What is the antigen-antibody reaction?

Antigen-antibody reaction refers to the specific binding reaction between an antigen and its corresponding antibody. This reaction can take place both inside and outside the body. The process of antigen-antibody reaction goes through a series of chemical and physical changes, including two stages: antigen-antibody specific binding and nonspecific aggregation, as well as the change from hydrophilic colloid to hydrophobic colloid.

Reaction Principle

Antibodies can specifically recognize and bind to corresponding antigens. This binding can also occur in vitro, and this characteristic antigen-antibody reaction pattern is the basis of many immunoassay methods. The interaction between antigen and antibody is non-covalent and reversible, and its characteristics conform to the basic principles of many chemical reactions. However, due to the structural characteristics of antibody molecules and the diversity of antigen molecular structures, the antigen-antibody binding reaction is complex.

application

Immunization of animals

(1) Antigen: Immunizing animals is the first step in preparing antiserum. The antigens used for immunization can be viruses, bacteria or other protein antigens. If haptens such as small molecule hormones are used, they must be connected to a macromolecular carrier. The amount of antigen used varies depending on the type of antigen and the animal. For mice, a single injection can be as little as a few micrograms, while for rabbits, sheep, and even larger animals, the amount of each injection increases accordingly, from several hundred μg/time to several mg/time.

[2] Adjuvants and emulsification: Adjuvants can help antigens be released slowly at the injection site to increase the immune stimulation effect. Adjuvants are divided into complete and incomplete adjuvants. Complete adjuvant contains killed mycobacteria (such as BCG) or Corynebacterium spp. Freund's adjuvant can be purchased from a reagent company, or it can be prepared by mixing lanolin and paraffin oil in a ratio of 1:2-4. The adjuvant and antigen are mixed and emulsified in a ratio of 1:1 to form a uniform emulsion, and oil-water separation will not occur after standing.

(3) Immunized animals: Animals commonly used for preparing antiserum include guinea pigs, rabbits, mice, rats, etc. If mass production is required, sheep, horses, etc. can be used. The amount of emulsion that the animal receives for immunization is 1.0-2.0 mL for mice and 2-4 mL for rabbits. The route of immunizing animals with antigens depends on the animal species, the characteristics of the antigen, and whether an adjuvant is used. Intraperitoneal injection (i.p.), muscle injection (i.m.), intradermal injection (i.d.) and subcutaneous injection (s.c.) are suitable for any antigen. These routes mainly stimulate local lymph nodes to produce immune responses and can be used for both primary immunization and immune booster injections. Intravenous injection (iv) is only suitable for soluble antigens and dispersed single-cell suspensions, and adjuvants cannot be used. The immune response it induces mainly occurs in the spleen. In addition, direct spleen injection or in vitro immunization methods can also be used when preparing monoclonal antibodies, which is particularly practical for trace amounts of antigens. In vitro immunization methods are also commonly used in the preparation of human monoclonal antibodies. During in vitro immunization, spleen cells or peripheral blood lymphocytes (including B cells, T cells and antigen-presenting cells) are cultured in vitro with antigens and then fused with myeloma cells. After the initial immunization, 2-3 more booster immunizations are required to ensure that a higher level of IgG antibodies can be formed. The time interval between two immunization injections is generally 3-4 weeks, which is more suitable for most animals. For small animals, the interval can be 10-14 days, and for large animals, it can be around 2 months. High levels of antibodies can be obtained by collecting antiserum within one week after the last booster injection.