1.What is rejection reaction? The body has a very well-developed defense mechanism against various internal and external pathogenic factors, among which the important role of foreign substances such as bacteria, viruses, foreign bodies and other “foreign components” is to attack, destroy and remove, which is a protective mechanism for the body under normal circumstances. However, after liver transplantation, the donor liver is recognized by the body as a foreign body and the immune system is mobilized to attack, destroy and remove the graft, which is called rejection. This is when the rejection becomes devastating for the organism. Once the rejection occurs, the transplanted liver will be damaged, which will lead to the loss of transplanted liver function in serious cases and endanger life safety. 2, what are the types of rejection reactions According to the time and mechanism of rejection reactions can be divided into two types of rejection reactions: acute rejection reactions and chronic rejection reactions. Acute rejection Acute rejection mostly occurs within one week to six months after surgery, with clinical manifestations such as fever, malaise, increased blood pressure, deterioration of liver function, and discomfort in the transplanted liver area. In recent years, with the use of immunosuppressive drugs, acute rejection is no longer typical and can occur in a milder form. If detected in time and treated properly, most of these rejection reactions can be reversed. Most acute rejection reactions are treated with methylprednisolone or anti-lymphocyte antibodies. Chronic rejection Chronic rejection occurs slowly, usually after 6 months postoperatively, with progressive aggravation and gradual deterioration of liver function, usually irreversible, and is the main cause of loss of function of the transplanted liver in the late stage of transplantation, as well as the main cause of long-term health survival of the patient. Most transplant doctors believe that the reduction of acute rejection can effectively delay or reduce the incidence of chronic rejection. 3. How to prevent rejection? In human organ transplantation, the rejection of the foreign organ by the body after surgery is almost inevitable. In order to make the new organ survive in the new environment and minimize the rejection reaction, immunosuppressants are clinically needed to help the new organ adapt to the new environment. The main role of immunosuppressants is to reduce the rejection of the organism to a lower level to allow the two to coexist peacefully, but the occurrence of infectious diseases such as bacteria and viruses will increase due to the reduction of the organism’s immunity. 4.Knowledge of immunosuppressants Basic immunosuppressants taken for life: Pulcoflora Pulcoflora is a macrolide antibiotic extracted from the broth medium of soil fungi by Fujisawa Pharmaceutical Company in Japan in 1982, which has an extremely strong immunosuppressive effect, and its immunosuppressive effect is about 10-100 times that of cyclosporine. Pulcolacofol can both prevent and treat rejection reactions. Clinical applications in recent years have shown that Pulcolax is a promising immunosuppressive agent in organ transplantation. Compared with CsA, it has great superiority in controlling rejection, maintaining graft function and improving patient survival rate, and has low infection rate and no dependence on hormones. Its toxic side effects mainly include nephrotoxicity, neurotoxicity, tumor, infection, allergic reaction, hypertension and hyperglycemia. Other commonly used adjuvant immunosuppressants Hormones The most commonly used for organ transplantation are prednisone and methylprednisolone, etc. High-dose methylprednisolone shock therapy is still the preferred treatment for acute rejection. The combination of prednisone and Prednisolone has achieved remarkable results in the prevention of rejection. The common side effects of long-term heavy use of adrenal glucocorticosteroids include: metabolic disorders of water, salt, sugar, protein and fat, manifested as centripetal obesity, acne, hirsutism, hypertension and urinary sugar, which can be relieved after stopping the drug; inducing or aggravating infections; delaying wound healing, inducing peptic ulcers and causing bleeding; osteoporosis and muscle atrophy; inhibiting the secretion of growth hormone, affecting growth and development; inducing cataracts. Increase the excitability of the central nervous system, leading to neuropsychiatric symptoms such as euphoria, agitation, insomnia, etc.; rebound phenomenon and withdrawal symptoms, after long-term use of the drug symptoms are basically controlled, if the drug is suddenly stopped or reduced too quickly the original symptoms can quickly appear or aggravate. In order to prevent rebound, the drug should be discontinued by slowly reducing the dosage. Mycophenolate (primidone) Mycophenolate can significantly prolong the survival of grafts by controlling cell- and antibody-mediated rejection and inhibiting antibody formation. Its toxic side effects mainly include gastrointestinal symptoms such as nausea, vomiting, diarrhea, gastritis, etc. Sometimes, leukopenia, infection, and tumor may also occur. Drugs used in case of rejection Anti-lymphocyte immunoglobulin Anti-lymphocyte antibodies are antibodies corresponding to lymphocyte membrane surface antigens. Anti-lymphocyte antibodies play an important role in immunosuppressive therapy and are mainly used for a short period of time after transplantation or in case of rejection. Monoclonal antibody OKT3 is used as an immunosuppressive agent mainly for the prevention and treatment of acute rejection after organ transplantation such as allogeneic liver transplantation.