Adjuvants are compounds/chemicals sometimes added to immunizing peptides when creating antibodies to promote and help stimulate the immune response. They increase the amount and quality of antibody produced. Adjuvants for use in vaccines only need to produce protective antibodies and good systemic memory for future protection. Adjuvant for antiserum production needs to create high titer, high avidity antibodies. Various adjuvants are available and the aim is to use one that has minimal toxicity while helping to promote maximum immune response. The most frequently used adjuvants for antibody production are Freund’s, Ribi, and Titermax.
Freund’s adjuvants
Freund’s Complete Adjuvant (FCA)
FCA is a water-in-oil emulsion that localizes antigen for slow release within the immunized host for up to six months. It contains mineral oil, the surfactant mannide monoleate and heat killed Mycobacterium tuberculosis, Mycobacterium butyricum or their extracts (for aggregation of macrophages at the inoculation site). It stimulates both cell mediated and humoral immunity. The disadvantage of this adjuvant is that it can product some immunologically toxic effects, due to the non-metabolizable mineral oil. For this reason, it is only used on laboratory animals.
Freund’s Incomplete Adjuvant (FIA).
Freund’s Incomplete Adjuvant has the same formulation as FCA but does not contain mycobacterium or its components. Its use is limited to booster doses of antigen as it is less effective than FCA for primary antibody induction.
Ribi Adjuvant System
Ribi adjuvants are oil-in-water emulsions. The antigens is mixed with metabolizable oil (squalene) which is emulsified with saline containing Tween 80. Ribi also contains refined mycobacterial products which act as immunostimulants and bacterial monophosphoryl lipid A. Ribi interacts with membranes of immune cells resulting in cytokine induction, which enhances antigen uptake, processing and presentation.
Titermax
Titermax adjuvants are less toxic and contain no biologically materials. They are based on mixtures of surfactant acting, linear, blocks or chains of non-ionic copolymers polyoxypropylene (POP) and polyoxyethylene (POE). Its properties induce chemotaxis, complement activation and antibody production. Titermax adjuvant forms a microparticulate water-in-oil emulsion with a copolymer and metabolizable squalene oil. The adjuvant active copolymer forms hydrophilic surfaces, which activate complement, immune cells and increased expression of class II major histocompatibility molecules on macrophages.
Specol
Specol adjuvant is water in purified mineral oil. It induces an immune response comparable to Freund's adjuvant while producing fewer toxic effects.
Aluminium salts
Aluminum salt adjuvants are used with antigens:
a) as aluminium-precipitated vaccines and
b) as aluminium-adsorbed vaccines.
Al(OH)] can be used to adsorb proteins in a ratio of 50 - 200 g protein/mg aluminum hydroxide. They are generally weaker adjuvants than emulsion adjuvants. However, they induce a mild inflammatory response. For safety reasons and for the efficacy for generating memory cells, they are the primary adjuvants utilized in human vaccinations.