Adjuvant is also known as immunological adjuvant, refers to all kinds of substances which are subject pre-injection or injection together with antigen and can increase the body's immune response to an antigen or change the type of response. The effects of the immunological adjuvant:
① be able to enhance the antigenicity of the weak antigenic material;
② increase the level of the specific circulating antibody or produce an effective protective immunity;
③ change the type of produced circulating antibodies;
④ enhance the cell-mediated hypersensitivity capacity;
⑤ protect the antigen (especially DNA, RNA) from the decomposition of the in vivo enzymes.
Adjuvant is able to especially enhance the effect of triggering specific response of certain polysaccharides of small molecular weight or polypeptide of weak antigenicity.

The BCG vaccine, bacterial endotoxin and Bordetella pertussis all have the effects of adjuvant. Adjuvant, when mixed with some tissue antigens for injection, can lead to allergy and autoimmune diseases. The commonly used laboratory adjuvant is Freund's adjuvant, which can be divided into:
① Incomplete Freund's adjuvant, made from the sufficient mixture of 1 to 6 parts of paraffin oil and 1 part of lanolin;
② Complete Freund's adjuvant; it is made through adding inactivated BCG (2 to 20 mg/mL) to incomplete Freund's adjuvant before usage. For experimental animals, during the first time of injection of antigen, the used antigen is usually mixed with complete Freund's adjuvant, and for the booster shot later again, we only need to simply mix it with incomplete Freund's adjuvant.

Adjuvant is mixed with the antigen in a 1: 1 ratio. When fully emulsification occurs until no oil-water separation occurs after standing static, it can be used to inject the animals.

The effects of adjuvant on the antigen
① increase the surface area of the antigen. After the adsorption of antigen, adjuvant can increase the surface area of the antigen and change the conformation of the active gene, and thus enhancing the immunogenicity of the antigen. For soluble antigen or hapten of small molecular weight, after adsorption of colloidal particles, they can increase the antibody production.
② enhance the synergy between T and B cells. After adjuvant and antigen are subject to macrophage phagocytosis, the adjuvant can perform further antigen processing and treatment, endow the antigen with strong immunogenicity, promote the immunity of the T lymphocyte, and enhance the synergies of T lymphocytes and B lymphocytes.
③ extend the storage time of antigen within the tissue, slow down the degradation and the release of antigen. Adjuvant can induce local granulomas; prolong the storage time of antigen in the local tissue; slow down the degradation rate of the antigen and enable the slow release of the antigen. For example, the retention phenomenon caused by the corynebacterium is much more long-lasting than the soluble antigens with the former can be up to several weeks while the later only lasts 2 to 3 days. Inoculation of the bacteria can cause local granulomas, but do not develop into epithelioid cells and multinucleated giant cells without causing tissue necrosis. After the mixing of the aluminum hydroxide gel with an antigen, the antigen will be adsorbed on aluminum gel. This can prolong the presence of the antigen in vivo and slow down the release of antigen, being capable of increasing the concentration of antibodies in the blood, and reducing the times of immunizations.

The effect of the adjuvant on the body;
① cause cell infiltration. Adjuvant can cause cell infiltration, results in the occurrence of the accumulation of macrophages, lymphocytes and plasma cells, further promoting the proliferation of these cells and playing a greater role. For example, after the injection of FCA, it can be visible from the tissue sections that, there are macrophages, epithelioid cells and lymphocytes and plasma cells gather in the local part of the injection. ② accelerate the transformation of lymphocytes. Adjuvant effect can accelerate the transformation from lymphocytes cells into effector cells, producing more sensitized lymphocytes and transformed into plasma cells to produce antibodies. ③the change of the membrane and cytoplasm. After the ligand stimulation of lymphocytes, the membrane phospholipids are activated by enzyme, leading to the occurrence of membrane movement and the synthesis of new membrane on the membrane or the nearby sites. Following this, there should be also corresponding change occurring in the cytoplasm and nucleus. The change of the intracellular AMP and GMP concentrations plays an important regulatory role and influence. Macrophages, after adjuvant effect, can also have similar changes, mainly exhibiting as the increased activity of the membrane and secretion of secondary factor. ④ the change of the cell function. The main changes occurring after the stimulation and activation of macrophages through adjuvant include an increase in the number, enlarged membrane surface area, and generation of a large amount of cofactors and other regulatory factors such as prostaglandins. The T and B cells, after the action of adjuvant, have their biggest change be the increase in the number of cells; entering into the cell cycle; the membrane surface composition changes; generation of a large number of cofactor (LK). B cells are then differentiated into plasma cells and secrete large amounts of antibody.

Mineral oil adjuvant
Mineral oil adjuvant is a kind of emulsion-type vaccine. It is manufactured through taking pharmaceutically standard acceptable light mineral oil (Trade name: “white oil”), adding an emulsifier and then mixing with an appropriate proportion of antigen solution and further emulsion. "Emulsion" reagent is a kind of dispersive system obtained through dispersing the solution into tiny particles and further suspension it into another immiscible liquid. The dispersed materials are known as the dispersed phase (internal phase); the liquid undertaking the dispersed phase is called as continuous phase (external phase); the active substances in the interface between the two phases are called as emulsifiers. When taking water as the dispersed phase and oil supplemented with emulsifier as the continuous phase, the emulsion reagent is made of water-in-oil type emulsion (W/O type or W/O type), and vice versa is oil-in-water type emulsions (oil/water type or O/W type). W/O type emulsion vaccine has a relative high adjuvant activity, but the characters are relatively more viscous and do not disperse easily upon being injected into animal body. O/W emulsion agent although has a dilute trait, has very low adjuvant activity. Therefore, we can add 2% Tween-80 saline to the W / O type emulsion vaccine for stirring to make it become dual phase emulsion, namely water - oil - water type emulsion or called polymorphic reagents. The bi-phase emulsion vaccine has a low viscosity and is easily dispersed after injection with mild local reactions and excellent adjuvant effect as well.