The following article presents a detailed description of adjuvants and the different types of adjuvant that are available.
Adjuvants are compounds or chemicals that can be added to immunizing peptides in order to promote and stimulate the immune response. One of their main advantages is that they increase the amount and quality of the antibody produced.
Adjuvants can also be used in vaccines to produce protective antibodies and good systemic memory for future protection. When they are used for antiserum production, they need to create high titer and high avidity antibodies.
There are several adjuvants that are available for use and the way to choose the best is to choose the one that has the least toxicity, while still helping to promote the highest immune response.
Freund's, Ribi, and Titermax are among the most commonly used adjuvants for both polyclonal and monoclonal antibody production.
Freund's Complete Adjuvant (FCA)
FCA is a water-in-oil emulsion that contains mineral oil, the surfactant mannide monoleate and heat-killed Mycobacterium tuberculosis, Mycobacterium butyricum or their extracts, used for aggregation of macrophages at the inoculation site.
One of the advantages of the FCA is that it has the ability to localize the antigen for slow release within the immunized host for up to six months. FCA also stimulates both cell mediated and humoral immunity. Furthermore, it could preferentially induce antibodies against epitopes on denatured proteins.
However, the FCA also has disadvantages. For instance, it can produce some immunologically toxic effects, due to the non-metabolizable mineral oil. In addition, the mycobacterial elements can create severe granulomatous reactions. Therefore, it is mainly used on laboratory animals.
Freund's Incomplete Adjuvant (FIA)
One of the differences between FIA and FCA is that the FIA does not contain mycobacterium or its components. The FCI is much less toxic than the FCA, but due to the lack of mycobacterium or its components, it is less effective than the FCA in inducing high antibody titers.
Ribi Adjuvant System
Ribi adjuvants are oil-in-water emulsions. The antigen is mixed with squalene, which is a metabolizable oil. It is then emulsified in a saline solution containing Tween 80. Ribi also consists of a product which fulfills the function of an immunostimulant, that is, a refined mycobacterial product; it also includes a gram negative bacterial product monophosphoryl lipid A.
Ribi can also produce cytokine induction by interacting with the membranes of immune cells. That induction enhances antigen uptake, processing, and presentation.
Titermax adjuvants have lower levels of toxicity and contain no biological materials. They are based on mixtures of surfactant acting, linear, blocks or chains of non-ionic copolymers polyoxypropylene (POP) and polyoxyethylene (POE).
The properties of Titermax induce chemotaxis, along with complementing activation and antibody production. The Titermax adjuvant also has the ability to form a microparticulate water-in-oil emulsion with a copolymer and metabolizable squalene oil.
The adjuvant active copolymer forms hydrophilic surfaces, which activates immune cells, and increases the expression of class II major histocompatibility molecules on macrophages.
Specol adjuvant is water in purified mineral oil. The number of toxic effects it produces is lower and it also induces an immune response comparable to Freund's adjuvant.
Aluminum salt adjuvants are used with antigens:
- As aluminum-precipitated vaccines
- As aluminum-adsorbed vaccines
Al (OH) can be used to adsorb proteins in a ratio of 50 to 200 g protein per mg aluminum hydroxide. They are generally weaker adjuvants than emulsion adjuvants. However, they induce a mild inflammatory response.
Due to their efficacy of generating memory cells and for safety reasons, the Al (OH) adjuvants are mainly used as primary adjuvants in human vaccinations.
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