The nature of the antigen

The nature of the antigen

Immunogenicity is the most important property of antigens. It mainly depends on the nature of the substance itself and its interaction with the body.

One, foreign body

Under normal circumstances, the immune system can recognize the host's own substances and non-self substances, and will not produce an immune response to its own substances, but only to non-self substances. Foreign body is the primary condition that constitutes the immunogenicity of antigens. "Foreign matter" is defined as "a substance that has not been in full contact with lymphocytes in the embryonic stage". The vast majority of antigens are non-substances. This type of immunological recognition is not judged by the spatial location of the substance, but by whether the lymphocytes are recognized. The farther the racial kinship between organisms, the greater the difference in chemical structure, the stronger the antigenicity; the closer the kinship, the weaker the antigenicity.

Second, physical and chemical substances

The substances that make up antigens usually have large molecular weights, generally above 10 kDa, and substances below 4.0 kDa are generally not immunogenic. The larger the molecular weight, the stronger the antigenicity. The reason is that there are many antigenic determinants on the surface of complex macromolecular substances, the chemical properties are relatively stable, the residence time in the body is long, and the degradation and elimination rate is slow, which is conducive to continuous stimulation of the body's immune system. Immune response.

Antigen substances must also have a certain chemical composition and structure. Most antigens are proteins. When they contain a large amount of aromatic amino acids such as tyrosine and phenylalanine, they are more antigenic. For example, gelatin protein has a molecular weight of up to 10 kDa, but its composition is linear amino acids, which are easily degraded into low molecular weight substances in the body, so its antigenicity is very weak. Insulin has a molecular weight of only 5.734 kDa, consisting of 51 amino acids, and its sequence contains 9 aromatic amino acids, so it is also immunogenic.

The spatial structure of antigens is the key to determine the binding of antigen molecules to lymphocyte antigen receptors to elicit an immune response. It is also the material basis for determining the binding of antigens to corresponding antibodies and the appearance of various immune responses.

The physical state of the antigen also affects its immunogenicity. Generally, the antigen in the polymerized state is more immunogenic than the monomer protein, and the particle antigen is more immunogenic than the soluble antigen. Therefore, for some substances with weak immunogenicity, they can be aggregated or adsorbed on the surface of some large molecular particles Way to enhance its immunogenicity.

Third, the way to enter the body

The same substance enters the body through different routes, and the intensity of its response to stimulate the immune system varies, from strong to weak: intradermal injection> subcutaneous injection> intramuscular injection> intraperitoneal injection> intravenous injection. Because antigens are mostly proteinaceous substances, they can be degraded into amino acids in the digestive tract and lose their immunogenicity. Therefore, they generally show strong immunogenicity when they enter the body through non-oral routes.