Please note that this presentation aims at summarizing currently available data only without the claim of representing established knowledge. Thus, information presented in this course may be subject to change in the future due to the rapid evolvement of the field of extracellular vesicles. The authors of this book is Professor Marca Wauben from Utrecht University, the Netherlands and Professor Edit Buzas from Semmelweis University, Hungary. This book focuses on the role of EVs in immunity and inflammation. My name is Carolina Soekmadji. I am a board member for ISEV and a member of the educational team. I will narrate this lecture. Let's begin. The immune system has two major arms; the innate immune system and the adaptive one. The innate immune system provides an immediate general defense while the adaptive immunity represents a more specialized protective immune mechanism. Both system work closely together. This slide shows the innate and adaptive arm of the immune system. Importantly, all innate and adaptive immune cells are capable of releasing EVs. If we have a look at the proteomic compositions of EVs isolated from various body fluids, we find numerous immune response related molecules on their surface. Beside this protein cargo, also nucleic acids and lipids present in EVs can have immune modulatory potential. Altogether, this strongly suggests that EVs can play a role in immune responses. In addition, there is evidence from studies with mice that demonstrate the presence of EVs in the lymph. It has been shown that lymph carries EVs rapidly to the draining lymph nodes. This finding further suggests a role of EVs in immunity. To understand the role of EVs in immunity, we have to remember that immune cells receive signals transmitted by EVs of microbes, other immune cells, non-immune cells, and tumor cells. On the other hand, immune cells themselves release EVs which convey signals to other cells. Engagement of various immune cell surface receptors such as Fc gamma receptor, cytokine receptors, TCR, and BCR, often triggers EV release which is preceded by increased cytosolic calcium ion concentration. Bacteria can induce the release of neutrophil derived EVs. Neutrophil derived EVs can form aggregates with bacteria and can thereby reduce bacterial growth. Neutrophil EVs have also been reported to have anti-inflammatory and pro-thrombotic affects. NK cells secrete EVs that carry NK cell markers, the FasL and perforin. NK cells are known to release EVs constitutively. However, the composition of the released vesicles are strongly dependent on the cellular environment. Monocytes and macrophages are rich sources of EVs which may participate in antigen presentation, affect myeloid cell proliferation, and differentiation. Infected macrophages had been shown to secrete EVs without the molecular composition and function. Also, secreted EVs have been shown to transfer functional pyroptotic caspase-1. A surprisingly wide variety of functions have been shown to associate with mass cell derived EVs. They carry functional RNAs, induce DC maturation, play a role in antigen delivery for cross presentation, they induce T and B-cell proliferation, and carry numerous immune modulatory proteins. Depending on the activation status, mast sell release clearly different amounts and subsets of EVs. Dendritic cells derived EVs contribute to antigen presentation and can directly activate prime T-cells. However, activation of naive T-cells require bystander mature DCs or B-cells. Mature DC derived EVs however can elicit potent immune response in contrast to immature DC derived vesicles. During cognate DC-T cell interaction, both the quantity and the quality of DC derived EVs changes. But dendritic cell derived EVs do not only direct adaptive immune responses, but also act on the innate arm of the immune system. Depending on the activation status and type of DC, their EVs modulate all these different immune cells in different ways. This cell derive EVs participate in various immune regulatory functions. They can be involved in immunosuppression as demonstrated for regulatory T cell derived EVs and in immune activation. For example, by inducing T cell proliferation and mast cell degranulation. T cell derived EVs can thus act on both arms of the immune system. Importantly, T cell EVs are not only released in the extracellular environment, but also in the immune synapes form between antigen presenting cells and T cells, or between target cells and cytotoxic T cells. The first demonstration that EVs from antigen presenting cells can participate in antigen presentation was described for B cell derived EVs. Similarly to what has been shown for EV release by other professional antigen presenting cells, B cell derived EVs can play a role in antigen presentation and can modulate T-cell activation and cytokines secretion. A special feature of B cell derived EVs are the surface immunoglobulins via which they can carry native antigens to other cells. EVs can carry many different pathogen associated molecular patterns, PAMPs and damage associated molecular patterns, DAMPs. Thus, EVs are conveyors of different danger signals. A very interesting feature of EVs is that they can carry cytokines. EV associated cytokines include for example, IL-1 Beta and IL-1 Alpha, TNF, and TGF Beta. When considering the EV induce effects on cells, we have to remember that paracrine media also includes soluble mediators. For example, cytokines and growth factors which may have combinatorial effect with EVs on cells. Evidence for synergistic effects of cytokines and EVs have been provided from different experimental system. An important aspect of infected cell derived EV is that they carry microbial or viral molecules. Thus, EV from infected cells can be involved in indirect antigen presentation via transfer to antigen presenting cells and immune modulation. Knowing the key players in acute inflammation, it is important to realize that these cells release EVs involved in intracellular communication between these key players. The amount of release EVs and their cargo is flexible and dependent on the cues the producing cells receives. So EV mediated communication is a way to tune and connect the different cellular players. An example how EV can accelerate the process of acute inflammation by attracting major key players is illustrated here. Bacterial components for example, fMLP activate neutrophils and induce the release of EVs containing the leukotriene B4. These EVs form a gradient of leukotriene B4, an EV trail which is necessary for neutrophil recruitment to the site of inflammation. IL-1 Beta is one of the best known pro-inflammatory cytokines. As early as in 2001, it has been demonstrated that ATP stimulated cells release IL-1 Betas in EVs. At early time points during acute inflammation, IL-1 Beta is even found predominantly in EVs. Not only IL-1 Beta is released via EVs, also other pro-inflammatory cytokines such as TNF and several different compliment proteins, and complement regulatory proteins are associated with EVs. As we mentioned before, EVs also serve as rich sources of PAMPs and DAMPs during inflammation. EV also play a role in chronic inflammatory processes. For example in allergy. In the example immune cell derive EVs perpetuate the Th2 environment. DC derived EVs stimulate Th2 cell responses and act as an antigen presenting unit. Macrophytely derived EVs contain functional inflammatory enzymes, synthesizes leukotrienes, LTs and recruiting granulocytes. EV from mast cells and B cells contribute to the promotion of the Th2 environment, and drive Th2 responses. Eosinophil derived EV's increase the pro inflammatory capacity of eosinophils. T cell produce EVs that stimulate Th2 cytokine release. Airway epithelial cell derived EVs carry different molecules implicated in the modulation of inflammation and the release of this EV's is increased by Th2 cytokine as interleukin 13. Like in allergies, if we also play a role in auto-immune disorders for example, rheumatoid arthritis. EV contain numerous known auto antigens implicated in auto-immune diseases. Since EVs have immune modulatory activity, the presentation or transfer of this auto antigens via EVs can influence the disease process. Furthermore, even patients with autoimmune diseases can inform immune complexes with auto antibodies. Immune complex deposition leading to type three hypersensitivity is the characteristic feature of several auto-immune diseases. The role of EVs in anti tumor immunity is increasingly recognized. Tumor derived EVs have multiple activating and inhibitory effects on immune cells. You will hear much more about this topic in the presentation about EVs, in the tumor immune system interaction.
