An adjuvant (from Latin, adiuvare: to aid) is a pharmacological or immunological agent that modifies the effect of other agents. It is an inorganic or organic chemical, macromolecule or whole cells of certain killed bacteria which enhance the immune response to given antigen. They are often included in vaccines to enhance the recipient's immune response to a supplied antigen, while keeping the injected foreign material to a minimum. Their purpose is to excite the immune system to a greater feedback than the vaccine itself, without the adjuvant. Firstly, there is greater "mobilization" of the immune system to the vaccine without which the organism had greater problems; adding adjuvant represents an opportunity to add the minimum amount of antigen  to the body and the way to replace several repeated vaccinations by only one. They are also used in the production of antibodies from immunized animals. The most commonly used adjuvants include aluminum hydroxide and paraffin oil. 
Immunologic adjuvants 
Immunologic adjuvants are added to vaccines to stimulate the immune system's response to the target antigen, but do not in themselves confer immunity. Adjuvants can act in various ways in presenting an antigen to the immune system. Adjuvants can act as a depot for the antigen, presenting the antigen over a long period of time, thus maximizing the immune response before the body clears the antigen. Examples of depot type adjuvants are oil emulsions. Adjuvants can also act as an irritant which causes the body to recruit and amplify its immune response. A tetanus, diphtheria, and pertussis vaccine, for example, contains minute quantities of toxins produced by each of the target bacteria, but also contains some aluminium hydroxide. Such aluminium salts are common adjuvants in vaccines sold in the United States and have been used in vaccines for over 70 years. The body's immune system develops an antitoxin to the bacteria's toxins, not to the aluminium, but would not respond enough without the help of the aluminium adjuvant.
Mechanisms of adjuvants 
Adjuvants are needed to improve the routing and adaptive immune responses to antigens. This reaction is mediated by two main types of lymphocytes, B and T cells. Adjuvants can apply their effects through different mechanisms. Some adjuvants, such as alum function as delivery systems by generating depots that trap antigens at the injection site, providing slow release in order to continue the stimulation of the immune system. 
Adjuvants as stabilizing agents 
Although immunological adjuvants have traditionally been viewed as substances that aid the immune response to antigen, adjuvants have also evolved as substances that can aid in stabilizing formulations of antigens, especially for vaccines administered for animal health. Adjuvants as stabilizing agents
Although immunological adjuvants have traditionally been viewed as substances that aid the immune response to antigen, adjuvants have also evolved as substances that can aid in stabilizing formulations of antigens, especially for vaccines administered for animal health.
The mechanism of amplification imunogentity antigen 
Adjuvants can enhance the immune response to the antigen in different ways: extend the presence of antigen in the blood help absorb the antigen presenting cells antigen activate macrophages and lymphocytes support the production of cytokines
Types of adjuvants 
inorganic compounds: aluminum hydroxide, aluminum phosphate, calcium phosphate hydroxide, beryllium Mineral oil: paraffin oil Bacterial products: killed bacteria Bordetella pertussis, Mycobacterium bovis, toxoidsDelivery systems: detergents (Quil A) Cytokines: IL-1, IL-2, IL-12 combination: Freund's complete adjuvant, Freund's incomplete adjuvant Squalene: Squalene thimerosal: ethylmercury
Alum is the most commonly used adjuvant in human vaccination. It is found in numerous vaccines, including diphtheria-tetanus-pertussis, human papillomavirus and hepatitis vaccines. 
See also 
- Adjuvant care
- Agricultural spray adjuvant
- Combination therapy
- Crop oil
- Freund's adjuvant
- Immunologic adjuvant
- Inactivated vaccine
- Pharmaceutic adjuvant
- Keyhole limpet hemocyanin (KLH)
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