Yuanmu for your doubts: What are the antigens and antibodies? What is the difference? - Huaqiang Electronic Network

An antigen is a substance that stimulates the production of antibodies or sensitized lymphocytes in the human or animal body and reacts specifically with these products in vivo or in vitro. The basic ability of an antigen is immunogenic and reactive. Immunogenicity, also known as antigenicity, refers to the ability to stimulate the body to form specific antibodies or sensitize lymphocytes. Reactivity refers to the specific reaction with antibodies or sensitized lymphocytes produced by its stimulation. Substances that have both immunogenic and reactive properties are called complete antigens, such as pathogens, xenogenic animal serum, and the like. A substance that is only reactive but not immunogenic is called a hapten such as penicillin or sulfonamide. The hapten is not immunogenic and does not cause an immune response. However, in some special cases, if the hapten and the macromolecular protein are combined, the immunogenicity is obtained and becomes a complete antigen, which can stimulate the immune system to produce antibodies and effector cells. After penicillin enters the body, if its degradation product binds to the tissue protein, it acquires immunogenicity and stimulates the immune system to produce anti-penicillin antibodies. When penicillin is injected into the body again, the anti-penicillin antibody immediately binds to penicillin, producing a pathological immune response, rash or anaphylactic shock, and even life-threatening.

The basic properties of antigens are heterogeneous, macromolecular and specific. Foreign body is an antigenic substance that enters the body tissues and must be different from the components of the body tissue cells. Antigen generally refers to foreign substances entering the body, such as bacteria, viruses, pollen, etc.; antigens can also be substances between different species, such as horse serum into rabbits, many proteins in horse serum become rabbit antigenic substances The substance of the same kind can also become an antigen, such as blood type, transplant immunity, etc. Some isolated components from the body can also become antigens, such as eye crystal proteins, sperm cells, thyroglobulin, etc. Under normal circumstances, It is fixed at a certain part of the body and is isolated from the antibody-producing cells, so it does not cause autologous antibody production. However, when they are traumatized or infected, these ingredients can cause autologous antibodies like foreign bodies. These substances that are antigenic to themselves are called autoantigens, and the antibodies produced are called autoantibodies.

Since autoantibodies react with autoantigens, they cause autoimmune diseases such as allergic ophthalmia and thyroiditis. Proteins in other tissues of the body can also become autoantigens due to denaturation of physicochemical and biological factors such as ionizing radiation, burns, certain chemicals and certain microorganisms, causing autoimmune diseases such as lupus erythematosus and leukopenia. Disease, chronic hepatitis, etc.

Macromolecular means that a substance constituting an antigen is a macromolecular substance having a relative molecular mass of more than 10,000, and the larger the molecular weight, the stronger the antigenicity. Most proteins are good antigens. Why are antigenic substances all macromolecules? This is because macromolecular substances can stay in the body for a long time, and have enough time to contact with immune cells (mainly macrophages, T lymphocytes and B lymphocytes), causing immune cells to respond. If the foreign substance is a small molecule, it will be quickly excreted by the body, and there is no chance to contact the immune cells. If the macromolecular protein is hydrolyzed into a small molecule, the antigenicity is lost.

Specificity means that an antigen can only specifically bind to the corresponding antibody or effector T cell. The specificity of an antigen is determined by a specific chemical gene on the surface of the molecule called an antigenic determinant. The antigen activates lymphocytes to cause an immune response by binding the antigenic determinant to the antigen receptor of the corresponding lymphocyte. In other words, the antigen recognition receptor on the surface of lymphocytes distinguishes between "self" and "dissident" by recognizing the antigenic determinant. The antigen also reacts with specific binding of the antigenic determinant to the corresponding antibody. Therefore, antigenic determinants are the material basis for specific responses to immune responses and immune responses.

Antibody: An immunoglobulin produced by a plasma cell differentiated by B cells under the stimulation of an antigenic substance and capable of specifically binding to a corresponding antigen. Since electrophoresis was first used to demonstrate that the antibody activity in the serum is in the gamma globulin fraction, the antibodies have been collectively referred to as two (gamma) globulins. It was later proved that the antibodies were not all in the γ region; and the globulins located in the γ region did not necessarily have antibody activity. In 1964, the World Health Organization held a special meeting to refer to antibody-related and antibody-related globulins as immunoglobulins (Ig). Such as myeloma protein, macroglobulinemia, cryoglobulinemia and other abnormal immunoglobulins present in the serum and "normal human" naturally occurring immunoglobulin subunits. Thus immunoglobulins are the concept of structure and chemistry, and antibodies are biological and functional concepts. It can be said that all antibodies are immunoglobulins, but not all immunoglobulins are antibodies.

The main function of the antibody is to combine with antigens (including foreign and self) to effectively remove foreign substances such as microorganisms and parasites that invade the body, neutralize the toxins released by them or eliminate certain autoantigens, so that the body remains Normal balance, but sometimes it will cause pathological damage to the body, such as anti-nuclear antibodies, anti-double-stranded DNA antibodies, anti-thyroglobulin antibodies and other autoantibodies, which can cause harm to the human body.