What is an Antigen?

An antigen (abbreviation Ag) refers to a substance that can cause antibody production, and is any substance that can induce an immune response. Foreign molecules can be recognized by immunoglobulins on B cells or processed by antigen-presenting cells and combined with major histocompatibility complexes to re-activate T cells, triggering a continuous immune response. ^[1]

Antigen (Ag) refers to all substances that can induce an immune response in the body. That is, it can be specifically recognized and bound by the antigen receptor (TCR / BCR) on the surface of T / B lymphocytes to activate T / B cells. Substances that proliferate and differentiate, produce immune response products (sensitized lymphocytes or antibodies), and can specifically bind to the corresponding products in vivo and in vitro. Therefore, the antigenic substance has two important characteristics: immunogenicity and immunoreactivity. Immunogenicity refers to the ability of an antigen to induce a specific immune response in the body to produce antibodies and / or sensitize lymphocytes; immunoreactivity refers to the ability to react with the corresponding immune effector substance (antibody or sensitized lymphocytes) in vivo and in The ability of things to specifically bind the response. ^[2]

The basic properties of an antigen are

Antigen in

Divided into two categories according to the nature of the antigen: complete antigen and

Antigen pathogenic microorganism

Vaccination of pathogenic microorganisms in medicine can improve human immunity. Various immunological tests can also be performed based on the specificity of microbial antigens to help diagnose the disease.

Antigen alloantigen

There are two major types, one is the red blood cell antigen, including A, B, O blood group antigens, Rh blood group antigens and so on. Transfusion of blood between different blood types can cause severe transfusion reactions; the other is the human leukocyte antigen (HLA), also known as the major histocompatibility antigen, which exists on the human leukocyte cell membrane. Like blood group antigens, they are genetically determined and controlled by genes on the chromosome. The histocompatibility antigens of histiocytes in different individuals (except identical twins) are not completely the same. Therefore, when allogeneic skin or organ transplantation is performed, recipients often exist in the donor graft. The absence of the antigen component stimulates the recipient to produce an immune response to the graft, leading to rejection and necrosis of the graft.

Antigen animal immune serum

Various antitoxin sera commonly used in clinical practice are generally prepared using immune horses. On the one hand, antitoxin can neutralize its corresponding exotoxin and play a role in preventing and treating diseases; on the other hand, it can stimulate the body to produce antibodies against horse serum protein. When the horse's immune serum is received again, hypersensitivity may occur reaction.

Heterophilic antigen

A class of antigens that are not related to species specificity and are of the same nature in humans and certain animals, plants, and microorganisms.

Tumor antigen

Specific antigens appear in cells or on the surface of experimental animal tumors induced by physical, chemical factors or certain viruses, and are called tumor-specific antigens. Virus-associated antigens have been demonstrated in some human tumor centers.