Response to an immunogen can be enhanced by mixing the antigen with certain adjuvants. Adjuvant is a group of structurally heterogeneous compounds capable of enhancing immunogenity of an antigen. The term adjuvant is derived from Latin. In Latin adjuvant means “to help”.

Adjuvant help to induce greater, more prolonged antibody production and increased effector cell count. When only small amounts of antigens are available, adjuvant can be mixed to get maximum effect from the minimum antigens. Certain oil emulsions, saponins, aluminums or calcium salts, derivatives of lipopolysaccharides, mycobacteria etc. can be used as adjuvants.

Adjutants stimulate nonspecific lymphocyte proliferation and granuloma formation. When an antigen is mixed with alum (as adjuvant) and injected, the adjuvant slowdown the release of antigen from the site of injection so that the effective time of exposure to the antigen is increased. The size of the antigen increases, when it is mixed with an adjuvant.

The increase in size of the antigen increases the likelihood of phagocytes. Adjuvant perhaps alters traffic of circulating lymphocytes. In various instance a combination of all the functions of adjuvant might occur.

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A commonly used adjuvant was initially formulated by Freund. It is “stable water in oil emulsion”, which may (complete) or may not (incomplete) contain killed Mycobacterium tuberculoses.