Exosome – Small but Mighty Player in Immune System

1. Exosome – Small but Mighty Player in Immune System Abstract: Exosomes released by immune cells can participate in various immune system-related activity and disease development by transporting substances such as proteins, lipids, mRNA and miRNA. Since being founded, exosomes have been considered as a cell waste for many years, but recently, studies have found that exosomes are an important medium for delivering proteins and lipids between cells. Just like a stuffed suitcase unloaded from the belly of a cargo plane, molecular backpacks called exosomes are constantly produced from the cells of the body. Each backpack is filled with a variety of contents, and another cell may open and use it. Exosomes derived from immune cells contain major histocompatibility complexes (MHC) and various antigens, which can control various immune responses, such as the exchange of antigen information between immune cells and the activation and suppression of immune cells. Studies have also found that secretory cell-derived mRNAs and miRNAs exist in exosomes and can participate in the transmission and control of genetic information between cells. Dendritic cells are the most active cells in the immune system that secrete exosomes. Dendritic cells are a type of antigen-presenting cells that can activate T cells by phagocytosing invaded foreign bodies such as bacteria. Exosomes secreted by dendritic cells carry MHC I and II molecules, which can also activate T cells away from dendritic cells. Exosomes can not only achieve direct antigen presentation by transporting antigen-peptide-MHC complexes, but also indirectly promote antigen presentation by infiltrating other antigen-presenting cells and delivering antigens to MHC molecules in the cells. In addition to antigen-peptide-MHC complexes, exosomes also contain various secreted cell-derived antigens that can be transported to antigen-presenting cells. By using this mechanism, cancer-derived exosomal immunotherapy can be developed. Phagocytic-derived exosomes, such as macrophages, contain phagocytic bacterial-derived antigens. Transferring these antigens to dendritic cells with stronger antigen presentation capabilities through exosomes can promote effective T cell activation. It is expected to use this mechanism to develop effective vaccines. Exosomes contain not only protein antigens, but also secreted cell-derived mRNA or non-coding RNA (especially miRNA), and their functions have attracted widespread attention. The exosomes entering the target cell are fused with the endosome membrane, releasing the exosome RNA into the cytoplasm of the target cell, thus indicating that exosomes can regulate gene expression in target cells. In the immune system, this mechanism means that immune cells invaded by foreign enemies can transmit their active state to cells that have not encountered invasion through RNA, which can be used as a means to resist foreign invasion. By understanding the role of exosomes in the immune system, they can be better used to develop new treatments. By inhibiting the function of cancer-derived exosomes, the effect of anti-tumor immunity can be improved. In addition, removing

2. cancer cell-derived exosomes from the blood may also be an effective treatment. Conversely, controlling the functions of dendritic cells to promote the production of immunosuppressive exosomes can also be applied to the treatment of patients with inflammation or autoimmune diseases. It is hoped that through future research and development, exosomal function and its application in clinical research will be better explored, and custom exosome will be applied to treatment of various diseases.