conveyors of immune responses

In multicellular organisms, communication between cells mainly involves the secretion of proteins that then bind to receptors on neighbouring cells. But another mode of intercellular communication - the release of membrane vesicles - has recently become the subject of increasing interest. Membrane vesicles are complex structures composed of a lipid bilayer that contains transmembrane proteins and encloses soluble hydrophilic components derived from the cytosol of the donor cell. These vesicles have been shown to affect the physiology of neighbouring recipient cells in various ways, from inducing intracellular signalling following binding to receptors to conferring new properties after the acquisition of new receptors, enzymes or even genetic material from the vesicles. This Review focuses on the role of membrane vesicles, in particular exosomes, in the communication between immune cells, and between tumour and immune cells.