What are antigens and antibodies

When you go to the hospital for a physical examination, you must often hear the doctor say that the antigens in some places are high and the antibodies in some places are low, but most people do not know what antigens and antibodies are. In fact, both of them are substances existing in the human body. Many diseases can reflect the health status of the body based on the levels of these two substances. Today we will specifically introduce what antigens and antibodies are.

Antigen (Ag) refers to any substance that can induce an immune response in the body. That is, substances that can be specifically recognized and bound by antigen receptors (TCR/BCR) on the surface of T/B lymphocytes, activate T/B cells, cause them to proliferate and differentiate, produce immune response products (sensitized lymphocytes or antibodies), and can specifically bind to corresponding products in vivo and in vitro. Therefore, antigens have two important properties: immunogenicity and immunoreactivity. Immunogenicity refers to the ability of an antigen to induce a specific immune response in the body and produce antibodies and/or sensitized lymphocytes; immunoreactivity refers to the ability to initiate a specific binding reaction with corresponding immune effector substances (antibodies or sensitized lymphocytes) in vivo and in vitro.

Antibodies are a type of immunoglobulin that can specifically bind to antigens. Antibodies are divided into agglutinins, sedimentins, antitoxins, lysins, opsonins, neutralizing antibodies, complement fixing antibodies, etc. according to their reaction form. According to the source of antibody production, it is divided into normal antibodies (natural antibodies), such as anti-A and anti-B antibodies in blood type ABO, and immune antibodies such as anti-microbial antibodies. According to the source of the reactive antigen, they are divided into xenoantibodies, heterophilic antibodies, alloantibodies and autoantibodies.

According to the agglutination state of the antigen reaction, it can be divided into complete antibody IgM and incomplete antibody IgG. Antibodies are widely used in medical practice. For example, it plays a certain role in the prevention, diagnosis and treatment of diseases. In clinical practice, immunoglobulin is used to prevent viral hepatitis, measles, rubella, etc., and anti-Rh immunoglobulin is used internationally to prevent hemolytic disease caused by Rh blood type incompatibility. In diagnosis, rheumatoid factor is used for rheumatoid arthritis, antinuclear antibodies (ANA) and anti-DNA antibodies are used for systemic lupus erythematosus, and antisperm antibodies are used for the diagnosis of primary infertility; in treatment, antitoxin treatment is used for poisoning and immunodeficiency diseases.