Immunity has three functions (1): it refers to the ability of the body to resist the infection of pathogenic microorganisms, and the immune defense function can effectively resist the invasion of germs and viruses to the body, thus maintaining the health of the body. If this ability of immune function is too low, the human body will repeatedly have various infections; On the contrary, this ability is too high, and the human body is prone to allergic reactions. (2) The stabilizing function of immunity: refers to the ability of the body to remove aging, dead or damaged cells in the body. Various tissues and cells of organisms have a certain life span and are constantly metabolized to maintain the health of the body. The body must constantly remove the aging and dead cells in the body to promote cell regeneration, which plays an important role in the stability of immunity. If this ability is too high, normal cells will be eliminated as aging or damaged cells, that is, they will have immune function to their normal cells, which will lead to autoimmune diseases. (3) Monitoring function of immunity: This function of immunity can identify and destroy mutant cells produced in vivo. Under the influence of the external environment, some cells often mutate in the body. Once these cells develop, they are tumor cells. The immune monitoring function in the body can find this abnormal cell in time and remove it in time. If this function declines, tumors will appear in the human body. The above three functions of immunity constitute a complete immune system, and the integrity of the three functions is the basic guarantee for the health and normality of the body. The loss or function of any one of them will lead to immune dysfunction, which will lead to diseases. How does the immune system work? There are two kinds of phagocytes in humans: large phagocytes and small phagocytes. Small phagocytes are neutrophils in peripheral blood. Macrophages Monocyte Macrophages are monocytes in blood and macrophages in various organs and tissues, which form a mononuclear phagocyte system. When the pathogen penetrates the skin or mucous membrane and reaches the tissues in the body, phagocytes first escape from the capillaries and gather at the location of the pathogen. In most cases, pathogens are swallowed and killed. If they are not killed, they will reach nearby lymph nodes through lymphatic vessels, where phagocytes will further destroy them. This filtering effect of lymph nodes plays an important role in human immune defense ability. Generally, only a large number of virulent pathogens can invade organs such as blood flow without being completely blocked. But phagocytes in blood, liver, spleen or bone marrow will continue to devour and kill pathogens. Taking pathogenic bacteria as an example, the process of phagocytosis and sterilization is divided into three stages, that is, phagocytic cells contact with pathogenic bacteria, phagocytosis of pathogenic bacteria, killing and destroying pathogenic bacteria. There are lysosomes in phagocytes, among which lysozyme, myeloperoxidase, lactoferrin, defensins, active oxygen substances and active nitrogen substances can kill bacteria, while protease, polysaccharide enzyme, nuclease and lipase can degrade bacteria. Finally, undigested bacterial residues will be discharged to the outside of phagocytes. Bacteria are swallowed by phagocytes to form phagocytes; Lysosomes and phagocytes fuse into phagocytes; A variety of bactericidal substances and hydrolases in lysosomes kill and digest bacteria; Bacterial residues are excreted from cells. After bacteria are swallowed by phagocytes, the results are different according to the types, virulence and human immunity of bacteria. After being swallowed, pyogenic cocci usually die in 5- 10 minutes, and are destroyed in 30-60 minutes, which is completely swallowed. Tuberculosis, Brucella, Typhoid Bacillus, Legionella, etc. It is an intracellular bacterium that has adapted to live in the host cell. In a human body without specific immunity, although it can be swallowed by phagocytes, it is not killed, which is incomplete phagocytosis. Incomplete phagocytosis can protect these bacteria from the harmful effects of specific antibodies, nonspecific antibacterial substances or antibacterial drugs in body fluids; Some bacteria can still grow and reproduce in phagocytes, which leads to the death of phagocytes; Some phagocytes that can swim with it spread to other parts of the human body through lymph or blood flow, causing large-scale lesions. In addition, in the process of phagocytosis, a variety of hydrolases released by lysosomes can also destroy adjacent normal tissues and cells, causing adverse immunopathological damage to human body. Normal human body fluids, such as blood, tissue fluid and secretion fluid, contain many substances that can kill or inhibit pathogens. There are mainly complement, lysozyme, defensin, B- lysin, phagocytin, histone, normal opsonin and so on. The direct killing effect of these substances on pathogens is not as strong as that of phagocytes, and they often only cooperate with other antibacterial factors. For example, complement has only a weak bacteriostatic effect on Vibrio cholerae, but if complement is added to the complex of Vibrio cholerae and its specific antibody, the bacteriolytic reaction of Vibrio cholerae will soon occur. The human immune system, like an excellent army, protects our health all the time. This is a great masterpiece! In any one second, the immune system can coordinate and dispatch countless immune "troops" with different functions to engage in complex tasks. It can not only protect us from foreign invaders at all times, but also prevent the threat of cancer caused by cell mutation in the body. Without the protection of the immune system, even a grain of dust is enough to kill people. According to medical research, more than 90% of human diseases are related to immune system disorder. The structure of human immune system is complicated, not in a specific position or organ. On the contrary, it is coordinated by multiple organs of the human body. Bone marrow and thymus are the main lymphatic organs of human body, and peripheral lymphatic organs include tonsil, spleen, lymph nodes, collective lymph nodes and appendix. These checkpoints are used to prevent the invasion of toxins and microorganisms. When we have an itchy throat or tears in our eyes, it is a signal that our immune system is working hard. For a long time, people choose to remove the cecum and tonsil because they have no obvious function, but recent research shows that there are a large number of lymph nodes in the cecum and tonsil, which can help the immune system to operate. Since the invention of antibiotics, the scientific community has been committed to the invention of drugs, hoping that they can treat diseases, but contrary to expectations, researchers have gradually found that people using chemical drugs will only stimulate a certain part of the immune system, but it cannot replace the function of the immune system, and it will also have harmful side effects on human health and disturb the balance of the immune system. On the contrary, it is the body's own defense mechanism-the immune system, which has incredible power. However, proper nutrition can make the immune system work fully and effectively, and help the human body to better defend against diseases and overcome environmental pollution and toxins. The inseparable and mutually promoting relationship between nutrition and immune system lays a theoretical foundation for the establishment of nutritional immunology. The working process of the immune system When pathogenic microorganisms such as germs and viruses enter the human body, macrophages in the immune system first attack and engulf them in the "stomach", and then break them into pieces through the action of enzymes. These microbial fragments appear on the surface of macrophages and become antigens, indicating that they have swallowed the invading germs and let T cells in the immune system know. T cells and microbial fragments on the surface of macrophages, or microbial antigens, react immediately after meeting, just like the original locks and keys. At this time, macrophages will produce a lymphatic factor substance, and its biggest function is to activate T cells. Once T cells "wake up", they immediately send out an "alarm" to the whole immune system and report the news of "enemy" invasion. At this time, the immune system will dispatch a killer T lymphocyte, which will emit special B lymphocytes, and finally produce specific antibodies through B lymphocytes. Killing T lymphocytes can find those infected human cells. Once found, they will destroy these infected cells like killers and prevent the further reproduction of pathogenic microorganisms. When the infected cells are destroyed, the antibodies produced by B lymphocytes combine with the pathogenic microorganisms in the cells, which is the role of knowledge in treating diseases. Through the above series of complicated processes, the immune system as the main body is finally protected. When the first infection is suppressed, the immune system will record all the process tools of this pathogenic microorganism. If the human body is invaded by the same pathogenic microorganism again, the immune system has clearly known how to deal with it, and can respond easily, accurately and quickly to destroy the invaded place.