Inhibitor refers to substance that can hinder the chemical reactions, biological reactions (including immune response) and biological activity. In present time, commonly used inhibitors include immunosuppressants and inhibitors. 1. Immunosuppressive agents: immunosuppressants system refers to drug that can reduce the immune response. It can selectively suppress certain steps of the immune response and immune cells. Immune response refers to the body’s response to a variety of pathogenic substances. Some reactions are favorable to the body and can enhance the body's resistance to disease; some have adverse effects on the body and can cause tissue damage or disorders of physiological functions (allergy). Therefore, patients suffering from allergic reactions being harmful to the body should be subject to the treatment of immunosuppressant to affect the related immune processes and reduce the immune response of the body. For the treatment of various autoimmune diseases and weakening the tissue incompatibility, it has been developed of a variety of immunosuppressive agents, some of which have been widely used in clinical practice. Commonly used immunosuppressants include glucocorticoids (prednisone, prednisolone, etc.), alkylating agents (nitric oxide mustard, cyclophosphamide, thiotepa, busulfan, etc.), and antimetabolites (6- mercaptopurine, azathioprine, methotrexate, etc.). The mechanism of immunosuppressants, though not entirely clear, but is characterized by the following several aspects: ① most kinds of immunosuppressants can simultaneously inhibit cellular and humoral immunity and can be used for organ transplantation and autoimmune disease. ②Its inhibitory effect is strong for the primary immune response while the inhibitory effect against secondary response is weak. ③It can simultaneously act on normal and pathological immunity, therefore, can often lead to some complications. ④These drugs often have strong with serious adverse reactions. 2. Enzyme