Note: the exocrine mentioned in this article refers to the exocrine secreted by stem cells. 

As two hot spots in the field of cell therapy, stem cells and exosomes have their own unique characteristics and potential, but there is also a close relationship between them. This article will explore the definition and characteristics of stem cells and exosomes, as well as their application and future development prospects in cell therapy.

一、A brief introduction to the basis of stem cells and exocrine

So what is stem cell exosome? 

Exocrine bodies are vesicles secreted by cells with a diameter of 30~150nm. Almost all cells secrete exocrine bodies. Stem cell exosomes are exocrine bodies secreted by stem cells. 

Exocrine bodies function in two ways:

（1）Direct effect. Protein molecules or lipid ligands on the surface of exocrine bodies can directly activate receptors on the surface of target cells, and this signal complex can further activate intracellular signal pathways.

（2）The carrier delivery function of exocrine. The exocrine can fuse with the lipids of the target cells or enter the cells by endocytosis, and bring the core components such as proteins, nucleic acids and lipids into the cells, and then exert their biological functions.

The exocrine bodies of different types of stem cells have the biological characteristics of source stem cells. For example, the exocrine of neural stem cells has the biological function of neural stem cells, which can mediate the immune response after ischemic stroke. 

Exosomes are currently considered to be part of cell function, loaded with information substances released by cells. at first, exosomes were thought to remove garbage from cells, but now studies have found that exosomes can perform a variety of biological functions. and exosomes can cross the biological barrier and the presence of exosomes can be detected in all body fluids.

二、Relationship between stem cells and exocrine bodies

（1）Stem cells can produce exosomes, regulate exocrine components, transmit biological information, and promote tissue repair and regeneration. The exosomes produced by stem cells are rich in bioactive substances, and the state and environment of stem cells will affect the production of exosomes. The exosomes contain the biological information of stem cells. After contact with recipient cells, the physiological state and function of receptor cells can be regulated.

（2）Exosomes can promote the proliferation, migration and differentiation of stem cells. Domestic animal studies have found that platelet-rich plasma exocrine can significantly promote the proliferation and migration of rat tendon stem / progenitor cells, and periodontal ligament stem cell exocrine can also promote the proliferation and differentiation of periodontal ligament stem cells.

三、Application of stem cells and exosomes in cell therapy

（1）The role of both in liver disease. 

The role in drug-induced liver injury. Drug-induced liver injury refers to liver injury caused by prescription or over-the-counter drugs such as chemicals, biological products, proprietary Chinese medicines, as well as traditional Chinese medicine, health products or their metabolites and even excipients, pollutants, magazines and so on. Mesenchymal stem cells (MSC) and their exosomes can effectively reduce hepatic inflammatory response and avoid further injury and deterioration of liver tissue; MSC secretes growth factors after migration to the damaged liver, and MSC exocrine can promote the expression of liver regeneration genes and cell proliferation markers, both of which promote stem cell proliferation and regeneration; MSC and its exocrine can inhibit the expression of pro-apoptotic proteins and play the role of anti-hepatocyte apoptosis. MSC and its exocrine can play a therapeutic role in the process of liver injury by improving oxidative stress; in addition, both of them can effectively inhibit the activation of pro-inflammatory immune cells and the secretion of cytokines through immune regulation, block the cascade activity of immune response and restore liver immune homeostasis.

The role in autoimmune hepatitis. MSC maintains immune tolerance by inhibiting immune activation after autoantigen presentation. MSC exocrine can also reduce the inflammatory response in the liver, which is related to the down-regulation of pro-inflammatory factors and the up-regulation of anti-inflammatory cytokines. In addition, MSC exocrine can be colonized in the liver as a drug carrier and internalized into macrophages, thus inhibiting the development of autoimmune hepatitis.

（2）The role of both in high altitude cerebral edema. High altitude cerebral edema is a serious and fatal disease related to high altitude disease. it belongs to severe acute altitude sickness, such as dizziness, headache, ataxia, confusion of consciousness and so on. The pathogenesis of high altitude cerebral edema includes increased cerebral blood flow, destruction of blood-brain barrier, brain cell damage, autophagy, inflammation and oxidative stress. MSC can inhibit inflammation, and MSC exocrine can cross the blood-brain barrier and play a role in tissue repair.

（3）The role of both in early-onset ovarian insufficiency. Early-onset ovarian insufficiency refers to menstrual disorder and fertility decline in women from puberty to 40 years old, amenorrhea for at least 4-6 months, follicular hormone > 25U/L, accompanied by decreased estrogen levels and follicular dysplasia. MSC and its exosomes can promote granulosa cell proliferation, inhibit granulosa cell apoptosis, anti-inflammation, anti-oxidation, anti-fibrosis, promote angiogenesis and follicular development, regulate immunity and repair ovarian function.

Stem cells and exosomes are important components in the field of cell therapy, which are bringing revolutionary changes to the field of medicine. An in-depth understanding of their relationship and characteristics can better tap their potential in disease treatment for the benefit of mankind.